[PATCH] Allow raw_notifier callouts to unregister themselves

Since raw_notifier chains don't benefit from any centralized locking
protections, they shouldn't suffer from the associated limitations.  Under
some circumstances it might make sense for a raw_notifier callout routine
to unregister itself from the notifier chain.  This patch (as678) changes
the notifier core to allow for such things.
Signed-off-by: NAlan Stern <stern@rowland.harvard.edu>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

kernel/sys.c

@@ -137,14 +137,15 @@ static int __kprobes notifier_call_chain(struct notifier_block **nl,
 		unsigned long val, void *v)
 {
 	int ret = NOTIFY_DONE;
-	struct notifier_block *nb;
+	struct notifier_block *nb, *next_nb;
 
 	nb = rcu_dereference(*nl);
 	while (nb) {
+		next_nb = rcu_dereference(nb->next);
 		ret = nb->notifier_call(nb, val, v);
 		if ((ret & NOTIFY_STOP_MASK) == NOTIFY_STOP_MASK)
 			break;
-		nb = rcu_dereference(nb->next);
+		nb = next_nb;
 	}
 	return ret;
 }