From ab69ae12ceef7f23c578a3c230144e94a167a821 Mon Sep 17 00:00:00 2001 From: NeilBrown Date: Tue, 31 Mar 2009 15:26:47 +1100 Subject: md/raid5: be more careful about write ordering when reshaping. When we are reshaping an array, it is very important that we read the data from a particular sector offset before writing new data at that offset. In most cases when growing or shrinking an array we read long before we even consider writing. But when restriping an array without changing it size, there is a small possibility that we might have some data to available write before the read has happened at the same location. This would require some stripes to be in cache already. To guard against this small possibility, we check, before writing, that the 'old' stripe at the same location is not in the process of being read. And we ensure that we mark all 'source' stripes as such before allowing new 'destination' stripes to proceed. Signed-off-by: NeilBrown --- drivers/md/raid5.c | 49 +++++++++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 47 insertions(+), 2 deletions(-) diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c index 4fdc6d02b44..062df846fd6 100644 --- a/drivers/md/raid5.c +++ b/drivers/md/raid5.c @@ -395,7 +395,8 @@ get_active_stripe(raid5_conf_t *conf, sector_t sector, init_stripe(sh, sector, previous); } else { if (atomic_read(&sh->count)) { - BUG_ON(!list_empty(&sh->lru)); + BUG_ON(!list_empty(&sh->lru) + && !test_bit(STRIPE_EXPANDING, &sh->state)); } else { if (!test_bit(STRIPE_HANDLE, &sh->state)) atomic_inc(&conf->active_stripes); @@ -2944,6 +2945,23 @@ static bool handle_stripe5(struct stripe_head *sh) /* Finish reconstruct operations initiated by the expansion process */ if (sh->reconstruct_state == reconstruct_state_result) { + struct stripe_head *sh2 + = get_active_stripe(conf, sh->sector, 1, 1); + if (sh2 && test_bit(STRIPE_EXPAND_SOURCE, &sh2->state)) { + /* sh cannot be written until sh2 has been read. + * so arrange for sh to be delayed a little + */ + set_bit(STRIPE_DELAYED, &sh->state); + set_bit(STRIPE_HANDLE, &sh->state); + if (!test_and_set_bit(STRIPE_PREREAD_ACTIVE, + &sh2->state)) + atomic_inc(&conf->preread_active_stripes); + release_stripe(sh2); + goto unlock; + } + if (sh2) + release_stripe(sh2); + sh->reconstruct_state = reconstruct_state_idle; clear_bit(STRIPE_EXPANDING, &sh->state); for (i = conf->raid_disks; i--; ) { @@ -3172,6 +3190,23 @@ static bool handle_stripe6(struct stripe_head *sh, struct page *tmp_page) } if (s.expanded && test_bit(STRIPE_EXPANDING, &sh->state)) { + struct stripe_head *sh2 + = get_active_stripe(conf, sh->sector, 1, 1); + if (sh2 && test_bit(STRIPE_EXPAND_SOURCE, &sh2->state)) { + /* sh cannot be written until sh2 has been read. + * so arrange for sh to be delayed a little + */ + set_bit(STRIPE_DELAYED, &sh->state); + set_bit(STRIPE_HANDLE, &sh->state); + if (!test_and_set_bit(STRIPE_PREREAD_ACTIVE, + &sh2->state)) + atomic_inc(&conf->preread_active_stripes); + release_stripe(sh2); + goto unlock; + } + if (sh2) + release_stripe(sh2); + /* Need to write out all blocks after computing P&Q */ sh->disks = conf->raid_disks; stripe_set_idx(sh->sector, conf, 0, sh); @@ -3739,6 +3774,7 @@ static sector_t reshape_request(mddev_t *mddev, sector_t sector_nr, int *skipped sector_t writepos, safepos, gap; sector_t stripe_addr; int reshape_sectors; + struct list_head stripes; if (sector_nr == 0) { /* If restarting in the middle, skip the initial sectors */ @@ -3816,6 +3852,7 @@ static sector_t reshape_request(mddev_t *mddev, sector_t sector_nr, int *skipped BUG_ON(writepos != sector_nr + reshape_sectors); stripe_addr = sector_nr; } + INIT_LIST_HEAD(&stripes); for (i = 0; i < reshape_sectors; i += STRIPE_SECTORS) { int j; int skipped = 0; @@ -3845,7 +3882,7 @@ static sector_t reshape_request(mddev_t *mddev, sector_t sector_nr, int *skipped set_bit(STRIPE_EXPAND_READY, &sh->state); set_bit(STRIPE_HANDLE, &sh->state); } - release_stripe(sh); + list_add(&sh->lru, &stripes); } spin_lock_irq(&conf->device_lock); if (mddev->delta_disks < 0) @@ -3874,6 +3911,14 @@ static sector_t reshape_request(mddev_t *mddev, sector_t sector_nr, int *skipped release_stripe(sh); first_sector += STRIPE_SECTORS; } + /* Now that the sources are clearly marked, we can release + * the destination stripes + */ + while (!list_empty(&stripes)) { + sh = list_entry(stripes.next, struct stripe_head, lru); + list_del_init(&sh->lru); + release_stripe(sh); + } /* If this takes us to the resync_max point where we have to pause, * then we need to write out the superblock. */ -- cgit v1.2.3