xfs: flatten the dquot lock ordering
Introduce a new XFS_DQ_FREEING flag that tells lookup and mplist walks
to skip a dquot that is beeing freed, and use this avoid the trylock
on the hash and mplist locks in xfs_qm_dqreclaim_one. Also simplify
xfs_dqpurge by moving the inodes to a dispose list after marking them
XFS_DQ_FREEING and avoid the locker ordering constraints.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Ben Myers <bpm@sgi.com>
diff --git a/fs/xfs/xfs_qm.c b/fs/xfs/xfs_qm.c
index 6a0c4f0..f418731 100644
--- a/fs/xfs/xfs_qm.c
+++ b/fs/xfs/xfs_qm.c
@@ -398,7 +398,8 @@
mutex_lock(&q->qi_dqlist_lock);
list_for_each_entry(dqp, &q->qi_dqlist, q_mplist) {
xfs_dqlock(dqp);
- if (! XFS_DQ_IS_DIRTY(dqp)) {
+ if ((dqp->dq_flags & XFS_DQ_FREEING) ||
+ !XFS_DQ_IS_DIRTY(dqp)) {
xfs_dqunlock(dqp);
continue;
}
@@ -437,6 +438,7 @@
/* return ! busy */
return 0;
}
+
/*
* Release the group dquot pointers the user dquots may be
* carrying around as a hint. mplist is locked on entry and exit.
@@ -453,6 +455,13 @@
ASSERT(mutex_is_locked(&q->qi_dqlist_lock));
list_for_each_entry(dqp, &q->qi_dqlist, q_mplist) {
xfs_dqlock(dqp);
+ if (dqp->dq_flags & XFS_DQ_FREEING) {
+ xfs_dqunlock(dqp);
+ mutex_unlock(&q->qi_dqlist_lock);
+ delay(1);
+ mutex_lock(&q->qi_dqlist_lock);
+ goto again;
+ }
if ((gdqp = dqp->q_gdquot)) {
xfs_dqlock(gdqp);
dqp->q_gdquot = NULL;
@@ -489,8 +498,8 @@
struct xfs_quotainfo *q = mp->m_quotainfo;
struct xfs_dquot *dqp, *n;
uint dqtype;
- int nrecl;
- int nmisses;
+ int nmisses = 0;
+ LIST_HEAD (dispose_list);
if (!q)
return 0;
@@ -509,46 +518,26 @@
*/
xfs_qm_detach_gdquots(mp);
- again:
- nmisses = 0;
- ASSERT(mutex_is_locked(&q->qi_dqlist_lock));
/*
- * Try to get rid of all of the unwanted dquots. The idea is to
- * get them off mplist and hashlist, but leave them on freelist.
+ * Try to get rid of all of the unwanted dquots.
*/
list_for_each_entry_safe(dqp, n, &q->qi_dqlist, q_mplist) {
xfs_dqlock(dqp);
- if ((dqp->dq_flags & dqtype) == 0) {
- xfs_dqunlock(dqp);
- continue;
+ if ((dqp->dq_flags & dqtype) != 0 &&
+ !(dqp->dq_flags & XFS_DQ_FREEING)) {
+ if (dqp->q_nrefs == 0) {
+ dqp->dq_flags |= XFS_DQ_FREEING;
+ list_move_tail(&dqp->q_mplist, &dispose_list);
+ } else
+ nmisses++;
}
xfs_dqunlock(dqp);
-
- if (!mutex_trylock(&dqp->q_hash->qh_lock)) {
- nrecl = q->qi_dqreclaims;
- mutex_unlock(&q->qi_dqlist_lock);
- mutex_lock(&dqp->q_hash->qh_lock);
- mutex_lock(&q->qi_dqlist_lock);
-
- /*
- * XXXTheoretically, we can get into a very long
- * ping pong game here.
- * No one can be adding dquots to the mplist at
- * this point, but somebody might be taking things off.
- */
- if (nrecl != q->qi_dqreclaims) {
- mutex_unlock(&dqp->q_hash->qh_lock);
- goto again;
- }
- }
-
- /*
- * Take the dquot off the mplist and hashlist. It may remain on
- * freelist in INACTIVE state.
- */
- nmisses += xfs_qm_dqpurge(dqp);
}
mutex_unlock(&q->qi_dqlist_lock);
+
+ list_for_each_entry_safe(dqp, n, &dispose_list, q_mplist)
+ xfs_qm_dqpurge(dqp);
+
return nmisses;
}
@@ -1667,25 +1656,16 @@
/*
- * Just pop the least recently used dquot off the freelist and
- * recycle it. The returned dquot is locked.
+ * Pop the least recently used dquot off the freelist and recycle it.
*/
-STATIC xfs_dquot_t *
+STATIC struct xfs_dquot *
xfs_qm_dqreclaim_one(void)
{
- xfs_dquot_t *dqpout;
- xfs_dquot_t *dqp;
- int restarts;
- int startagain;
+ struct xfs_dquot *dqp;
+ int restarts = 0;
- restarts = 0;
- dqpout = NULL;
-
- /* lockorder: hashchainlock, freelistlock, mplistlock, dqlock, dqflock */
-again:
- startagain = 0;
mutex_lock(&xfs_Gqm->qm_dqfrlist_lock);
-
+restart:
list_for_each_entry(dqp, &xfs_Gqm->qm_dqfrlist, q_freelist) {
struct xfs_mount *mp = dqp->q_mount;
xfs_dqlock(dqp);
@@ -1701,7 +1681,6 @@
list_del_init(&dqp->q_freelist);
xfs_Gqm->qm_dqfrlist_cnt--;
restarts++;
- startagain = 1;
goto dqunlock;
}
@@ -1737,57 +1716,42 @@
}
goto dqunlock;
}
+ xfs_dqfunlock(dqp);
/*
- * We're trying to get the hashlock out of order. This races
- * with dqlookup; so, we giveup and goto the next dquot if
- * we couldn't get the hashlock. This way, we won't starve
- * a dqlookup process that holds the hashlock that is
- * waiting for the freelist lock.
+ * Prevent lookup now that we are going to reclaim the dquot.
+ * Once XFS_DQ_FREEING is set lookup won't touch the dquot,
+ * thus we can drop the lock now.
*/
- if (!mutex_trylock(&dqp->q_hash->qh_lock)) {
- restarts++;
- goto dqfunlock;
- }
+ dqp->dq_flags |= XFS_DQ_FREEING;
+ xfs_dqunlock(dqp);
- /*
- * This races with dquot allocation code as well as dqflush_all
- * and reclaim code. So, if we failed to grab the mplist lock,
- * giveup everything and start over.
- */
- if (!mutex_trylock(&mp->m_quotainfo->qi_dqlist_lock)) {
- restarts++;
- startagain = 1;
- goto qhunlock;
- }
+ mutex_lock(&dqp->q_hash->qh_lock);
+ list_del_init(&dqp->q_hashlist);
+ dqp->q_hash->qh_version++;
+ mutex_unlock(&dqp->q_hash->qh_lock);
- ASSERT(dqp->q_nrefs == 0);
+ mutex_lock(&mp->m_quotainfo->qi_dqlist_lock);
list_del_init(&dqp->q_mplist);
mp->m_quotainfo->qi_dquots--;
mp->m_quotainfo->qi_dqreclaims++;
- list_del_init(&dqp->q_hashlist);
- dqp->q_hash->qh_version++;
+ mutex_unlock(&mp->m_quotainfo->qi_dqlist_lock);
+
+ ASSERT(dqp->q_nrefs == 0);
list_del_init(&dqp->q_freelist);
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);
+
+ mutex_unlock(&xfs_Gqm->qm_dqfrlist_lock);
+ return dqp;
dqunlock:
xfs_dqunlock(dqp);
- if (dqpout)
- break;
if (restarts >= XFS_QM_RECLAIM_MAX_RESTARTS)
break;
- if (startagain) {
- mutex_unlock(&xfs_Gqm->qm_dqfrlist_lock);
- goto again;
- }
+ goto restart;
}
+
mutex_unlock(&xfs_Gqm->qm_dqfrlist_lock);
- return dqpout;
+ return NULL;
}
/*