From a40687ff73a5b14909d6aa522f7d778b158911c5 Mon Sep 17 00:00:00 2001 From: NeilBrown Date: Wed, 13 Aug 2014 09:48:45 +1000 Subject: [PATCH] md/raid5: avoid livelock caused by non-aligned writes. If a stripe in a raid6 array received a write to each data block while the array is degraded, and if any of these writes to a missing device are not page-aligned, then a live-lock happens. In this case the P and Q blocks need to be read so that the part of the missing block which is *not* being updated by the write can be constructed. Due to a logic error, these blocks are not loaded, so the update cannot proceed and the stripe is 'handled' repeatedly in an infinite loop. This bug is unlikely as most writes are page aligned. However as it can lead to a livelock it is suitable for -stable. It was introduced in 3.16. Cc: stable@vger.kernel.org (v3.16) Fixed: 67f455486d2ea20b2d94d6adf5b9b783d079e321 Signed-off-by: NeilBrown --- drivers/md/raid5.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c index 6234b2e84587..6b2d615d1094 100644 --- a/drivers/md/raid5.c +++ b/drivers/md/raid5.c @@ -2922,7 +2922,7 @@ static int fetch_block(struct stripe_head *sh, struct stripe_head_state *s, (!test_bit(R5_Insync, &dev->flags) || test_bit(STRIPE_PREREAD_ACTIVE, &sh->state)) && !test_bit(R5_OVERWRITE, &fdev[0]->flags)) || (sh->raid_conf->level == 6 && s->failed && s->to_write && - s->to_write < sh->raid_conf->raid_disks - 2 && + s->to_write - s->non_overwrite < sh->raid_conf->raid_disks - 2 && (!test_bit(R5_Insync, &dev->flags) || test_bit(STRIPE_PREREAD_ACTIVE, &sh->state))))) { /* we would like to get this block, possibly by computing it, * otherwise read it if the backing disk is insync -- 2.20.1