linux-kernel - Re: Linux 3.11-rc4

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Message-ID: <CA+55aFy61PbNZda8f+42T9e7TioWd+W1s70UA6h+xnARjX3usA@mail.gmail.com>
Date:	Mon, 5 Aug 2013 10:39:15 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Felipe Contreras <felipe.contreras@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Linux 3.11-rc4

On Mon, Aug 5, 2013 at 6:29 AM, Oleg Nesterov <oleg@...hat.com> wrote:
>
> I never used wine, but I am puzzled anyway. This patch really looks
> like a simple and minor bugfix.

The patch is indeed trivial, but.. What's the locking here?

Afaik, ptrace_detach() by the parent can race with do_exit() by the
child, and they now _both_ do flush_ptrace_hw_breakpoint(). Or am I
wrong? We have that whole "get tasklist_lock for writing and then
check child->ptrace" logic there exactly due to that race, no?

That said, Felipe, can you double-check that it's not timing-related
in some subtle way, and test multiple times with just that commit
reverted (and not reverted) to make sure that it's 100% that one
single line by that particular commit? Because it does seem very
benign..

               Linus
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