Messages in this thread | | | Date | Fri, 24 Aug 2007 17:29:47 -0400 | From | taoyue <> | Subject | Re: [PATCH] sigqueue_free: fix the race with collect_signal() |
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Oleg Nesterov wrote: > On 08/24, taoyue wrote: > >> Oleg Nesterov wrote: >> >>> --- t/kernel/signal.c~SQFREE 2007-08-22 20:06:31.000000000 +0400 >>> +++ 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); >>> } >>> >>> >>> >>> >> Applying previous patch???it seems likely that the __sigqueue_free() is >> also called twice. >> >> 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. > > I know, using current->sighand->siglock to prevent one sigqueue is free twice. I want to know whether it is possible that the two function is called in different thread. If that, the spin_lock is useless.
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