Messages in this thread Patch in this message | | | Date | Wed, 30 Sep 2015 09:10:46 +0200 | From | Peter Zijlstra <> | Subject | [PATCH v2 11/12] sched: More notrace |
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preempt_schedule_common() is marked notrace, but it does not use _notrace() preempt_count functions and __schedule() is also not marked notrace, which means that its perfectly possible to end up in the tracer from preempt_schedule_common().
Steve says:
| Yep, there's some history to this. This was originally the issue that | caused function tracing to go into infinite recursion. But now we have | preempt_schedule_notrace(), which is used by the function tracer, and | that function must not be traced till preemption is disabled. | | Now if function tracing is running and we take an interrupt when | NEED_RESCHED is set, it calls | | preempt_schedule_common() (not traced) | | But then that calls preempt_disable() (traced) | | function tracer calls preempt_disable_notrace() followed by | preempt_enable_notrace() which will see NEED_RESCHED set, and it will | call preempt_schedule_notrace(), which stops the recursion, but | still calls __schedule() here, and that means when we return, we call | the __schedule() from preempt_schedule_common(). | | That said, I prefer this patch. Preemption is disabled before calling | __schedule(), and we get rid of a one round recursion with the | scheduler.
Reviewed-by: Thomas Gleixner <tglx@linutronix.de> Acked-by: Steven Rostedt <rostedt@goodmis.org> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> --- kernel/sched/core.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)
--- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -3057,7 +3057,7 @@ pick_next_task(struct rq *rq, struct tas * * WARNING: must be called with preemption disabled! */ -static void __sched __schedule(bool preempt) +static void __sched notrace __schedule(bool preempt) { struct task_struct *prev, *next; unsigned long *switch_count; @@ -3203,9 +3203,9 @@ void __sched schedule_preempt_disabled(v static void __sched notrace preempt_schedule_common(void) { do { - preempt_disable(); + preempt_disable_notrace(); __schedule(true); - sched_preempt_enable_no_resched(); + preempt_enable_no_resched_notrace(); /* * Check again in case we missed a preemption opportunity
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