Commit 93472aff authored Jun 24, 2015 by Peter Zijlstra Committed by Ingo Molnar Jun 30, 2015

perf/x86: Fix 'active_events' imbalance



Commit 1b7b938f ("perf/x86/intel: Fix PMI handling for Intel PT") conditionally
increments active_events in x86_add_exclusive() but unconditionally decrements in
x86_del_exclusive().

These extra decrements can lead to the situation where
active_events is zero and thus the PMI handler is 'disabled'
while we have active events on the PMU generating PMIs.

This leads to a truckload of:

  Uhhuh. NMI received for unknown reason 21 on CPU 28.
  Do you have a strange power saving mode enabled?
  Dazed and confused, but trying to continue

messages and generally messes up perf.

Remove the condition on the increment, double increment balanced
by a double decrement is perfectly fine.

Restructure the code a little bit to make the unconditional inc
a bit more natural.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: alexander.shishkin@linux.intel.com
Cc: brgerst@gmail.com
Cc: dvlasenk@redhat.com
Cc: luto@amacapital.net
Cc: oleg@redhat.com
Fixes: 1b7b938f ("perf/x86/intel: Fix PMI handling for Intel PT")
Link: http://lkml.kernel.org/r/20150624144750.GJ18673@twins.programming.kicks-ass.net


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 2d6dac2f

arch/x86/kernel/cpu/perf_event.c

+13 −23

Original line number	Diff line number	Diff line
		@@ -357,34 +357,24 @@ void x86_release_hardware(void)
		*/
		int x86_add_exclusive(unsigned int what)
		{
		int ret = -EBUSY, i;

		if (atomic_inc_not_zero(&x86_pmu.lbr_exclusive[what]))
		return 0;
		int i;

		if (!atomic_inc_not_zero(&x86_pmu.lbr_exclusive[what])) {
		mutex_lock(&pmc_reserve_mutex);
		for (i = 0; i < ARRAY_SIZE(x86_pmu.lbr_exclusive); i++) {
		if (i != what && atomic_read(&x86_pmu.lbr_exclusive[i]))
		goto out;
		goto fail_unlock;
		}

		atomic_inc(&x86_pmu.lbr_exclusive[what]);
		ret = 0;

		out:
		mutex_unlock(&pmc_reserve_mutex);
		}

		/*
		* Assuming that all exclusive events will share the PMI handler
		* (which checks active_events for whether there is work to do),
		* we can bump active_events counter right here, except for
		* x86_lbr_exclusive_lbr events that go through x86_pmu_event_init()
		* path, which already bumps active_events for them.
		*/
		if (!ret && what != x86_lbr_exclusive_lbr)
		atomic_inc(&active_events);
		return 0;

		return ret;
		fail_unlock:
		mutex_unlock(&pmc_reserve_mutex);
		return -EBUSY;
		}

		void x86_del_exclusive(unsigned int what)

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