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perf/core: Fix system hang caused by cpu-clock usage

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cpu-clock usage by the async-profiler tool can trigger a system hang,
which got bisected back to the following commit by Octavia Togami:

  18dbcbfabf ("perf: Fix the POLL_HUP delivery breakage") causes this issue

The root cause of the hang is that cpu-clock is a special type of SW
event which relies on hrtimers. The __perf_event_overflow() callback
is invoked from the hrtimer handler for cpu-clock events, and
__perf_event_overflow() tries to call cpu_clock_event_stop()
to stop the event, which calls htimer_cancel() to cancel the hrtimer.

But that's a recursion into the hrtimer code from a hrtimer handler,
which (unsurprisingly) deadlocks.

To fix this bug, use hrtimer_try_to_cancel() instead, and set
the PERF_HES_STOPPED flag, which causes perf_swevent_hrtimer()
to stop the event once it sees the PERF_HES_STOPPED flag.

[ mingo: Fixed the comments and improved the changelog. ]

Closes: https://lore.kernel.org/all/CAHPNGSQpXEopYreir+uDDEbtXTBvBvi8c6fYXJvceqtgTPao3Q@mail.gmail.com/
Fixes: 18dbcbfabf ("perf: Fix the POLL_HUP delivery breakage")
Reported-by: Octavia Togami <octavia.togami@gmail.com>
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Tested-by: Octavia Togami <octavia.togami@gmail.com>
Cc: stable@vger.kernel.org
Link: https://github.com/lucko/spark/issues/530
Link: https://patch.msgid.link/20251015051828.12809-1-dapeng1.mi@linux.intel.com
This commit is contained in:
Dapeng Mi
2025-10-15 13:18:28 +08:00
committed by Ingo Molnar
parent 6146a0f1df
commit eb3182ef04
1 changed files with 15 additions and 5 deletions
Download Patch File Download Diff File Expand all files Collapse all files

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);