PR10177: init/kill time in sleepy context only

Previously, _stp_init_time and _stp_kill_time were being called from
begin/end/error probes, which will run with preemption disabled.  The
BUG reported on RT kernels showed that cpufreq_unregister_notifier can
end up sleeping, which violates our preemption block.

This patch moves the init/kill into systemtap_module_init/exit, where it
is safe to sleep.  The code maintains a new predicate with the define
STAP_NEED_GETTIMEOFDAY, so we don't still incur any timer overhead if
it's not used.

5 files changed, 42 insertions, 44 deletions

diff --git a/tapset/timestamp_gtod.stp b/tapset/timestamp_gtod.stp
index 43b127dc..b916a3b1 100644
--- a/tapset/timestamp_gtod.stp
+++ b/tapset/timestamp_gtod.stp
@@ -7,23 +7,10 @@
 // Public License (GPL); either version 2, or (at your option) any
 // later version.
 
-function _gettimeofday_init:long() %{
-  THIS->__retvalue = _stp_init_time(); /* Kick off the Big Bang.  */
+%{
+#define STAP_NEED_GETTIMEOFDAY 1
 %}
 
-probe begin(-0x8000000000000000) {
-  if (_gettimeofday_init() != 0)
-    error("couldn't initialize gettimeofday")
-}
-
-function _gettimeofday_kill() %{
-  _stp_kill_time();  /* Go to a beach.  Drink a beer.  */
-%}
-
-probe end(0x7FFFFFFFFFFFFFFF), error(0x7FFFFFFFFFFFFFFF) {
-  _gettimeofday_kill()
-}
-
 
 /**
  * sfunction gettimeofday_ns - Number of nanoseconds since UNIX epoch.
diff --git a/testsuite/buildok/gtod_init.stp b/testsuite/buildok/gtod_init.stp
new file mode 100755
index 00000000..1d76aeab
--- /dev/null
+++ b/testsuite/buildok/gtod_init.stp
@@ -0,0 +1,13 @@
+#! stap -gp4
+
+# check that STAP_NEED_GETTIMEOFDAY is defined with a gettimeofday
+function check() %{
+#ifndef STAP_NEED_GETTIMEOFDAY
+#error "gettimeofday should define STAP_NEED_GETTIMEOFDAY!"
+#endif
+%}
+
+probe begin {
+    check()
+    println(gettimeofday_s())
+}
diff --git a/testsuite/buildok/gtod_noinit.stp b/testsuite/buildok/gtod_noinit.stp
new file mode 100755
index 00000000..94a9dfdc
--- /dev/null
+++ b/testsuite/buildok/gtod_noinit.stp
@@ -0,0 +1,13 @@
+#! stap -gp4
+
+# check that STAP_NEED_GETTIMEOFDAY is NOT defined without a gettimeofday
+function check() %{
+#ifdef STAP_NEED_GETTIMEOFDAY
+#error "STAP_NEED_GETTIMEOFDAY should not be defined!"
+#endif
+%}
+
+probe begin {
+    check()
+    println(get_cycles())
+}
diff --git a/testsuite/systemtap.base/gtod_init.exp b/testsuite/systemtap.base/gtod_init.exp
deleted file mode 100644
index 48616b1f..00000000
--- a/testsuite/systemtap.base/gtod_init.exp
+++ /dev/null
@@ -1,29 +0,0 @@
-# test for checking initialization of the time subsystem
-set test "gtod_init"
-
-# check that init and kill are both present with a gettimeofday
-set time_init 0
-set time_kill 0
-spawn stap -p2 -e {probe begin { println(gettimeofday_s()) }}
-expect {
-	-timeout 120
-	-re {\n_gettimeofday_init:} { incr time_init; exp_continue }
-	-re {\n_gettimeofday_kill:} { incr time_kill; exp_continue }
-	timeout { fail "$test (timeout)" }
-	eof {
-        if {$time_init == 1} { pass "$test (init)" } { fail "$test (init $time_init)" }
-        if {$time_kill == 1} { pass "$test (kill)" } { fail "$test (kill $time_kill)" }
-    }
-}
-wait
-
-# check that init and kill are both NOT present without a gettimeofday
-spawn stap -p2 -e {probe begin { println(get_cycles()) }}
-expect {
-	-timeout 120
-	-re {\n_gettimeofday_init:} { fail "$test (bad init)" }
-	-re {\n_gettimeofday_kill:} { fail "$test (bad kill)" }
-	timeout { fail "$test (timeout)" }
-	eof { pass "$test (no init/kill)" }
-}
-wait
diff --git a/translate.cxx b/translate.cxx
index 62c71aeb..9f45f5d1 100644
--- a/translate.cxx
+++ b/translate.cxx
@@ -1133,6 +1133,15 @@ c_unparser::emit_module_init ()
   o->newline(-1) << "}";
   o->newline() << "if (rc) goto out;";
 
+  // initialize gettimeofday (if needed)
+  o->newline() << "#ifdef STAP_NEED_GETTIMEOFDAY";
+  o->newline() << "rc = _stp_init_time();";  // Kick off the Big Bang.
+  o->newline() << "if (rc) {";
+  o->newline(1) << "_stp_error (\"couldn't initialize gettimeofday\");";
+  o->newline() << "goto out;";
+  o->newline(-1) << "}";
+  o->newline() << "#endif";
+
   o->newline() << "(void) probe_point;";
   o->newline() << "(void) i;";
   o->newline() << "(void) j;";
@@ -1359,6 +1368,11 @@ c_unparser::emit_module_exit ()
     o->newline() << "#endif";
   }
 
+  // teardown gettimeofday (if needed)
+  o->newline() << "#ifdef STAP_NEED_GETTIMEOFDAY";
+  o->newline() << " _stp_kill_time();";  // Go to a beach.  Drink a beer.
+  o->newline() << "#endif";
+
   // print final error/skipped counts if non-zero
   o->newline() << "if (atomic_read (& skipped_count) || "
                << "atomic_read (& error_count) || "