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xfs: fix dquot shaker deadlock

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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@malc.org.uk>
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Alex Elder <aelder@sgi.com>
This commit is contained in:
Dave Chinner 2011-01-28 11:20:46 +11:00 committed by Alex Elder
parent c6f990d1ff
commit 0fbca4d1c3
1 changed files with 21 additions and 25 deletions
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46
fs/xfs/quota/xfs_qm.c
View file

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