[PATCH 2/2 v2] optimize for perf_event_init_task()

[Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>]

We can traverse ctx->group_list to get all group leader, it should be safe
since we hold ctx->mutex

Changlog v1->v2:
- remove WARN_ON_ONCE() as Peter Zijlstra's suggestion

Signed-off-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
---
 kernel/perf_event.c |    4 +---
 1 files changed, 1 insertions(+), 3 deletions(-)

diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index 2a15cd6..0276fb4 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -4767,9 +4767,7 @@ int perf_event_init_task(struct task_struct *child)
 	 * We dont have to disable NMIs - we are only looking at
 	 * the list, not manipulating it:
 	 */
-	list_for_each_entry_rcu(event, &parent_ctx->event_list, event_entry) {
-		if (event != event->group_leader)
-			continue;
+	list_for_each_entry(event, &parent_ctx->group_list, group_entry) {
 
 		if (!event->attr.inherit) {
 			inherited_all = 0;
-- 
1.6.1.2