linux-kernel - [21/70] xfs: fix dquot shaker deadlock

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Date:	Tue, 22 Feb 2011 14:17:00 -0800
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Dave Chinner <dchinner@...hat.com>,
	Arkadiusz Miskiewicz <a.miskiewicz@...il.com>
Subject: [21/70] xfs: fix dquot shaker deadlock

2.6.37-stable review patch.  If anyone has any objections, please let us know.

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

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

commit 0fbca4d1c3932c27c4794bf5c2b5fc961cf5a54f upstream.

Commit 368e136 ("xfs: remove duplicate code from dquot reclaim") fails
to unlock the dquot freelist when the number of loop restarts is
exceeded in xfs_qm_dqreclaim_one(). This causes hangs in memory
reclaim.

Rework the loop control logic into an unwind stack that all the
different cases jump into. This means there is only one set of code
that processes the loop exit criteria, and simplifies the unlocking
of all the items from different points in the loop. It also fixes a
double increment of the restart counter from the qi_dqlist_lock
case.

Reported-by: Malcolm Scott <lkml@...c.org.uk>
Signed-off-by: Dave Chinner <dchinner@...hat.com>
Reviewed-by: Alex Elder <aelder@....com>
Cc: Arkadiusz Miskiewicz <a.miskiewicz@...il.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 fs/xfs/quota/xfs_qm.c |   46 +++++++++++++++++++++-------------------------
 1 file changed, 21 insertions(+), 25 deletions(-)

--- a/fs/xfs/quota/xfs_qm.c
+++ b/fs/xfs/quota/xfs_qm.c
@@ -1863,12 +1863,14 @@ xfs_qm_dqreclaim_one(void)
 	xfs_dquot_t	*dqpout;
 	xfs_dquot_t	*dqp;
 	int		restarts;
+	int		startagain;
 
 	restarts = 0;
 	dqpout = NULL;
 
 	/* lockorder: hashchainlock, freelistlock, mplistlock, dqlock, dqflock */
-startagain:
+again:
+	startagain = 0;
 	mutex_lock(&xfs_Gqm->qm_dqfrlist_lock);
 
 	list_for_each_entry(dqp, &xfs_Gqm->qm_dqfrlist, q_freelist) {
@@ -1885,13 +1887,10 @@ startagain:
 			ASSERT(! (dqp->dq_flags & XFS_DQ_INACTIVE));
 
 			trace_xfs_dqreclaim_want(dqp);
-
-			xfs_dqunlock(dqp);
-			mutex_unlock(&xfs_Gqm->qm_dqfrlist_lock);
-			if (++restarts >= XFS_QM_RECLAIM_MAX_RESTARTS)
-				return NULL;
 			XQM_STATS_INC(xqmstats.xs_qm_dqwants);
-			goto startagain;
+			restarts++;
+			startagain = 1;
+			goto dqunlock;
 		}
 
 		/*
@@ -1906,23 +1905,20 @@ startagain:
 			ASSERT(list_empty(&dqp->q_mplist));
 			list_del_init(&dqp->q_freelist);
 			xfs_Gqm->qm_dqfrlist_cnt--;
-			xfs_dqunlock(dqp);
 			dqpout = dqp;
 			XQM_STATS_INC(xqmstats.xs_qm_dqinact_reclaims);
-			break;
+			goto dqunlock;
 		}
 
 		ASSERT(dqp->q_hash);
 		ASSERT(!list_empty(&dqp->q_mplist));
 
 		/*
-		 * Try to grab the flush lock. If this dquot is in the process of
-		 * getting flushed to disk, we don't want to reclaim it.
+		 * Try to grab the flush lock. If this dquot is in the process
+		 * of getting flushed to disk, we don't want to reclaim it.
 		 */
-		if (!xfs_dqflock_nowait(dqp)) {
-			xfs_dqunlock(dqp);
-			continue;
-		}
+		if (!xfs_dqflock_nowait(dqp))
+			goto dqunlock;
 
 		/*
 		 * We have the flush lock so we know that this is not in the
@@ -1944,8 +1940,7 @@ startagain:
 				xfs_fs_cmn_err(CE_WARN, mp,
 			"xfs_qm_dqreclaim: dquot %p flush failed", dqp);
 			}
-			xfs_dqunlock(dqp); /* dqflush unlocks dqflock */
-			continue;
+			goto dqunlock;
 		}
 
 		/*
@@ -1967,13 +1962,8 @@ startagain:
 		 */
 		if (!mutex_trylock(&mp->m_quotainfo->qi_dqlist_lock)) {
 			restarts++;
-			mutex_unlock(&dqp->q_hash->qh_lock);
-			xfs_dqfunlock(dqp);
-			xfs_dqunlock(dqp);
-			mutex_unlock(&xfs_Gqm->qm_dqfrlist_lock);
-			if (restarts++ >= XFS_QM_RECLAIM_MAX_RESTARTS)
-				return NULL;
-			goto startagain;
+			startagain = 1;
+			goto qhunlock;
 		}
 
 		ASSERT(dqp->q_nrefs == 0);
@@ -1986,14 +1976,20 @@ startagain:
 		xfs_Gqm->qm_dqfrlist_cnt--;
 		dqpout = dqp;
 		mutex_unlock(&mp->m_quotainfo->qi_dqlist_lock);
+qhunlock:
 		mutex_unlock(&dqp->q_hash->qh_lock);
 dqfunlock:
 		xfs_dqfunlock(dqp);
+dqunlock:
 		xfs_dqunlock(dqp);
 		if (dqpout)
 			break;
 		if (restarts >= XFS_QM_RECLAIM_MAX_RESTARTS)
-			return NULL;
+			break;
+		if (startagain) {
+			mutex_unlock(&xfs_Gqm->qm_dqfrlist_lock);
+			goto again;
+		}
 	}
 	mutex_unlock(&xfs_Gqm->qm_dqfrlist_lock);
 	return dqpout;


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