linux-kernel - Re: [PATCH 1/1] ptrace: fix ptrace_signal() && STOP

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Message-ID: <20110713100404.GG2872@htj.dyndns.org>
Date:	Wed, 13 Jul 2011 12:04:04 +0200
From:	Tejun Heo <tj@...nel.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	vda.linux@...glemail.com, jan.kratochvil@...hat.com,
	pedro@...esourcery.com, indan@....nu, bdonlan@...il.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] ptrace: fix ptrace_signal() && STOP_DEQUEUED
 interaction

Hello, Oleg.  Sorry about the long delay.  Was lost somewhere else. :)

On Thu, Jul 07, 2011 at 09:03:24PM +0200, Oleg Nesterov wrote:
> Without the patch it hangs. After the patch SIGSTOP "injected" by the
> tracer is not ignored and stops the tracee.

I always felt the ability to 'inject' different signal there is rather
useless and prone to induce weird issues.  It would be better if
ptrace_signal() is part of signal delivery action after all the checks
so that the ptracer says whether to proceed with the action or not but
no more.  Well...

> So lets add STOP_DEQUEUED _before_ we report the signal. It has no effect
> unless sig_kernel_stop() == T after the tracer resumes us, and in the
> latter case the pending STOP_DEQUEUED means no SIGCONT in between, we
> should stop.

Anyways, yes, this seems to be a nice improvement but it looks very
weird (and difficult to comprehend) to be setting STOP_DEQUEUED
unconditionally in ptrace_signal().  Wouldn't it be better to flip the
flag so that we have CONT_RECEIVED before doing this?

Thanks.

-- 
tejun
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