initial srpm import

1 files changed, 4163 insertions, 0 deletions

diff --git a/linux-2.6-utrace.patch b/linux-2.6-utrace.patch
new file mode 100644
index 0000000..8d1adf8
--- /dev/null
+++ b/linux-2.6-utrace.patch
@@ -0,0 +1,4163 @@
+utrace core
+
+This adds the utrace facility, a new modular interface in the kernel for
+implementing user thread tracing and debugging.  This fits on top of the
+tracehook_* layer, so the new code is well-isolated.
+
+The new interface is in <linux/utrace.h> and the DocBook utrace book
+describes it.  It allows for multiple separate tracing engines to work in
+parallel without interfering with each other.  Higher-level tracing
+facilities can be implemented as loadable kernel modules using this layer.
+
+The new facility is made optional under CONFIG_UTRACE.
+When this is not enabled, no new code is added.
+It can only be enabled on machines that have all the
+prerequisites and select CONFIG_HAVE_ARCH_TRACEHOOK.
+
+In this initial version, utrace and ptrace do not play together at all.
+If ptrace is attached to a thread, the attach calls in the utrace kernel
+API return -EBUSY.  If utrace is attached to a thread, the PTRACE_ATTACH
+or PTRACE_TRACEME request will return EBUSY to userland.  The old ptrace
+code is otherwise unchanged and nothing using ptrace should be affected
+by this patch as long as utrace is not used at the same time.  In the
+future we can clean up the ptrace implementation and rework it to use
+the utrace API.
+
+Signed-off-by: Roland McGrath <roland@redhat.com>
+---
+ Documentation/DocBook/Makefile    |    2 +-
+ Documentation/DocBook/utrace.tmpl |  590 +++++++++
+ fs/proc/array.c                   |    3 +
+ include/linux/sched.h             |    5 +
+ include/linux/tracehook.h         |   87 ++-
+ include/linux/utrace.h            |  692 +++++++++++
+ init/Kconfig                      |    9 +
+ kernel/Makefile                   |    1 +
+ kernel/fork.c                     |    3 +
+ kernel/ptrace.c                   |   14 +
+ kernel/utrace.c                   | 2436 +++++++++++++++++++++++++++++++++++++
+ 11 files changed, 3840 insertions(+), 2 deletions(-)
+
+diff --git a/Documentation/DocBook/Makefile b/Documentation/DocBook/Makefile
+index ab8300f..95f59e4 100644  
+--- a/Documentation/DocBook/Makefile
++++ b/Documentation/DocBook/Makefile
+@@ -9,7 +9,7 @@
+ DOCBOOKS := z8530book.xml mcabook.xml device-drivers.xml \
+ 	    kernel-hacking.xml kernel-locking.xml deviceiobook.xml \
+ 	    procfs-guide.xml writing_usb_driver.xml networking.xml \
+-	    kernel-api.xml filesystems.xml lsm.xml usb.xml kgdb.xml \
++	    kernel-api.xml filesystems.xml lsm.xml usb.xml kgdb.xml utrace.xml \
+ 	    gadget.xml libata.xml mtdnand.xml librs.xml rapidio.xml \
+ 	    genericirq.xml s390-drivers.xml uio-howto.xml scsi.xml \
+ 	    mac80211.xml debugobjects.xml sh.xml regulator.xml \
+diff --git a/Documentation/DocBook/utrace.tmpl b/Documentation/DocBook/utrace.tmpl
+new file mode 100644
+index ...e149f49 100644  
+--- /dev/null
++++ b/Documentation/DocBook/utrace.tmpl
+@@ -0,0 +1,590 @@
++<?xml version="1.0" encoding="UTF-8"?>
++<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
++"http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []>
++
++<book id="utrace">
++  <bookinfo>
++    <title>The utrace User Debugging Infrastructure</title>
++  </bookinfo>
++
++  <toc></toc>
++
++  <chapter id="concepts"><title>utrace concepts</title>
++
++  <sect1 id="intro"><title>Introduction</title>
++
++  <para>
++    <application>utrace</application> is infrastructure code for tracing
++    and controlling user threads.  This is the foundation for writing
++    tracing engines, which can be loadable kernel modules.
++  </para>
++
++  <para>
++    The basic actors in <application>utrace</application> are the thread
++    and the tracing engine.  A tracing engine is some body of code that
++    calls into the <filename>&lt;linux/utrace.h&gt;</filename>
++    interfaces, represented by a <structname>struct
++    utrace_engine_ops</structname>.  (Usually it's a kernel module,
++    though the legacy <function>ptrace</function> support is a tracing
++    engine that is not in a kernel module.)  The interface operates on
++    individual threads (<structname>struct task_struct</structname>).
++    If an engine wants to treat several threads as a group, that is up
++    to its higher-level code.
++  </para>
++
++  <para>
++    Tracing begins by attaching an engine to a thread, using
++    <function>utrace_attach_task</function> or
++    <function>utrace_attach_pid</function>.  If successful, it returns a
++    pointer that is the handle used in all other calls.
++  </para>
++
++  </sect1>
++
++  <sect1 id="callbacks"><title>Events and Callbacks</title>
++
++  <para>
++    An attached engine does nothing by default.  An engine makes something
++    happen by requesting callbacks via <function>utrace_set_events</function>
++    and poking the thread with <function>utrace_control</function>.
++    The synchronization issues related to these two calls
++    are discussed further below in <xref linkend="teardown"/>.
++  </para>
++
++  <para>
++    Events are specified using the macro
++    <constant>UTRACE_EVENT(<replaceable>type</replaceable>)</constant>.
++    Each event type is associated with a callback in <structname>struct
++    utrace_engine_ops</structname>.  A tracing engine can leave unused
++    callbacks <constant>NULL</constant>.  The only callbacks required
++    are those used by the event flags it sets.
++  </para>
++
++  <para>
++    Many engines can be attached to each thread.  When a thread has an
++    event, each engine gets a callback if it has set the event flag for
++    that event type.  For most events, engines are called in the order they
++    attached.  Engines that attach after the event has occurred do not get
++    callbacks for that event.  This includes any new engines just attached
++    by an existing engine's callback function.  Once the sequence of
++    callbacks for that one event has completed, such new engines are then
++    eligible in the next sequence that starts when there is another event.
++  </para>
++
++  <para>
++    Event reporting callbacks have details particular to the event type,
++    but are all called in similar environments and have the same
++    constraints.  Callbacks are made from safe points, where no locks
++    are held, no special resources are pinned (usually), and the
++    user-mode state of the thread is accessible.  So, callback code has
++    a pretty free hand.  But to be a good citizen, callback code should
++    never block for long periods.  It is fine to block in
++    <function>kmalloc</function> and the like, but never wait for i/o or
++    for user mode to do something.  If you need the thread to wait, use
++    <constant>UTRACE_STOP</constant> and return from the callback
++    quickly.  When your i/o finishes or whatever, you can use
++    <function>utrace_control</function> to resume the thread.
++  </para>
++
++  <para>
++    The <constant>UTRACE_EVENT(SYSCALL_ENTRY)</constant> event is a special
++    case.  While other events happen in the kernel when it will return to
++    user mode soon, this event happens when entering the kernel before it
++    will proceed with the work requested from user mode.  Because of this
++    difference, the <function>report_syscall_entry</function> callback is
++    special in two ways.  For this event, engines are called in reverse of
++    the normal order (this includes the <function>report_quiesce</function>
++    call that precedes a <function>report_syscall_entry</function> call).
++    This preserves the semantics that the last engine to attach is called
++    "closest to user mode"--the engine that is first to see a thread's user
++    state when it enters the kernel is also the last to see that state when
++    the thread returns to user mode.  For the same reason, if these
++    callbacks use <constant>UTRACE_STOP</constant> (see the next section),
++    the thread stops immediately after callbacks rather than only when it's
++    ready to return to user mode; when allowed to resume, it will actually
++    attempt the system call indicated by the register values at that time.
++  </para>
++
++  </sect1>
++
++  <sect1 id="safely"><title>Stopping Safely</title>
++
++  <sect2 id="well-behaved"><title>Writing well-behaved callbacks</title>
++
++  <para>
++    Well-behaved callbacks are important to maintain two essential
++    properties of the interface.  The first of these is that unrelated
++    tracing engines should not interfere with each other.  If your engine's
++    event callback does not return quickly, then another engine won't get
++    the event notification in a timely manner.  The second important
++    property is that tracing should be as noninvasive as possible to the
++    normal operation of the system overall and of the traced thread in
++    particular.  That is, attached tracing engines should not perturb a
++    thread's behavior, except to the extent that changing its user-visible
++    state is explicitly what you want to do.  (Obviously some perturbation
++    is unavoidable, primarily timing changes, ranging from small delays due
++    to the overhead of tracing, to arbitrary pauses in user code execution
++    when a user stops a thread with a debugger for examination.)  Even when
++    you explicitly want the perturbation of making the traced thread block,
++    just blocking directly in your callback has more unwanted effects.  For
++    example, the <constant>CLONE</constant> event callbacks are called when
++    the new child thread has been created but not yet started running; the
++    child can never be scheduled until the <constant>CLONE</constant>
++    tracing callbacks return.  (This allows engines tracing the parent to
++    attach to the child.)  If a <constant>CLONE</constant> event callback
++    blocks the parent thread, it also prevents the child thread from
++    running (even to process a <constant>SIGKILL</constant>).  If what you
++    want is to make both the parent and child block, then use
++    <function>utrace_attach_task</function> on the child and then use
++    <constant>UTRACE_STOP</constant> on both threads.  A more crucial
++    problem with blocking in callbacks is that it can prevent
++    <constant>SIGKILL</constant> from working.  A thread that is blocking
++    due to <constant>UTRACE_STOP</constant> will still wake up and die
++    immediately when sent a <constant>SIGKILL</constant>, as all threads
++    should.  Relying on the <application>utrace</application>
++    infrastructure rather than on private synchronization calls in event
++    callbacks is an important way to help keep tracing robustly
++    noninvasive.
++  </para>
++
++  </sect2>
++
++  <sect2 id="UTRACE_STOP"><title>Using <constant>UTRACE_STOP</constant></title>
++
++  <para>
++    To control another thread and access its state, it must be stopped
++    with <constant>UTRACE_STOP</constant>.  This means that it is
++    stopped and won't start running again while we access it.  When a
++    thread is not already stopped, <function>utrace_control</function>
++    returns <constant>-EINPROGRESS</constant> and an engine must wait
++    for an event callback when the thread is ready to stop.  The thread
++    may be running on another CPU or may be blocked.  When it is ready
++    to be examined, it will make callbacks to engines that set the
++    <constant>UTRACE_EVENT(QUIESCE)</constant> event bit.  To wake up an
++    interruptible wait, use <constant>UTRACE_INTERRUPT</constant>.
++  </para>
++
++  <para>
++    As long as some engine has used <constant>UTRACE_STOP</constant> and
++    not called <function>utrace_control</function> to resume the thread,
++    then the thread will remain stopped.  <constant>SIGKILL</constant>
++    will wake it up, but it will not run user code.  When the stop is
++    cleared with <function>utrace_control</function> or a callback
++    return value, the thread starts running again.
++    (See also <xref linkend="teardown"/>.)
++  </para>
++
++  </sect2>
++
++  </sect1>
++
++  <sect1 id="teardown"><title>Tear-down Races</title>
++
++  <sect2 id="SIGKILL"><title>Primacy of <constant>SIGKILL</constant></title>
++  <para>
++    Ordinarily synchronization issues for tracing engines are kept fairly
++    straightforward by using <constant>UTRACE_STOP</constant>.  You ask a
++    thread to stop, and then once it makes the
++    <function>report_quiesce</function> callback it cannot do anything else
++    that would result in another callback, until you let it with a
++    <function>utrace_control</function> call.  This simple arrangement
++    avoids complex and error-prone code in each one of a tracing engine's
++    event callbacks to keep them serialized with the engine's other
++    operations done on that thread from another thread of control.
++    However, giving tracing engines complete power to keep a traced thread
++    stuck in place runs afoul of a more important kind of simplicity that
++    the kernel overall guarantees: nothing can prevent or delay
++    <constant>SIGKILL</constant> from making a thread die and release its
++    resources.  To preserve this important property of
++    <constant>SIGKILL</constant>, it as a special case can break
++    <constant>UTRACE_STOP</constant> like nothing else normally can.  This
++    includes both explicit <constant>SIGKILL</constant> signals and the
++    implicit <constant>SIGKILL</constant> sent to each other thread in the
++    same thread group by a thread doing an exec, or processing a fatal
++    signal, or making an <function>exit_group</function> system call.  A
++    tracing engine can prevent a thread from beginning the exit or exec or
++    dying by signal (other than <constant>SIGKILL</constant>) if it is
++    attached to that thread, but once the operation begins, no tracing
++    engine can prevent or delay all other threads in the same thread group
++    dying.
++  </para>
++  </sect2>
++
++  <sect2 id="reap"><title>Final callbacks</title>
++  <para>
++    The <function>report_reap</function> callback is always the final event
++    in the life cycle of a traced thread.  Tracing engines can use this as
++    the trigger to clean up their own data structures.  The
++    <function>report_death</function> callback is always the penultimate
++    event a tracing engine might see; it's seen unless the thread was
++    already in the midst of dying when the engine attached.  Many tracing
++    engines will have no interest in when a parent reaps a dead process,
++    and nothing they want to do with a zombie thread once it dies; for
++    them, the <function>report_death</function> callback is the natural
++    place to clean up data structures and detach.  To facilitate writing
++    such engines robustly, given the asynchrony of
++    <constant>SIGKILL</constant>, and without error-prone manual
++    implementation of synchronization schemes, the
++    <application>utrace</application> infrastructure provides some special
++    guarantees about the <function>report_death</function> and
++    <function>report_reap</function> callbacks.  It still takes some care
++    to be sure your tracing engine is robust to tear-down races, but these
++    rules make it reasonably straightforward and concise to handle a lot of
++    corner cases correctly.
++  </para>
++  </sect2>
++
++  <sect2 id="refcount"><title>Engine and task pointers</title>
++  <para>
++    The first sort of guarantee concerns the core data structures
++    themselves.  <structname>struct utrace_engine</structname> is
++    a reference-counted data structure.  While you hold a reference, an
++    engine pointer will always stay valid so that you can safely pass it to
++    any <application>utrace</application> call.  Each call to
++    <function>utrace_attach_task</function> or
++    <function>utrace_attach_pid</function> returns an engine pointer with a
++    reference belonging to the caller.  You own that reference until you
++    drop it using <function>utrace_engine_put</function>.  There is an
++    implicit reference on the engine while it is attached.  So if you drop
++    your only reference, and then use
++    <function>utrace_attach_task</function> without
++    <constant>UTRACE_ATTACH_CREATE</constant> to look up that same engine,
++    you will get the same pointer with a new reference to replace the one
++    you dropped, just like calling <function>utrace_engine_get</function>.
++    When an engine has been detached, either explicitly with
++    <constant>UTRACE_DETACH</constant> or implicitly after
++    <function>report_reap</function>, then any references you hold are all
++    that keep the old engine pointer alive.
++  </para>
++
++  <para>
++    There is nothing a kernel module can do to keep a <structname>struct
++    task_struct</structname> alive outside of
++    <function>rcu_read_lock</function>.  When the task dies and is reaped
++    by its parent (or itself), that structure can be freed so that any
++    dangling pointers you have stored become invalid.
++    <application>utrace</application> will not prevent this, but it can
++    help you detect it safely.  By definition, a task that has been reaped
++    has had all its engines detached.  All
++    <application>utrace</application> calls can be safely called on a
++    detached engine if the caller holds a reference on that engine pointer,
++    even if the task pointer passed in the call is invalid.  All calls
++    return <constant>-ESRCH</constant> for a detached engine, which tells
++    you that the task pointer you passed could be invalid now.  Since
++    <function>utrace_control</function> and
++    <function>utrace_set_events</function> do not block, you can call those
++    inside a <function>rcu_read_lock</function> section and be sure after
++    they don't return <constant>-ESRCH</constant> that the task pointer is
++    still valid until <function>rcu_read_unlock</function>.  The
++    infrastructure never holds task references of its own.  Though neither
++    <function>rcu_read_lock</function> nor any other lock is held while
++    making a callback, it's always guaranteed that the <structname>struct
++    task_struct</structname> and the <structname>struct
++    utrace_engine</structname> passed as arguments remain valid
++    until the callback function returns.
++  </para>
++
++  <para>
++    The common means for safely holding task pointers that is available to
++    kernel modules is to use <structname>struct pid</structname>, which
++    permits <function>put_pid</function> from kernel modules.  When using
++    that, the calls <function>utrace_attach_pid</function>,
++    <function>utrace_control_pid</function>,
++    <function>utrace_set_events_pid</function>, and
++    <function>utrace_barrier_pid</function> are available.
++  </para>
++  </sect2>
++
++  <sect2 id="reap-after-death">
++    <title>
++      Serialization of <constant>DEATH</constant> and <constant>REAP</constant>
++    </title>
++    <para>
++      The second guarantee is the serialization of
++      <constant>DEATH</constant> and <constant>REAP</constant> event
++      callbacks for a given thread.  The actual reaping by the parent
++      (<function>release_task</function> call) can occur simultaneously
++      while the thread is still doing the final steps of dying, including
++      the <function>report_death</function> callback.  If a tracing engine
++      has requested both <constant>DEATH</constant> and
++      <constant>REAP</constant> event reports, it's guaranteed that the
++      <function>report_reap</function> callback will not be made until
++      after the <function>report_death</function> callback has returned.
++      If the <function>report_death</function> callback itself detaches
++      from the thread, then the <function>report_reap</function> callback
++      will never be made.  Thus it is safe for a
++      <function>report_death</function> callback to clean up data
++      structures and detach.
++    </para>
++  </sect2>
++
++  <sect2 id="interlock"><title>Interlock with final callbacks</title>
++  <para>
++    The final sort of guarantee is that a tracing engine will know for sure
++    whether or not the <function>report_death</function> and/or
++    <function>report_reap</function> callbacks will be made for a certain
++    thread.  These tear-down races are disambiguated by the error return
++    values of <function>utrace_set_events</function> and
++    <function>utrace_control</function>.  Normally
++    <function>utrace_control</function> called with
++    <constant>UTRACE_DETACH</constant> returns zero, and this means that no
++    more callbacks will be made.  If the thread is in the midst of dying,
++    it returns <constant>-EALREADY</constant> to indicate that the
++    <constant>report_death</constant> callback may already be in progress;
++    when you get this error, you know that any cleanup your
++    <function>report_death</function> callback does is about to happen or
++    has just happened--note that if the <function>report_death</function>
++    callback does not detach, the engine remains attached until the thread
++    gets reaped.  If the thread is in the midst of being reaped,
++    <function>utrace_control</function> returns <constant>-ESRCH</constant>
++    to indicate that the <function>report_reap</function> callback may
++    already be in progress; this means the engine is implicitly detached
++    when the callback completes.  This makes it possible for a tracing
++    engine that has decided asynchronously to detach from a thread to
++    safely clean up its data structures, knowing that no
++    <function>report_death</function> or <function>report_reap</function>
++    callback will try to do the same.  <constant>utrace_detach</constant>
++    returns <constant>-ESRCH</constant> when the <structname>struct
++    utrace_engine</structname> has already been detached, but is
++    still a valid pointer because of its reference count.  A tracing engine
++    can use this to safely synchronize its own independent multiple threads
++    of control with each other and with its event callbacks that detach.
++  </para>
++
++  <para>
++    In the same vein, <function>utrace_set_events</function> normally
++    returns zero; if the target thread was stopped before the call, then
++    after a successful call, no event callbacks not requested in the new
++    flags will be made.  It fails with <constant>-EALREADY</constant> if
++    you try to clear <constant>UTRACE_EVENT(DEATH)</constant> when the
++    <function>report_death</function> callback may already have begun, if
++    you try to clear <constant>UTRACE_EVENT(REAP)</constant> when the
++    <function>report_reap</function> callback may already have begun, or if
++    you try to newly set <constant>UTRACE_EVENT(DEATH)</constant> or
++    <constant>UTRACE_EVENT(QUIESCE)</constant> when the target is already
++    dead or dying.  Like <function>utrace_control</function>, it returns
++    <constant>-ESRCH</constant> when the thread has already been detached
++    (including forcible detach on reaping).  This lets the tracing engine
++    know for sure which event callbacks it will or won't see after
++    <function>utrace_set_events</function> has returned.  By checking for
++    errors, it can know whether to clean up its data structures immediately
++    or to let its callbacks do the work.
++  </para>
++  </sect2>
++
++  <sect2 id="barrier"><title>Using <function>utrace_barrier</function></title>
++  <para>
++    When a thread is safely stopped, calling
++    <function>utrace_control</function> with <constant>UTRACE_DETACH</constant>
++    or calling <function>utrace_set_events</function> to disable some events
++    ensures synchronously that your engine won't get any more of the callbacks
++    that have been disabled (none at all when detaching).  But these can also
++    be used while the thread is not stopped, when it might be simultaneously
++    making a callback to your engine.  For this situation, these calls return
++    <constant>-EINPROGRESS</constant> when it's possible a callback is in
++    progress.  If you are not prepared to have your old callbacks still run,
++    then you can synchronize to be sure all the old callbacks are finished,
++    using <function>utrace_barrier</function>.  This is necessary if the
++    kernel module containing your callback code is going to be unloaded.
++  </para>
++  <para>
++    After using <constant>UTRACE_DETACH</constant> once, further calls to
++    <function>utrace_control</function> with the same engine pointer will
++    return <constant>-ESRCH</constant>.  In contrast, after getting
++    <constant>-EINPROGRESS</constant> from
++    <function>utrace_set_events</function>, you can call
++    <function>utrace_set_events</function> again later and if it returns zero
++    then know the old callbacks have finished.
++  </para>
++  <para>
++    Unlike all other calls, <function>utrace_barrier</function> (and
++    <function>utrace_barrier_pid</function>) will accept any engine pointer you
++    hold a reference on, even if <constant>UTRACE_DETACH</constant> has already
++    been used.  After any <function>utrace_control</function> or
++    <function>utrace_set_events</function> call (these do not block), you can
++    call <function>utrace_barrier</function> to block until callbacks have
++    finished.  This returns <constant>-ESRCH</constant> only if the engine is
++    completely detached (finished all callbacks).  Otherwise it waits
++    until the thread is definitely not in the midst of a callback to this
++    engine and then returns zero, but can return
++    <constant>-ERESTARTSYS</constant> if its wait is interrupted.
++  </para>
++  </sect2>
++
++</sect1>
++
++</chapter>
++
++<chapter id="core"><title>utrace core API</title>
++
++<para>
++  The utrace API is declared in <filename>&lt;linux/utrace.h&gt;</filename>.
++</para>
++
++!Iinclude/linux/utrace.h
++!Ekernel/utrace.c
++
++</chapter>
++
++<chapter id="machine"><title>Machine State</title>
++
++<para>
++  The <function>task_current_syscall</function> function can be used on any
++  valid <structname>struct task_struct</structname> at any time, and does
++  not even require that <function>utrace_attach_task</function> was used at all.
++</para>
++
++<para>
++  The other ways to access the registers and other machine-dependent state of
++  a task can only be used on a task that is at a known safe point.  The safe
++  points are all the places where <function>utrace_set_events</function> can
++  request callbacks (except for the <constant>DEATH</constant> and
++  <constant>REAP</constant> events).  So at any event callback, it is safe to
++  examine <varname>current</varname>.
++</para>
++
++<para>
++  One task can examine another only after a callback in the target task that
++  returns <constant>UTRACE_STOP</constant> so that task will not return to user
++  mode after the safe point.  This guarantees that the task will not resume
++  until the same engine uses <function>utrace_control</function>, unless the
++  task dies suddenly.  To examine safely, one must use a pair of calls to
++  <function>utrace_prepare_examine</function> and
++  <function>utrace_finish_examine</function> surrounding the calls to
++  <structname>struct user_regset</structname> functions or direct examination
++  of task data structures.  <function>utrace_prepare_examine</function> returns
++  an error if the task is not properly stopped, or is dead.  After a
++  successful examination, the paired <function>utrace_finish_examine</function>
++  call returns an error if the task ever woke up during the examination.  If
++  so, any data gathered may be scrambled and should be discarded.  This means
++  there was a spurious wake-up (which should not happen), or a sudden death.
++</para>
++
++<sect1 id="regset"><title><structname>struct user_regset</structname></title>
++
++<para>
++  The <structname>struct user_regset</structname> API
++  is declared in <filename>&lt;linux/regset.h&gt;</filename>.
++</para>
++
++!Finclude/linux/regset.h
++
++</sect1>
++
++<sect1 id="task_current_syscall">
++  <title><filename>System Call Information</filename></title>
++
++<para>
++  This function is declared in <filename>&lt;linux/ptrace.h&gt;</filename>.
++</para>
++
++!Elib/syscall.c
++
++</sect1>
++
++<sect1 id="syscall"><title><filename>System Call Tracing</filename></title>
++
++<para>
++  The arch API for system call information is declared in
++  <filename>&lt;asm/syscall.h&gt;</filename>.
++  Each of these calls can be used only at system call entry tracing,
++  or can be used only at system call exit and the subsequent safe points
++  before returning to user mode.
++  At system call entry tracing means either during a
++  <structfield>report_syscall_entry</structfield> callback,
++  or any time after that callback has returned <constant>UTRACE_STOP</constant>.
++</para>
++
++!Finclude/asm-generic/syscall.h
++
++</sect1>
++
++</chapter>
++
++<chapter id="internals"><title>Kernel Internals</title>
++
++<para>
++  This chapter covers the interface to the tracing infrastructure
++  from the core of the kernel and the architecture-specific code.
++  This is for maintainers of the kernel and arch code, and not relevant
++  to using the tracing facilities described in preceding chapters.
++</para>
++
++<sect1 id="tracehook"><title>Core Calls In</title>
++
++<para>
++  These calls are declared in <filename>&lt;linux/tracehook.h&gt;</filename>.
++  The core kernel calls these functions at various important places.
++</para>
++
++!Finclude/linux/tracehook.h
++
++</sect1>
++
++<sect1 id="arch"><title>Architecture Calls Out</title>
++
++<para>
++  An arch that has done all these things sets
++  <constant>CONFIG_HAVE_ARCH_TRACEHOOK</constant>.
++  This is required to enable the <application>utrace</application> code.
++</para>
++
++<sect2 id="arch-ptrace"><title><filename>&lt;asm/ptrace.h&gt;</filename></title>
++
++<para>
++  An arch defines these in <filename>&lt;asm/ptrace.h&gt;</filename>
++  if it supports hardware single-step or block-step features.
++</para>
++
++!Finclude/linux/ptrace.h arch_has_single_step arch_has_block_step
++!Finclude/linux/ptrace.h user_enable_single_step user_enable_block_step
++!Finclude/linux/ptrace.h user_disable_single_step
++
++</sect2>
++
++<sect2 id="arch-syscall">
++  <title><filename>&lt;asm/syscall.h&gt;</filename></title>
++
++  <para>
++    An arch provides <filename>&lt;asm/syscall.h&gt;</filename> that
++    defines these as inlines, or declares them as exported functions.
++    These interfaces are described in <xref linkend="syscall"/>.
++  </para>
++
++</sect2>
++
++<sect2 id="arch-tracehook">
++  <title><filename>&lt;linux/tracehook.h&gt;</filename></title>
++
++  <para>
++    An arch must define <constant>TIF_NOTIFY_RESUME</constant>
++    and <constant>TIF_SYSCALL_TRACE</constant>
++    in its <filename>&lt;asm/thread_info.h&gt;</filename>.
++    The arch code must call the following functions, all declared
++    in <filename>&lt;linux/tracehook.h&gt;</filename> and
++    described in <xref linkend="tracehook"/>:
++
++    <itemizedlist>
++      <listitem>
++	<para><function>tracehook_notify_resume</function></para>
++      </listitem>
++      <listitem>
++	<para><function>tracehook_report_syscall_entry</function></para>
++      </listitem>
++      <listitem>
++	<para><function>tracehook_report_syscall_exit</function></para>
++      </listitem>
++      <listitem>
++	<para><function>tracehook_signal_handler</function></para>
++      </listitem>
++    </itemizedlist>
++
++  </para>
++
++</sect2>
++
++</sect1>
++
++</chapter>
++
++</book>
+diff --git a/fs/proc/array.c b/fs/proc/array.c
+index 822c2d5..9069c91 100644  
+--- a/fs/proc/array.c
++++ b/fs/proc/array.c
+@@ -82,6 +82,7 @@
+ #include <linux/pid_namespace.h>
+ #include <linux/ptrace.h>
+ #include <linux/tracehook.h>
++#include <linux/utrace.h>
+ 
+ #include <asm/pgtable.h>
+ #include <asm/processor.h>
+@@ -189,6 +190,8 @@ static inline void task_state(struct seq
+ 		cred->uid, cred->euid, cred->suid, cred->fsuid,
+ 		cred->gid, cred->egid, cred->sgid, cred->fsgid);
+ 
++	task_utrace_proc_status(m, p);
++
+ 	task_lock(p);
+ 	if (p->files)
+ 		fdt = files_fdtable(p->files);
+diff --git a/include/linux/sched.h b/include/linux/sched.h
+index 6c8928b..139d300 100644  
+--- a/include/linux/sched.h
++++ b/include/linux/sched.h
+@@ -1393,6 +1393,11 @@ struct task_struct {
+ #endif
+ 	seccomp_t seccomp;
+ 
++#ifdef CONFIG_UTRACE
++	struct utrace *utrace;
++	unsigned long utrace_flags;
++#endif
++
+ /* Thread group tracking */
+    	u32 parent_exec_id;
+    	u32 self_exec_id;
+diff --git a/include/linux/tracehook.h b/include/linux/tracehook.h
+index c78b2f4..71fa250 100644  
+--- a/include/linux/tracehook.h
++++ b/include/linux/tracehook.h
+@@ -49,6 +49,7 @@
+ #include <linux/sched.h>
+ #include <linux/ptrace.h>
+ #include <linux/security.h>
++#include <linux/utrace.h>
+ struct linux_binprm;
+ 
+ /**
+@@ -63,6 +64,8 @@ struct linux_binprm;
+  */
+ static inline int tracehook_expect_breakpoints(struct task_struct *task)
+ {
++	if (unlikely(task_utrace_flags(task) & UTRACE_EVENT(SIGNAL_CORE)))
++		return 1;
+ 	return (task_ptrace(task) & PT_PTRACED) != 0;
+ }
+ 
+@@ -111,6 +114,9 @@ static inline void ptrace_report_syscall
+ static inline __must_check int tracehook_report_syscall_entry(
+ 	struct pt_regs *regs)
+ {
++	if ((task_utrace_flags(current) & UTRACE_EVENT(SYSCALL_ENTRY)) &&
++	    utrace_report_syscall_entry(regs))
++		return 1;
+ 	ptrace_report_syscall(regs);
+ 	return 0;
+ }
+@@ -134,6 +140,9 @@ static inline __must_check int tracehook
+  */
+ static inline void tracehook_report_syscall_exit(struct pt_regs *regs, int step)
+ {
++	if (task_utrace_flags(current) & UTRACE_EVENT(SYSCALL_EXIT))
++		utrace_report_syscall_exit(regs);
++
+ 	if (step && (task_ptrace(current) & PT_PTRACED)) {
+ 		siginfo_t info;
+ 		user_single_step_siginfo(current, regs, &info);
+@@ -201,6 +210,8 @@ static inline void tracehook_report_exec
+ 					 struct linux_binprm *bprm,
+ 					 struct pt_regs *regs)
+ {
++	if (unlikely(task_utrace_flags(current) & UTRACE_EVENT(EXEC)))
++		utrace_report_exec(fmt, bprm, regs);
+ 	if (!ptrace_event(PT_TRACE_EXEC, PTRACE_EVENT_EXEC, 0) &&
+ 	    unlikely(task_ptrace(current) & PT_PTRACED))
+ 		send_sig(SIGTRAP, current, 0);
+@@ -218,10 +229,37 @@ static inline void tracehook_report_exec
+  */
+ static inline void tracehook_report_exit(long *exit_code)
+ {
++	if (unlikely(task_utrace_flags(current) & UTRACE_EVENT(EXIT)))
++		utrace_report_exit(exit_code);
+ 	ptrace_event(PT_TRACE_EXIT, PTRACE_EVENT_EXIT, *exit_code);
+ }
+ 
+ /**
++ * tracehook_init_task - task_struct has just been copied
++ * @task:		new &struct task_struct just copied from parent
++ *
++ * Called from do_fork() when @task has just been duplicated.
++ * After this, @task will be passed to tracehook_free_task()
++ * even if the rest of its setup fails before it is fully created.
++ */
++static inline void tracehook_init_task(struct task_struct *task)
++{
++	utrace_init_task(task);
++}
++
++/**
++ * tracehook_free_task - task_struct is being freed
++ * @task:		dead &struct task_struct being freed
++ *
++ * Called from free_task() when @task is no longer in use.
++ */
++static inline void tracehook_free_task(struct task_struct *task)
++{
++	if (task_utrace_struct(task))
++		utrace_free_task(task);
++}
++
++/**
+  * tracehook_prepare_clone - prepare for new child to be cloned
+  * @clone_flags:	%CLONE_* flags from clone/fork/vfork system call
+  *
+@@ -285,6 +323,8 @@ static inline void tracehook_report_clon
+ 					  unsigned long clone_flags,
+ 					  pid_t pid, struct task_struct *child)
+ {
++	if (unlikely(task_utrace_flags(current) & UTRACE_EVENT(CLONE)))
++		utrace_report_clone(clone_flags, child);
+ 	if (unlikely(task_ptrace(child))) {
+ 		/*
+ 		 * It doesn't matter who attached/attaching to this
+@@ -317,6 +357,9 @@ static inline void tracehook_report_clon
+ 						   pid_t pid,
+ 						   struct task_struct *child)
+ {
++	if (unlikely(task_utrace_flags(current) & UTRACE_EVENT(CLONE)) &&
++	    (clone_flags & CLONE_VFORK))
++		utrace_finish_vfork(current);
+ 	if (unlikely(trace))
+ 		ptrace_event(0, trace, pid);
+ }
+@@ -351,6 +394,10 @@ static inline void tracehook_report_vfor
+  */
+ static inline void tracehook_prepare_release_task(struct task_struct *task)
+ {
++	/* see utrace_add_engine() about this barrier */
++	smp_mb();
++	if (task_utrace_flags(task))
++		utrace_maybe_reap(task, task_utrace_struct(task), true);
+ }
+ 
+ /**
+@@ -365,6 +412,7 @@ static inline void tracehook_prepare_rel
+ static inline void tracehook_finish_release_task(struct task_struct *task)
+ {
+ 	ptrace_release_task(task);
++	BUG_ON(task->exit_state != EXIT_DEAD);
+ }
+ 
+ /**
+@@ -386,6 +434,8 @@ static inline void tracehook_signal_hand
+ 					    const struct k_sigaction *ka,
+ 					    struct pt_regs *regs, int stepping)
+ {
++	if (task_utrace_flags(current))
++		utrace_signal_handler(current, stepping);
+ 	if (stepping && (task_ptrace(current) & PT_PTRACED))
+ 		ptrace_notify(SIGTRAP);
+ }
+@@ -403,6 +453,8 @@ static inline void tracehook_signal_hand
+ static inline int tracehook_consider_ignored_signal(struct task_struct *task,
+ 						    int sig)
+ {
++	if (unlikely(task_utrace_flags(task) & UTRACE_EVENT(SIGNAL_IGN)))
++		return 1;
+ 	return (task_ptrace(task) & PT_PTRACED) != 0;
+ }
+ 
+@@ -422,6 +474,9 @@ static inline int tracehook_consider_ign
+ static inline int tracehook_consider_fatal_signal(struct task_struct *task,
+ 						  int sig)
+ {
++	if (unlikely(task_utrace_flags(task) & (UTRACE_EVENT(SIGNAL_TERM) |
++						UTRACE_EVENT(SIGNAL_CORE))))
++		return 1;
+ 	return (task_ptrace(task) & PT_PTRACED) != 0;
+ }
+ 
+@@ -436,6 +491,8 @@ static inline int tracehook_consider_fat
+  */
+ static inline int tracehook_force_sigpending(void)
+ {
++	if (unlikely(task_utrace_flags(current)))
++		return utrace_interrupt_pending();
+ 	return 0;
+ }
+ 
+@@ -465,6 +522,8 @@ static inline int tracehook_get_signal(s
+ 				       siginfo_t *info,
+ 				       struct k_sigaction *return_ka)
+ {
++	if (unlikely(task_utrace_flags(task)))
++		return utrace_get_signal(task, regs, info, return_ka);
+ 	return 0;
+ }
+ 
+@@ -492,6 +551,8 @@ static inline int tracehook_get_signal(s
+  */
+ static inline int tracehook_notify_jctl(int notify, int why)
+ {
++	if (task_utrace_flags(current) & UTRACE_EVENT(JCTL))
++		utrace_report_jctl(notify, why);
+ 	return notify ?: task_ptrace(current) ? why : 0;
+ }
+ 
+@@ -502,6 +563,8 @@ static inline int tracehook_notify_jctl(
+  */
+ static inline void tracehook_finish_jctl(void)
+ {
++	if (task_utrace_flags(current))
++		utrace_finish_stop();
+ }
+ 
+ #define DEATH_REAP			-1
+@@ -524,6 +587,8 @@ static inline void tracehook_finish_jctl
+ static inline int tracehook_notify_death(struct task_struct *task,
+ 					 void **death_cookie, int group_dead)
+ {
++	*death_cookie = task_utrace_struct(task);
++
+ 	if (task_detached(task))
+ 		return task->ptrace ? SIGCHLD : DEATH_REAP;
+ 
+@@ -560,6 +625,15 @@ static inline void tracehook_report_deat
+ 					  int signal, void *death_cookie,
+ 					  int group_dead)
+ {
++	/*
++	 * If utrace_set_events() was just called to enable
++	 * UTRACE_EVENT(DEATH), then we are obliged to call
++	 * utrace_report_death() and not miss it.  utrace_set_events()
++	 * checks @task->exit_state under tasklist_lock to synchronize
++	 * with exit_notify(), the caller.
++	 */
++	if (task_utrace_flags(task) & _UTRACE_DEATH_EVENTS)
++		utrace_report_death(task, death_cookie, group_dead, signal);
+ }
+ 
+ #ifdef TIF_NOTIFY_RESUME
+@@ -589,10 +663,21 @@ static inline void set_notify_resume(str
+  * asynchronously, this will be called again before we return to
+  * user mode.
+  *
+- * Called without locks.
++ * Called without locks.  However, on some machines this may be
++ * called with interrupts disabled.
+  */
+ static inline void tracehook_notify_resume(struct pt_regs *regs)
+ {
++	struct task_struct *task = current;
++	/*
++	 * Prevent the following store/load from getting ahead of the
++	 * caller which clears TIF_NOTIFY_RESUME. This pairs with the
++	 * implicit mb() before setting TIF_NOTIFY_RESUME in
++	 * set_notify_resume().
++	 */
++	smp_mb();
++	if (task_utrace_flags(task))
++		utrace_resume(task, regs);
+ }
+ #endif	/* TIF_NOTIFY_RESUME */
+ 
+diff --git a/include/linux/utrace.h b/include/linux/utrace.h
+new file mode 100644
+index ...f251efe 100644  
+--- /dev/null
++++ b/include/linux/utrace.h
+@@ -0,0 +1,692 @@
++/*
++ * utrace infrastructure interface for debugging user processes
++ *
++ * Copyright (C) 2006-2009 Red Hat, Inc.  All rights reserved.
++ *
++ * This copyrighted material is made available to anyone wishing to use,
++ * modify, copy, or redistribute it subject to the terms and conditions
++ * of the GNU General Public License v.2.
++ *
++ * Red Hat Author: Roland McGrath.
++ *
++ * This interface allows for notification of interesting events in a
++ * thread.  It also mediates access to thread state such as registers.
++ * Multiple unrelated users can be associated with a single thread.
++ * We call each of these a tracing engine.
++ *
++ * A tracing engine starts by calling utrace_attach_task() or
++ * utrace_attach_pid() on the chosen thread, passing in a set of hooks
++ * (&struct utrace_engine_ops), and some associated data.  This produces a
++ * &struct utrace_engine, which is the handle used for all other
++ * operations.  An attached engine has its ops vector, its data, and an
++ * event mask controlled by utrace_set_events().
++ *
++ * For each event bit that is set, that engine will get the
++ * appropriate ops->report_*() callback when the event occurs.  The
++ * &struct utrace_engine_ops need not provide callbacks for an event
++ * unless the engine sets one of the associated event bits.
++ */
++
++#ifndef _LINUX_UTRACE_H
++#define _LINUX_UTRACE_H	1
++
++#include <linux/list.h>
++#include <linux/kref.h>
++#include <linux/signal.h>
++#include <linux/sched.h>
++
++struct linux_binprm;
++struct pt_regs;
++struct utrace;
++struct user_regset;
++struct user_regset_view;
++
++/*
++ * Event bits passed to utrace_set_events().
++ * These appear in &struct task_struct.@utrace_flags
++ * and &struct utrace_engine.@flags.
++ */
++enum utrace_events {
++	_UTRACE_EVENT_QUIESCE,	/* Thread is available for examination.  */
++	_UTRACE_EVENT_REAP,  	/* Zombie reaped, no more tracing possible.  */
++	_UTRACE_EVENT_CLONE,	/* Successful clone/fork/vfork just done.  */
++	_UTRACE_EVENT_EXEC,	/* Successful execve just completed.  */
++	_UTRACE_EVENT_EXIT,	/* Thread exit in progress.  */
++	_UTRACE_EVENT_DEATH,	/* Thread has died.  */
++	_UTRACE_EVENT_SYSCALL_ENTRY, /* User entered kernel for system call. */
++	_UTRACE_EVENT_SYSCALL_EXIT, /* Returning to user after system call.  */
++	_UTRACE_EVENT_SIGNAL,	/* Signal delivery will run a user handler.  */
++	_UTRACE_EVENT_SIGNAL_IGN, /* No-op signal to be delivered.  */
++	_UTRACE_EVENT_SIGNAL_STOP, /* Signal delivery will suspend.  */
++	_UTRACE_EVENT_SIGNAL_TERM, /* Signal delivery will terminate.  */
++	_UTRACE_EVENT_SIGNAL_CORE, /* Signal delivery will dump core.  */
++	_UTRACE_EVENT_JCTL,	/* Job control stop or continue completed.  */
++	_UTRACE_NEVENTS
++};
++#define UTRACE_EVENT(type)	(1UL << _UTRACE_EVENT_##type)
++
++/*
++ * All the kinds of signal events.
++ * These all use the @report_signal() callback.
++ */
++#define UTRACE_EVENT_SIGNAL_ALL	(UTRACE_EVENT(SIGNAL) \
++				 | UTRACE_EVENT(SIGNAL_IGN) \
++				 | UTRACE_EVENT(SIGNAL_STOP) \
++				 | UTRACE_EVENT(SIGNAL_TERM) \
++				 | UTRACE_EVENT(SIGNAL_CORE))
++/*
++ * Both kinds of syscall events; these call the @report_syscall_entry()
++ * and @report_syscall_exit() callbacks, respectively.
++ */
++#define UTRACE_EVENT_SYSCALL	\
++	(UTRACE_EVENT(SYSCALL_ENTRY) | UTRACE_EVENT(SYSCALL_EXIT))
++
++/*
++ * The event reports triggered synchronously by task death.
++ */
++#define _UTRACE_DEATH_EVENTS (UTRACE_EVENT(DEATH) | UTRACE_EVENT(QUIESCE))
++
++/*
++ * Hooks in <linux/tracehook.h> call these entry points to the utrace dispatch.
++ */
++void utrace_free_task(struct task_struct *);
++bool utrace_interrupt_pending(void);
++void utrace_resume(struct task_struct *, struct pt_regs *);
++void utrace_finish_stop(void);
++void utrace_maybe_reap(struct task_struct *, struct utrace *, bool);
++int utrace_get_signal(struct task_struct *, struct pt_regs *,
++		      siginfo_t *, struct k_sigaction *);
++void utrace_report_clone(unsigned long, struct task_struct *);
++void utrace_finish_vfork(struct task_struct *);
++void utrace_report_exit(long *exit_code);
++void utrace_report_death(struct task_struct *, struct utrace *, bool, int);
++void utrace_report_jctl(int notify, int type);
++void utrace_report_exec(struct linux_binfmt *, struct linux_binprm *,
++			struct pt_regs *regs);
++bool utrace_report_syscall_entry(struct pt_regs *);
++void utrace_report_syscall_exit(struct pt_regs *);
++void utrace_signal_handler(struct task_struct *, int);
++
++#ifndef CONFIG_UTRACE
++
++/*
++ * <linux/tracehook.h> uses these accessors to avoid #ifdef CONFIG_UTRACE.
++ */
++static inline unsigned long task_utrace_flags(struct task_struct *task)
++{
++	return 0;
++}
++static inline struct utrace *task_utrace_struct(struct task_struct *task)
++{
++	return NULL;
++}
++static inline void utrace_init_task(struct task_struct *child)
++{
++}
++
++static inline void task_utrace_proc_status(struct seq_file *m,
++					   struct task_struct *p)
++{
++}
++
++#else  /* CONFIG_UTRACE */
++
++static inline unsigned long task_utrace_flags(struct task_struct *task)
++{
++	return task->utrace_flags;
++}
++
++static inline struct utrace *task_utrace_struct(struct task_struct *task)
++{
++	struct utrace *utrace;
++
++	/*
++	 * This barrier ensures that any prior load of task->utrace_flags
++	 * is ordered before this load of task->utrace.  We use those
++	 * utrace_flags checks in the hot path to decide to call into
++	 * the utrace code.  The first attach installs task->utrace before
++	 * setting task->utrace_flags nonzero with implicit barrier in
++	 * between, see utrace_add_engine().
++	 */
++	smp_rmb();
++	utrace = task->utrace;
++
++	smp_read_barrier_depends(); /* See utrace_task_alloc().  */
++	return utrace;
++}
++
++static inline void utrace_init_task(struct task_struct *task)
++{
++	task->utrace_flags = 0;
++	task->utrace = NULL;
++}
++
++void task_utrace_proc_status(struct seq_file *m, struct task_struct *p);
++
++
++/*
++ * Version number of the API defined in this file.  This will change
++ * whenever a tracing engine's code would need some updates to keep
++ * working.  We maintain this here for the benefit of tracing engine code
++ * that is developed concurrently with utrace API improvements before they
++ * are merged into the kernel, making LINUX_VERSION_CODE checks unwieldy.
++ */
++#define UTRACE_API_VERSION	20091216
++
++/**
++ * enum utrace_resume_action - engine's choice of action for a traced task
++ * @UTRACE_STOP:		Stay quiescent after callbacks.
++ * @UTRACE_INTERRUPT:		Make @report_signal() callback soon.
++ * @UTRACE_REPORT:		Make some callback soon.
++ * @UTRACE_SINGLESTEP:		Resume in user mode for one instruction.
++ * @UTRACE_BLOCKSTEP:		Resume in user mode until next branch.
++ * @UTRACE_RESUME:		Resume normally in user mode.
++ * @UTRACE_DETACH:		Detach my engine (implies %UTRACE_RESUME).
++ *
++ * See utrace_control() for detailed descriptions of each action.  This is
++ * encoded in the @action argument and the return value for every callback
++ * with a &u32 return value.
++ *
++ * The order of these is important.  When there is more than one engine,
++ * each supplies its choice and the smallest value prevails.
++ */
++enum utrace_resume_action {
++	UTRACE_STOP,
++	UTRACE_INTERRUPT,
++	UTRACE_REPORT,
++	UTRACE_SINGLESTEP,
++	UTRACE_BLOCKSTEP,
++	UTRACE_RESUME,
++	UTRACE_DETACH,
++	UTRACE_RESUME_MAX
++};
++#define UTRACE_RESUME_BITS	(ilog2(UTRACE_RESUME_MAX) + 1)
++#define UTRACE_RESUME_MASK	((1 << UTRACE_RESUME_BITS) - 1)
++
++/**
++ * utrace_resume_action - &enum utrace_resume_action from callback action
++ * @action:		&u32 callback @action argument or return value
++ *
++ * This extracts the &enum utrace_resume_action from @action,
++ * which is the @action argument to a &struct utrace_engine_ops
++ * callback or the return value from one.
++ */
++static inline enum utrace_resume_action utrace_resume_action(u32 action)
++{
++	return action & UTRACE_RESUME_MASK;
++}
++
++/**
++ * enum utrace_signal_action - disposition of signal
++ * @UTRACE_SIGNAL_DELIVER:	Deliver according to sigaction.
++ * @UTRACE_SIGNAL_IGN:		Ignore the signal.
++ * @UTRACE_SIGNAL_TERM:		Terminate the process.
++ * @UTRACE_SIGNAL_CORE:		Terminate with core dump.
++ * @UTRACE_SIGNAL_STOP:		Deliver as absolute stop.
++ * @UTRACE_SIGNAL_TSTP:		Deliver as job control stop.
++ * @UTRACE_SIGNAL_REPORT:	Reporting before pending signals.
++ * @UTRACE_SIGNAL_HANDLER:	Reporting after signal handler setup.
++ *
++ * This is encoded in the @action argument and the return value for
++ * a @report_signal() callback.  It says what will happen to the
++ * signal described by the &siginfo_t parameter to the callback.
++ *
++ * The %UTRACE_SIGNAL_REPORT value is used in an @action argument when
++ * a tracing report is being made before dequeuing any pending signal.
++ * If this is immediately after a signal handler has been set up, then
++ * %UTRACE_SIGNAL_HANDLER is used instead.  A @report_signal callback
++ * that uses %UTRACE_SIGNAL_DELIVER|%UTRACE_SINGLESTEP will ensure
++ * it sees a %UTRACE_SIGNAL_HANDLER report.
++ */
++enum utrace_signal_action {
++	UTRACE_SIGNAL_DELIVER	= 0x00,
++	UTRACE_SIGNAL_IGN	= 0x10,
++	UTRACE_SIGNAL_TERM	= 0x20,
++	UTRACE_SIGNAL_CORE	= 0x30,
++	UTRACE_SIGNAL_STOP	= 0x40,
++	UTRACE_SIGNAL_TSTP	= 0x50,
++	UTRACE_SIGNAL_REPORT	= 0x60,
++	UTRACE_SIGNAL_HANDLER	= 0x70
++};
++#define	UTRACE_SIGNAL_MASK	0xf0
++#define UTRACE_SIGNAL_HOLD	0x100 /* Flag, push signal back on queue.  */
++
++/**
++ * utrace_signal_action - &enum utrace_signal_action from callback action
++ * @action:		@report_signal callback @action argument or return value
++ *
++ * This extracts the &enum utrace_signal_action from @action, which
++ * is the @action argument to a @report_signal callback or the
++ * return value from one.
++ */
++static inline enum utrace_signal_action utrace_signal_action(u32 action)
++{
++	return action & UTRACE_SIGNAL_MASK;
++}
++
++/**
++ * enum utrace_syscall_action - disposition of system call attempt
++ * @UTRACE_SYSCALL_RUN:		Run the system call.
++ * @UTRACE_SYSCALL_ABORT:	Don't run the system call.
++ *
++ * This is encoded in the @action argument and the return value for
++ * a @report_syscall_entry callback.
++ */
++enum utrace_syscall_action {
++	UTRACE_SYSCALL_RUN	= 0x00,
++	UTRACE_SYSCALL_ABORT	= 0x10
++};
++#define	UTRACE_SYSCALL_MASK	0xf0
++#define	UTRACE_SYSCALL_RESUMED	0x100 /* Flag, report_syscall_entry() repeats */
++
++/**
++ * utrace_syscall_action - &enum utrace_syscall_action from callback action
++ * @action:		@report_syscall_entry callback @action or return value
++ *
++ * This extracts the &enum utrace_syscall_action from @action, which
++ * is the @action argument to a @report_syscall_entry callback or the
++ * return value from one.
++ */
++static inline enum utrace_syscall_action utrace_syscall_action(u32 action)
++{
++	return action & UTRACE_SYSCALL_MASK;
++}
++
++/*
++ * Flags for utrace_attach_task() and utrace_attach_pid().
++ */
++#define UTRACE_ATTACH_MATCH_OPS		0x0001 /* Match engines on ops.  */
++#define UTRACE_ATTACH_MATCH_DATA	0x0002 /* Match engines on data.  */
++#define UTRACE_ATTACH_MATCH_MASK	0x000f
++#define UTRACE_ATTACH_CREATE		0x0010 /* Attach a new engine.  */
++#define UTRACE_ATTACH_EXCLUSIVE		0x0020 /* Refuse if existing match.  */
++
++/**
++ * struct utrace_engine - per-engine structure
++ * @ops:	&struct utrace_engine_ops pointer passed to utrace_attach_task()
++ * @data:	engine-private &void * passed to utrace_attach_task()
++ * @flags:	event mask set by utrace_set_events() plus internal flag bits
++ *
++ * The task itself never has to worry about engines detaching while
++ * it's doing event callbacks.  These structures are removed from the
++ * task's active list only when it's stopped, or by the task itself.
++ *
++ * utrace_engine_get() and utrace_engine_put() maintain a reference count.
++ * When it drops to zero, the structure is freed.  One reference is held
++ * implicitly while the engine is attached to its task.
++ */
++struct utrace_engine {
++/* private: */
++	struct kref kref;
++	void (*release)(void *);
++	struct list_head entry;
++
++/* public: */
++	const struct utrace_engine_ops *ops;
++	void *data;
++
++	unsigned long flags;
++};
++
++/**
++ * utrace_engine_get - acquire a reference on a &struct utrace_engine
++ * @engine:	&struct utrace_engine pointer
++ *
++ * You must hold a reference on @engine, and you get another.
++ */
++static inline void utrace_engine_get(struct utrace_engine *engine)
++{
++	kref_get(&engine->kref);
++}
++
++void __utrace_engine_release(struct kref *);
++
++/**
++ * utrace_engine_put - release a reference on a &struct utrace_engine
++ * @engine:	&struct utrace_engine pointer
++ *
++ * You must hold a reference on @engine, and you lose that reference.
++ * If it was the last one, @engine becomes an invalid pointer.
++ */
++static inline void utrace_engine_put(struct utrace_engine *engine)
++{
++	kref_put(&engine->kref, __utrace_engine_release);
++}
++
++/**
++ * struct utrace_engine_ops - tracing engine callbacks
++ *
++ * Each @report_*() callback corresponds to an %UTRACE_EVENT(*) bit.
++ * utrace_set_events() calls on @engine choose which callbacks will
++ * be made to @engine from @task.
++ *
++ * Most callbacks take an @action argument, giving the resume action
++ * chosen by other tracing engines.  All callbacks take an @engine
++ * argument.  The @report_reap callback takes a @task argument that
++ * might or might not be @current.  All other @report_* callbacks
++ * report an event in the @current task.
++ *
++ * For some calls, @action also includes bits specific to that event
++ * and utrace_resume_action() is used to extract the resume action.
++ * This shows what would happen if @engine wasn't there, or will if
++ * the callback's return value uses %UTRACE_RESUME.  This always
++ * starts as %UTRACE_RESUME when no other tracing is being done on
++ * this task.
++ *
++ * All return values contain &enum utrace_resume_action bits.  For
++ * some calls, other bits specific to that kind of event are added to
++ * the resume action bits with OR.  These are the same bits used in
++ * the @action argument.  The resume action returned by a callback
++ * does not override previous engines' choices, it only says what
++ * @engine wants done.  What @current actually does is the action that's
++ * most constrained among the choices made by all attached engines.
++ * See utrace_control() for more information on the actions.
++ *
++ * When %UTRACE_STOP is used in @report_syscall_entry, then @current
++ * stops before attempting the system call.  In this case, another
++ * @report_syscall_entry callback will follow after @current resumes if
++ * %UTRACE_REPORT or %UTRACE_INTERRUPT was returned by some callback
++ * or passed to utrace_control().  In a second or later callback,
++ * %UTRACE_SYSCALL_RESUMED is set in the @action argument to indicate
++ * a repeat callback still waiting to attempt the same system call
++ * invocation.  This repeat callback gives each engine an opportunity
++ * to reexamine registers another engine might have changed while
++ * @current was held in %UTRACE_STOP.
++ *
++ * In other cases, the resume action does not take effect until @current
++ * is ready to check for signals and return to user mode.  If there
++ * are more callbacks to be made, the last round of calls determines
++ * the final action.  A @report_quiesce callback with @event zero, or
++ * a @report_signal callback, will always be the last one made before
++ * @current resumes.  Only %UTRACE_STOP is "sticky"--if @engine returned
++ * %UTRACE_STOP then @current stays stopped unless @engine returns
++ * different from a following callback.
++ *
++ * The report_death() and report_reap() callbacks do not take @action
++ * arguments, and only %UTRACE_DETACH is meaningful in the return value
++ * from a report_death() callback.  None of the resume actions applies
++ * to a dead thread.
++ *
++ * All @report_*() hooks are called with no locks held, in a generally
++ * safe environment when we will be returning to user mode soon (or just
++ * entered the kernel).  It is fine to block for memory allocation and
++ * the like, but all hooks are asynchronous and must not block on
++ * external events!  If you want the thread to block, use %UTRACE_STOP
++ * in your hook's return value; then later wake it up with utrace_control().
++ *
++ * @report_quiesce:
++ *	Requested by %UTRACE_EVENT(%QUIESCE).
++ *	This does not indicate any event, but just that @current is in a
++ *	safe place for examination.  This call is made before each specific
++ *	event callback, except for @report_reap.  The @event argument gives
++ *	the %UTRACE_EVENT(@which) value for the event occurring.  This
++ *	callback might be made for events @engine has not requested, if
++ *	some other engine is tracing the event; calling utrace_set_events()
++ *	call here can request the immediate callback for this occurrence of
++ *	@event.  @event is zero when there is no other event, @current is
++ *	now ready to check for signals and return to user mode, and some
++ *	engine has used %UTRACE_REPORT or %UTRACE_INTERRUPT to request this
++ *	callback.  For this case, if @report_signal is not %NULL, the
++ *	@report_quiesce callback may be replaced with a @report_signal
++ *	callback passing %UTRACE_SIGNAL_REPORT in its @action argument,
++ *	whenever @current is entering the signal-check path anyway.
++ *
++ * @report_signal:
++ *	Requested by %UTRACE_EVENT(%SIGNAL_*) or %UTRACE_EVENT(%QUIESCE).
++ *	Use utrace_signal_action() and utrace_resume_action() on @action.
++ *	The signal action is %UTRACE_SIGNAL_REPORT when some engine has
++ *	used %UTRACE_REPORT or %UTRACE_INTERRUPT; the callback can choose
++ *	to stop or to deliver an artificial signal, before pending signals.
++ *	It's %UTRACE_SIGNAL_HANDLER instead when signal handler setup just
++ *	finished (after a previous %UTRACE_SIGNAL_DELIVER return); this
++ *	serves in lieu of any %UTRACE_SIGNAL_REPORT callback requested by
++ *	%UTRACE_REPORT or %UTRACE_INTERRUPT, and is also implicitly
++ *	requested by %UTRACE_SINGLESTEP or %UTRACE_BLOCKSTEP into the
++ *	signal delivery.  The other signal actions indicate a signal about
++ *	to be delivered; the previous engine's return value sets the signal
++ *	action seen by the the following engine's callback.  The @info data
++ *	can be changed at will, including @info->si_signo.  The settings in
++ *	@return_ka determines what %UTRACE_SIGNAL_DELIVER does.  @orig_ka
++ *	is what was in force before other tracing engines intervened, and
++ *	it's %NULL when this report began as %UTRACE_SIGNAL_REPORT or
++ *	%UTRACE_SIGNAL_HANDLER.  For a report without a new signal, @info
++ *	is left uninitialized and must be set completely by an engine that
++ *	chooses to deliver a signal; if there was a previous @report_signal
++ *	callback ending in %UTRACE_STOP and it was just resumed using
++ *	%UTRACE_REPORT or %UTRACE_INTERRUPT, then @info is left unchanged
++ *	from the previous callback.  In this way, the original signal can
++ *	be left in @info while returning %UTRACE_STOP|%UTRACE_SIGNAL_IGN
++ *	and then found again when resuming with %UTRACE_INTERRUPT.
++ *	The %UTRACE_SIGNAL_HOLD flag bit can be OR'd into the return value,
++ *	and might be in @action if the previous engine returned it.  This
++ *	flag asks that the signal in @info be pushed back on @current's queue
++ *	so that it will be seen again after whatever action is taken now.
++ *
++ * @report_clone:
++ *	Requested by %UTRACE_EVENT(%CLONE).
++ *	Event reported for parent, before the new task @child might run.
++ *	@clone_flags gives the flags used in the clone system call, or
++ *	equivalent flags for a fork() or vfork() system call.  This
++ *	function can use utrace_attach_task() on @child.  Then passing
++ *	%UTRACE_STOP to utrace_control() on @child here keeps the child
++ *	stopped before it ever runs in user mode, %UTRACE_REPORT or
++ *	%UTRACE_INTERRUPT ensures a callback from @child before it
++ *	starts in user mode.
++ *
++ * @report_jctl:
++ *	Requested by %UTRACE_EVENT(%JCTL).
++ *	Job control event; @type is %CLD_STOPPED or %CLD_CONTINUED,
++ *	indicating whether we are stopping or resuming now.  If @notify
++ *	is nonzero, @current is the last thread to stop and so will send
++ *	%SIGCHLD to its parent after this callback; @notify reflects
++ *	what the parent's %SIGCHLD has in @si_code, which can sometimes
++ *	be %CLD_STOPPED even when @type is %CLD_CONTINUED.
++ *
++ * @report_exec:
++ *	Requested by %UTRACE_EVENT(%EXEC).
++ *	An execve system call has succeeded and the new program is about to
++ *	start running.  The initial user register state is handy to be tweaked
++ *	directly in @regs.  @fmt and @bprm gives the details of this exec.
++ *
++ * @report_syscall_entry:
++ *	Requested by %UTRACE_EVENT(%SYSCALL_ENTRY).
++ *	Thread has entered the kernel to request a system call.
++ *	The user register state is handy to be tweaked directly in @regs.
++ *	The @action argument contains an &enum utrace_syscall_action,
++ *	use utrace_syscall_action() to extract it.  The return value
++ *	overrides the last engine's action for the system call.
++ *	If the final action is %UTRACE_SYSCALL_ABORT, no system call
++ *	is made.  The details of the system call being attempted can
++ *	be fetched here with syscall_get_nr() and syscall_get_arguments().
++ *	The parameter registers can be changed with syscall_set_arguments().
++ *	See above about the %UTRACE_SYSCALL_RESUMED flag in @action.
++ *	Use %UTRACE_REPORT in the return value to guarantee you get
++ *	another callback (with %UTRACE_SYSCALL_RESUMED flag) in case
++ *	@current stops with %UTRACE_STOP before attempting the system call.
++ *
++ * @report_syscall_exit:
++ *	Requested by %UTRACE_EVENT(%SYSCALL_EXIT).
++ *	Thread is about to leave the kernel after a system call request.
++ *	The user register state is handy to be tweaked directly in @regs.
++ *	The results of the system call attempt can be examined here using
++ *	syscall_get_error() and syscall_get_return_value().  It is safe
++ *	here to call syscall_set_return_value() or syscall_rollback().
++ *
++ * @report_exit:
++ *	Requested by %UTRACE_EVENT(%EXIT).
++ *	Thread is exiting and cannot be prevented from doing so,
++ *	but all its state is still live.  The @code value will be
++ *	the wait result seen by the parent, and can be changed by
++ *	this engine or others.  The @orig_code value is the real
++ *	status, not changed by any tracing engine.  Returning %UTRACE_STOP
++ *	here keeps @current stopped before it cleans up its state and dies,
++ *	so it can be examined by other processes.  When @current is allowed
++ *	to run, it will die and get to the @report_death callback.
++ *
++ * @report_death:
++ *	Requested by %UTRACE_EVENT(%DEATH).
++ *	Thread is really dead now.  It might be reaped by its parent at
++ *	any time, or self-reap immediately.  Though the actual reaping
++ *	may happen in parallel, a report_reap() callback will always be
++ *	ordered after a report_death() callback.
++ *
++ * @report_reap:
++ *	Requested by %UTRACE_EVENT(%REAP).
++ *	Called when someone reaps the dead task (parent, init, or self).
++ *	This means the parent called wait, or else this was a detached
++ *	thread or a process whose parent ignores SIGCHLD.
++ *	No more callbacks are made after this one.
++ *	The engine is always detached.
++ *	There is nothing more a tracing engine can do about this thread.
++ *	After this callback, the @engine pointer will become invalid.
++ *	The @task pointer may become invalid if get_task_struct() hasn't
++ *	been used to keep it alive.
++ *	An engine should always request this callback if it stores the
++ *	@engine pointer or stores any pointer in @engine->data, so it
++ *	can clean up its data structures.
++ *	Unlike other callbacks, this can be called from the parent's context
++ *	rather than from the traced thread itself--it must not delay the
++ *	parent by blocking.
++ *
++ * @release:
++ *	If not %NULL, this is called after the last utrace_engine_put()
++ *	call for a &struct utrace_engine, which could be implicit after
++ *	a %UTRACE_DETACH return from another callback.  Its argument is
++ *	the engine's @data member.
++ */
++struct utrace_engine_ops {
++	u32 (*report_quiesce)(u32 action, struct utrace_engine *engine,
++			      unsigned long event);
++	u32 (*report_signal)(u32 action, struct utrace_engine *engine,
++			     struct pt_regs *regs,
++			     siginfo_t *info,
++			     const struct k_sigaction *orig_ka,
++			     struct k_sigaction *return_ka);
++	u32 (*report_clone)(u32 action, struct utrace_engine *engine,
++			    unsigned long clone_flags,
++			    struct task_struct *child);
++	u32 (*report_jctl)(u32 action, struct utrace_engine *engine,
++			   int type, int notify);
++	u32 (*report_exec)(u32 action, struct utrace_engine *engine,
++			   const struct linux_binfmt *fmt,
++			   const struct linux_binprm *bprm,
++			   struct pt_regs *regs);
++	u32 (*report_syscall_entry)(u32 action, struct utrace_engine *engine,
++				    struct pt_regs *regs);
++	u32 (*report_syscall_exit)(u32 action, struct utrace_engine *engine,
++				   struct pt_regs *regs);
++	u32 (*report_exit)(u32 action, struct utrace_engine *engine,
++			   long orig_code, long *code);
++	u32 (*report_death)(struct utrace_engine *engine,
++			    bool group_dead, int signal);
++	void (*report_reap)(struct utrace_engine *engine,
++			    struct task_struct *task);
++	void (*release)(void *data);
++};
++
++/**
++ * struct utrace_examiner - private state for using utrace_prepare_examine()
++ *
++ * The members of &struct utrace_examiner are private to the implementation.
++ * This data type holds the state from a call to utrace_prepare_examine()
++ * to be used by a call to utrace_finish_examine().
++ */
++struct utrace_examiner {
++/* private: */
++	long state;
++	unsigned long ncsw;
++};
++
++/*
++ * These are the exported entry points for tracing engines to use.
++ * See kernel/utrace.c for their kerneldoc comments with interface details.
++ */
++struct utrace_engine *utrace_attach_task(struct task_struct *, int,
++					 const struct utrace_engine_ops *,
++					 void *);
++struct utrace_engine *utrace_attach_pid(struct pid *, int,
++					const struct utrace_engine_ops *,
++					void *);
++int __must_check utrace_control(struct task_struct *,
++				struct utrace_engine *,
++				enum utrace_resume_action);
++int __must_check utrace_set_events(struct task_struct *,
++				   struct utrace_engine *,
++				   unsigned long eventmask);
++int __must_check utrace_barrier(struct task_struct *,
++				struct utrace_engine *);
++int __must_check utrace_prepare_examine(struct task_struct *,
++					struct utrace_engine *,
++					struct utrace_examiner *);
++int __must_check utrace_finish_examine(struct task_struct *,
++				       struct utrace_engine *,
++				       struct utrace_examiner *);
++
++/**
++ * utrace_control_pid - control a thread being traced by a tracing engine
++ * @pid:		thread to affect
++ * @engine:		attached engine to affect
++ * @action:		&enum utrace_resume_action for thread to do
++ *
++ * This is the same as utrace_control(), but takes a &struct pid
++ * pointer rather than a &struct task_struct pointer.  The caller must
++ * hold a ref on @pid, but does not need to worry about the task
++ * staying valid.  If it's been reaped so that @pid points nowhere,
++ * then this call returns -%ESRCH.
++ */
++static inline __must_check int utrace_control_pid(
++	struct pid *pid, struct utrace_engine *engine,
++	enum utrace_resume_action action)
++{
++	/*
++	 * We don't bother with rcu_read_lock() here to protect the
++	 * task_struct pointer, because utrace_control will return
++	 * -ESRCH without looking at that pointer if the engine is
++	 * already detached.  A task_struct pointer can't die before
++	 * all the engines are detached in release_task() first.
++	 */
++	struct task_struct *task = pid_task(pid, PIDTYPE_PID);
++	return unlikely(!task) ? -ESRCH : utrace_control(task, engine, action);
++}
++
++/**
++ * utrace_set_events_pid - choose which event reports a tracing engine gets
++ * @pid:		thread to affect
++ * @engine:		attached engine to affect
++ * @eventmask:		new event mask
++ *
++ * This is the same as utrace_set_events(), but takes a &struct pid
++ * pointer rather than a &struct task_struct pointer.  The caller must
++ * hold a ref on @pid, but does not need to worry about the task
++ * staying valid.  If it's been reaped so that @pid points nowhere,
++ * then this call returns -%ESRCH.
++ */
++static inline __must_check int utrace_set_events_pid(
++	struct pid *pid, struct utrace_engine *engine, unsigned long eventmask)
++{
++	struct task_struct *task = pid_task(pid, PIDTYPE_PID);
++	return unlikely(!task) ? -ESRCH :
++		utrace_set_events(task, engine, eventmask);
++}
++
++/**
++ * utrace_barrier_pid - synchronize with simultaneous tracing callbacks
++ * @pid:		thread to affect
++ * @engine:		engine to affect (can be detached)
++ *
++ * This is the same as utrace_barrier(), but takes a &struct pid
++ * pointer rather than a &struct task_struct pointer.  The caller must
++ * hold a ref on @pid, but does not need to worry about the task
++ * staying valid.  If it's been reaped so that @pid points nowhere,
++ * then this call returns -%ESRCH.
++ */
++static inline __must_check int utrace_barrier_pid(struct pid *pid,
++						  struct utrace_engine *engine)
++{
++	struct task_struct *task = pid_task(pid, PIDTYPE_PID);
++	return unlikely(!task) ? -ESRCH : utrace_barrier(task, engine);
++}
++
++#endif	/* CONFIG_UTRACE */
++
++#endif	/* linux/utrace.h */
+diff --git a/init/Kconfig b/init/Kconfig
+index eb4b337..140e636 100644  
+--- a/init/Kconfig
++++ b/init/Kconfig
+@@ -310,6 +310,15 @@ config AUDIT_TREE
+ 	depends on AUDITSYSCALL
+ 	select INOTIFY
+ 
++config UTRACE
++	bool "Infrastructure for tracing and debugging user processes"
++	depends on EXPERIMENTAL
++	depends on HAVE_ARCH_TRACEHOOK
++	help
++	  Enable the utrace process tracing interface.  This is an internal
++	  kernel interface exported to kernel modules, to track events in
++	  user threads, extract and change user thread state.
++
+ menu "RCU Subsystem"
+ 
+ choice
+diff --git a/kernel/Makefile b/kernel/Makefile
+index d7c13d2..263bb19 100644  
+--- a/kernel/Makefile
++++ b/kernel/Makefile
+@@ -68,6 +68,7 @@ obj-$(CONFIG_IKCONFIG) += configs.o
+ obj-$(CONFIG_RESOURCE_COUNTERS) += res_counter.o
+ obj-$(CONFIG_STOP_MACHINE) += stop_machine.o
+ obj-$(CONFIG_KPROBES_SANITY_TEST) += test_kprobes.o
++obj-$(CONFIG_UTRACE) += utrace.o
+ obj-$(CONFIG_AUDIT) += audit.o auditfilter.o audit_watch.o
+ obj-$(CONFIG_AUDITSYSCALL) += auditsc.o
+ obj-$(CONFIG_GCOV_KERNEL) += gcov/
+diff --git a/kernel/fork.c b/kernel/fork.c
+index 166b8c4..3ac952e 100644  
+--- a/kernel/fork.c
++++ b/kernel/fork.c
+@@ -152,6 +152,7 @@ void free_task(struct task_struct *tsk)
+ 	free_thread_info(tsk->stack);
+ 	rt_mutex_debug_task_free(tsk);
+ 	ftrace_graph_exit_task(tsk);
++	tracehook_free_task(tsk);
+ 	free_task_struct(tsk);
+ }
+ EXPORT_SYMBOL(free_task);
+@@ -1018,6 +1019,8 @@ static struct task_struct *copy_process(
+ 	if (!p)
+ 		goto fork_out;
+ 
++	tracehook_init_task(p);
++
+ 	ftrace_graph_init_task(p);
+ 
+ 	rt_mutex_init_task(p);
+diff --git a/kernel/ptrace.c b/kernel/ptrace.c
+index b7c1d32..a408bf7 100644  
+--- a/kernel/ptrace.c
++++ b/kernel/ptrace.c
+@@ -16,6 +16,7 @@
+ #include <linux/pagemap.h>
+ #include <linux/smp_lock.h>
+ #include <linux/ptrace.h>
++#include <linux/utrace.h>
+ #include <linux/security.h>
+ #include <linux/signal.h>
+ #include <linux/audit.h>
+@@ -164,6 +165,14 @@ bool ptrace_may_access(struct task_struc
+ 	return !err;
+ }
+ 
++/*
++ * For experimental use of utrace, exclude ptrace on the same task.
++ */
++static inline bool exclude_ptrace(struct task_struct *task)
++{
++	return unlikely(!!task_utrace_flags(task));
++}
++
+ int ptrace_attach(struct task_struct *task)
+ {
+ 	int retval;
+@@ -187,6 +196,8 @@ int ptrace_attach(struct task_struct *ta
+ 
+ 	task_lock(task);
+ 	retval = __ptrace_may_access(task, PTRACE_MODE_ATTACH);
++	if (!retval && exclude_ptrace(task))
++		retval = -EBUSY;
+ 	task_unlock(task);
+ 	if (retval)
+ 		goto unlock_creds;
+@@ -224,6 +235,9 @@ int ptrace_traceme(void)
+ {
+ 	int ret = -EPERM;
+ 
++	if (exclude_ptrace(current)) /* XXX locking */
++		return -EBUSY;
++
+ 	write_lock_irq(&tasklist_lock);
+ 	/* Are we already being traced? */
+ 	if (!current->ptrace) {
+diff --git a/kernel/utrace.c b/kernel/utrace.c
+new file mode 100644
+index ...f003e34 100644  
+--- /dev/null
++++ b/kernel/utrace.c
+@@ -0,0 +1,2436 @@
++/*
++ * utrace infrastructure interface for debugging user processes
++ *
++ * Copyright (C) 2006-2010 Red Hat, Inc.  All rights reserved.
++ *
++ * This copyrighted material is made available to anyone wishing to use,
++ * modify, copy, or redistribute it subject to the terms and conditions
++ * of the GNU General Public License v.2.
++ *
++ * Red Hat Author: Roland McGrath.
++ */
++
++#include <linux/utrace.h>
++#include <linux/tracehook.h>
++#include <linux/regset.h>
++#include <asm/syscall.h>
++#include <linux/ptrace.h>
++#include <linux/err.h>
++#include <linux/sched.h>
++#include <linux/freezer.h>
++#include <linux/module.h>
++#include <linux/init.h>
++#include <linux/slab.h>
++#include <linux/seq_file.h>
++
++
++/*
++ * Per-thread structure private to utrace implementation.
++ * If task_struct.utrace_flags is nonzero, task_struct.utrace
++ * has always been allocated first.  Once allocated, it is
++ * never freed until free_task().
++ *
++ * The common event reporting loops are done by the task making the
++ * report without ever taking any locks.  To facilitate this, the two
++ * lists @attached and @attaching work together for smooth asynchronous
++ * attaching with low overhead.  Modifying either list requires @lock.
++ * The @attaching list can be modified any time while holding @lock.
++ * New engines being attached always go on this list.
++ *
++ * The @attached list is what the task itself uses for its reporting
++ * loops.  When the task itself is not quiescent, it can use the
++ * @attached list without taking any lock.  Nobody may modify the list
++ * when the task is not quiescent.  When it is quiescent, that means
++ * that it won't run again without taking @lock itself before using
++ * the list.
++ *
++ * At each place where we know the task is quiescent (or it's current),
++ * while holding @lock, we call splice_attaching(), below.  This moves
++ * the @attaching list members on to the end of the @attached list.
++ * Since this happens at the start of any reporting pass, any new
++ * engines attached asynchronously go on the stable @attached list
++ * in time to have their callbacks seen.
++ */
++struct utrace {
++	spinlock_t lock;
++	struct list_head attached, attaching;
++
++	struct task_struct *cloning;
++
++	struct utrace_engine *reporting;
++
++	enum utrace_resume_action resume:UTRACE_RESUME_BITS;
++	unsigned int signal_handler:1;
++	unsigned int vfork_stop:1; /* need utrace_stop() before vfork wait */
++	unsigned int death:1;	/* in utrace_report_death() now */
++	unsigned int reap:1;	/* release_task() has run */
++	unsigned int pending_attach:1; /* need splice_attaching() */
++};
++
++static struct kmem_cache *utrace_cachep;
++static struct kmem_cache *utrace_engine_cachep;
++static const struct utrace_engine_ops utrace_detached_ops; /* forward decl */
++
++static int __init utrace_init(void)
++{
++	utrace_cachep = KMEM_CACHE(utrace, SLAB_PANIC);
++	utrace_engine_cachep = KMEM_CACHE(utrace_engine, SLAB_PANIC);
++	return 0;
++}
++module_init(utrace_init);
++
++/*
++ * Set up @task.utrace for the first time.  We can have races
++ * between two utrace_attach_task() calls here.  The task_lock()
++ * governs installing the new pointer.  If another one got in first,
++ * we just punt the new one we allocated.
++ *
++ * This returns false only in case of a memory allocation failure.
++ */
++static bool utrace_task_alloc(struct task_struct *task)
++{
++	struct utrace *utrace = kmem_cache_zalloc(utrace_cachep, GFP_KERNEL);
++	if (unlikely(!utrace))
++		return false;
++	spin_lock_init(&utrace->lock);
++	INIT_LIST_HEAD(&utrace->attached);
++	INIT_LIST_HEAD(&utrace->attaching);
++	utrace->resume = UTRACE_RESUME;
++	task_lock(task);
++	if (likely(!task->utrace)) {
++		/*
++		 * This barrier makes sure the initialization of the struct
++		 * precedes the installation of the pointer.  This pairs
++		 * with smp_read_barrier_depends() in task_utrace_struct().
++		 */
++		smp_wmb();
++		task->utrace = utrace;
++	}
++	task_unlock(task);
++
++	if (unlikely(task->utrace != utrace))
++		kmem_cache_free(utrace_cachep, utrace);
++	return true;
++}
++
++/*
++ * This is called via tracehook_free_task() from free_task()
++ * when @task is being deallocated.
++ */
++void utrace_free_task(struct task_struct *task)
++{
++	kmem_cache_free(utrace_cachep, task->utrace);
++}
++
++/*
++ * This is calledwhen the task is safely quiescent, i.e. it won't consult
++ * utrace->attached without the lock.  Move any engines attached
++ * asynchronously from @utrace->attaching onto the @utrace->attached list.
++ */
++static void splice_attaching(struct utrace *utrace)
++{
++	lockdep_assert_held(&utrace->lock);
++	list_splice_tail_init(&utrace->attaching, &utrace->attached);
++	utrace->pending_attach = 0;
++}
++
++/*
++ * This is the exported function used by the utrace_engine_put() inline.
++ */
++void __utrace_engine_release(struct kref *kref)
++{
++	struct utrace_engine *engine = container_of(kref, struct utrace_engine,
++						    kref);
++	BUG_ON(!list_empty(&engine->entry));
++	if (engine->release)
++		(*engine->release)(engine->data);
++	kmem_cache_free(utrace_engine_cachep, engine);
++}
++EXPORT_SYMBOL_GPL(__utrace_engine_release);
++
++static bool engine_matches(struct utrace_engine *engine, int flags,
++			   const struct utrace_engine_ops *ops, void *data)
++{
++	if ((flags & UTRACE_ATTACH_MATCH_OPS) && engine->ops != ops)
++		return false;
++	if ((flags & UTRACE_ATTACH_MATCH_DATA) && engine->data != data)
++		return false;
++	return engine->ops && engine->ops != &utrace_detached_ops;
++}
++
++static struct utrace_engine *find_matching_engine(
++	struct utrace *utrace, int flags,
++	const struct utrace_engine_ops *ops, void *data)
++{
++	struct utrace_engine *engine;
++	list_for_each_entry(engine, &utrace->attached, entry)
++		if (engine_matches(engine, flags, ops, data))
++			return engine;
++	list_for_each_entry(engine, &utrace->attaching, entry)
++		if (engine_matches(engine, flags, ops, data))
++			return engine;
++	return NULL;
++}
++
++/*
++ * Enqueue @engine, or maybe don't if UTRACE_ATTACH_EXCLUSIVE.
++ */
++static int utrace_add_engine(struct task_struct *target,
++			     struct utrace *utrace,
++			     struct utrace_engine *engine,
++			     int flags,
++			     const struct utrace_engine_ops *ops,
++			     void *data)
++{
++	int ret;
++
++	spin_lock(&utrace->lock);
++
++	ret = -EEXIST;
++	if ((flags & UTRACE_ATTACH_EXCLUSIVE) &&
++	     unlikely(find_matching_engine(utrace, flags, ops, data)))
++		goto unlock;
++
++	/*
++	 * In case we had no engines before, make sure that
++	 * utrace_flags is not zero. Since we did unlock+lock
++	 * at least once after utrace_task_alloc() installed
++	 * ->utrace, we have the necessary barrier which pairs
++	 * with rmb() in task_utrace_struct().
++	 */
++	ret = -ESRCH;
++	if (!target->utrace_flags) {
++		target->utrace_flags = UTRACE_EVENT(REAP);
++		/*
++		 * If we race with tracehook_prepare_release_task()
++		 * make sure that either it sees utrace_flags != 0
++		 * or we see exit_state == EXIT_DEAD.
++		 */
++		smp_mb();
++		if (unlikely(target->exit_state == EXIT_DEAD)) {
++			target->utrace_flags = 0;
++			goto unlock;
++		}
++	}
++
++	/*
++	 * Put the new engine on the pending ->attaching list.
++	 * Make sure it gets onto the ->attached list by the next
++	 * time it's examined.  Setting ->pending_attach ensures
++	 * that start_report() takes the lock and splices the lists
++	 * before the next new reporting pass.
++	 *
++	 * When target == current, it would be safe just to call
++	 * splice_attaching() right here.  But if we're inside a
++	 * callback, that would mean the new engine also gets
++	 * notified about the event that precipitated its own
++	 * creation.  This is not what the user wants.
++	 */
++	list_add_tail(&engine->entry, &utrace->attaching);
++	utrace->pending_attach = 1;
++	ret = 0;
++unlock:
++	spin_unlock(&utrace->lock);
++
++	return ret;
++}
++
++/**
++ * utrace_attach_task - attach new engine, or look up an attached engine
++ * @target:	thread to attach to
++ * @flags:	flag bits combined with OR, see below
++ * @ops:	callback table for new engine
++ * @data:	engine private data pointer
++ *
++ * The caller must ensure that the @target thread does not get freed,
++ * i.e. hold a ref or be its parent.  It is always safe to call this
++ * on @current, or on the @child pointer in a @report_clone callback.
++ * For most other cases, it's easier to use utrace_attach_pid() instead.
++ *
++ * UTRACE_ATTACH_CREATE:
++ * Create a new engine.  If %UTRACE_ATTACH_CREATE is not specified, you
++ * only look up an existing engine already attached to the thread.
++ *
++ * UTRACE_ATTACH_EXCLUSIVE:
++ * Attempting to attach a second (matching) engine fails with -%EEXIST.
++ *
++ * UTRACE_ATTACH_MATCH_OPS: Only consider engines matching @ops.
++ * UTRACE_ATTACH_MATCH_DATA: Only consider engines matching @data.
++ *
++ * Calls with neither %UTRACE_ATTACH_MATCH_OPS nor %UTRACE_ATTACH_MATCH_DATA
++ * match the first among any engines attached to @target.  That means that
++ * %UTRACE_ATTACH_EXCLUSIVE in such a call fails with -%EEXIST if there
++ * are any engines on @target at all.
++ */
++struct utrace_engine *utrace_attach_task(
++	struct task_struct *target, int flags,
++	const struct utrace_engine_ops *ops, void *data)
++{
++	struct utrace *utrace = task_utrace_struct(target);
++	struct utrace_engine *engine;
++	int ret;
++
++	if (!(flags & UTRACE_ATTACH_CREATE)) {
++		if (unlikely(!utrace))
++			return ERR_PTR(-ENOENT);
++		spin_lock(&utrace->lock);
++		engine = find_matching_engine(utrace, flags, ops, data);
++		if (engine)
++			utrace_engine_get(engine);
++		spin_unlock(&utrace->lock);
++		return engine ?: ERR_PTR(-ENOENT);
++	}
++
++	if (unlikely(!ops) || unlikely(ops == &utrace_detached_ops))
++		return ERR_PTR(-EINVAL);
++
++	if (unlikely(target->flags & PF_KTHREAD))
++		/*
++		 * Silly kernel, utrace is for users!
++		 */
++		return ERR_PTR(-EPERM);
++
++	if (!utrace) {
++		if (unlikely(!utrace_task_alloc(target)))
++			return ERR_PTR(-ENOMEM);
++		utrace = task_utrace_struct(target);
++	}
++
++	engine = kmem_cache_alloc(utrace_engine_cachep, GFP_KERNEL);
++	if (unlikely(!engine))
++		return ERR_PTR(-ENOMEM);
++
++	/*
++	 * Initialize the new engine structure.  It starts out with two
++	 * refs: one ref to return, and one ref for being attached.
++	 */
++	kref_set(&engine->kref, 2);
++	engine->flags = 0;
++	engine->ops = ops;
++	engine->data = data;
++	engine->release = ops->release;
++
++	ret = utrace_add_engine(target, utrace, engine, flags, ops, data);
++
++	if (unlikely(ret)) {
++		kmem_cache_free(utrace_engine_cachep, engine);
++		engine = ERR_PTR(ret);
++	}
++
++	return engine;
++}
++EXPORT_SYMBOL_GPL(utrace_attach_task);
++
++/**
++ * utrace_attach_pid - attach new engine, or look up an attached engine
++ * @pid:	&struct pid pointer representing thread to attach to
++ * @flags:	flag bits combined with OR, see utrace_attach_task()
++ * @ops:	callback table for new engine
++ * @data:	engine private data pointer
++ *
++ * This is the same as utrace_attach_task(), but takes a &struct pid
++ * pointer rather than a &struct task_struct pointer.  The caller must
++ * hold a ref on @pid, but does not need to worry about the task
++ * staying valid.  If it's been reaped so that @pid points nowhere,
++ * then this call returns -%ESRCH.
++ */
++struct utrace_engine *utrace_attach_pid(
++	struct pid *pid, int flags,
++	const struct utrace_engine_ops *ops, void *data)
++{
++	struct utrace_engine *engine = ERR_PTR(-ESRCH);
++	struct task_struct *task = get_pid_task(pid, PIDTYPE_PID);
++	if (task) {
++		engine = utrace_attach_task(task, flags, ops, data);
++		put_task_struct(task);
++	}
++	return engine;
++}
++EXPORT_SYMBOL_GPL(utrace_attach_pid);
++
++/*
++ * When an engine is detached, the target thread may still see it and
++ * make callbacks until it quiesces.  We install a special ops vector
++ * with these two callbacks.  When the target thread quiesces, it can
++ * safely free the engine itself.  For any event we will always get
++ * the report_quiesce() callback first, so we only need this one
++ * pointer to be set.  The only exception is report_reap(), so we
++ * supply that callback too.
++ */
++static u32 utrace_detached_quiesce(u32 action, struct utrace_engine *engine,
++				   unsigned long event)
++{
++	return UTRACE_DETACH;
++}
++
++static void utrace_detached_reap(struct utrace_engine *engine,
++				 struct task_struct *task)
++{
++}
++
++static const struct utrace_engine_ops utrace_detached_ops = {
++	.report_quiesce = &utrace_detached_quiesce,
++	.report_reap = &utrace_detached_reap
++};
++
++/*
++ * The caller has to hold a ref on the engine.  If the attached flag is
++ * true (all but utrace_barrier() calls), the engine is supposed to be
++ * attached.  If the attached flag is false (utrace_barrier() only),
++ * then return -ERESTARTSYS for an engine marked for detach but not yet
++ * fully detached.  The task pointer can be invalid if the engine is
++ * detached.
++ *
++ * Get the utrace lock for the target task.
++ * Returns the struct if locked, or ERR_PTR(-errno).
++ *
++ * This has to be robust against races with:
++ *	utrace_control(target, UTRACE_DETACH) calls
++ *	UTRACE_DETACH after reports
++ *	utrace_report_death
++ *	utrace_release_task
++ */
++static struct utrace *get_utrace_lock(struct task_struct *target,
++				      struct utrace_engine *engine,
++				      bool attached)
++	__acquires(utrace->lock)
++{
++	struct utrace *utrace;
++
++	rcu_read_lock();
++
++	/*
++	 * If this engine was already detached, bail out before we look at
++	 * the task_struct pointer at all.  If it's detached after this
++	 * check, then RCU is still keeping this task_struct pointer valid.
++	 *
++	 * The ops pointer is NULL when the engine is fully detached.
++	 * It's &utrace_detached_ops when it's marked detached but still
++	 * on the list.  In the latter case, utrace_barrier() still works,
++	 * since the target might be in the middle of an old callback.
++	 */
++	if (unlikely(!engine->ops)) {
++		rcu_read_unlock();
++		return ERR_PTR(-ESRCH);
++	}
++
++	if (unlikely(engine->ops == &utrace_detached_ops)) {
++		rcu_read_unlock();
++		return attached ? ERR_PTR(-ESRCH) : ERR_PTR(-ERESTARTSYS);
++	}
++
++	utrace = task_utrace_struct(target);
++	spin_lock(&utrace->lock);
++	if (unlikely(!engine->ops) ||
++	    unlikely(engine->ops == &utrace_detached_ops)) {
++		/*
++		 * By the time we got the utrace lock,
++		 * it had been reaped or detached already.
++		 */
++		spin_unlock(&utrace->lock);
++		utrace = ERR_PTR(-ESRCH);
++		if (!attached && engine->ops == &utrace_detached_ops)
++			utrace = ERR_PTR(-ERESTARTSYS);
++	}
++	rcu_read_unlock();
++
++	return utrace;
++}
++
++/*
++ * Now that we don't hold any locks, run through any
++ * detached engines and free their references.  Each
++ * engine had one implicit ref while it was attached.
++ */
++static void put_detached_list(struct list_head *list)
++{
++	struct utrace_engine *engine, *next;
++	list_for_each_entry_safe(engine, next, list, entry) {
++		list_del_init(&engine->entry);
++		utrace_engine_put(engine);
++	}
++}
++
++/*
++ * We use an extra bit in utrace_engine.flags past the event bits,
++ * to record whether the engine is keeping the target thread stopped.
++ *
++ * This bit is set in task_struct.utrace_flags whenever it is set in any
++ * engine's flags.  Only utrace_reset() resets it in utrace_flags.
++ */
++#define ENGINE_STOP		(1UL << _UTRACE_NEVENTS)
++
++static void mark_engine_wants_stop(struct task_struct *task,
++				   struct utrace_engine *engine)
++{
++	engine->flags |= ENGINE_STOP;
++	task->utrace_flags |= ENGINE_STOP;
++}
++
++static void clear_engine_wants_stop(struct utrace_engine *engine)
++{
++	engine->flags &= ~ENGINE_STOP;
++}
++
++static bool engine_wants_stop(struct utrace_engine *engine)
++{
++	return (engine->flags & ENGINE_STOP) != 0;
++}
++
++/**
++ * utrace_set_events - choose which event reports a tracing engine gets
++ * @target:		thread to affect
++ * @engine:		attached engine to affect
++ * @events:		new event mask
++ *
++ * This changes the set of events for which @engine wants callbacks made.
++ *
++ * This fails with -%EALREADY and does nothing if you try to clear
++ * %UTRACE_EVENT(%DEATH) when the @report_death callback may already have
++ * begun, if you try to clear %UTRACE_EVENT(%REAP) when the @report_reap
++ * callback may already have begun, or if you try to newly set
++ * %UTRACE_EVENT(%DEATH) or %UTRACE_EVENT(%QUIESCE) when @target is
++ * already dead or dying.
++ *
++ * This can fail with -%ESRCH when @target has already been detached,
++ * including forcible detach on reaping.
++ *
++ * If @target was stopped before the call, then after a successful call,
++ * no event callbacks not requested in @events will be made; if
++ * %UTRACE_EVENT(%QUIESCE) is included in @events, then a
++ * @report_quiesce callback will be made when @target resumes.
++ *
++ * If @target was not stopped and @events excludes some bits that were
++ * set before, this can return -%EINPROGRESS to indicate that @target
++ * may have been making some callback to @engine.  When this returns
++ * zero, you can be sure that no event callbacks you've disabled in
++ * @events can be made.  If @events only sets new bits that were not set
++ * before on @engine, then -%EINPROGRESS will never be returned.
++ *
++ * To synchronize after an -%EINPROGRESS return, see utrace_barrier().
++ *
++ * When @target is @current, -%EINPROGRESS is not returned.  But note
++ * that a newly-created engine will not receive any callbacks related to
++ * an event notification already in progress.  This call enables @events
++ * callbacks to be made as soon as @engine becomes eligible for any
++ * callbacks, see utrace_attach_task().
++ *
++ * These rules provide for coherent synchronization based on %UTRACE_STOP,
++ * even when %SIGKILL is breaking its normal simple rules.
++ */
++int utrace_set_events(struct task_struct *target,
++		      struct utrace_engine *engine,
++		      unsigned long events)
++{
++	struct utrace *utrace;
++	unsigned long old_flags, old_utrace_flags;
++	int ret;
++
++	/*
++	 * We just ignore the internal bit, so callers can use
++	 * engine->flags to seed bitwise ops for our argument.
++	 */
++	events &= ~ENGINE_STOP;
++
++	utrace = get_utrace_lock(target, engine, true);
++	if (unlikely(IS_ERR(utrace)))
++		return PTR_ERR(utrace);
++
++	old_utrace_flags = target->utrace_flags;
++	old_flags = engine->flags & ~ENGINE_STOP;
++
++	if (target->exit_state &&
++	    (((events & ~old_flags) & _UTRACE_DEATH_EVENTS) ||
++	     (utrace->death &&
++	      ((old_flags & ~events) & _UTRACE_DEATH_EVENTS)) ||
++	     (utrace->reap && ((old_flags & ~events) & UTRACE_EVENT(REAP))))) {
++		spin_unlock(&utrace->lock);
++		return -EALREADY;
++	}
++
++	/*
++	 * When setting these flags, it's essential that we really
++	 * synchronize with exit_notify().  They cannot be set after
++	 * exit_notify() takes the tasklist_lock.  By holding the read
++	 * lock here while setting the flags, we ensure that the calls
++	 * to tracehook_notify_death() and tracehook_report_death() will
++	 * see the new flags.  This ensures that utrace_release_task()
++	 * knows positively that utrace_report_death() will be called or
++	 * that it won't.
++	 */
++	if ((events & ~old_utrace_flags) & _UTRACE_DEATH_EVENTS) {
++		read_lock(&tasklist_lock);
++		if (unlikely(target->exit_state)) {
++			read_unlock(&tasklist_lock);
++			spin_unlock(&utrace->lock);
++			return -EALREADY;
++		}
++		target->utrace_flags |= events;
++		read_unlock(&tasklist_lock);
++	}
++
++	engine->flags = events | (engine->flags & ENGINE_STOP);
++	target->utrace_flags |= events;
++
++	if ((events & UTRACE_EVENT_SYSCALL) &&
++	    !(old_utrace_flags & UTRACE_EVENT_SYSCALL))
++		set_tsk_thread_flag(target, TIF_SYSCALL_TRACE);
++
++	ret = 0;
++	if ((old_flags & ~events) && target != current &&
++	    !task_is_stopped_or_traced(target) && !target->exit_state) {
++		/*
++		 * This barrier ensures that our engine->flags changes
++		 * have hit before we examine utrace->reporting,
++		 * pairing with the barrier in start_callback().  If
++		 * @target has not yet hit finish_callback() to clear
++		 * utrace->reporting, we might be in the middle of a
++		 * callback to @engine.
++		 */
++		smp_mb();
++		if (utrace->reporting == engine)
++			ret = -EINPROGRESS;
++	}
++
++	spin_unlock(&utrace->lock);
++
++	return ret;
++}
++EXPORT_SYMBOL_GPL(utrace_set_events);
++
++/*
++ * Asynchronously mark an engine as being detached.
++ *
++ * This must work while the target thread races with us doing
++ * start_callback(), defined below.  It uses smp_rmb() between checking
++ * @engine->flags and using @engine->ops.  Here we change @engine->ops
++ * first, then use smp_wmb() before changing @engine->flags.  This ensures
++ * it can check the old flags before using the old ops, or check the old
++ * flags before using the new ops, or check the new flags before using the
++ * new ops, but can never check the new flags before using the old ops.
++ * Hence, utrace_detached_ops might be used with any old flags in place.
++ * It has report_quiesce() and report_reap() callbacks to handle all cases.
++ */
++static void mark_engine_detached(struct utrace_engine *engine)
++{
++	engine->ops = &utrace_detached_ops;
++	smp_wmb();
++	engine->flags = UTRACE_EVENT(QUIESCE);
++}
++
++/*
++ * Get @target to stop and return true if it is already stopped now.
++ * If we return false, it will make some event callback soonish.
++ * Called with @utrace locked.
++ */
++static bool utrace_do_stop(struct task_struct *target, struct utrace *utrace)
++{
++	if (task_is_stopped(target)) {
++		/*
++		 * Stopped is considered quiescent; when it wakes up, it will
++		 * go through utrace_finish_stop() before doing anything else.
++		 */
++		spin_lock_irq(&target->sighand->siglock);
++		if (likely(task_is_stopped(target)))
++			__set_task_state(target, TASK_TRACED);
++		spin_unlock_irq(&target->sighand->siglock);
++	} else if (utrace->resume > UTRACE_REPORT) {
++		utrace->resume = UTRACE_REPORT;
++		set_notify_resume(target);
++	}
++
++	return task_is_traced(target);
++}
++
++/*
++ * If the target is not dead it should not be in tracing
++ * stop any more.  Wake it unless it's in job control stop.
++ */
++static void utrace_wakeup(struct task_struct *target, struct utrace *utrace)
++{
++	lockdep_assert_held(&utrace->lock);
++	spin_lock_irq(&target->sighand->siglock);
++	if (target->signal->flags & SIGNAL_STOP_STOPPED ||
++	    target->signal->group_stop_count)
++		target->state = TASK_STOPPED;
++	else
++		wake_up_state(target, __TASK_TRACED);
++	spin_unlock_irq(&target->sighand->siglock);
++}
++
++/*
++ * This is called when there might be some detached engines on the list or
++ * some stale bits in @task->utrace_flags.  Clean them up and recompute the
++ * flags.  Returns true if we're now fully detached.
++ *
++ * Called with @utrace->lock held, returns with it released.
++ * After this returns, @utrace might be freed if everything detached.
++ */
++static bool utrace_reset(struct task_struct *task, struct utrace *utrace)
++	__releases(utrace->lock)
++{
++	struct utrace_engine *engine, *next;
++	unsigned long flags = 0;
++	LIST_HEAD(detached);
++
++	splice_attaching(utrace);
++
++	/*
++	 * Update the set of events of interest from the union
++	 * of the interests of the remaining tracing engines.
++	 * For any engine marked detached, remove it from the list.
++	 * We'll collect them on the detached list.
++	 */
++	list_for_each_entry_safe(engine, next, &utrace->attached, entry) {
++		if (engine->ops == &utrace_detached_ops) {
++			engine->ops = NULL;
++			list_move(&engine->entry, &detached);
++		} else {
++			flags |= engine->flags | UTRACE_EVENT(REAP);
++		}
++	}
++
++	if (task->exit_state) {
++		/*
++		 * Once it's already dead, we never install any flags
++		 * except REAP.  When ->exit_state is set and events
++		 * like DEATH are not set, then they never can be set.
++		 * This ensures that utrace_release_task() knows
++		 * positively that utrace_report_death() can never run.
++		 */
++		BUG_ON(utrace->death);
++		flags &= UTRACE_EVENT(REAP);
++	} else if (!(flags & UTRACE_EVENT_SYSCALL) &&
++		   test_tsk_thread_flag(task, TIF_SYSCALL_TRACE)) {
++		clear_tsk_thread_flag(task, TIF_SYSCALL_TRACE);
++	}
++
++	if (!flags) {
++		/*
++		 * No more engines, cleared out the utrace.
++		 */
++		utrace->resume = UTRACE_RESUME;
++		utrace->signal_handler = 0;
++	}
++
++	/*
++	 * If no more engines want it stopped, wake it up.
++	 */
++	if (task_is_traced(task) && !(flags & ENGINE_STOP))
++		utrace_wakeup(task, utrace);
++
++	/*
++	 * In theory spin_lock() doesn't imply rcu_read_lock().
++	 * Once we clear ->utrace_flags this task_struct can go away
++	 * because tracehook_prepare_release_task() path does not take
++	 * utrace->lock when ->utrace_flags == 0.
++	 */
++	rcu_read_lock();
++	task->utrace_flags = flags;
++	spin_unlock(&utrace->lock);
++	rcu_read_unlock();
++
++	put_detached_list(&detached);
++
++	return !flags;
++}
++
++void utrace_finish_stop(void)
++{
++	/*
++	 * If we were task_is_traced() and then SIGKILL'ed, make
++	 * sure we do nothing until the tracer drops utrace->lock.
++	 */
++	if (unlikely(__fatal_signal_pending(current))) {
++		struct utrace *utrace = task_utrace_struct(current);
++		spin_unlock_wait(&utrace->lock);
++	}
++}
++
++/*
++ * Perform %UTRACE_STOP, i.e. block in TASK_TRACED until woken up.
++ * @task == current, @utrace == current->utrace, which is not locked.
++ * Return true if we were woken up by SIGKILL even though some utrace
++ * engine may still want us to stay stopped.
++ */
++static void utrace_stop(struct task_struct *task, struct utrace *utrace,
++			enum utrace_resume_action action)
++{
++relock:
++	spin_lock(&utrace->lock);
++
++	if (action < utrace->resume) {
++		/*
++		 * Ensure a reporting pass when we're resumed.
++		 */
++		utrace->resume = action;
++		if (action == UTRACE_INTERRUPT)
++			set_thread_flag(TIF_SIGPENDING);
++		else
++			set_thread_flag(TIF_NOTIFY_RESUME);
++	}
++
++	/*
++	 * If the ENGINE_STOP bit is clear in utrace_flags, that means
++	 * utrace_reset() ran after we processed some UTRACE_STOP return
++	 * values from callbacks to get here.  If all engines have detached
++	 * or resumed us, we don't stop.  This check doesn't require
++	 * siglock, but it should follow the interrupt/report bookkeeping
++	 * steps (this can matter for UTRACE_RESUME but not UTRACE_DETACH).
++	 */
++	if (unlikely(!(task->utrace_flags & ENGINE_STOP))) {
++		utrace_reset(task, utrace);
++		if (task->utrace_flags & ENGINE_STOP)
++			goto relock;
++		return;
++	}
++
++	/*
++	 * The siglock protects us against signals.  As well as SIGKILL
++	 * waking us up, we must synchronize with the signal bookkeeping
++	 * for stop signals and SIGCONT.
++	 */
++	spin_lock_irq(&task->sighand->siglock);
++
++	if (unlikely(__fatal_signal_pending(task))) {
++		spin_unlock_irq(&task->sighand->siglock);
++		spin_unlock(&utrace->lock);
++		return;
++	}
++
++	__set_current_state(TASK_TRACED);
++
++	/*
++	 * If there is a group stop in progress,
++	 * we must participate in the bookkeeping.
++	 */
++	if (unlikely(task->signal->group_stop_count) &&
++			!--task->signal->group_stop_count)
++		task->signal->flags = SIGNAL_STOP_STOPPED;
++
++	spin_unlock_irq(&task->sighand->siglock);
++	spin_unlock(&utrace->lock);
++
++	schedule();
++
++	utrace_finish_stop();
++
++	/*
++	 * While in TASK_TRACED, we were considered "frozen enough".
++	 * Now that we woke up, it's crucial if we're supposed to be
++	 * frozen that we freeze now before running anything substantial.
++	 */
++	try_to_freeze();
++
++	/*
++	 * While we were in TASK_TRACED, complete_signal() considered
++	 * us "uninterested" in signal wakeups.  Now make sure our
++	 * TIF_SIGPENDING state is correct for normal running.
++	 */
++	spin_lock_irq(&task->sighand->siglock);
++	recalc_sigpending();
++	spin_unlock_irq(&task->sighand->siglock);
++}
++
++/*
++ * Called by release_task() with @reap set to true.
++ * Called by utrace_report_death() with @reap set to false.
++ * On reap, make report_reap callbacks and clean out @utrace
++ * unless still making callbacks.  On death, update bookkeeping
++ * and handle the reap work if release_task() came in first.
++ */
++void utrace_maybe_reap(struct task_struct *target, struct utrace *utrace,
++		       bool reap)
++{
++	struct utrace_engine *engine, *next;
++	struct list_head attached;
++
++	spin_lock(&utrace->lock);
++
++	if (reap) {
++		/*
++		 * If the target will do some final callbacks but hasn't
++		 * finished them yet, we know because it clears these event
++		 * bits after it's done.  Instead of cleaning up here and
++		 * requiring utrace_report_death() to cope with it, we
++		 * delay the REAP report and the teardown until after the
++		 * target finishes its death reports.
++		 */
++		utrace->reap = 1;
++
++		if (target->utrace_flags & _UTRACE_DEATH_EVENTS) {
++			spin_unlock(&utrace->lock);
++			return;
++		}
++	} else {
++		/*
++		 * After we unlock with this flag clear, any competing
++		 * utrace_control/utrace_set_events calls know that we've
++		 * finished our callbacks and any detach bookkeeping.
++		 */
++		utrace->death = 0;
++
++		if (!utrace->reap) {
++			/*
++			 * We're just dead, not reaped yet.  This will
++			 * reset @target->utrace_flags so the later call
++			 * with @reap set won't hit the check above.
++			 */
++			utrace_reset(target, utrace);
++			return;
++		}
++	}
++
++	/*
++	 * utrace_add_engine() checks ->utrace_flags != 0.  Since
++	 * @utrace->reap is set, nobody can set or clear UTRACE_EVENT(REAP)
++	 * in @engine->flags or change @engine->ops and nobody can change
++	 * @utrace->attached after we drop the lock.
++	 */
++	target->utrace_flags = 0;
++
++	/*
++	 * We clear out @utrace->attached before we drop the lock so
++	 * that find_matching_engine() can't come across any old engine
++	 * while we are busy tearing it down.
++	 */
++	list_replace_init(&utrace->attached, &attached);
++	list_splice_tail_init(&utrace->attaching, &attached);
++
++	spin_unlock(&utrace->lock);
++
++	list_for_each_entry_safe(engine, next, &attached, entry) {
++		if (engine->flags & UTRACE_EVENT(REAP))
++			engine->ops->report_reap(engine, target);
++
++		engine->ops = NULL;
++		engine->flags = 0;
++		list_del_init(&engine->entry);
++
++		utrace_engine_put(engine);
++	}
++}
++
++/*
++ * You can't do anything to a dead task but detach it.
++ * If release_task() has been called, you can't do that.
++ *
++ * On the exit path, DEATH and QUIESCE event bits are set only
++ * before utrace_report_death() has taken the lock.  At that point,
++ * the death report will come soon, so disallow detach until it's
++ * done.  This prevents us from racing with it detaching itself.
++ *
++ * Called only when @target->exit_state is nonzero.
++ */
++static inline int utrace_control_dead(struct task_struct *target,
++				      struct utrace *utrace,
++				      enum utrace_resume_action action)
++{
++	lockdep_assert_held(&utrace->lock);
++
++	if (action != UTRACE_DETACH || unlikely(utrace->reap))
++		return -ESRCH;
++
++	if (unlikely(utrace->death))
++		/*
++		 * We have already started the death report.  We can't
++		 * prevent the report_death and report_reap callbacks,
++		 * so tell the caller they will happen.
++		 */
++		return -EALREADY;
++
++	return 0;
++}
++
++/**
++ * utrace_control - control a thread being traced by a tracing engine
++ * @target:		thread to affect
++ * @engine:		attached engine to affect
++ * @action:		&enum utrace_resume_action for thread to do
++ *
++ * This is how a tracing engine asks a traced thread to do something.
++ * This call is controlled by the @action argument, which has the
++ * same meaning as the &enum utrace_resume_action value returned by
++ * event reporting callbacks.
++ *
++ * If @target is already dead (@target->exit_state nonzero),
++ * all actions except %UTRACE_DETACH fail with -%ESRCH.
++ *
++ * The following sections describe each option for the @action argument.
++ *
++ * UTRACE_DETACH:
++ *
++ * After this, the @engine data structure is no longer accessible,
++ * and the thread might be reaped.  The thread will start running
++ * again if it was stopped and no longer has any attached engines
++ * that want it stopped.
++ *
++ * If the @report_reap callback may already have begun, this fails
++ * with -%ESRCH.  If the @report_death callback may already have
++ * begun, this fails with -%EALREADY.
++ *
++ * If @target is not already stopped, then a callback to this engine
++ * might be in progress or about to start on another CPU.  If so,
++ * then this returns -%EINPROGRESS; the detach happens as soon as
++ * the pending callback is finished.  To synchronize after an
++ * -%EINPROGRESS return, see utrace_barrier().
++ *
++ * If @target is properly stopped before utrace_control() is called,
++ * then after successful return it's guaranteed that no more callbacks
++ * to the @engine->ops vector will be made.
++ *
++ * The only exception is %SIGKILL (and exec or group-exit by another
++ * thread in the group), which can cause asynchronous @report_death
++ * and/or @report_reap callbacks even when %UTRACE_STOP was used.
++ * (In that event, this fails with -%ESRCH or -%EALREADY, see above.)
++ *
++ * UTRACE_STOP:
++ *
++ * This asks that @target stop running.  This returns 0 only if
++ * @target is already stopped, either for tracing or for job
++ * control.  Then @target will remain stopped until another
++ * utrace_control() call is made on @engine; @target can be woken
++ * only by %SIGKILL (or equivalent, such as exec or termination by
++ * another thread in the same thread group).
++ *
++ * This returns -%EINPROGRESS if @target is not already stopped.
++ * Then the effect is like %UTRACE_REPORT.  A @report_quiesce or
++ * @report_signal callback will be made soon.  Your callback can
++ * then return %UTRACE_STOP to keep @target stopped.
++ *
++ * This does not interrupt system calls in progress, including ones
++ * that sleep for a long time.  For that, use %UTRACE_INTERRUPT.
++ * To interrupt system calls and then keep @target stopped, your
++ * @report_signal callback can return %UTRACE_STOP.
++ *
++ * UTRACE_RESUME:
++ *
++ * Just let @target continue running normally, reversing the effect
++ * of a previous %UTRACE_STOP.  If another engine is keeping @target
++ * stopped, then it remains stopped until all engines let it resume.
++ * If @target was not stopped, this has no effect.
++ *
++ * UTRACE_REPORT:
++ *
++ * This is like %UTRACE_RESUME, but also ensures that there will be
++ * a @report_quiesce or @report_signal callback made soon.  If
++ * @target had been stopped, then there will be a callback before it
++ * resumes running normally.  If another engine is keeping @target
++ * stopped, then there might be no callbacks until all engines let
++ * it resume.
++ *
++ * Since this is meaningless unless @report_quiesce callbacks will
++ * be made, it returns -%EINVAL if @engine lacks %UTRACE_EVENT(%QUIESCE).
++ *
++ * UTRACE_INTERRUPT:
++ *
++ * This is like %UTRACE_REPORT, but ensures that @target will make a
++ * @report_signal callback before it resumes or delivers signals.
++ * If @target was in a system call or about to enter one, work in
++ * progress will be interrupted as if by %SIGSTOP.  If another
++ * engine is keeping @target stopped, then there might be no
++ * callbacks until all engines let it resume.
++ *
++ * This gives @engine an opportunity to introduce a forced signal
++ * disposition via its @report_signal callback.
++ *
++ * UTRACE_SINGLESTEP:
++ *
++ * It's invalid to use this unless arch_has_single_step() returned true.
++ * This is like %UTRACE_RESUME, but resumes for one user instruction only.
++ *
++ * Note that passing %UTRACE_SINGLESTEP or %UTRACE_BLOCKSTEP to
++ * utrace_control() or returning it from an event callback alone does
++ * not necessarily ensure that stepping will be enabled.  If there are
++ * more callbacks made to any engine before returning to user mode,
++ * then the resume action is chosen only by the last set of callbacks.
++ * To be sure, enable %UTRACE_EVENT(%QUIESCE) and look for the
++ * @report_quiesce callback with a zero event mask, or the
++ * @report_signal callback with %UTRACE_SIGNAL_REPORT.
++ *
++ * Since this is not robust unless @report_quiesce callbacks will
++ * be made, it returns -%EINVAL if @engine lacks %UTRACE_EVENT(%QUIESCE).
++ *
++ * UTRACE_BLOCKSTEP:
++ *
++ * It's invalid to use this unless arch_has_block_step() returned true.
++ * This is like %UTRACE_SINGLESTEP, but resumes for one whole basic
++ * block of user instructions.
++ *
++ * Since this is not robust unless @report_quiesce callbacks will
++ * be made, it returns -%EINVAL if @engine lacks %UTRACE_EVENT(%QUIESCE).
++ *
++ * %UTRACE_BLOCKSTEP devolves to %UTRACE_SINGLESTEP when another
++ * tracing engine is using %UTRACE_SINGLESTEP at the same time.
++ */
++int utrace_control(struct task_struct *target,
++		   struct utrace_engine *engine,
++		   enum utrace_resume_action action)
++{
++	struct utrace *utrace;
++	bool reset;
++	int ret;
++
++	if (unlikely(action >= UTRACE_RESUME_MAX)) {
++		WARN(1, "invalid action argument to utrace_control()!");
++		return -EINVAL;
++	}
++
++	/*
++	 * This is a sanity check for a programming error in the caller.
++	 * Their request can only work properly in all cases by relying on
++	 * a follow-up callback, but they didn't set one up!  This check
++	 * doesn't do locking, but it shouldn't matter.  The caller has to
++	 * be synchronously sure the callback is set up to be operating the
++	 * interface properly.
++	 */
++	if (action >= UTRACE_REPORT && action < UTRACE_RESUME &&
++	    unlikely(!(engine->flags & UTRACE_EVENT(QUIESCE)))) {
++		WARN(1, "utrace_control() with no QUIESCE callback in place!");
++		return -EINVAL;
++	}
++
++	utrace = get_utrace_lock(target, engine, true);
++	if (unlikely(IS_ERR(utrace)))
++		return PTR_ERR(utrace);
++
++	reset = task_is_traced(target);
++	ret = 0;
++
++	/*
++	 * ->exit_state can change under us, this doesn't matter.
++	 * We do not care about ->exit_state in fact, but we do
++	 * care about ->reap and ->death. If either flag is set,
++	 * we must also see ->exit_state != 0.
++	 */
++	if (unlikely(target->exit_state)) {
++		ret = utrace_control_dead(target, utrace, action);
++		if (ret) {
++			spin_unlock(&utrace->lock);
++			return ret;
++		}
++		reset = true;
++	}
++
++	switch (action) {
++	case UTRACE_STOP:
++		mark_engine_wants_stop(target, engine);
++		if (!reset && !utrace_do_stop(target, utrace))
++			ret = -EINPROGRESS;
++		reset = false;
++		break;
++
++	case UTRACE_DETACH:
++		if (engine_wants_stop(engine))
++			target->utrace_flags &= ~ENGINE_STOP;
++		mark_engine_detached(engine);
++		reset = reset || utrace_do_stop(target, utrace);
++		if (!reset) {
++			/*
++			 * As in utrace_set_events(), this barrier ensures
++			 * that our engine->flags changes have hit before we
++			 * examine utrace->reporting, pairing with the barrier
++			 * in start_callback().  If @target has not yet hit
++			 * finish_callback() to clear utrace->reporting, we
++			 * might be in the middle of a callback to @engine.
++			 */
++			smp_mb();
++			if (utrace->reporting == engine)
++				ret = -EINPROGRESS;
++		}
++		break;
++
++	case UTRACE_RESUME:
++		/*
++		 * This and all other cases imply resuming if stopped.
++		 * There might not be another report before it just
++		 * resumes, so make sure single-step is not left set.
++		 */
++		clear_engine_wants_stop(engine);
++		if (likely(reset))
++			user_disable_single_step(target);
++		break;
++
++	case UTRACE_BLOCKSTEP:
++		/*
++		 * Resume from stopped, step one block.
++		 * We fall through to treat it like UTRACE_SINGLESTEP.
++		 */
++		if (unlikely(!arch_has_block_step())) {
++			WARN(1, "UTRACE_BLOCKSTEP when !arch_has_block_step()");
++			action = UTRACE_SINGLESTEP;
++		}
++
++	case UTRACE_SINGLESTEP:
++		/*
++		 * Resume from stopped, step one instruction.
++		 * We fall through to the UTRACE_REPORT case.
++		 */
++		if (unlikely(!arch_has_single_step())) {
++			WARN(1,
++			     "UTRACE_SINGLESTEP when !arch_has_single_step()");
++			reset = false;
++			ret = -EOPNOTSUPP;
++			break;
++		}
++
++	case UTRACE_REPORT:
++		/*
++		 * Make the thread call tracehook_notify_resume() soon.
++		 * But don't bother if it's already been interrupted.
++		 * In that case, utrace_get_signal() will be reporting soon.
++		 */
++		clear_engine_wants_stop(engine);
++		if (action < utrace->resume) {
++			utrace->resume = action;
++			set_notify_resume(target);
++		}
++		break;
++
++	case UTRACE_INTERRUPT:
++		/*
++		 * Make the thread call tracehook_get_signal() soon.
++		 */
++		clear_engine_wants_stop(engine);
++		if (utrace->resume == UTRACE_INTERRUPT)
++			break;
++		utrace->resume = UTRACE_INTERRUPT;
++
++		/*
++		 * If it's not already stopped, interrupt it now.  We need
++		 * the siglock here in case it calls recalc_sigpending()
++		 * and clears its own TIF_SIGPENDING.  By taking the lock,
++		 * we've serialized any later recalc_sigpending() after our
++		 * setting of utrace->resume to force it on.
++		 */
++		if (reset) {
++			/*
++			 * This is really just to keep the invariant that
++			 * TIF_SIGPENDING is set with UTRACE_INTERRUPT.
++			 * When it's stopped, we know it's always going
++			 * through utrace_get_signal() and will recalculate.
++			 */
++			set_tsk_thread_flag(target, TIF_SIGPENDING);
++		} else {
++			struct sighand_struct *sighand;
++			unsigned long irqflags;
++			sighand = lock_task_sighand(target, &irqflags);
++			if (likely(sighand)) {
++				signal_wake_up(target, 0);
++				unlock_task_sighand(target, &irqflags);
++			}
++		}
++		break;
++
++	default:
++		BUG();		/* We checked it on entry.  */
++	}
++
++	/*
++	 * Let the thread resume running.  If it's not stopped now,
++	 * there is nothing more we need to do.
++	 */
++	if (reset)
++		utrace_reset(target, utrace);
++	else
++		spin_unlock(&utrace->lock);
++
++	return ret;
++}
++EXPORT_SYMBOL_GPL(utrace_control);
++
++/**
++ * utrace_barrier - synchronize with simultaneous tracing callbacks
++ * @target:		thread to affect
++ * @engine:		engine to affect (can be detached)
++ *
++ * This blocks while @target might be in the midst of making a callback to
++ * @engine.  It can be interrupted by signals and will return -%ERESTARTSYS.
++ * A return value of zero means no callback from @target to @engine was
++ * in progress.  Any effect of its return value (such as %UTRACE_STOP) has
++ * already been applied to @engine.
++ *
++ * It's not necessary to keep the @target pointer alive for this call.
++ * It's only necessary to hold a ref on @engine.  This will return
++ * safely even if @target has been reaped and has no task refs.
++ *
++ * A successful return from utrace_barrier() guarantees its ordering
++ * with respect to utrace_set_events() and utrace_control() calls.  If
++ * @target was not properly stopped, event callbacks just disabled might
++ * still be in progress; utrace_barrier() waits until there is no chance
++ * an unwanted callback can be in progress.
++ */
++int utrace_barrier(struct task_struct *target, struct utrace_engine *engine)
++{
++	struct utrace *utrace;
++	int ret = -ERESTARTSYS;
++
++	if (unlikely(target == current))
++		return 0;
++
++	do {
++		utrace = get_utrace_lock(target, engine, false);
++		if (unlikely(IS_ERR(utrace))) {
++			ret = PTR_ERR(utrace);
++			if (ret != -ERESTARTSYS)
++				break;
++		} else {
++			/*
++			 * All engine state changes are done while
++			 * holding the lock, i.e. before we get here.
++			 * Since we have the lock, we only need to
++			 * worry about @target making a callback.
++			 * When it has entered start_callback() but
++			 * not yet gotten to finish_callback(), we
++			 * will see utrace->reporting == @engine.
++			 * When @target doesn't take the lock, it uses
++			 * barriers to order setting utrace->reporting
++			 * before it examines the engine state.
++			 */
++			if (utrace->reporting != engine)
++				ret = 0;
++			spin_unlock(&utrace->lock);
++			if (!ret)
++				break;
++		}
++		schedule_timeout_interruptible(1);
++	} while (!signal_pending(current));
++
++	return ret;
++}
++EXPORT_SYMBOL_GPL(utrace_barrier);
++
++/*
++ * This is local state used for reporting loops, perhaps optimized away.
++ */
++struct utrace_report {
++	u32 result;
++	enum utrace_resume_action action;
++	enum utrace_resume_action resume_action;
++	bool detaches;
++	bool spurious;
++};
++
++#define INIT_REPORT(var)			\
++	struct utrace_report var = {		\
++		.action = UTRACE_RESUME,	\
++		.resume_action = UTRACE_RESUME,	\
++		.spurious = true 		\
++	}
++
++/*
++ * We are now making the report, so clear the flag saying we need one.
++ * When there is a new attach, ->pending_attach is set just so we will
++ * know to do splice_attaching() here before the callback loop.
++ */
++static enum utrace_resume_action start_report(struct utrace *utrace)
++{
++	enum utrace_resume_action resume = utrace->resume;
++	if (utrace->pending_attach ||
++	    (resume > UTRACE_INTERRUPT && resume < UTRACE_RESUME)) {
++		spin_lock(&utrace->lock);
++		splice_attaching(utrace);
++		resume = utrace->resume;
++		if (resume > UTRACE_INTERRUPT)
++			utrace->resume = UTRACE_RESUME;
++		spin_unlock(&utrace->lock);
++	}
++	return resume;
++}
++
++static inline void finish_report_reset(struct task_struct *task,
++				       struct utrace *utrace,
++				       struct utrace_report *report)
++{
++	if (unlikely(report->spurious || report->detaches)) {
++		spin_lock(&utrace->lock);
++		if (utrace_reset(task, utrace))
++			report->action = UTRACE_RESUME;
++	}
++}
++
++/*
++ * Complete a normal reporting pass, pairing with a start_report() call.
++ * This handles any UTRACE_DETACH or UTRACE_REPORT or UTRACE_INTERRUPT
++ * returns from engine callbacks.  If @will_not_stop is true and any
++ * engine's last callback used UTRACE_STOP, we do UTRACE_REPORT here to
++ * ensure we stop before user mode.  If there were no callbacks made, it
++ * will recompute @task->utrace_flags to avoid another false-positive.
++ */
++static void finish_report(struct task_struct *task, struct utrace *utrace,
++			  struct utrace_report *report, bool will_not_stop)
++{
++	enum utrace_resume_action resume = report->action;
++
++	if (resume == UTRACE_STOP)
++		resume = will_not_stop ? UTRACE_REPORT : UTRACE_RESUME;
++
++	if (resume < utrace->resume) {
++		spin_lock(&utrace->lock);
++		utrace->resume = resume;
++		if (resume == UTRACE_INTERRUPT)
++			set_tsk_thread_flag(task, TIF_SIGPENDING);
++		else
++			set_tsk_thread_flag(task, TIF_NOTIFY_RESUME);
++		spin_unlock(&utrace->lock);
++	}
++
++	finish_report_reset(task, utrace, report);
++}
++
++static void finish_callback_report(struct task_struct *task,
++				   struct utrace *utrace,
++				   struct utrace_report *report,
++				   struct utrace_engine *engine,
++				   enum utrace_resume_action action)
++{
++	if (action == UTRACE_DETACH) {
++		/*
++		 * By holding the lock here, we make sure that
++		 * utrace_barrier() (really get_utrace_lock()) sees the
++		 * effect of this detach.  Otherwise utrace_barrier() could
++		 * return 0 after this callback had returned UTRACE_DETACH.
++		 * This way, a 0 return is an unambiguous indicator that any
++		 * callback returning UTRACE_DETACH has indeed caused detach.
++		 */
++		spin_lock(&utrace->lock);
++		engine->ops = &utrace_detached_ops;
++		spin_unlock(&utrace->lock);
++	}
++
++	/*
++	 * If utrace_control() was used, treat that like UTRACE_DETACH here.
++	 */
++	if (engine->ops == &utrace_detached_ops) {
++		report->detaches = true;
++		return;
++	}
++
++	if (action < report->action)
++		report->action = action;
++
++	if (action != UTRACE_STOP) {
++		if (action < report->resume_action)
++			report->resume_action = action;
++
++		if (engine_wants_stop(engine)) {
++			spin_lock(&utrace->lock);
++			clear_engine_wants_stop(engine);
++			spin_unlock(&utrace->lock);
++		}
++
++		return;
++	}
++
++	if (!engine_wants_stop(engine)) {
++		spin_lock(&utrace->lock);
++		/*
++		 * If utrace_control() came in and detached us
++		 * before we got the lock, we must not stop now.
++		 */
++		if (unlikely(engine->ops == &utrace_detached_ops))
++			report->detaches = true;
++		else
++			mark_engine_wants_stop(task, engine);
++		spin_unlock(&utrace->lock);
++	}
++}
++
++/*
++ * Apply the return value of one engine callback to @report.
++ * Returns true if @engine detached and should not get any more callbacks.
++ */
++static bool finish_callback(struct task_struct *task, struct utrace *utrace,
++			    struct utrace_report *report,
++			    struct utrace_engine *engine,
++			    u32 ret)
++{
++	report->result = ret & ~UTRACE_RESUME_MASK;
++	finish_callback_report(task, utrace, report, engine,
++			       utrace_resume_action(ret));
++
++	/*
++	 * Now that we have applied the effect of the return value,
++	 * clear this so that utrace_barrier() can stop waiting.
++	 * A subsequent utrace_control() can stop or resume @engine
++	 * and know this was ordered after its callback's action.
++	 *
++	 * We don't need any barriers here because utrace_barrier()
++	 * takes utrace->lock.  If we touched engine->flags above,
++	 * the lock guaranteed this change was before utrace_barrier()
++	 * examined utrace->reporting.
++	 */
++	utrace->reporting = NULL;
++
++	/*
++	 * We've just done an engine callback.  These are allowed to sleep,
++	 * though all well-behaved ones restrict that to blocking kalloc()
++	 * or quickly-acquired mutex_lock() and the like.  This is a good
++	 * place to make sure tracing engines don't introduce too much
++	 * latency under voluntary preemption.
++	 */
++	might_sleep();
++
++	return engine->ops == &utrace_detached_ops;
++}
++
++/*
++ * Start the callbacks for @engine to consider @event (a bit mask).
++ * This makes the report_quiesce() callback first.  If @engine wants
++ * a specific callback for @event, we return the ops vector to use.
++ * If not, we return NULL.  The return value from the ops->callback
++ * function called should be passed to finish_callback().
++ */
++static const struct utrace_engine_ops *start_callback(
++	struct utrace *utrace, struct utrace_report *report,
++	struct utrace_engine *engine, struct task_struct *task,
++	unsigned long event)
++{
++	const struct utrace_engine_ops *ops;
++	unsigned long want;
++
++	/*
++	 * This barrier ensures that we've set utrace->reporting before
++	 * we examine engine->flags or engine->ops.  utrace_barrier()
++	 * relies on this ordering to indicate that the effect of any
++	 * utrace_control() and utrace_set_events() calls is in place
++	 * by the time utrace->reporting can be seen to be NULL.
++	 */
++	utrace->reporting = engine;
++	smp_mb();
++
++	/*
++	 * This pairs with the barrier in mark_engine_detached().
++	 * It makes sure that we never see the old ops vector with
++	 * the new flags, in case the original vector had no report_quiesce.
++	 */
++	want = engine->flags;
++	smp_rmb();
++	ops = engine->ops;
++
++	if (want & UTRACE_EVENT(QUIESCE)) {
++		if (finish_callback(task, utrace, report, engine,
++				    (*ops->report_quiesce)(report->action,
++							   engine, event)))
++			return NULL;
++
++		/*
++		 * finish_callback() reset utrace->reporting after the
++		 * quiesce callback.  Now we set it again (as above)
++		 * before re-examining engine->flags, which could have
++		 * been changed synchronously by ->report_quiesce or
++		 * asynchronously by utrace_control() or utrace_set_events().
++		 */
++		utrace->reporting = engine;
++		smp_mb();
++		want = engine->flags;
++	}
++
++	if (want & ENGINE_STOP)
++		report->action = UTRACE_STOP;
++
++	if (want & event) {
++		report->spurious = false;
++		return ops;
++	}
++
++	utrace->reporting = NULL;
++	return NULL;
++}
++
++/*
++ * Do a normal reporting pass for engines interested in @event.
++ * @callback is the name of the member in the ops vector, and remaining
++ * args are the extras it takes after the standard three args.
++ */
++#define REPORT_CALLBACKS(rev, task, utrace, report, event, callback, ...)     \
++	do {								      \
++		struct utrace_engine *engine;				      \
++		const struct utrace_engine_ops *ops;			      \
++		list_for_each_entry##rev(engine, &utrace->attached, entry) {  \
++			ops = start_callback(utrace, report, engine, task,    \
++					     event);			      \
++			if (!ops)					      \
++				continue;				      \
++			finish_callback(task, utrace, report, engine,	      \
++					(*ops->callback)(__VA_ARGS__));	      \
++		}							      \
++	} while (0)
++#define REPORT(task, utrace, report, event, callback, ...)		      \
++	do {								      \
++		start_report(utrace);					      \
++		REPORT_CALLBACKS(, task, utrace, report, event, callback,     \
++				 (report)->action, engine, ## __VA_ARGS__);   \
++		finish_report(task, utrace, report, true);		      \
++	} while (0)
++
++/*
++ * Called iff UTRACE_EVENT(EXEC) flag is set.
++ */
++void utrace_report_exec(struct linux_binfmt *fmt, struct linux_binprm *bprm,
++			struct pt_regs *regs)
++{
++	struct task_struct *task = current;
++	struct utrace *utrace = task_utrace_struct(task);
++	INIT_REPORT(report);
++
++	REPORT(task, utrace, &report, UTRACE_EVENT(EXEC),
++	       report_exec, fmt, bprm, regs);
++}
++
++static u32 do_report_syscall_entry(struct pt_regs *regs,
++				   struct task_struct *task,
++				   struct utrace *utrace,
++				   struct utrace_report *report,
++				   u32 resume_report)
++{
++	start_report(utrace);
++	REPORT_CALLBACKS(_reverse, task, utrace, report,
++			 UTRACE_EVENT(SYSCALL_ENTRY), report_syscall_entry,
++			 resume_report | report->result | report->action,
++			 engine, regs);
++	finish_report(task, utrace, report, false);
++
++	if (report->action != UTRACE_STOP)
++		return 0;
++
++	utrace_stop(task, utrace, report->resume_action);
++
++	if (fatal_signal_pending(task)) {
++		/*
++		 * We are continuing despite UTRACE_STOP because of a
++		 * SIGKILL.  Don't let the system call actually proceed.
++		 */
++		report->result = UTRACE_SYSCALL_ABORT;
++	} else if (utrace->resume <= UTRACE_REPORT) {
++		/*
++		 * If we've been asked for another report after our stop,
++		 * go back to report (and maybe stop) again before we run
++		 * the system call.  The second (and later) reports are
++		 * marked with the UTRACE_SYSCALL_RESUMED flag so that
++		 * engines know this is a second report at the same
++		 * entry.  This gives them the chance to examine the
++		 * registers anew after they might have been changed
++		 * while we were stopped.
++		 */
++		report->detaches = false;
++		report->spurious = true;
++		report->action = report->resume_action = UTRACE_RESUME;
++		return UTRACE_SYSCALL_RESUMED;
++	}
++
++	return 0;
++}
++
++/*
++ * Called iff UTRACE_EVENT(SYSCALL_ENTRY) flag is set.
++ * Return true to prevent the system call.
++ */
++bool utrace_report_syscall_entry(struct pt_regs *regs)
++{
++	struct task_struct *task = current;
++	struct utrace *utrace = task_utrace_struct(task);
++	INIT_REPORT(report);
++	u32 resume_report = 0;
++
++	do {
++		resume_report = do_report_syscall_entry(regs, task, utrace,
++							&report, resume_report);
++	} while (resume_report);
++
++	return utrace_syscall_action(report.result) == UTRACE_SYSCALL_ABORT;
++}
++
++/*
++ * Called iff UTRACE_EVENT(SYSCALL_EXIT) flag is set.
++ */
++void utrace_report_syscall_exit(struct pt_regs *regs)
++{
++	struct task_struct *task = current;
++	struct utrace *utrace = task_utrace_struct(task);
++	INIT_REPORT(report);
++
++	REPORT(task, utrace, &report, UTRACE_EVENT(SYSCALL_EXIT),
++	       report_syscall_exit, regs);
++}
++
++/*
++ * Called iff UTRACE_EVENT(CLONE) flag is set.
++ * This notification call blocks the wake_up_new_task call on the child.
++ * So we must not quiesce here.  tracehook_report_clone_complete will do
++ * a quiescence check momentarily.
++ */
++void utrace_report_clone(unsigned long clone_flags, struct task_struct *child)
++{
++	struct task_struct *task = current;
++	struct utrace *utrace = task_utrace_struct(task);
++	INIT_REPORT(report);
++
++	/*
++	 * We don't use the REPORT() macro here, because we need
++	 * to clear utrace->cloning before finish_report().
++	 * After finish_report(), utrace can be a stale pointer
++	 * in cases when report.action is still UTRACE_RESUME.
++	 */
++	start_report(utrace);
++	utrace->cloning = child;
++
++	REPORT_CALLBACKS(, task, utrace, &report,
++			 UTRACE_EVENT(CLONE), report_clone,
++			 report.action, engine, clone_flags, child);
++
++	utrace->cloning = NULL;
++	finish_report(task, utrace, &report, !(clone_flags & CLONE_VFORK));
++
++	/*
++	 * For a vfork, we will go into an uninterruptible block waiting
++	 * for the child.  We need UTRACE_STOP to happen before this, not
++	 * after.  For CLONE_VFORK, utrace_finish_vfork() will be called.
++	 */
++	if (report.action == UTRACE_STOP && (clone_flags & CLONE_VFORK)) {
++		spin_lock(&utrace->lock);
++		utrace->vfork_stop = 1;
++		spin_unlock(&utrace->lock);
++	}
++}
++
++/*
++ * We're called after utrace_report_clone() for a CLONE_VFORK.
++ * If UTRACE_STOP was left from the clone report, we stop here.
++ * After this, we'll enter the uninterruptible wait_for_completion()
++ * waiting for the child.
++ */
++void utrace_finish_vfork(struct task_struct *task)
++{
++	struct utrace *utrace = task_utrace_struct(task);
++
++	if (utrace->vfork_stop) {
++		spin_lock(&utrace->lock);
++		utrace->vfork_stop = 0;
++		spin_unlock(&utrace->lock);
++		utrace_stop(task, utrace, UTRACE_RESUME); /* XXX */
++	}
++}
++
++/*
++ * Called iff UTRACE_EVENT(JCTL) flag is set.
++ *
++ * Called with siglock held.
++ */
++void utrace_report_jctl(int notify, int what)
++{
++	struct task_struct *task = current;
++	struct utrace *utrace = task_utrace_struct(task);
++	INIT_REPORT(report);
++
++	spin_unlock_irq(&task->sighand->siglock);
++
++	REPORT(task, utrace, &report, UTRACE_EVENT(JCTL),
++	       report_jctl, what, notify);
++
++	spin_lock_irq(&task->sighand->siglock);
++}
++
++/*
++ * Called iff UTRACE_EVENT(EXIT) flag is set.
++ */
++void utrace_report_exit(long *exit_code)
++{
++	struct task_struct *task = current;
++	struct utrace *utrace = task_utrace_struct(task);
++	INIT_REPORT(report);
++	long orig_code = *exit_code;
++
++	REPORT(task, utrace, &report, UTRACE_EVENT(EXIT),
++	       report_exit, orig_code, exit_code);
++
++	if (report.action == UTRACE_STOP)
++		utrace_stop(task, utrace, report.resume_action);
++}
++
++/*
++ * Called iff UTRACE_EVENT(DEATH) or UTRACE_EVENT(QUIESCE) flag is set.
++ *
++ * It is always possible that we are racing with utrace_release_task here.
++ * For this reason, utrace_release_task checks for the event bits that get
++ * us here, and delays its cleanup for us to do.
++ */
++void utrace_report_death(struct task_struct *task, struct utrace *utrace,
++			 bool group_dead, int signal)
++{
++	INIT_REPORT(report);
++
++	BUG_ON(!task->exit_state);
++
++	/*
++	 * We are presently considered "quiescent"--which is accurate
++	 * inasmuch as we won't run any more user instructions ever again.
++	 * But for utrace_control and utrace_set_events to be robust, they
++	 * must be sure whether or not we will run any more callbacks.  If
++	 * a call comes in before we do, taking the lock here synchronizes
++	 * us so we don't run any callbacks just disabled.  Calls that come
++	 * in while we're running the callbacks will see the exit.death
++	 * flag and know that we are not yet fully quiescent for purposes
++	 * of detach bookkeeping.
++	 */
++	spin_lock(&utrace->lock);
++	BUG_ON(utrace->death);
++	utrace->death = 1;
++	utrace->resume = UTRACE_RESUME;
++	splice_attaching(utrace);
++	spin_unlock(&utrace->lock);
++
++	REPORT_CALLBACKS(, task, utrace, &report, UTRACE_EVENT(DEATH),
++			 report_death, engine, group_dead, signal);
++
++	utrace_maybe_reap(task, utrace, false);
++}
++
++/*
++ * Finish the last reporting pass before returning to user mode.
++ */
++static void finish_resume_report(struct task_struct *task,
++				 struct utrace *utrace,
++				 struct utrace_report *report)
++{
++	finish_report_reset(task, utrace, report);
++
++	switch (report->action) {
++	case UTRACE_STOP:
++		utrace_stop(task, utrace, report->resume_action);
++		break;
++
++	case UTRACE_INTERRUPT:
++		if (!signal_pending(task))
++			set_tsk_thread_flag(task, TIF_SIGPENDING);
++		break;
++
++	case UTRACE_BLOCKSTEP:
++		if (likely(arch_has_block_step())) {
++			user_enable_block_step(task);
++			break;
++		}
++
++		/*
++		 * This means some callback is to blame for failing
++		 * to check arch_has_block_step() itself.  Warn and
++		 * then fall through to treat it as SINGLESTEP.
++		 */
++		WARN(1, "UTRACE_BLOCKSTEP when !arch_has_block_step()");
++
++	case UTRACE_SINGLESTEP:
++		if (likely(arch_has_single_step())) {
++			user_enable_single_step(task);
++		} else {
++			/*
++			 * This means some callback is to blame for failing
++			 * to check arch_has_single_step() itself.  Spew
++			 * about it so the loser will fix his module.
++			 */
++			WARN(1,
++			     "UTRACE_SINGLESTEP when !arch_has_single_step()");
++		}
++		break;
++
++	case UTRACE_REPORT:
++	case UTRACE_RESUME:
++	default:
++		user_disable_single_step(task);
++		break;
++	}
++}
++
++/*
++ * This is called when TIF_NOTIFY_RESUME had been set (and is now clear).
++ * We are close to user mode, and this is the place to report or stop.
++ * When we return, we're going to user mode or into the signals code.
++ */
++void utrace_resume(struct task_struct *task, struct pt_regs *regs)
++{
++	struct utrace *utrace = task_utrace_struct(task);
++	INIT_REPORT(report);
++	struct utrace_engine *engine;
++
++	/*
++	 * Some machines get here with interrupts disabled.  The same arch
++	 * code path leads to calling into get_signal_to_deliver(), which
++	 * implicitly reenables them by virtue of spin_unlock_irq.
++	 */
++	local_irq_enable();
++
++	/*
++	 * If this flag is still set it's because there was a signal
++	 * handler setup done but no report_signal following it.  Clear
++	 * the flag before we get to user so it doesn't confuse us later.
++	 */
++	if (unlikely(utrace->signal_handler)) {
++		spin_lock(&utrace->lock);
++		utrace->signal_handler = 0;
++		spin_unlock(&utrace->lock);
++	}
++
++	/*
++	 * Update our bookkeeping even if there are no callbacks made here.
++	 */
++	report.action = start_report(utrace);
++
++	switch (report.action) {
++	case UTRACE_RESUME:
++		/*
++		 * Anything we might have done was already handled by
++		 * utrace_get_signal(), or this is an entirely spurious
++		 * call.  (The arch might use TIF_NOTIFY_RESUME for other
++		 * purposes as well as calling us.)
++		 */
++		return;
++	case UTRACE_REPORT:
++		if (unlikely(!(task->utrace_flags & UTRACE_EVENT(QUIESCE))))
++			break;
++		/*
++		 * Do a simple reporting pass, with no specific
++		 * callback after report_quiesce.
++		 */
++		report.action = UTRACE_RESUME;
++		list_for_each_entry(engine, &utrace->attached, entry)
++			start_callback(utrace, &report, engine, task, 0);
++		break;
++	default:
++		/*
++		 * Even if this report was truly spurious, there is no need
++		 * for utrace_reset() now.  TIF_NOTIFY_RESUME was already
++		 * cleared--it doesn't stay spuriously set.
++		 */
++		report.spurious = false;
++		break;
++	}
++
++	/*
++	 * Finish the report and either stop or get ready to resume.
++	 * If utrace->resume was not UTRACE_REPORT, this applies its
++	 * effect now (i.e. step or interrupt).
++	 */
++	finish_resume_report(task, utrace, &report);
++}
++
++/*
++ * Return true if current has forced signal_pending().
++ *
++ * This is called only when current->utrace_flags is nonzero, so we know
++ * that current->utrace must be set.  It's not inlined in tracehook.h
++ * just so that struct utrace can stay opaque outside this file.
++ */
++bool utrace_interrupt_pending(void)
++{
++	return task_utrace_struct(current)->resume == UTRACE_INTERRUPT;
++}
++
++/*
++ * Take the siglock and push @info back on our queue.
++ * Returns with @task->sighand->siglock held.
++ */
++static void push_back_signal(struct task_struct *task, siginfo_t *info)
++	__acquires(task->sighand->siglock)
++{
++	struct sigqueue *q;
++
++	if (unlikely(!info->si_signo)) { /* Oh, a wise guy! */
++		spin_lock_irq(&task->sighand->siglock);
++		return;
++	}
++
++	q = sigqueue_alloc();
++	if (likely(q)) {
++		q->flags = 0;
++		copy_siginfo(&q->info, info);
++	}
++
++	spin_lock_irq(&task->sighand->siglock);
++
++	sigaddset(&task->pending.signal, info->si_signo);
++	if (likely(q))
++		list_add(&q->list, &task->pending.list);
++
++	set_tsk_thread_flag(task, TIF_SIGPENDING);
++}
++
++/*
++ * This is the hook from the signals code, called with the siglock held.
++ * Here is the ideal place to stop.  We also dequeue and intercept signals.
++ */
++int utrace_get_signal(struct task_struct *task, struct pt_regs *regs,
++		      siginfo_t *info, struct k_sigaction *return_ka)
++	__releases(task->sighand->siglock)
++	__acquires(task->sighand->siglock)
++{
++	struct utrace *utrace;
++	struct k_sigaction *ka;
++	INIT_REPORT(report);
++	struct utrace_engine *engine;
++	const struct utrace_engine_ops *ops;
++	unsigned long event, want;
++	u32 ret;
++	int signr;
++
++	utrace = task_utrace_struct(task);
++	if (utrace->resume < UTRACE_RESUME ||
++	    utrace->pending_attach || utrace->signal_handler) {
++		enum utrace_resume_action resume;
++
++		/*
++		 * We've been asked for an explicit report before we
++		 * even check for pending signals.
++		 */
++
++		spin_unlock_irq(&task->sighand->siglock);
++
++		spin_lock(&utrace->lock);
++
++		splice_attaching(utrace);
++
++		report.result = utrace->signal_handler ?
++			UTRACE_SIGNAL_HANDLER : UTRACE_SIGNAL_REPORT;
++		utrace->signal_handler = 0;
++
++		resume = utrace->resume;
++		utrace->resume = UTRACE_RESUME;
++
++		spin_unlock(&utrace->lock);
++
++		/*
++		 * Make sure signal_pending() only returns true
++		 * if there are real signals pending.
++		 */
++		if (signal_pending(task)) {
++			spin_lock_irq(&task->sighand->siglock);
++			recalc_sigpending();
++			spin_unlock_irq(&task->sighand->siglock);
++		}
++
++		if (resume > UTRACE_REPORT) {
++			/*
++			 * We only got here to process utrace->resume.
++			 * Despite no callbacks, this report is not spurious.
++			 */
++			report.action = resume;
++			report.spurious = false;
++			finish_resume_report(task, utrace, &report);
++			return -1;
++		} else if (!(task->utrace_flags & UTRACE_EVENT(QUIESCE))) {
++			/*
++			 * We only got here to clear utrace->signal_handler.
++			 */
++			return -1;
++		}
++
++		/*
++		 * Do a reporting pass for no signal, just for EVENT(QUIESCE).
++		 * The engine callbacks can fill in *info and *return_ka.
++		 * We'll pass NULL for the @orig_ka argument to indicate
++		 * that there was no original signal.
++		 */
++		event = 0;
++		ka = NULL;
++		memset(return_ka, 0, sizeof *return_ka);
++	} else if (!(task->utrace_flags & UTRACE_EVENT_SIGNAL_ALL) ||
++		   unlikely(task->signal->group_stop_count)) {
++		/*
++		 * If no engine is interested in intercepting signals or
++		 * we must stop, let the caller just dequeue them normally
++		 * or participate in group-stop.
++		 */
++		return 0;
++	} else {
++		/*
++		 * Steal the next signal so we can let tracing engines
++		 * examine it.  From the signal number and sigaction,
++		 * determine what normal delivery would do.  If no
++		 * engine perturbs it, we'll do that by returning the
++		 * signal number after setting *return_ka.
++		 */
++		signr = dequeue_signal(task, &task->blocked, info);
++		if (signr == 0)
++			return signr;
++		BUG_ON(signr != info->si_signo);
++
++		ka = &task->sighand->action[signr - 1];
++		*return_ka = *ka;
++
++		/*
++		 * We are never allowed to interfere with SIGKILL.
++		 * Just punt after filling in *return_ka for our caller.
++		 */
++		if (signr == SIGKILL)
++			return signr;
++
++		if (ka->sa.sa_handler == SIG_IGN) {
++			event = UTRACE_EVENT(SIGNAL_IGN);
++			report.result = UTRACE_SIGNAL_IGN;
++		} else if (ka->sa.sa_handler != SIG_DFL) {
++			event = UTRACE_EVENT(SIGNAL);
++			report.result = UTRACE_SIGNAL_DELIVER;
++		} else if (sig_kernel_coredump(signr)) {
++			event = UTRACE_EVENT(SIGNAL_CORE);
++			report.result = UTRACE_SIGNAL_CORE;
++		} else if (sig_kernel_ignore(signr)) {
++			event = UTRACE_EVENT(SIGNAL_IGN);
++			report.result = UTRACE_SIGNAL_IGN;
++		} else if (signr == SIGSTOP) {
++			event = UTRACE_EVENT(SIGNAL_STOP);
++			report.result = UTRACE_SIGNAL_STOP;
++		} else if (sig_kernel_stop(signr)) {
++			event = UTRACE_EVENT(SIGNAL_STOP);
++			report.result = UTRACE_SIGNAL_TSTP;
++		} else {
++			event = UTRACE_EVENT(SIGNAL_TERM);
++			report.result = UTRACE_SIGNAL_TERM;
++		}
++
++		/*
++		 * Now that we know what event type this signal is, we
++		 * can short-circuit if no engines care about those.
++		 */
++		if ((task->utrace_flags & (event | UTRACE_EVENT(QUIESCE))) == 0)
++			return signr;
++
++		/*
++		 * We have some interested engines, so tell them about
++		 * the signal and let them change its disposition.
++		 */
++		spin_unlock_irq(&task->sighand->siglock);
++	}
++
++	/*
++	 * This reporting pass chooses what signal disposition we'll act on.
++	 */
++	list_for_each_entry(engine, &utrace->attached, entry) {
++		/*
++		 * See start_callback() comment about this barrier.
++		 */
++		utrace->reporting = engine;
++		smp_mb();
++
++		/*
++		 * This pairs with the barrier in mark_engine_detached(),
++		 * see start_callback() comments.
++		 */
++		want = engine->flags;
++		smp_rmb();
++		ops = engine->ops;
++
++		if ((want & (event | UTRACE_EVENT(QUIESCE))) == 0) {
++			utrace->reporting = NULL;
++			continue;
++		}
++
++		if (ops->report_signal)
++			ret = (*ops->report_signal)(
++				report.result | report.action, engine,
++				regs, info, ka, return_ka);
++		else
++			ret = (report.result | (*ops->report_quiesce)(
++				       report.action, engine, event));
++
++		/*
++		 * Avoid a tight loop reporting again and again if some
++		 * engine is too stupid.
++		 */
++		switch (utrace_resume_action(ret)) {
++		default:
++			break;
++		case UTRACE_INTERRUPT:
++		case UTRACE_REPORT:
++			ret = (ret & ~UTRACE_RESUME_MASK) | UTRACE_RESUME;
++			break;
++		}
++
++		finish_callback(task, utrace, &report, engine, ret);
++	}
++
++	/*
++	 * We express the chosen action to the signals code in terms
++	 * of a representative signal whose default action does it.
++	 * Our caller uses our return value (signr) to decide what to
++	 * do, but uses info->si_signo as the signal number to report.
++	 */
++	switch (utrace_signal_action(report.result)) {
++	case UTRACE_SIGNAL_TERM:
++		signr = SIGTERM;
++		break;
++
++	case UTRACE_SIGNAL_CORE:
++		signr = SIGQUIT;
++		break;
++
++	case UTRACE_SIGNAL_STOP:
++		signr = SIGSTOP;
++		break;
++
++	case UTRACE_SIGNAL_TSTP:
++		signr = SIGTSTP;
++		break;
++
++	case UTRACE_SIGNAL_DELIVER:
++		signr = info->si_signo;
++
++		if (return_ka->sa.sa_handler == SIG_DFL) {
++			/*
++			 * We'll do signr's normal default action.
++			 * For ignore, we'll fall through below.
++			 * For stop/death, break locks and returns it.
++			 */
++			if (likely(signr) && !sig_kernel_ignore(signr))
++				break;
++		} else if (return_ka->sa.sa_handler != SIG_IGN &&
++			   likely(signr)) {
++			/*
++			 * Complete the bookkeeping after the report.
++			 * The handler will run.  If an engine wanted to
++			 * stop or step, then make sure we do another
++			 * report after signal handler setup.
++			 */
++			if (report.action != UTRACE_RESUME)
++				report.action = UTRACE_INTERRUPT;
++			finish_report(task, utrace, &report, true);
++
++			if (unlikely(report.result & UTRACE_SIGNAL_HOLD))
++				push_back_signal(task, info);
++			else
++				spin_lock_irq(&task->sighand->siglock);
++
++			/*
++			 * We do the SA_ONESHOT work here since the
++			 * normal path will only touch *return_ka now.
++			 */
++			if (unlikely(return_ka->sa.sa_flags & SA_ONESHOT)) {
++				return_ka->sa.sa_flags &= ~SA_ONESHOT;
++				if (likely(valid_signal(signr))) {
++					ka = &task->sighand->action[signr - 1];
++					ka->sa.sa_handler = SIG_DFL;
++				}
++			}
++
++			return signr;
++		}
++
++		/* Fall through for an ignored signal.  */
++
++	case UTRACE_SIGNAL_IGN:
++	case UTRACE_SIGNAL_REPORT:
++	default:
++		/*
++		 * If the signal is being ignored, then we are on the way
++		 * directly back to user mode.  We can stop here, or step,
++		 * as in utrace_resume(), above.  After we've dealt with that,
++		 * our caller will relock and come back through here.
++		 */
++		finish_resume_report(task, utrace, &report);
++
++		if (unlikely(fatal_signal_pending(task))) {
++			/*
++			 * The only reason we woke up now was because of a
++			 * SIGKILL.  Don't do normal dequeuing in case it
++			 * might get a signal other than SIGKILL.  That would
++			 * perturb the death state so it might differ from
++			 * what the debugger would have allowed to happen.
++			 * Instead, pluck out just the SIGKILL to be sure
++			 * we'll die immediately with nothing else different
++			 * from the quiescent state the debugger wanted us in.
++			 */
++			sigset_t sigkill_only;
++			siginitsetinv(&sigkill_only, sigmask(SIGKILL));
++			spin_lock_irq(&task->sighand->siglock);
++			signr = dequeue_signal(task, &sigkill_only, info);
++			BUG_ON(signr != SIGKILL);
++			*return_ka = task->sighand->action[SIGKILL - 1];
++			return signr;
++		}
++
++		if (unlikely(report.result & UTRACE_SIGNAL_HOLD)) {
++			push_back_signal(task, info);
++			spin_unlock_irq(&task->sighand->siglock);
++		}
++
++		return -1;
++	}
++
++	/*
++	 * Complete the bookkeeping after the report.
++	 * This sets utrace->resume if UTRACE_STOP was used.
++	 */
++	finish_report(task, utrace, &report, true);
++
++	return_ka->sa.sa_handler = SIG_DFL;
++
++	/*
++	 * If this signal is fatal, si_signo gets through as exit_code.
++	 * We can't allow a completely bogus value there or else core
++	 * kernel code can freak out.  (If an engine wants to control
++	 * the exit_code value exactly, it can do so in report_exit.)
++	 * We'll produce a big complaint in dmesg, but won't crash.
++	 * That's nicer for debugging your utrace engine.
++	 */
++	if (unlikely(info->si_signo & 0x80)) {
++		WARN(1, "utrace engine left bogus si_signo value!");
++		info->si_signo = SIGTRAP;
++	}
++
++	if (unlikely(report.result & UTRACE_SIGNAL_HOLD))
++		push_back_signal(task, info);
++	else
++		spin_lock_irq(&task->sighand->siglock);
++
++	if (sig_kernel_stop(signr))
++		task->signal->flags |= SIGNAL_STOP_DEQUEUED;
++
++	return signr;
++}
++
++/*
++ * This gets called after a signal handler has been set up.
++ * We set a flag so the next report knows it happened.
++ * If we're already stepping, make sure we do a report_signal.
++ * If not, make sure we get into utrace_resume() where we can
++ * clear the signal_handler flag before resuming.
++ */
++void utrace_signal_handler(struct task_struct *task, int stepping)
++{
++	struct utrace *utrace = task_utrace_struct(task);
++
++	spin_lock(&utrace->lock);
++
++	utrace->signal_handler = 1;
++	if (utrace->resume > UTRACE_INTERRUPT) {
++		if (stepping) {
++			utrace->resume = UTRACE_INTERRUPT;
++			set_tsk_thread_flag(task, TIF_SIGPENDING);
++		} else if (utrace->resume == UTRACE_RESUME) {
++			set_tsk_thread_flag(task, TIF_NOTIFY_RESUME);
++		}
++	}
++
++	spin_unlock(&utrace->lock);
++}
++
++/**
++ * utrace_prepare_examine - prepare to examine thread state
++ * @target:		thread of interest, a &struct task_struct pointer
++ * @engine:		engine pointer returned by utrace_attach_task()
++ * @exam:		temporary state, a &struct utrace_examiner pointer
++ *
++ * This call prepares to safely examine the thread @target using
++ * &struct user_regset calls, or direct access to thread-synchronous fields.
++ *
++ * When @target is current, this call is superfluous.  When @target is
++ * another thread, it must be held stopped via %UTRACE_STOP by @engine.
++ *
++ * This call may block the caller until @target stays stopped, so it must
++ * be called only after the caller is sure @target is about to unschedule.
++ * This means a zero return from a utrace_control() call on @engine giving
++ * %UTRACE_STOP, or a report_quiesce() or report_signal() callback to
++ * @engine that used %UTRACE_STOP in its return value.
++ *
++ * Returns -%ESRCH if @target is dead or -%EINVAL if %UTRACE_STOP was
++ * not used.  If @target has started running again despite %UTRACE_STOP
++ * (for %SIGKILL or a spurious wakeup), this call returns -%EAGAIN.
++ *
++ * When this call returns zero, it's safe to use &struct user_regset
++ * calls and task_user_regset_view() on @target and to examine some of
++ * its fields directly.  When the examination is complete, a
++ * utrace_finish_examine() call must follow to check whether it was
++ * completed safely.
++ */
++int utrace_prepare_examine(struct task_struct *target,
++			   struct utrace_engine *engine,
++			   struct utrace_examiner *exam)
++{
++	int ret = 0;
++
++	if (unlikely(target == current))
++		return 0;
++
++	rcu_read_lock();
++	if (unlikely(!engine_wants_stop(engine)))
++		ret = -EINVAL;
++	else if (unlikely(target->exit_state))
++		ret = -ESRCH;
++	else {
++		exam->state = target->state;
++		if (unlikely(exam->state == TASK_RUNNING))
++			ret = -EAGAIN;
++		else
++			get_task_struct(target);
++	}
++	rcu_read_unlock();
++
++	if (likely(!ret)) {
++		exam->ncsw = wait_task_inactive(target, exam->state);
++		put_task_struct(target);
++		if (unlikely(!exam->ncsw))
++			ret = -EAGAIN;
++	}
++
++	return ret;
++}
++EXPORT_SYMBOL_GPL(utrace_prepare_examine);
++
++/**
++ * utrace_finish_examine - complete an examination of thread state
++ * @target:		thread of interest, a &struct task_struct pointer
++ * @engine:		engine pointer returned by utrace_attach_task()
++ * @exam:		pointer passed to utrace_prepare_examine() call
++ *
++ * This call completes an examination on the thread @target begun by a
++ * paired utrace_prepare_examine() call with the same arguments that
++ * returned success (zero).
++ *
++ * When @target is current, this call is superfluous.  When @target is
++ * another thread, this returns zero if @target has remained unscheduled
++ * since the paired utrace_prepare_examine() call returned zero.
++ *
++ * When this returns an error, any examination done since the paired
++ * utrace_prepare_examine() call is unreliable and the data extracted
++ * should be discarded.  The error is -%EINVAL if @engine is not
++ * keeping @target stopped, or -%EAGAIN if @target woke up unexpectedly.
++ */
++int utrace_finish_examine(struct task_struct *target,
++			  struct utrace_engine *engine,
++			  struct utrace_examiner *exam)
++{
++	int ret = 0;
++
++	if (unlikely(target == current))
++		return 0;
++
++	rcu_read_lock();
++	if (unlikely(!engine_wants_stop(engine)))
++		ret = -EINVAL;
++	else if (unlikely(target->state != exam->state))
++		ret = -EAGAIN;
++	else
++		get_task_struct(target);
++	rcu_read_unlock();
++
++	if (likely(!ret)) {
++		unsigned long ncsw = wait_task_inactive(target, exam->state);
++		if (unlikely(ncsw != exam->ncsw))
++			ret = -EAGAIN;
++		put_task_struct(target);
++	}
++
++	return ret;
++}
++EXPORT_SYMBOL_GPL(utrace_finish_examine);
++
++/*
++ * This is declared in linux/regset.h and defined in machine-dependent
++ * code.  We put the export here to ensure no machine forgets it.
++ */
++EXPORT_SYMBOL_GPL(task_user_regset_view);
++
++/*
++ * Called with rcu_read_lock() held.
++ */
++void task_utrace_proc_status(struct seq_file *m, struct task_struct *p)
++{
++	seq_printf(m, "Utrace:\t%lx\n", p->utrace_flags);
++}