perf: Fix double start/stop in x86_pmu_start() (f39d47ff) · Commits · 戴 / test

The following patch fixes a bug introduced by the following commit: ("perf: Fix broken interrupt rate throttling") The patch caused the following warning to pop up depending on the sampling frequency adjustments: ------------[ cut here ]------------ WARNING: at arch/x86/kernel/cpu/perf_event.c:995 x86_pmu_start+0x79/0xd4() It was caused by the following call sequence: perf_adjust_freq_unthr_context.part() { stop() if (delta > 0) { perf_adjust_period() { if (period > 8*...) { stop() ... start() } } } start() } Which caused a double start and a double stop, thus triggering the assert in x86_pmu_start(). The patch fixes the problem by avoiding the double calls. We pass a new argument to perf_adjust_period() to indicate whether or not the event is already stopped. We can't just remove the start/stop from that function because it's called from __perf_event_overflow where the event needs to be reloaded via a stop/start back-toback call. The patch reintroduces the assertion in x86_pmu_start() which was removed by commit: ("perf: Remove deprecated WARN_ON_ONCE()") In this second version, we've added calls to disable/enable PMU during unthrottling or frequency adjustment based on bug report of spurious NMI interrupts from Eric Dumazet. Reported-and-tested-by:

Eric Dumazet <eric.dumazet@gmail.com> Signed-off-by:

Stephane Eranian <eranian@google.com> Acked-by:

Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: markus@trippelsdorf.de Cc: paulus@samba.org Link: http://lkml.kernel.org/r/20120207133956.GA4932@quad [ Minor edits to the changelog and to the code ] Signed-off-by:

Ingo Molnar <mingo@elte.hu>

arch/x86/kernel/cpu/perf_event.c

+3 −0

Original line number	Diff line number	Diff line
		@@ -986,6 +986,9 @@ static void x86_pmu_start(struct perf_event *event, int flags)
		struct cpu_hw_events *cpuc = &__get_cpu_var(cpu_hw_events);
		int idx = event->hw.idx;

		if (WARN_ON_ONCE(!(event->hw.state & PERF_HES_STOPPED)))
		return;

		if (WARN_ON_ONCE(idx == -1))
		return;

kernel/events/core.c

+14 −5

Original line number	Diff line number	Diff line
		@@ -2303,7 +2303,7 @@ do { \
		static DEFINE_PER_CPU(int, perf_throttled_count);
		static DEFINE_PER_CPU(u64, perf_throttled_seq);

		static void perf_adjust_period(struct perf_event *event, u64 nsec, u64 count)
		static void perf_adjust_period(struct perf_event *event, u64 nsec, u64 count, bool disable)
		{
		struct hw_perf_event *hwc = &event->hw;
		s64 period, sample_period;
		@@ -2322,8 +2322,12 @@ static void perf_adjust_period(struct perf_event *event, u64 nsec, u64 count)
		hwc->sample_period = sample_period;

		if (local64_read(&hwc->period_left) > 8*sample_period) {
		if (disable)
		event->pmu->stop(event, PERF_EF_UPDATE);

		local64_set(&hwc->period_left, 0);

		if (disable)
		event->pmu->start(event, PERF_EF_RELOAD);
		}
		}
		@@ -2350,6 +2354,7 @@ static void perf_adjust_freq_unthr_context(struct perf_event_context *ctx,
		return;

		raw_spin_lock(&ctx->lock);
		perf_pmu_disable(ctx->pmu);

		list_for_each_entry_rcu(event, &ctx->event_list, event_entry) {
		if (event->state != PERF_EVENT_STATE_ACTIVE)
		@@ -2381,13 +2386,17 @@ static void perf_adjust_freq_unthr_context(struct perf_event_context *ctx,
		/*
		* restart the event
		* reload only if value has changed
		* we have stopped the event so tell that
		* to perf_adjust_period() to avoid stopping it
		* twice.
		*/
		if (delta > 0)
		perf_adjust_period(event, period, delta);
		perf_adjust_period(event, period, delta, false);

		event->pmu->start(event, delta > 0 ? PERF_EF_RELOAD : 0);
		}

		perf_pmu_enable(ctx->pmu);
		raw_spin_unlock(&ctx->lock);
		}

		@@ -4562,7 +4571,7 @@ static int __perf_event_overflow(struct perf_event *event,
		hwc->freq_time_stamp = now;

		if (delta > 0 && delta < 2*TICK_NSEC)
		perf_adjust_period(event, delta, hwc->last_period);
		perf_adjust_period(event, delta, hwc->last_period, true);
		}

		/*

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