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Fix a system hang caused by cpu-clock events. 

Signed-off-by: Ingo Molnar <mingo@kernel.org>
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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
This commit is contained in:
Linus Torvalds 2025-11-08 08:54:13 -08:00
parent e6f55fe790 eb3182ef04
commit 133262cae9
1 changed files with 15 additions and 5 deletions
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20
kernel/events/core.c
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@ -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);