From 6d183de4077191d1201283a9035ce57a9b05254d Mon Sep 17 00:00:00 2001 From: NeilBrown Date: Thu, 28 Nov 2013 10:55:27 +1100 Subject: [PATCH] md/raid5: fix newly-broken locking in get_active_stripe. commit 566c09c53455d7c4f1 raid5: relieve lock contention in get_active_stripe() modified the locking in get_active_stripe() reducing the range protected by the (highly contended) device_lock. Unfortunately it reduced the range too much opening up some races. One race can occur if get_priority_stripe runs between the test on sh->count and device_lock being taken. This will mean that sh->lru is not empty while get_active_stripe thinks ->count is zero resulting in a 'BUG' firing. Another race happens if __release_stripe is called immediately after sh->count is tested and found to be non-zero. If STRIPE_HANDLE is not set, get_active_stripe should increment ->active_stripes when it increments ->count from 0, but as it didn't think it was 0, it doesn't. Extending device_lock to cover the test on sh->count close these races. While we are here, fix the two BUG tests: -If count is zero, then lru really must not be empty, or we've lock the stripe_head somehow - no other tests are relevant. -STRIPE_ON_RELEASE_LIST is completely independent of ->lru so testing it is pointless. Reported-and-tested-by: Brassow Jonathan Reviewed-by: Shaohua Li Fixes: 566c09c53455d7c4f1 Signed-off-by: NeilBrown --- drivers/md/raid5.c | 11 ++++------- 1 file changed, 4 insertions(+), 7 deletions(-) diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c index 676d8b7c5117..cc055da02e2a 100644 --- a/drivers/md/raid5.c +++ b/drivers/md/raid5.c @@ -678,26 +678,23 @@ get_active_stripe(struct r5conf *conf, sector_t sector, } else init_stripe(sh, sector, previous); } else { + spin_lock(&conf->device_lock); if (atomic_read(&sh->count)) { BUG_ON(!list_empty(&sh->lru) && !test_bit(STRIPE_EXPANDING, &sh->state) && !test_bit(STRIPE_ON_UNPLUG_LIST, &sh->state) - && !test_bit(STRIPE_ON_RELEASE_LIST, &sh->state)); + ); } else { - spin_lock(&conf->device_lock); if (!test_bit(STRIPE_HANDLE, &sh->state)) atomic_inc(&conf->active_stripes); - if (list_empty(&sh->lru) && - !test_bit(STRIPE_ON_RELEASE_LIST, &sh->state) && - !test_bit(STRIPE_EXPANDING, &sh->state)) - BUG(); + BUG_ON(list_empty(&sh->lru)); list_del_init(&sh->lru); if (sh->group) { sh->group->stripes_cnt--; sh->group = NULL; } - spin_unlock(&conf->device_lock); } + spin_unlock(&conf->device_lock); } } while (sh == NULL); -- 2.30.2