Messages in this thread Patch in this message | | | From | Duoming Zhou <> | Subject | [PATCH V2] perf/x86/rapl: fix deadlock in rapl_pmu_event_stop | Date | Tue, 20 Sep 2022 09:44:47 +0800 |
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There is a deadlock in rapl_pmu_event_stop(), the process is shown below:
(thread 1) | (thread 2) rapl_pmu_event_stop() | rapl_hrtimer_handle() ... | if (!pmu->n_active) raw_spin_lock_irqsave() //(1) | ... ... | hrtimer_cancel() | raw_spin_lock_irqsave() //(2) (block forever)
We hold pmu->lock in position (1) and use hrtimer_cancel() to wait rapl_hrtimer_handle() to stop, but rapl_hrtimer_handle() also need pmu->lock in position (2). As a result, the rapl_pmu_event_stop() will be blocked forever.
This patch extracts hrtimer_cancel() from the protection of raw_spin_lock_irqsave(). As a result, the rapl_hrtimer_handle() could obtain the pmu->lock.
Fixes: 65661f96d3b3 ("perf/x86: Add RAPL hrtimer support") Signed-off-by: Duoming Zhou <duoming@zju.edu.cn> --- Changes in v2: - Move hrtimer_cancel() to the end of rapl_pmu_event_stop() function.
arch/x86/events/rapl.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/arch/x86/events/rapl.c b/arch/x86/events/rapl.c index 77e3a47af5a..7c110092c83 100644 --- a/arch/x86/events/rapl.c +++ b/arch/x86/events/rapl.c @@ -281,8 +281,6 @@ static void rapl_pmu_event_stop(struct perf_event *event, int mode) if (!(hwc->state & PERF_HES_STOPPED)) { WARN_ON_ONCE(pmu->n_active <= 0); pmu->n_active--; - if (pmu->n_active == 0) - hrtimer_cancel(&pmu->hrtimer); list_del(&event->active_entry); @@ -300,6 +298,11 @@ static void rapl_pmu_event_stop(struct perf_event *event, int mode) hwc->state |= PERF_HES_UPTODATE; } + if (!pmu->n_active) { + raw_spin_unlock_irqrestore(&pmu->lock, flags); + hrtimer_cancel(&pmu->hrtimer); + return; + } raw_spin_unlock_irqrestore(&pmu->lock, flags); } -- 2.17.1
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