linux-kernel - Re: [PATCH] fix handling of SIGCHILD from reaped child

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Message-Id: <20070221002526.c6b7edb0.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Wed, 21 Feb 2007 00:25:26 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Oleg Nesterov <oleg@...sign.ru>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu,
	akpm@...ux-foundation.org, roland@...hat.com
Subject: Re: [PATCH] fix handling of SIGCHILD from reaped child

On Tue, 20 Feb 2007 17:22:57 +0300
Oleg Nesterov <oleg@...sign.ru> wrote:

>
> I'd suggest to make a separate function, but not complicate collect_signal().
>
okay. I'll try again if people admit me to go ahead. 

> > --- linux-2.6.20-devel.orig/kernel/exit.c
> > +++ linux-2.6.20-devel/kernel/exit.c
> > @@ -1252,8 +1252,12 @@ static int wait_task_zombie(struct task_
> >  		}
> >  		write_unlock_irq(&tasklist_lock);
> >  	}
> > -	if (p != NULL)
> > +	if (p != NULL) {
> >  		release_task(p);
> > +		/* if we received sigchild from "p" and p is released,
> > +		   we remove sigchild from it. */
> 
> current may be ptracer, not a parent. Should be ok, clear_stale_sigchild(pid)
> can't have a false positive (until we have namespace for pid_t), but the comment
> is misleading a bit.
> 
I'll rewrite and make this clearer.

> > +		clear_stale_sigchild(current, retval);
> 
> But we are not checking that SIGCHLD is blocked?
> 
I'm sorry if I don't read SUSv3 correctly. SUSv3 doesn't define how we should
do if SIGCHLD is not blocked.(so I don't check not-blocked case.)

IMHO, user's sig-child-handler is tend to call wait()/waitpid() and expects
successful return. So removing stale signal here may be good.

If this breaks assumptions of applications on Linux, I'll not go eagerly.

Thanks,
-Kame





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