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Date: Tue, 26 Jan 2010 14:24:30 +0800
Message-ID: <2375c9f91001252224g6712cbady339dbe486a5112ac@mail.gmail.com>
Subject: Re: [2.6.33-rc5] starting emacs makes lockdep warning
From: =?UTF-8?Q?Am=C3=A9rico_Wang?= <xiyou.wangcong@gmail.com>
To: Al Viro <viro@zeniv.linux.org.uk>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
       "Eric W. Biederman" <ebiederm@xmission.com>,
       Tavis Ormandy <taviso@google.com>, Jeff Dike <jdike@addtoit.com>,
       Julien Tinnes <jln@google.com>, Matt Mackall <mpm@selenic.com>,
       LKML <linux-kernel@vger.kernel.org>, Oleg Nesterov <oleg@redhat.com>,
       Alan Cox <alan@lxorguk.ukuu.org.uk>
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On Tue, Jan 26, 2010 at 2:07 PM, Al Viro <viro@zeniv.linux.org.uk> wrote:
> On Tue, Jan 26, 2010 at 02:01:12PM +0800, Am??rico Wang wrote:
>
>> I agree, it seems that patch is useless, since we already
>> do lock_kernel() before calling __f_setown()...
>
> What's to prevent pid from being freed under us?  BKL won't...
>

Hmm, I don't fully understand the race here. If it is used to protect
'pid' which we get from 'tty->pgrp' or 'current', in the former case,
it is protected by 'tty->ctrl_lock', in the later case, it doesn't need
the lock. So it's not necessary to protect 'pid' by 'tty->crtl_lock'.

Am i missing something?