sched/core: More notrace annotations

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.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index ca260cc5d881d5c70595be16814eb1d867fdae07..98c4cf8182cf2a1712060d5106eaa9abb2d18344 100644 (file)
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3057,7 +3057,7 @@ again:
  *
  * 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(void)
 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