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 <t...@linutronix.de>
Acked-by: Steven Rostedt <rost...@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <pet...@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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