linux-kernel - Re: [BUG] signal: multithread program returns with wrong errno on receiving SIGSTOP

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Date:	Mon, 28 May 2007 14:13:40 +0400
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Satoru Takeuchi <takeuchi_satoru@...fujitsu.com>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Ingo Molnar <mingo@...e.hu>,
	Roland McGrath <roland@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [BUG] signal: multithread program returns with wrong errno on receiving SIGSTOP

On 05/28, Satoru Takeuchi wrote:
> 
> At Mon, 28 May 2007 11:07:53 +0400,
> Oleg Nesterov wrote:
> > 
> > 	drivers/char/n_tty.c:job_control()
> > 
> > 		kill_pgrp(task_pgrp(current), SIGTTIN, 1);
> > 		return -ERESTARTSYS;
> > 
> > This is wrong. kill_pgrp()->__group_send_sig_info() sends SIGTTIN
> > to the thread group, but can choose any sub-thread as a target for
> > signal_wake_up().
> > 
> > This means we return ERESTARTSYS, but signal_pending() != true, bug.
> > 
> > Satoru, could you re-test with the untested patch below?
> 
> I tested this patch on my ia64 box and it works fine.

Thanks! A quick grep shows that tty_check_change() may have the same problem.

> # Since I don't know anything about tty driver, I can't determine its
> # adequacy immediately, sorry.

/dev/tty is a black magic to me too. I'll send the patch later unless
maintainers have any objections.

> > --- t/drivers/char/n_tty.c~	2007-04-05 12:18:26.000000000 +0400
> > +++ t/drivers/char/n_tty.c	2007-05-28 10:57:58.000000000 +0400
> > @@ -1191,6 +1191,7 @@ static int job_control(struct tty_struct
> >  			    is_current_pgrp_orphaned())
> >  				return -EIO;
> >  			kill_pgrp(task_pgrp(current), SIGTTIN, 1);
> > +			set_thread_flag(TIF_SIGPENDING);
> >  			return -ERESTARTSYS;
> >  		}
> >  	}
> >

Oleg.

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