Re: [PATCH 1/3] signals: sigqueue_free: don't free sigqueue if it is queued

From: Oleg Nesterov
Date: Thu May 22 2008 - 08:13:28 EST

On 05/21, Roland McGrath wrote:
> -void flush_sigqueue(struct sigpending *queue)
> +static void __flush_sigqueue(struct sigpending *queue, int timers)
> {
> struct sigqueue *q;
> sigemptyset(&queue->signal);
> while (!list_empty(&queue->list)) {
> q = list_entry(queue->, struct sigqueue , list);
> + if (timers && q->info.si_code != SI_TIMER)
> + continue;
> list_del_init(&q->list);
> __sigqueue_free(q);
> }
> }

This is not enough. Again, we remove and free sigqueue but don't discard
the pending signal. (and we must take into account other rt signals with
the same si_signo if we want to discard the signal).

Oh, this problem is unexpectedly nasty. It is trivial and minor, we can
solve it in may ways, but personally I can't find a simple/clean way.

Let's look at my first attempt,

the patch was "almost" correct.
We can add the "bool cancel" parameter to sigqueue_free(), true when
called from exec (or exit_itimers). In that case SIGQUEUE_SHARED_PENDING
is enough: the pending signal was either sent to current, or it is group
wide. Not nice too of course, but afaics a bit simpler. Actually, the
patch exists:

What do you think?

(instead of SIGQUEUE_SHARED_PENDING, we can encode "struct sigpending *"
in q->flags, but this is really awful and I agree with Linus on the
EINTR/etc issues).

I'll try to think more on Weekend.


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