linux-kernel - Re: Strange stop-signal behavior in multithreaded program with defunct main

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Date:	Thu, 30 Oct 2008 19:10:51 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Michael Kerrisk <mtk.manpages@...glemail.com>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Bert Wesarg <bert.wesarg@...glemail.com>,
	Ingo Molnar <mingo@...e.hu>,
	Roland McGrath <roland@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: Strange stop-signal behavior in multithreaded program with
	defunct main

On 10/30, Michael Kerrisk wrote:
>
> On Thu, Oct 30, 2008 at 6:00 AM, Oleg Nesterov <oleg@...hat.com> wrote:
> > On 10/28, Michael Kerrisk wrote:
> >>
> >> Bert Wesarg described a scenario that I quickly replicated on
> >> 2.6.28-rc2 (and 2.6.25 -- it's not a regression in 2.6.28-rc)
> >> using the program below: if we have a multithreaded process
> >> with a defunct main thread running on a tty, and that
> >> process is sent a stop signal (either ^Z (SIGTSTP) or a stop
> >> signal sent from another terminal using kill(1)), then:
> >>
> >> a) the terminal is locked up; and
> >>
> >> b) the program is unresponsive to any other signal, except SIGKILL
> >> or SIGCONT.
> >
> > Yes, known problem. Please look at
> >
> >        [RFC,PATCH 3/3] do_wait: fix waiting for stopped group with dead leader
> >        http://marc.info/?t=119713920000003
> 
> Okay -- thanks for the info.  I've added some text to man-pages to
> cover this bug.

Well, we should fix this bug, of course.

I'll try to redo my old patch, but fyi I am very busy right now, and
most probably I will be completely offline during the next week.

Oleg.

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