linux-kernel - Re: [PATCH 1/1] ptrace: make sure do_wait() won't hang after PTRACE

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Date:	Mon, 14 Feb 2011 17:33:46 +0100
From:	Tejun Heo <tj@...nel.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Denys Vlasenko <vda.linux@...glemail.com>,
	Roland McGrath <roland@...hat.com>, jan.kratochvil@...hat.com,
	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org
Subject: Re: [PATCH 1/1] ptrace: make sure do_wait() won't hang after
 PTRACE_ATTACH

Hello,

On Mon, Feb 14, 2011 at 05:15:15PM +0100, Oleg Nesterov wrote:
> > > PTRACE_CONT in this situation would do the same.
> >
> > This can be fixed by updating strace, right?  strace can look at the
> > wait(2) exit code and if the tracee stopped for group stop, wait for
> > the tracee to be continued instead of issuing PTRACE_SYSCALL.
> 
> Yes, in this particular case strace could be more clever.
> 
> But. The tracee should react to SIGCONT after that, this means we
> shouldn't "delay" this stop or force the TASK_TRACED state.

Yeap, which is achievable by treating group stop differently from
ptrace traps and make it proceed to TASK_TRACED only if ptrace wants
to issue commands.  (reiterating just to make sure there's no
misunderstanding)

> And note that in this case real_parent == debugger. Another case
> is more interesting, and this means we shouldn't delay or hide the
> notifications.
> 
> (I just tried to summarize the previous discussion for Denys)

Agreed.  We should be notifying both the real parent and ptracer.

Thanks.

-- 
tejun
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