linux-kernel - Re: [ 64/66] GFS2: Test bufdata with buffer locked and gfs2_log

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Date:	Sun, 25 Nov 2012 14:11:55 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	Benjamin Marzinski <bmarzins@...hat.com>,
	Steven Whitehouse <swhiteho@...hat.com>
Cc:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	alan@...rguk.ukuu.org.uk,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [ 64/66] GFS2: Test bufdata with buffer locked and
 gfs2_log_lock held

On Wed, 2012-11-14 at 20:11 -0800, Greg Kroah-Hartman wrote:
> 3.6-stable review patch.  If anyone has any objections, please let me know.
> 
> ------------------
> 
> From: Benjamin Marzinski <bmarzins@...hat.com>
> 
> commit 96e5d1d3adf56f1c7eeb07258f6a1a0a7ae9c489 upstream.
> 
> In gfs2_trans_add_bh(), gfs2 was testing if a there was a bd attached to the
> buffer without having the gfs2_log_lock held. It was then assuming it would
> stay attached for the rest of the function. However, without either the log
> lock being held of the buffer locked, __gfs2_ail_flush() could detach bd at any
> time.  This patch moves the locking before the test.  If there isn't a bd
> already attached, gfs2 can safely allocate one and attach it before locking.
> There is no way that the newly allocated bd could be on the ail list,
> and thus no way for __gfs2_ail_flush() to detach it.
> 
> Signed-off-by: Benjamin Marzinski <bmarzins@...hat.com>
> Signed-off-by: Steven Whitehouse <swhiteho@...hat.com>
> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
[...]

Is this needed for any earlier versions?  It looks applicable to 3.2
(with minor changes).

Ben.

-- 
Ben Hutchings
Never attribute to conspiracy what can adequately be explained by stupidity.

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