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From: Oleg Nesterov <oleg@tv-sign.ru>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Pavel Emelyanov <xemul@openvz.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Roland McGrath <roland@redhat.com>
Subject: Re: [PATCH 3/3] Consolidate send_sigqueue and send_group_sigqueue
Date: Thu, 28 Feb 2008 09:17:23 +0300	[thread overview]
Message-ID: <20080228061723.GB108@tv-sign.ru> (raw)
In-Reply-To: <alpine.LFD.1.00.0802280546360.7583@apollo.tec.linutronix.de>

On 02/28, Thomas Gleixner wrote:
>
> On Fri, 22 Feb 2008, Oleg Nesterov wrote:
> > > -
> > > -	if (unlikely(!list_empty(&q->list))) {
> > > -		/*
> > > -		 * If an SI_TIMER entry is already queue just increment
> > > -		 * the overrun count.
> > > -		 */
> > > -		BUG_ON(q->info.si_code != SI_TIMER);
> > > -		q->info.si_overrun++;
> > > -		goto out;
> > > -	}
> > > -	/* Short-circuit ignored signals.  */
> > > -	if (sig_ignored(p, sig)) {
> > > -		ret = 1;
> > > -		goto out;
> > > -	}
> 
> > >  send_group_sigqueue(int sig, struct sigqueue *q, struct task_struct *p)
> 
> > > -	/* Short-circuit ignored signals.  */
> > > -	if (sig_ignored(p, sig)) {
> > > -		ret = 1;
> > > -		goto out;
> > > -	}
> > > -
> > > -	if (unlikely(!list_empty(&q->list))) {
> > > -		/*
> > > -		 * If an SI_TIMER entry is already queue just increment
> > > -		 * the overrun count.  Other uses should not try to
> > > -		 * send the signal multiple times.
> > > -		 */
> > > -		BUG_ON(q->info.si_code != SI_TIMER);
> > > -		q->info.si_overrun++;
> > > -		goto out;
> > > -	} 
> > 
> > Personally, I think this change is very good. But send_sigqueue() and
> > send_group_sigqueue() have a very subtle difference which I was never
> > able to understand.
> > 
> > Let's suppose that sigqueue is already queued, and the signal is ignored
> > (the latter means we should re-schedule cpu timer or handle overrruns).
> > In that case send_sigqueue() returns 0, but send_group_sigqueue() returns 1.
> > 
> > I think this is not the problem (in fact, I think this patch makes the
> > behaviour more correct), but I hope Thomas can take a look and confirm.
> 
> It should not change anything. We should never have a signal enqueued
> when it's ignored anyway.

Well, it _is_ possible. Suppose that the signal is both ignored and blocked.
Now, if the task unblocks the signal, it could be ignored, queued, and
sig_ignored() == T.

But yes, I think you are right, this can't change anything. I just wanted
to be sure there is no subtle reason to prefer one way or another.

> Roland, any insight why this is different aside of a copy and paste
> error ?

I guess this was the reason for the difference.

Oleg.


  reply	other threads:[~2008-02-28  6:18 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-02-22 12:56 Pavel Emelyanov
2008-02-22 14:41 ` Oleg Nesterov
2008-02-28  4:54   ` Thomas Gleixner
2008-02-28  6:17     ` Oleg Nesterov [this message]
     [not found]       ` <20080228113633.7431C2700FD@magilla.localdomain>
2008-02-28 15:36         ` Oleg Nesterov
2008-02-28 20:14           ` Roland McGrath
2008-02-29 11:32             ` Oleg Nesterov
2008-02-28 22:32         ` Thomas Gleixner
2008-02-28 22:41           ` Roland McGrath
2008-02-29  8:04             ` Thomas Gleixner

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