Messages in this thread | | | Date | Fri, 24 Aug 2007 13:03:20 -0700 | From | Sukadev Bhattiprolu <> | 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: >> >>>> 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. >> > > Not sure I understand. Yes, it is possible they are called by 2 different > threads, that is why we had a race. But all threads in the same thread > group have the same ->sighand, and thus the same ->sighand->siglock. >
Oleg, if one thread can be in collect_signal() and another in sigqueue_free() and both operate on the exact same sigqueue object, its not clear how we prevent two calls to __sigqueue_free() to the same object. In that case the lock (or some lock) should be around __sigqueue_free() - no ?
i.e if we enter sigqueue_free(), we will call __sigqueue_free() regardless of the state.
> Oleg. > > - > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ > >
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