Commit 108cef3a authored Dec 03, 2014 by NeilBrown

md/raid5: fetch_block must fetch all the blocks handle_stripe_dirtying wants.



It is critical that fetch_block() and handle_stripe_dirtying()
are consistent in their analysis of what needs to be loaded.
Otherwise raid5 can wait forever for a block that won't be loaded.

Currently when writing to a RAID5 that is resyncing, to a location
beyond the resync offset, handle_stripe_dirtying chooses a
reconstruct-write cycle, but fetch_block() assumes a
read-modify-write, and a lockup can happen.

So treat that case just like RAID6, just as we do in
handle_stripe_dirtying.  RAID6 always does reconstruct-write.

This bug was introduced when the behaviour of handle_stripe_dirtying
was changed in 3.7, so the patch is suitable for any kernel since,
though it will need careful merging for some versions.

Cc: stable@vger.kernel.org (v3.7+)
Fixes: a7854487
Reported-by: Henry Cai <henryplusplus@gmail.com>
Signed-off-by: NeilBrown <neilb@suse.de>

parent 3a18ca06

drivers/md/raid5.c

+5 −2

Original line number	Diff line number	Diff line
		@@ -2917,8 +2917,11 @@ static int fetch_block(struct stripe_head sh, struct stripe_head_state s,
		(sh->raid_conf->level <= 5 && s->failed && fdev[0]->towrite &&
		(!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 - s->non_overwrite < sh->raid_conf->raid_disks - 2 &&
		((sh->raid_conf->level == 6 \|\|
		sh->sector >= sh->raid_conf->mddev->recovery_cp)
		&& s->failed && s->to_write &&
		(s->to_write - s->non_overwrite <
		sh->raid_conf->raid_disks - sh->raid_conf->max_degraded) &&
		(!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