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[PATCH 3/4] xfs: fix stray dquot unlock when reclaiming dquots

To: xfs@xxxxxxxxxxx
Subject: [PATCH 3/4] xfs: fix stray dquot unlock when reclaiming dquots
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Wed, 28 Nov 2012 13:01:02 +1100
In-reply-to: <1354068063-1692-1-git-send-email-david@xxxxxxxxxxxxx>
References: <1354068063-1692-1-git-send-email-david@xxxxxxxxxxxxx>
From: Dave Chinner <dchinner@xxxxxxxxxx>

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.

cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
---
 fs/xfs/xfs_qm.c |   15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

diff --git a/fs/xfs/xfs_qm.c b/fs/xfs/xfs_qm.c
index e6a0af0..60eff47 100644
--- a/fs/xfs/xfs_qm.c
+++ b/fs/xfs/xfs_qm.c
@@ -1456,7 +1456,7 @@ 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
@@ -1479,7 +1479,7 @@ 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;
@@ -1490,7 +1490,7 @@ 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);
@@ -1499,7 +1499,7 @@ 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);
 
@@ -1518,14 +1518,13 @@ 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);
 }
-- 
1.7.10

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