[RFC PATCH v2 4/5] arm: perf: Make v7 support FIQ-safe

[Daniel Thompson]

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 at 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