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

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Message-ID: <20110214200130.GA21559@redhat.com>
Date:	Mon, 14 Feb 2011 21:01:30 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Denys Vlasenko <vda.linux@...glemail.com>
Cc:	Tejun Heo <tj@...nel.org>, 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

On 02/14, Denys Vlasenko wrote:
>
> Basically, we have TASK_RUNNING, TASK_STOPPED and TASK_TRACED
> states, and after entering TASK_TRACED state we lose information
> in which state we were before entering it. We need to remember
> old state and restore it in order for this example to work.

Actually, we do not lose this info. So the kernel can change it
back to TASK_STOPPED after ptrace(PTRACE_CONT), and this is what
PTRACE_CONT-doesnt-resume-until-SIGCONT was supposed to do.

> Or we can avoid entering TASK_TRACED on ptrace(PTRACE_GETSIGINFO) et al.
> Can we remain in TASK_STOPPED?

Oh, unlikely, I think.

Oleg.

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