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

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Message-ID: <20081030110000.GA3767@redhat.com>
Date:	Thu, 30 Oct 2008 12:00:00 +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 10/28, 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

Oleg.

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