[PATCH] perf: fix WARNING in perf_event_open

[Edward Adam Davis]

The new version of __perf_event_read_size() only has a read action and does not
require a mutex, so the mutex assertion in the original loop is removed.

Fixes: 382c27f4ed28 ("perf: Fix perf_event_validate_size()")
Reported-and-tested-by: syzbot+07144c543a5c002c7305@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Edward Adam Davis <eadavis@xxxxxx>
---
 kernel/events/core.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 9efd0d7775e7..e71e61b46416 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -1924,6 +1924,10 @@ static void perf_event__id_header_size(struct perf_event *event)
 	event->id_header_size = size;
 }
 
+#define read_for_each_sibling_event(sibling, event)		\
+	if ((event)->group_leader == (event))			\
+		list_for_each_entry((sibling), &(event)->sibling_list, sibling_list)
+
 /*
  * Check that adding an event to the group does not result in anybody
  * overflowing the 64k event limit imposed by the output buffer.
@@ -1957,7 +1961,7 @@ static bool perf_event_validate_size(struct perf_event *event)
 	if (event == group_leader)
 		return true;
 
-	for_each_sibling_event(sibling, group_leader) {
+	read_for_each_sibling_event(sibling, group_leader) {
 		if (__perf_event_read_size(sibling->attr.read_format,
 					   group_leader->nr_siblings + 1) > 16*1024)
 			return false;
-- 
2.43.0