Messages in this thread Patch in this message | | | From | Duoming Zhou <> | Subject | [PATCH] perf/x86/rapl: fix deadlock in rapl_pmu_event_stop | Date | Sat, 17 Sep 2022 22:47:29 +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. In order to prevent race conditions, we put "if (!pmu->n_active)" in rapl_hrtimer_handle() under the protection of raw_spin_lock_irqsave().
Fixes: 65661f96d3b3 ("perf/x86: Add RAPL hrtimer support") Signed-off-by: Duoming Zhou <duoming@zju.edu.cn> --- arch/x86/events/rapl.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-)
diff --git a/arch/x86/events/rapl.c b/arch/x86/events/rapl.c index 77e3a47af5a..97c71538d01 100644 --- a/arch/x86/events/rapl.c +++ b/arch/x86/events/rapl.c @@ -219,11 +219,11 @@ static enum hrtimer_restart rapl_hrtimer_handle(struct hrtimer *hrtimer) struct perf_event *event; unsigned long flags; + raw_spin_lock_irqsave(&pmu->lock, flags); + if (!pmu->n_active) return HRTIMER_NORESTART; - raw_spin_lock_irqsave(&pmu->lock, flags); - list_for_each_entry(event, &pmu->active_list, active_entry) rapl_event_update(event); @@ -281,8 +281,11 @@ 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) + if (!pmu->n_active) { + raw_spin_unlock_irqrestore(&pmu->lock, flags); hrtimer_cancel(&pmu->hrtimer); + raw_spin_lock_irqsave(&pmu->lock, flags); + } list_del(&event->active_entry); -- 2.17.1
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