linux-kernel - Re: [2.6.33-rc5] starting emacs makes lockdep warning

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Message-ID: <2375c9f91001252224g6712cbady339dbe486a5112ac@mail.gmail.com>
Date:	Tue, 26 Jan 2010 14:24:30 +0800
From:	Américo Wang <xiyou.wangcong@...il.com>
To:	Al Viro <viro@...iv.linux.org.uk>
Cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Tavis Ormandy <taviso@...gle.com>,
	Jeff Dike <jdike@...toit.com>, Julien Tinnes <jln@...gle.com>,
	Matt Mackall <mpm@...enic.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: [2.6.33-rc5] starting emacs makes lockdep warning

On Tue, Jan 26, 2010 at 2:07 PM, Al Viro <viro@...iv.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?
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