kernel/events/core.c: Replace rcu_dereference() with rcu_access_pointer()

The "rcu_dereference()" call is used directly in a condition. Since its return value is never dereferenced it is recommended to use "rcu_access_pointer()" instead of "rcu_dereference()". Therefore, this patch makes the replacement.

The following Coccinelle semantic patch was used:
@@
@@

(
if(
(<+...
- rcu_dereference
+ rcu_access_pointer
(...)
...+>)) {...}
|
while(
(<+...
- rcu_dereference
+ rcu_access_pointer
(...)
...+>)) {...}
)

---
 kernel/events/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index 5fa58e4..0d735be 100644
@@ -980,7 +980,7 @@ retry:
 		 * can't get swapped on us any more.
 		 */
 		raw_spin_lock_irqsave(&ctx->lock, *flags);
-		if (ctx != rcu_dereference(task->perf_event_ctxp[ctxn])) {
+		if (ctx != rcu_access_pointer(task->perf_event_ctxp[ctxn])) {
 			raw_spin_unlock_irqrestore(&ctx->lock, *flags);
 			rcu_read_unlock();
 			preempt_enable();

1.9.1