linux-kernel - Re: [PATCH 09/11] job control: reorganize wait_task

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Date:	Sat, 14 May 2011 12:56:53 +0200
From:	Tejun Heo <tj@...nel.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	jan.kratochvil@...hat.com, vda.linux@...glemail.com,
	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, indan@....nu
Subject: Re: [PATCH 09/11] job control: reorganize wait_task_stopped()

Hello, Oleg.

On Fri, May 13, 2011 at 07:21:17PM +0200, Oleg Nesterov wrote:
> We already checked ->exit_state != ZOMBIE, and we are holding tasklist.
> The child can't exit. I mean, it can't change its ->exit_state.
> 
> However, SIGKILL can clear SIGNAL_STOP_STOPPED, and we can "miss" it.
> But this looks correct, the child is no longer stopped but it is still
> not dead. So I think in this case wait(WNOHANG | WEXITED | WSTOPPED)
> can fail, notabug.

Hmmm... I don't know.

> OTOH, perhaps SIGKILL should set SIGNAL_STOP_CONTINUED in this case?
> And keep it if it was already set.

I'd rather avoid that.  First of all, it's an extreme corner case and
I think introducing an extra state transition there is more likely to
cause trouble than helping anything.  It might be theoretically
correct but there's no reason to introduce that at this point.  If at
all possible, I think it would be better to make it either see STOPPED
or EXIT.

Thanks.

-- 
tejun
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