From: Steven Rostedt Date: Thu, 29 Sep 2011 12:24:30 -0500 Subject: tracing: Account for preempt off in preempt_schedule() The preempt_schedule() uses the preempt_disable_notrace() version because it can cause infinite recursion by the function tracer as the function tracer uses preempt_enable_notrace() which may call back into the preempt_schedule() code as the NEED_RESCHED is still set and the PREEMPT_ACTIVE has not been set yet. See commit: d1f74e20b5b064a130cd0743a256c2d3cfe84010 that made this change. The preemptoff and preemptirqsoff latency tracers require the first and last preempt count modifiers to enable tracing. But this skips the checks. Since we can not convert them back to the non notrace version, we can use the idle() hooks for the latency tracers here. That is, the start/stop_critical_timings() works well to manually start and stop the latency tracer for preempt off timings. Signed-off-by: Steven Rostedt Signed-off-by: Clark Williams Signed-off-by: Thomas Gleixner --- kernel/sched/core.c | 9 +++++++++ 1 file changed, 9 insertions(+) Index: linux-stable/kernel/sched/core.c =================================================================== --- linux-stable.orig/kernel/sched/core.c +++ linux-stable/kernel/sched/core.c @@ -3544,7 +3544,16 @@ asmlinkage void __sched notrace preempt_ do { add_preempt_count_notrace(PREEMPT_ACTIVE); + /* + * The add/subtract must not be traced by the function + * tracer. But we still want to account for the + * preempt off latency tracer. Since the _notrace versions + * of add/subtract skip the accounting for latency tracer + * we must force it manually. + */ + start_critical_timings(); __schedule(); + stop_critical_timings(); sub_preempt_count_notrace(PREEMPT_ACTIVE); /*