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xfs: fix stray dquot unlock when reclaiming dquots 

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@vger.kernel.org>
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Ben Myers <bpm@sgi.com>
This commit is contained in:
Dave Chinner 2012-11-28 13:01:02 +11:00 committed by Ben Myers
parent 437a255aa2
commit b870553cde
1 changed files with 7 additions and 8 deletions
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15
fs/xfs/xfs_qm.c
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@ -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);
}