TTY: restore tty_ldisc_wait_idle

2 files changed, 126 insertions, 1 deletions

diff --git a/kernel.spec b/kernel.spec
index ebe9ea95d..319981471 100644
--- a/kernel.spec
+++ b/kernel.spec
@@ -51,7 +51,7 @@ Summary: The Linux kernel
 # For non-released -rc kernels, this will be prepended with "0.", so
 # for example a 3 here will become 0.3
 #
-%global baserelease 7
+%global baserelease 8
 %global fedora_build %{baserelease}
 
 # base_sublevel is the kernel version we're starting with and patching
@@ -726,6 +726,8 @@ Patch12305: xhci_hcd-suspend-resume.patch
 
 Patch12306: secmark-do-not-return-early-if-there-was-no-error.patch
 
+Patch12307: tty-restore-tty_ldisc_wait_idle.patch
+
 %endif
 
 BuildRoot: %{_tmppath}/kernel-%{KVERREL}-root
@@ -1346,6 +1348,8 @@ ApplyPatch xhci_hcd-suspend-resume.patch
 
 #ApplyPatch secmark-do-not-return-early-if-there-was-no-error.patch
 
+ApplyPatch tty-restore-tty_ldisc_wait_idle.patch
+
 # END OF PATCH APPLICATIONS
 
 %endif
@@ -1959,6 +1963,10 @@ fi
 #                 ||     ||
 
 %changelog
+* Mon Nov 22 2010 Kyle McMartin <kyle@redhat.com> 2.6.36.1-8.rc1
+- Merge 100eeae2 (TTY: restore tty_ldisc_wait_idle) which should fix the WARN
+  in tty_open in rawhide.
+
 * Mon Nov 22 2010 Kyle McMartin <kyle@redhat.com> 2.6.36.1-7.rc1
 - Make vmlinuz world readable again.
 
diff --git a/tty-restore-tty_ldisc_wait_idle.patch b/tty-restore-tty_ldisc_wait_idle.patch
new file mode 100644
index 000000000..3e784dd57
--- /dev/null
+++ b/tty-restore-tty_ldisc_wait_idle.patch
@@ -0,0 +1,117 @@
+From 4d458f558d5b904f14080b073b549d18c9503f93 Mon Sep 17 00:00:00 2001
+From: Jiri Slaby <jslaby@suse.cz>
+Date: Sun, 31 Oct 2010 23:17:51 +0100
+Subject: TTY: restore tty_ldisc_wait_idle
+
+It was removed in 65b770468e98 (tty-ldisc: turn ldisc user count into
+a proper refcount), but we need to wait for last user to quit the
+ldisc before we close it in tty_set_ldisc.
+
+Otherwise weird things start to happen. There might be processes
+waiting in tty_read->n_tty_read on tty->read_wait for input to appear
+and at that moment, a change of ldisc is fatal. n_tty_close is called,
+it frees read_buf and the waiting process is still in the middle of
+reading and goes nuts after it is woken.
+
+Previously we prevented close to happen when others are in ldisc ops
+by tty_ldisc_wait_idle in tty_set_ldisc. But the commit above removed
+that. So revoke the change and test whether there is 1 user (=we), and
+allow the close then.
+
+We can do that without ldisc/tty locks, because nobody else can open
+the device due to TTY_LDISC_CHANGING bit set, so we in fact wait for
+everybody to leave.
+
+I don't understand why tty_ldisc_lock would be needed either when the
+counter is an atomic variable, so this is a lockless
+tty_ldisc_wait_idle.
+
+On the other hand, if we fail to wait (timeout or signal), we have to
+reenable the halted ldiscs, so we take ldisc lock and reuse the setup
+path at the end of tty_set_ldisc.
+
+Signed-off-by: Jiri Slaby <jslaby@suse.cz>
+Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
+Tested-by: Sebastian Andrzej Siewior <bigeasy@breakpoint.cc>
+LKML-Reference: <20101031104136.GA511@Chamillionaire.breakpoint.cc>
+LKML-Reference: <1287669539-22644-1-git-send-email-jslaby@suse.cz>
+Cc: Alan Cox <alan@linux.intel.com>
+Cc: stable@kernel.org [32, 33, 36]
+Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
+---
+ drivers/char/tty_ldisc.c |   29 +++++++++++++++++++++++++++++
+ 1 files changed, 29 insertions(+), 0 deletions(-)
+
+diff --git a/drivers/char/tty_ldisc.c b/drivers/char/tty_ldisc.c
+index 412f977..5bbf33a 100644
+--- a/drivers/char/tty_ldisc.c
++++ b/drivers/char/tty_ldisc.c
+@@ -47,6 +47,7 @@
+ 
+ static DEFINE_SPINLOCK(tty_ldisc_lock);
+ static DECLARE_WAIT_QUEUE_HEAD(tty_ldisc_wait);
++static DECLARE_WAIT_QUEUE_HEAD(tty_ldisc_idle);
+ /* Line disc dispatch table */
+ static struct tty_ldisc_ops *tty_ldiscs[NR_LDISCS];
+ 
+@@ -83,6 +84,7 @@ static void put_ldisc(struct tty_ldisc *ld)
+ 		return;
+ 	}
+ 	local_irq_restore(flags);
++	wake_up(&tty_ldisc_idle);
+ }
+ 
+ /**
+@@ -531,6 +533,23 @@ static int tty_ldisc_halt(struct tty_struct *tty)
+ }
+ 
+ /**
++ *	tty_ldisc_wait_idle	-	wait for the ldisc to become idle
++ *	@tty: tty to wait for
++ *
++ *	Wait for the line discipline to become idle. The discipline must
++ *	have been halted for this to guarantee it remains idle.
++ */
++static int tty_ldisc_wait_idle(struct tty_struct *tty)
++{
++	int ret;
++	ret = wait_event_interruptible_timeout(tty_ldisc_idle,
++			atomic_read(&tty->ldisc->users) == 1, 5 * HZ);
++	if (ret < 0)
++		return ret;
++	return ret > 0 ? 0 : -EBUSY;
++}
++
++/**
+  *	tty_set_ldisc		-	set line discipline
+  *	@tty: the terminal to set
+  *	@ldisc: the line discipline
+@@ -634,8 +653,17 @@ int tty_set_ldisc(struct tty_struct *tty, int ldisc)
+ 
+ 	flush_scheduled_work();
+ 
++	retval = tty_ldisc_wait_idle(tty);
++
+ 	tty_lock();
+ 	mutex_lock(&tty->ldisc_mutex);
++
++	/* handle wait idle failure locked */
++	if (retval) {
++		tty_ldisc_put(new_ldisc);
++		goto enable;
++	}
++
+ 	if (test_bit(TTY_HUPPED, &tty->flags)) {
+ 		/* We were raced by the hangup method. It will have stomped
+ 		   the ldisc data and closed the ldisc down */
+@@ -669,6 +697,7 @@ int tty_set_ldisc(struct tty_struct *tty, int ldisc)
+ 
+ 	tty_ldisc_put(o_ldisc);
+ 
++enable:
+ 	/*
+ 	 *	Allow ldisc referencing to occur again
+ 	 */
+-- 
+1.7.3.2
+