linux-kernel - Re: [PATCH 04/11] ptrace: implement PTRACE

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Date:	Wed, 11 May 2011 15:22:18 +0200
From:	Tejun Heo <tj@...nel.org>
To:	Denys Vlasenko <vda.linux@...glemail.com>
Cc:	Oleg Nesterov <oleg@...hat.com>, jan.kratochvil@...hat.com,
	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, indan@....nu
Subject: Re: [PATCH 04/11] ptrace: implement PTRACE_INTERRUPT

Hey,

On Wed, May 11, 2011 at 02:23:44PM +0200, Denys Vlasenko wrote:
> I understand this. I am trying to understand what feature are you trying
> to provide to userland, or what problematic race scenario you are trying
> to make resolve-able *in userland* by making "stop" and "cont"
> notifications sticky wrt GETSIGINFO. I just don't see this scenario.

If you still don't see how events can get lost, I'm afraid I can't
explain any better.  You're repeating that exit_code can record the
event until it's fetched but it doesn't queue and any trap will
overwrite it and debuggers don't have to call GETSIGINFO after each
trap - it only has to do so for signal delivery, group stop and
INTERRUPT trap.  So, it can just look at the exit_code (which doesn't
indicate continuation) and let tracee return to userland.

Maybe I'm horribly confused.  Oleg, am I?

Thanks.

-- 
tejun
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