linux-kernel - Re: [PATCH 10/11] ptrace: move JOBCTL_TRAPPING wait to wait(2) and ptrace_check

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Message-ID: <20110511194551.GD24245@mtj.dyndns.org>
Date:	Wed, 11 May 2011 21:45:51 +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 10/11] ptrace: move JOBCTL_TRAPPING wait to wait(2) and
 ptrace_check_attach()

Hello,

On Wed, May 11, 2011 at 07:00:58PM +0200, Oleg Nesterov wrote:
> On 05/11, Oleg Nesterov wrote:
> >
> > You know, I'd wish I could find the serious bugs in this patch. The
> > code becomes really hairy. -EAGAIN in do_wait() doesn't make it more
> > simple ;)
> 
> Mwahaha! I seem to see the bug ;)

:-)

> When the caller is do_wait(), we can't assume we are the tracer when
> we drop tasklist. Original tracer can detach, then another unrelated
> process can attach again and provoke JOBCTL_TRAPPING. wait_event()
> can hang forever.
> 
> Unfortunately, this is easy to fix :/

Yeah, it's basically the same problem raised in other two patches.
Making wait interruptible and clearing pending stop/traps on
detach/kill/cont/whatever should do the trick.  I'll reply the
previous message for the suggested change.

Thanks.

-- 
tejun
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