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

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Date:	Mon, 26 Nov 2012 15:13:21 +0000
From:	Steven Whitehouse <swhiteho@...hat.com>
To:	Ben Hutchings <ben@...adent.org.uk>
Cc:	Benjamin Marzinski <bmarzins@...hat.com>,
	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

Hi,

On Sun, 2012-11-25 at 14:11 +0100, Ben Hutchings wrote:
> 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.
> 

Potentially yes, although I don't think we've had any reports from that
far back,

Steve.


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