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Subject[RFC PATCH v2 4/5] arm: perf: Make v7 support FIQ-safe
Date
armv7pmu_disable_event() is called during irq handling. If irq handling
switches over to fiq then the spin locks in this function risk deadlock.
Both armv7_pmnc_disable_counter() and armv7_pmnc_disable_intens() are
unconditional co-processor writes. I haven't yet come up with an
schedule where other users of pmu_lock would break if interleaved with
these calls so I have simply removed them.

The other change required us to avoid calling irq_work_run() when run
from a FIQ handler. The pended work will either be dispatched by the
irq work IPI or by a timer handler.

Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
---
arch/arm/kernel/perf_event_v7.c | 11 ++---------
1 file changed, 2 insertions(+), 9 deletions(-)

diff --git a/arch/arm/kernel/perf_event_v7.c b/arch/arm/kernel/perf_event_v7.c
index 8993770c47de..08f426486d3e 100644
--- a/arch/arm/kernel/perf_event_v7.c
+++ b/arch/arm/kernel/perf_event_v7.c
@@ -744,7 +744,6 @@ static void armv7pmu_enable_event(struct perf_event *event)

static void armv7pmu_disable_event(struct perf_event *event)
{
- unsigned long flags;
struct hw_perf_event *hwc = &event->hw;
struct arm_pmu *cpu_pmu = to_arm_pmu(event->pmu);
struct pmu_hw_events *events = this_cpu_ptr(cpu_pmu->hw_events);
@@ -757,11 +756,6 @@ static void armv7pmu_disable_event(struct perf_event *event)
}

/*
- * Disable counter and interrupt
- */
- raw_spin_lock_irqsave(&events->pmu_lock, flags);
-
- /*
* Disable counter
*/
armv7_pmnc_disable_counter(idx);
@@ -770,8 +764,6 @@ static void armv7pmu_disable_event(struct perf_event *event)
* Disable interrupt for this counter
*/
armv7_pmnc_disable_intens(idx);
-
- raw_spin_unlock_irqrestore(&events->pmu_lock, flags);
}

static irqreturn_t armv7pmu_handle_irq(int irq_num, void *dev)
@@ -831,7 +823,8 @@ static irqreturn_t armv7pmu_handle_irq(int irq_num, void *dev)
* platforms that can have the PMU interrupts raised as an NMI, this
* will not work.
*/
- irq_work_run();
+ if (!in_nmi())
+ irq_work_run();

return IRQ_HANDLED;
}
--
1.9.3


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