Commit a40687ff authored Aug 13, 2014 by NeilBrown

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: 67f45548
Signed-off-by: NeilBrown <neilb@suse.de>

parent 7d1311b9

drivers/md/raid5.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -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

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