perf,rcu: convert call_rcu(free_ctx) to kfree_rcu()

The rcu callback free_ctx() just calls a kfree(),
so we use kfree_rcu() instead of the call_rcu(free_ctx).
Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>

kernel/perf_event.c

@@ -586,14 +586,6 @@ static void get_ctx(struct perf_event_context *ctx)
 	WARN_ON(!atomic_inc_not_zero(&ctx->refcount));
 }
 
-static void free_ctx(struct rcu_head *head)
-{
-	struct perf_event_context *ctx;
-
-	ctx = container_of(head, struct perf_event_context, rcu_head);
-	kfree(ctx);
-}
-
 static void put_ctx(struct perf_event_context *ctx)
 {
 	if (atomic_dec_and_test(&ctx->refcount)) {
@@ -601,7 +593,7 @@ static void put_ctx(struct perf_event_context *ctx)
 			put_ctx(ctx->parent_ctx);
 		if (ctx->task)
 			put_task_struct(ctx->task);
-		call_rcu(&ctx->rcu_head, free_ctx);
+		kfree_rcu(ctx, rcu_head);
 	}
 }