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Date: Thu, 09 May 2013 10:57:21 -0500
From: Mark Tinguely <tinguely@sgi.com>
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Subject: Re: Rambling noise #1: generic/230 can trigger kernel debug lock
	detector
References: <518B08D9.1060906@gmail.com> <20130509031646.GN24635@dastard>
In-Reply-To: <20130509031646.GN24635@dastard>
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To: Dave Chinner <david@fromorbit.com>
Cc: "Michael L. Semon" <mlsemon35@gmail.com>, "xfs@oss.sgi.com" <xfs@oss.sgi.com>

On 05/08/13 22:16, Dave Chinner wrote:
> xfs: avoid nesting transactions in xfs_qm_scall_setqlim()
>
> From: Dave Chinner<dchinner@redhat.com>
>
> Lockdep reports:
>
> =============================================
> [ INFO: possible recursive locking detected ]
> 3.9.0+ #3 Not tainted
> ---------------------------------------------
> setquota/28368 is trying to acquire lock:
>   (sb_internal){++++.?}, at: [<c11e8846>] xfs_trans_alloc+0x26/0x50
>
> but task is already holding lock:
>   (sb_internal){++++.?}, at: [<c11e8846>] xfs_trans_alloc+0x26/0x50
>
> from xfs_qm_scall_setqlim()->xfs_dqread() when a dquot needs to be
> allocated.
>
> xfs_qm_scall_setqlim() is starting a transaction and then not
> passing it into xfs_qm_dqet() and so it starts it's own transaction
> when allocating the dquot.  Splat!
>
> Fix this by not allocating the dquot in xfs_qm_scall_setqlim()
> inside the setqlim transaction. This requires getting the dquot
> first (and allocating it if necessary) then dropping and relocking
> the dquot before joining it to the setqlim transaction.
>
> Reported-by: Michael L. Semon<mlsemon35@gmail.com>
> Signed-off-by: Dave Chinner<dchinner@redhat.com>
> ---
>   fs/xfs/xfs_qm_syscalls.c |   35 ++++++++++++++++++++---------------
>   1 file changed, 20 insertions(+), 15 deletions(-)

Looks good.

Reviewed-by: Mark Tinguely <tinguely@sgi.com>

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