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Subject[17/70] ARM: 6989/1: perf: do not start the PMU when no events are present
2.6.39-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Will Deacon <will.deacon@arm.com>

commit f4f38430c94c38187db73a2cf3892cc8b12a2713 upstream.

armpmu_enable can be called in situations where no events are present
(for example, from the event rotation tick after a profiled task has
exited). In this case, we currently start the PMU anyway which may
leave it active inevitably without any events being monitored.

This patch adds a simple check to the enabling code so that we avoid
starting the PMU when no events are present.

Reported-by: Ashwin Chaugle <ashwinc@codeaurora.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
arch/arm/kernel/perf_event.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

--- a/arch/arm/kernel/perf_event.c
+++ b/arch/arm/kernel/perf_event.c
@@ -588,7 +588,7 @@ static int armpmu_event_init(struct perf
static void armpmu_enable(struct pmu *pmu)
{
/* Enable all of the perf events on hardware. */
- int idx;
+ int idx, enabled = 0;
struct cpu_hw_events *cpuc = &__get_cpu_var(cpu_hw_events);

if (!armpmu)
@@ -601,9 +601,11 @@ static void armpmu_enable(struct pmu *pm
continue;

armpmu->enable(&event->hw, idx);
+ enabled = 1;
}

- armpmu->start();
+ if (enabled)
+ armpmu->start();
}

static void armpmu_disable(struct pmu *pmu)



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