linux-kernel - Re: [PATCH 1/4] signal: fix SIGCONT notification code

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Date:	Thu, 13 Jan 2011 12:27:47 +0100
From:	Tejun Heo <tj@...nel.org>
To:	Jan Kratochvil <jan.kratochvil@...hat.com>
Cc:	oleg@...hat.com, roland@...hat.com, linux-kernel@...r.kernel.org,
	rjw@...k.pl
Subject: Re: [PATCH 1/4] signal: fix SIGCONT notification code

Hello, Jan.

On Wed, Jan 12, 2011 at 09:41:36PM +0100, Jan Kratochvil wrote:
> On Wed, 22 Dec 2010 12:13:15 +0100, Tejun Heo wrote:
> > If SIGCONT is received while the child process is stopped, the code should
> > be CLD_CONTINUED.  If SIGCONT is recieved while the child process is in the
> > process of being stopped, it should be CLD_STOPPED.
> 
> If a process does
> 	kill (PID, SIGSTOP);
> 	<varying delay, possibly even from a different process>
> 	kill (PID, SIGCONT);
> 
> does it mean the PID's parent may get different waitid() results?
> Or even that PID will finally remain still `T (stopped)'?

Yeah, the @why part could be different with the fix.  Before the fix
the result was indeterministic.

> I do not see it has any userland impact, the
> PTRACE_ATTACH-to-T(stopped)-process is already racy for different reasons.

I agree that it wouldn't have any userland impact especially given
that the previous behavior was rather indeterministic.  It just fixes
an obvious bug which tested the wrong flag.

Thanks.

-- 
tejun
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