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)

--

You know what, I think there might be an even simple solution.

How about just setting a bit saying it is canceled - and nothing more. 
Then, the dequeue logic can be just taught to ignore those things.

Doesn't that sound like the simple way to cancel signals? Make 
collect_signal() just do a "return 0" if the signal has been flushed..

			Linus
--

Yes, good idea, I'll send the patch in a minute.


Unless I missed something again, "nothing more" can't work. We still
need this patch (re-sended). We still need to free sigqueue if it is
not queued, and we must not dequeue it if it is queued - otherwise we
will free it along with the new "canceled" bit.

Oleg.

--

I see the light! Will return on May 10.

(Damn, you have proved I'm stupid twice on the same issue! OK, OK, thanks ;)

Oleg.

--

In that case perhaps we can do something like (uncompiled, just for illustration)
patch below.

While I don't know what is the "right" behaviour, I hate this patch because
it "looks ugly" (even if correct).

Oleg.

--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1709,7 +1709,7 @@ extern int send_sig(int, struct task_str
 extern void zap_other_threads(struct task_struct *p);
 extern int kill_proc(pid_t, int, int);
 extern struct sigqueue *sigqueue_alloc(void);
-extern void sigqueue_free(struct sigqueue *);
+extern void sigqueue_free(struct sigqueue *, struct sigpending *pending);
 extern int send_sigqueue(struct sigqueue *,  struct task_struct *, int group);
 extern int do_sigaction(int, struct k_sigaction *, struct k_sigaction *);
 extern int do_sigaltstack(const stack_t __user *, stack_t __user *, unsigned long);
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -1233,7 +1233,24 @@ struct sigqueue *sigqueue_alloc(void)
 	return(q);
 }
 
-void sigqueue_free(struct sigqueue *q)
+static void sigqueue_cancel(struct sigqueue *q, struct sigpending *pending)
+{
+	int sig;
+
+	list_del_init(&q->list);
+
+	sig = q->info.si_signo;
+	if (sig >= SIGRTMIN) {
+		list_for_each_entry(q, &pending->list, list)
+			if (q->info.si_signo == sig)
+				return;
+	}
+
+	sigdelset(&pending->signal, sig);
+}
+
+
+void sigqueue_free(struct sigqueue *q, struct sigpending *pending)
 {
 	unsigned long flags;
 	spinlock_t *lock = &current->sighand->siglock;
@@ -1245,17 +1262,12 @@ void sigqueue_free(struct sigqueue *q)
 	 * __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))
-		q = NULL;
+		sigqueue_cancel(q, pending);
 	spin_unlock_irqrestore(lock, flags);
 
-	if (q)
-		__sigqueue_free(q);
+	q->flags &= ~SIGQUEUE_PREALLOC;
+	...
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