perf_counter: convert perf_resource_mutex to a spinlock

Now percpu counters can be initialized very early. But the init
sequence uses mutex_lock(). Fortunately, perf_resource_mutex should
be a spinlock anyway, so convert it.

[ Impact: fix crash due to early init mutex use ]

LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/perf_counter.c

@@ -46,9 +46,9 @@ static atomic_t nr_comm_tracking __read_mostly;
 int sysctl_perf_counter_priv __read_mostly; /* do we need to be privileged */
 
 /*
- * Mutex for (sysadmin-configurable) counter reservations:
+ * Lock for (sysadmin-configurable) counter reservations:
  */
-static DEFINE_MUTEX(perf_resource_mutex);
+static DEFINE_SPINLOCK(perf_resource_lock);
 
 /*
  * Architecture provided APIs - weak aliases:
@@ -3207,9 +3207,9 @@ static void __cpuinit perf_counter_init_cpu(int cpu)
 	cpuctx = &per_cpu(perf_cpu_context, cpu);
 	__perf_counter_init_context(&cpuctx->ctx, NULL);
 
-	mutex_lock(&perf_resource_mutex);
+	spin_lock(&perf_resource_lock);
 	cpuctx->max_pertask = perf_max_counters - perf_reserved_percpu;
-	mutex_unlock(&perf_resource_mutex);
+	spin_unlock(&perf_resource_lock);
 
 	hw_perf_counter_setup(cpu);
 }
@@ -3292,7 +3292,7 @@ perf_set_reserve_percpu(struct sysdev_class *class,
 	if (val > perf_max_counters)
 		return -EINVAL;
 
-	mutex_lock(&perf_resource_mutex);
+	spin_lock(&perf_resource_lock);
 	perf_reserved_percpu = val;
 	for_each_online_cpu(cpu) {
 		cpuctx = &per_cpu(perf_cpu_context, cpu);
@@ -3302,7 +3302,7 @@ perf_set_reserve_percpu(struct sysdev_class *class,
 		cpuctx->max_pertask = mpt;
 		spin_unlock_irq(&cpuctx->ctx.lock);
 	}
-	mutex_unlock(&perf_resource_mutex);
+	spin_unlock(&perf_resource_lock);
 
 	return count;
 }
@@ -3324,9 +3324,9 @@ perf_set_overcommit(struct sysdev_class *class, const char *buf, size_t count)
 	if (val > 1)
 		return -EINVAL;
 
-	mutex_lock(&perf_resource_mutex);
+	spin_lock(&perf_resource_lock);
 	perf_overcommit = val;
-	mutex_unlock(&perf_resource_mutex);
+	spin_unlock(&perf_resource_lock);
 
 	return count;
 }