Commit 133262ca authored by Linus Torvalds's avatar Linus Torvalds
Browse files

Merge tag 'perf-urgent-2025-11-08' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 

Pull perf event fix from Ingo Molnar:
 "Fix a system hang caused by cpu-clock events deadlock"

* tag 'perf-urgent-2025-11-08' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  perf/core: Fix system hang caused by cpu-clock usage
parents e6f55fe7 eb3182ef

kernel/events/core.c

+15 −5
Original line number Diff line number Diff line
@@ -11773,7 +11773,8 @@ static enum hrtimer_restart perf_swevent_hrtimer(struct hrtimer *hrtimer) 


	event = container_of(hrtimer, struct perf_event, hw.hrtimer);



	if (event->state != PERF_EVENT_STATE_ACTIVE)

	if (event->state != PERF_EVENT_STATE_ACTIVE ||

	    event->hw.state & PERF_HES_STOPPED)

		return HRTIMER_NORESTART;



	event->pmu->read(event);
@@ -11819,15 +11820,20 @@ static void perf_swevent_cancel_hrtimer(struct perf_event *event) 
	struct hw_perf_event *hwc = &event->hw;



	/*

	 * The throttle can be triggered in the hrtimer handler.

	 * The HRTIMER_NORESTART should be used to stop the timer,

	 * rather than hrtimer_cancel(). See perf_swevent_hrtimer()

	 * Careful: this function can be triggered in the hrtimer handler,

	 * for cpu-clock events, so hrtimer_cancel() would cause a

	 * deadlock.

	 *

	 * So use hrtimer_try_to_cancel() to try to stop the hrtimer,

	 * and the cpu-clock handler also sets the PERF_HES_STOPPED flag,

	 * which guarantees that perf_swevent_hrtimer() will stop the

	 * hrtimer once it sees the PERF_HES_STOPPED flag.

	 */

	if (is_sampling_event(event) && (hwc->interrupts != MAX_INTERRUPTS)) {

		ktime_t remaining = hrtimer_get_remaining(&hwc->hrtimer);

		local64_set(&hwc->period_left, ktime_to_ns(remaining));



		hrtimer_cancel(&hwc->hrtimer);

		hrtimer_try_to_cancel(&hwc->hrtimer);

	}

}
@@ -11871,12 +11877,14 @@ static void cpu_clock_event_update(struct perf_event *event) 


static void cpu_clock_event_start(struct perf_event *event, int flags)

{

	event->hw.state = 0;

	local64_set(&event->hw.prev_count, local_clock());

	perf_swevent_start_hrtimer(event);

}



static void cpu_clock_event_stop(struct perf_event *event, int flags)

{

	event->hw.state = PERF_HES_STOPPED;

	perf_swevent_cancel_hrtimer(event);

	if (flags & PERF_EF_UPDATE)

		cpu_clock_event_update(event);
@@ -11950,12 +11958,14 @@ static void task_clock_event_update(struct perf_event *event, u64 now) 


static void task_clock_event_start(struct perf_event *event, int flags)

{

	event->hw.state = 0;

	local64_set(&event->hw.prev_count, event->ctx->time);

	perf_swevent_start_hrtimer(event);

}



static void task_clock_event_stop(struct perf_event *event, int flags)

{

	event->hw.state = PERF_HES_STOPPED;

	perf_swevent_cancel_hrtimer(event);

	if (flags & PERF_EF_UPDATE)

		task_clock_event_update(event, event->ctx->time);