From: tip-bot for Stephane Eranian <eranian@google.com>
To: linux-tip-commits@vger.kernel.org
Cc: linux-kernel@vger.kernel.org, eranian@google.com, hpa@zytor.com,
mingo@redhat.com, eric.dumazet@gmail.com, a.p.zijlstra@chello.nl,
tglx@linutronix.de, mingo@elte.hu
Subject: [tip:perf/urgent] perf: Fix double start/stop in x86_pmu_start()
Date: Tue, 7 Feb 2012 11:44:06 -0800 [thread overview]
Message-ID: <tip-f39d47ff819ed52a2afbdbecbe35f23f7755f58d@git.kernel.org> (raw)
In-Reply-To: <20120207133956.GA4932@quad>
Commit-ID: f39d47ff819ed52a2afbdbecbe35f23f7755f58d
Gitweb: http://git.kernel.org/tip/f39d47ff819ed52a2afbdbecbe35f23f7755f58d
Author: Stephane Eranian <eranian@google.com>
AuthorDate: Tue, 7 Feb 2012 14:39:57 +0100
Committer: Ingo Molnar <mingo@elte.hu>
CommitDate: Tue, 7 Feb 2012 16:58:56 +0100
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 <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 +++
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 2a30e5a..5adce10 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 ba36013..1b5c081 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);
}
/*
prev parent reply other threads:[~2012-02-07 19:44 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-02-07 13:39 [PATCH v2] perf: fix assertion failure in x86_pmu_start() Stephane Eranian
2012-02-07 14:36 ` Eric Dumazet
2012-02-07 19:44 ` tip-bot for Stephane Eranian [this message]
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