linux-kernel - Re: [PATCH] sigwait eats blocked default-ignore signals

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Date:	Wed, 14 Nov 2007 18:53:00 +0300
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Roland McGrath <roland@...hat.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sigwait eats blocked default-ignore signals

On 11/13, Roland McGrath wrote:
>
> > But I suspect we have other issues here. Let's suppose we have threads T1
> > (main) and T2. T2 blocks SIGCHLD and does sigwait(SIGCHLD).
> > 
> > Now, we send SIGCHLD to the thread group. The signal is lost again because
> > sig_ignored() returns true on T1's side.
> > 
> > Is this OK? [...]
> 
> Yes, it's OK if T1 has SIGCHLD unblocked.  When there are multiple threads
> that either don't block the signal or are in sigwait for it, then it can go
> to any of them and there are no guarantees at all about which.  So we
> simply say that the signal went to the thread not in sigwait that has that
> signal unblocked (T1).  When it got there, it was ignored.  The user
> semantics are equivalent even if that thread never actually woke and
> dequeued the signal to ignore it.

Yes.

I misunderstood the required semantics for sigwait(), thanks Roland.

Oleg.

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