linux-kernel - [ 094/123] xfs: fix stray dquot unlock when reclaiming dquots

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Message-Id: <20130109201510.663378387@linuxfoundation.org>
Date:	Wed,  9 Jan 2013 12:35:33 -0800
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	alan@...rguk.ukuu.org.uk, Dave Chinner <dchinner@...hat.com>,
	Christoph Hellwig <hch@....de>, Ben Myers <bpm@....com>
Subject: [ 094/123] xfs: fix stray dquot unlock when reclaiming dquots

3.7-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Dave Chinner <dchinner@...hat.com>

commit b870553cdecb26d5291af09602352b763e323df2 upstream.

When we fail to get a dquot lock during reclaim, we jump to an error
handler that unlocks the dquot. This is wrong as we didn't lock the
dquot, and unlocking it means who-ever is holding the lock has had
it silently taken away, and hence it results in a lock imbalance.

Found by inspection while modifying the code for the numa-lru
patchset. This fixes a random hang I've been seeing on xfstest 232
for the past several months.

Signed-off-by: Dave Chinner <dchinner@...hat.com>
Reviewed-by: Christoph Hellwig <hch@....de>
Signed-off-by: Ben Myers <bpm@....com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 fs/xfs/xfs_qm.c |   15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

--- a/fs/xfs/xfs_qm.c
+++ b/fs/xfs/xfs_qm.c
@@ -1453,7 +1453,7 @@ xfs_qm_dqreclaim_one(
 	int			error;
 
 	if (!xfs_dqlock_nowait(dqp))
-		goto out_busy;
+		goto out_move_tail;
 
 	/*
 	 * This dquot has acquired a reference in the meantime remove it from
@@ -1476,7 +1476,7 @@ xfs_qm_dqreclaim_one(
 	 * getting flushed to disk, we don't want to reclaim it.
 	 */
 	if (!xfs_dqflock_nowait(dqp))
-		goto out_busy;
+		goto out_unlock_move_tail;
 
 	if (XFS_DQ_IS_DIRTY(dqp)) {
 		struct xfs_buf	*bp = NULL;
@@ -1487,7 +1487,7 @@ xfs_qm_dqreclaim_one(
 		if (error) {
 			xfs_warn(mp, "%s: dquot %p flush failed",
 				 __func__, dqp);
-			goto out_busy;
+			goto out_unlock_move_tail;
 		}
 
 		xfs_buf_delwri_queue(bp, buffer_list);
@@ -1496,7 +1496,7 @@ xfs_qm_dqreclaim_one(
 		 * Give the dquot another try on the freelist, as the
 		 * flushing will take some time.
 		 */
-		goto out_busy;
+		goto out_unlock_move_tail;
 	}
 	xfs_dqfunlock(dqp);
 
@@ -1515,14 +1515,13 @@ xfs_qm_dqreclaim_one(
 	XFS_STATS_INC(xs_qm_dqreclaims);
 	return;
 
-out_busy:
-	xfs_dqunlock(dqp);
-
 	/*
 	 * Move the dquot to the tail of the list so that we don't spin on it.
 	 */
+out_unlock_move_tail:
+	xfs_dqunlock(dqp);
+out_move_tail:
 	list_move_tail(&dqp->q_lru, &qi->qi_lru_list);
-
 	trace_xfs_dqreclaim_busy(dqp);
 	XFS_STATS_INC(xs_qm_dqreclaim_misses);
 }


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