watch_queue: Fix missing rcu annotation

Since __post_watch_notification() walks wlist->watchers with only the
RCU read lock held, we need to use RCU methods to add to the list (we
already use RCU methods to remove from the list).

Fix add_watch_to_object() to use hlist_add_head_rcu() instead of
hlist_add_head() for that list.

Fixes: c73be61 ("pipe: Add general notification queue support")
Signed-off-by: David Howells <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Author: dhowells

kernel/watch_queue.c

@@ -494,7 +494,7 @@ int add_watch_to_object(struct watch *watch, struct watch_list *wlist)
 		unlock_wqueue(wqueue);
 	}
 
-	hlist_add_head(&watch->list_node, &wlist->watchers);
+	hlist_add_head_rcu(&watch->list_node, &wlist->watchers);
 	return 0;
 }
 EXPORT_SYMBOL(add_watch_to_object);