linux-kernel - Re: Fix signalfd interaction with thread-private signals

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Date:	Tue, 19 Jun 2007 13:14:52 +0400
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Davide Libenzi <davidel@...ilserver.org>,
	Nicholas Miell <nmiell@...cast.net>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Fix signalfd interaction with thread-private signals

On 06/18, Linus Torvalds wrote:
>
> On Mon, 18 Jun 2007, Benjamin Herrenschmidt wrote:
> > On Sun, 2007-06-17 at 17:20 -0700, Davide Libenzi wrote:
> > >
> > > Andrew or Linus, did you get Ben's patch?
> > 
> > It might have been missed... I can resend later today.
> 
> I did indeed just miss it. I intended to apply it (and actually thought I 
> had), but I see it's still just an email in that long thread. 
> 
> (It's often a good idea to re-write the subject line and make it be that 
> standard "[PATCH] ..description..", because that just makes it show up 
> much better when I go through my unread emails.. Not that that is any 
> kind of *guarantee* that I won't miss it).
> 
> Anyway, no need to re-send, it's now *really* in my queue of things to 
> apply.

>From another message on this thread,

	Davide Libenzi wrote:
	>
	> On Sun, 17 Jun 2007, Nicholas Miell wrote:
	>
	> > But there's still no way for multiple threads to read from a single
	> > signalfd and get their own thread-specific signals in addition to
	> > process-wide signals, right? I think this was agreed to be the least
	> > surprising behavior.
	>
	> Multiple threads can wait on the signalfd. Each one will dequeue either
	> its own private signals (tsk->pending) or the process shared ones
	> (tsk->signal->shared_pending). This will be the behaviour once Ben's patch
	> is applied.

The commited "Fix signalfd interaction with thread-private signals"
(commit caec4e8dc85e0644ec24aeb36285e1ba02da58cc) doesn't implement
this.

We can do something like

	int signalfd_dequeue_signal(struct task_struct *tsk, sigset_t *mask, siginfo_t *info)
	{
		if (tsk->tgid == current->tgid)
			tsk = current;

		return dequeue_signal(tsk, mask, info);
	}

(still I can't understand why should we change signalfd).

Oleg.

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