---

yaml --- r: 45745 b: refs/heads/master c: 1b5180b h: refs/heads/master i: 45743: 072457a v: v3
git-mirror · Jan 23, 2007 · 038bd5c · 038bd5c
1 parent 84eb6fc
commit 038bd5c
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Showing 2 changed files with 12 additions and 5 deletions.
diff --git a/[refs] b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: b53d0b919ebe227e2b8e49b6e0ddee506be83aa8
+refs/heads/master: 1b5180b65122666a36a1a232b7b9b38b21a9dcdd
diff --git a/trunk/kernel/sys.c b/trunk/kernel/sys.c
@@ -323,11 +323,18 @@ EXPORT_SYMBOL_GPL(blocking_notifier_chain_unregister);
 int blocking_notifier_call_chain(struct blocking_notifier_head *nh,
 		unsigned long val, void *v)
 {
-	int ret;
+	int ret = NOTIFY_DONE;
 
-	down_read(&nh->rwsem);
-	ret = notifier_call_chain(&nh->head, val, v);
-	up_read(&nh->rwsem);
+	/*
+	 * We check the head outside the lock, but if this access is
+	 * racy then it does not matter what the result of the test
+	 * is, we re-check the list after having taken the lock anyway:
+	 */
+	if (rcu_dereference(nh->head)) {
+		down_read(&nh->rwsem);
+		ret = notifier_call_chain(&nh->head, val, v);
+		up_read(&nh->rwsem);
+	}
 	return ret;
 }