Messages in this thread | | | Date | Wed, 21 May 2008 15:54:14 +0400 | From | Oleg Nesterov <> | Subject | Re: [PATCH 1/3] signals: sigqueue_free: don't free sigqueue if it is queued |
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On 05/20, Roland McGrath wrote: > > > This patch doesn't change the behaviour of sys_timer_delete() and friends, > > just makes it more correct and allows us to introduce other SIGQUEUE_ flags > > passed to the receiver. > > To clarify, this certainly does change the behavior. > There are two changes. > > Firstly, a pending timer-firing signal currently gets its siginfo_t > zeroed out synchronously by timer_delete and now will have its info > preserved. That change alone is a potential problem for userland, so > it should not go in without the following changes to prevent userland > from seeing the signal at all. (Currently userland may see a spurious > signal, but its si_code and si_value don't indicate a timer firing. > With the correct info, userland might try to use a pointer from > si_value that was freed around the time it called timer_delete.)
Yes, yes, I meant doesn't change the behaviour in a sense that the signal is still "visible" to the application.
> Second, a pending timer-firing signal currently stops counting towards > the RLIMIT_SIGPENDING limit immediately upon a timer_delete call and > now will keep counting toward that limit until it gets dequeued and > discarded. This change is not necessarily a problem. (POSIX does not > specify how we decide when resources are too short to create a new > timer or queue a signal.) But it deserves mention somewhere. > Applications can just get fixed to always unblock the signal number or > flush old signals out with sigwait, if they are averse to timer > signals with intact siginfo_t arriving after timer_delete.
Yes, thanks, I didn't think about this.
> For this reason, I don't think this set of changes should be > considered for any -stable branch.
Yes sure.
> > q->flags |= SIGQUEUE_CANCELLED; > > spin_lock_irqsave(lock, flags); > > q->flags &= ~SIGQUEUE_PREALLOC; > > Just make it: > > spin_lock_irqsave(lock, flags); > q->flags |= SIGQUEUE_CANCELLED; > q->flags &= ~SIGQUEUE_PREALLOC; > > and we needn't wax philosophical about the meaning of locking rules. That > patch would have my ACK, but I concur with Linus about the undesireability > of the plain = version.
OK, will do tomorrow, but...
Oh well. I just realized SIGQUEUE_CANCELLED breaks sys_sigpending() ?
Oleg.
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