[PATCH 2/4] posix timers: sigqueue_free: don't free sigqueue if it is queued

[Oleg Nesterov <oleg@tv-sign.ru>]

Currently sigqueue_free() removes sigqueue from list, but doesn't cancel the
pending signal. This is not consistent, the task should either receive the
"full" signal along with siginfo_t, or it shouldn't see the signal at all.

Change sigqueue_free() to clear SIGQUEUE_PREALLOC but leave sigqueue on list
if it is queued.

Note: I am not sure we shouldn't do the opposite, free sigqueue + cancel the
pending signal, but this needs some ugly changes. Perhaps we should reconsider
this change later. See also http://bugzilla.kernel.org/show_bug.cgi?id=10460

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>

--- 25/kernel/signal.c~2_SF_DONT_REMOVE	2008-05-03 18:27:03.000000000 +0400
+++ 25/kernel/signal.c	2008-05-03 19:12:36.000000000 +0400
@@ -1240,18 +1240,22 @@ void sigqueue_free(struct sigqueue *q)
 
 	BUG_ON(!(q->flags & SIGQUEUE_PREALLOC));
 	/*
-	 * If the signal is still pending remove it from the
-	 * pending queue. We must hold ->siglock while testing
-	 * q->list to serialize with collect_signal() or with
+	 * We must hold ->siglock while testing q->list
+	 * to serialize with collect_signal() or with
 	 * __exit_signal()->flush_sigqueue().
 	 */
 	spin_lock_irqsave(lock, flags);
+	/*
+	 * If it is queued it will be freed when dequeued,
+	 * like the "regular" sigqueue.
+	 */
+	q->flags &= ~SIGQUEUE_PREALLOC;
 	if (!list_empty(&q->list))
-		list_del_init(&q->list);
+		q = NULL;
 	spin_unlock_irqrestore(lock, flags);
 
-	q->flags &= ~SIGQUEUE_PREALLOC;
-	__sigqueue_free(q);
+	if (q)
+		__sigqueue_free(q);
 }
 
 int send_sigqueue(struct sigqueue *q, struct task_struct *t, int group)