On 08/24, taoyue wrote:I know, using current->sighand->siglock to prevent one sigqueue
Oleg Nesterov wrote:^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
--- t/kernel/signal.c~SQFREE 2007-08-22 20:06:31.000000000 +0400Applying previous patch???it seems likely that the __sigqueue_free() is also called twice.
+++ t/kernel/signal.c 2007-08-23 16:02:57.000000000 +0400
@@ -1297,20 +1297,19 @@ struct sigqueue *sigqueue_alloc(void)
void sigqueue_free(struct sigqueue *q)
{
unsigned long flags;
+ spinlock_t *lock = ¤t->sighand->siglock;
+
BUG_ON(!(q->flags & SIGQUEUE_PREALLOC));
/*
* If the signal is still pending remove it from the
- * pending queue.
+ * pending queue. We must hold ->siglock while testing
+ * q->list to serialize with collect_signal().
*/
- if (unlikely(!list_empty(&q->list))) {
- spinlock_t *lock = ¤t->sighand->siglock;
- read_lock(&tasklist_lock);
- spin_lock_irqsave(lock, flags);
- if (!list_empty(&q->list))
- list_del_init(&q->list);
- spin_unlock_irqrestore(lock, flags);
- read_unlock(&tasklist_lock);
- }
+ spin_lock_irqsave(lock, flags);
+ if (!list_empty(&q->list))
+ list_del_init(&q->list);
+ spin_unlock_irqrestore(lock, flags);
+
q->flags &= ~SIGQUEUE_PREALLOC;
__sigqueue_free(q);
}
collect_signal: sigqueue_free:
list_del_init(&first->list);
spin_lock_irqsave(lock, flags);
if (!list_empty(&q->list))
list_del_init(&q->list);
spin_unlock_irqrestore(lock, flags);
q->flags &= ~SIGQUEUE_PREALLOC;
__sigqueue_free(first); __sigqueue_free(q);
collect_signal() is always called under ->siglock which is also taken by
sigqueue_free(), so this is not possible.
Basically, this patch is the same one-liner I sent you before
http://marc.info/?l=linux-kernel&m=118772206603453&w=2
(Thanks for the additional testing and report, btw).
P.S. It would be nice to know if this patch solves the problems reported
by Jeremy, but his email is disabled.
Oleg.