From f39d47ff819ed52a2afbdbecbe35f23f7755f58d Mon Sep 17 00:00:00 2001 From: Stephane Eranian Date: Tue, 7 Feb 2012 14:39:57 +0100 Subject: [PATCH] perf: Fix double start/stop in x86_pmu_start() The following patch fixes a bug introduced by the following commit: e050e3f0a71b ("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: 84f2b9b ("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 Signed-off-by: Stephane Eranian Acked-by: Peter Zijlstra 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 --- arch/x86/kernel/cpu/perf_event.c | 3 +++ kernel/events/core.c | 19 ++++++++++++++----- 2 files changed, 17 insertions(+), 5 deletions(-) diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c index 2a30e5ae6acf..5adce1040b11 100644 --- a/arch/x86/kernel/cpu/perf_event.c +++ b/arch/x86/kernel/cpu/perf_event.c @@ -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; diff --git a/kernel/events/core.c b/kernel/events/core.c index ba36013cfb21..1b5c081d8b9f 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -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; @@ -2322,9 +2322,13 @@ 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) { - event->pmu->stop(event, PERF_EF_UPDATE); + if (disable) + event->pmu->stop(event, PERF_EF_UPDATE); + local64_set(&hwc->period_left, 0); - event->pmu->start(event, PERF_EF_RELOAD); + + 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); } /*