drivers/perf: arm-pmu: convert arm_pmu_mutex to spinlock

sudeep-holla · wildea01 · commit a026bb12cc57 · 2016-08-09T17:33:38.000+01:00
arm_pmu_mutex is never held long and we don't want to sleep while the lock is being held as it's executed in the context of hotplug notifiers. So it can be converted to a simple spinlock instead. Without this patch we get the following warning: BUG: sleeping function called from invalid context at kernel/locking/mutex.c:620 in_atomic(): 1, irqs_disabled(): 128, pid: 0, name: swapper/2 no locks held by swapper/2/0. irq event stamp: 381314 hardirqs last enabled at (381313): _raw_spin_unlock_irqrestore+0x7c/0x88 hardirqs last disabled at (381314): cpu_die+0x28/0x48 softirqs last enabled at (381294): _local_bh_enable+0x28/0x50 softirqs last disabled at (381293): irq_enter+0x58/0x78 CPU: 2 PID: 0 Comm: swapper/2 Not tainted 4.7.0 torvalds#12 Call trace: dump_backtrace+0x0/0x220 show_stack+0x24/0x30 dump_stack+0xb4/0xf0 ___might_sleep+0x1d8/0x1f0 __might_sleep+0x5c/0x98 mutex_lock_nested+0x54/0x400 arm_perf_starting_cpu+0x34/0xb0 cpuhp_invoke_callback+0x88/0x3d8 notify_cpu_starting+0x78/0x98 secondary_start_kernel+0x108/0x1a8 This patch converts the mutex to spinlock to eliminate the above warnings. This constraints pmu->reset to be non-blocking call which is the case with all the ARM PMU backends. Cc: Stephen Boyd <sboyd@codeaurora.org> Fixes: 37b502f ("arm/perf: Fix hotplug state machine conversion") Acked-by: Mark Rutland <mark.rutland@arm.com> Signed-off-by: Sudeep Holla <sudeep.holla@arm.com> Signed-off-by: Will Deacon <will.deacon@arm.com>
diff --git a/drivers/perf/arm_pmu.c b/drivers/perf/arm_pmu.c
@@ -688,7 +688,7 @@ static int cpu_pmu_request_irq(struct arm_pmu *cpu_pmu, irq_handler_t handler)
 	return 0;
 }
 
-static DEFINE_MUTEX(arm_pmu_mutex);
+static DEFINE_SPINLOCK(arm_pmu_lock);
 static LIST_HEAD(arm_pmu_list);
 
 /*
@@ -701,15 +701,15 @@ static int arm_perf_starting_cpu(unsigned int cpu)
 {
 	struct arm_pmu *pmu;
 
-	mutex_lock(&arm_pmu_mutex);
+	spin_lock(&arm_pmu_lock);
 	list_for_each_entry(pmu, &arm_pmu_list, entry) {
 
 		if (!cpumask_test_cpu(cpu, &pmu->supported_cpus))
 			continue;
 		if (pmu->reset)
 			pmu->reset(pmu);
 	}
-	mutex_unlock(&arm_pmu_mutex);
+	spin_unlock(&arm_pmu_lock);
 	return 0;
 }
 
@@ -821,9 +821,9 @@ static int cpu_pmu_init(struct arm_pmu *cpu_pmu)
 	if (!cpu_hw_events)
 		return -ENOMEM;
 
-	mutex_lock(&arm_pmu_mutex);
+	spin_lock(&arm_pmu_lock);
 	list_add_tail(&cpu_pmu->entry, &arm_pmu_list);
-	mutex_unlock(&arm_pmu_mutex);
+	spin_unlock(&arm_pmu_lock);
 
 	err = cpu_pm_pmu_register(cpu_pmu);
 	if (err)
@@ -859,19 +859,19 @@ static int cpu_pmu_init(struct arm_pmu *cpu_pmu)
 	return 0;
 
 out_unregister:
-	mutex_lock(&arm_pmu_mutex);
+	spin_lock(&arm_pmu_lock);
 	list_del(&cpu_pmu->entry);
-	mutex_unlock(&arm_pmu_mutex);
+	spin_unlock(&arm_pmu_lock);
 	free_percpu(cpu_hw_events);
 	return err;
 }
 
 static void cpu_pmu_destroy(struct arm_pmu *cpu_pmu)
 {
 	cpu_pm_pmu_unregister(cpu_pmu);
-	mutex_lock(&arm_pmu_mutex);
+	spin_lock(&arm_pmu_lock);
 	list_del(&cpu_pmu->entry);
-	mutex_unlock(&arm_pmu_mutex);
+	spin_unlock(&arm_pmu_lock);
 	free_percpu(cpu_pmu->hw_events);
 }
 
