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Date: Wed, 22 Dec 2010 11:54:36 +0100
From: Tejun Heo <tj@kernel.org>
To: Oleg Nesterov <oleg@redhat.com>
Cc: roland@redhat.com, linux-kernel@vger.kernel.org,
        torvalds@linux-foundation.org, akpm@linux-foundation.org, rjw@sisk.pl,
        jan.kratochvil@redhat.com
Subject: Re: [PATCH 10/16] ptrace: clean transitions between TASK_STOPPED
 and TRACED
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References: <1291654624-6230-1-git-send-email-tj@kernel.org>
 <1291654624-6230-11-git-send-email-tj@kernel.org>
 <20101220150037.GE11583@redhat.com>
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Hello,

On Tue, Dec 21, 2010 at 06:31:55PM +0100, Tejun Heo wrote:
> > This looks racy. Suppose that "current" is ptraced, in this case
> > it can initiate the new group-stop even if SIGNAL_STOP_STOPPED
> > is set and we have another TASK_STOPPED thead T.
> > 
> > Suppose that another (or same) debugger ataches to this thread T,
> > wakes it up and sets GROUP_STOP_TRAPPING.
> > 
> > T resumes, calls ptrace_stop() in TASK_STOPPED, and temporary drops
> > ->siglock.
> > 
> > Now, this task_clear_group_stop(T) confuses ptrace_check_attach(T).
> > 
> > I think ptrace_stop() should be called in TASK_RUNNING state.
> > This also makes sense because we may call arch_ptrace_stop().
> 
> I'm feeling a bit too dense to process the above right now.  I'll
> respond to the above next morning after a strong cup of coffee. :-)

Ah, right, the lock drop across arch_ptrace_stop().  Yeah, I agree
calling ptrace_stop() with TASK_RUNNING would solve it.  I'll think
about it a bit more.

Thank you.

-- 
tejun
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