[dm-devel] [PATCH] md: fix raid5 livelock
NeilBrown
neilb at suse.de
Wed Jan 28 02:37:54 UTC 2015
On Sun, 25 Jan 2015 21:06:20 +0100 Heinz Mauelshagen <heinzm at redhat.com>
wrote:
> From: Heinz Mauelshagen <heinzm at redhat.com>
>
> Hi Neil,
>
> the reconstruct write optimization in raid5, function fetch_block causes
> livelocks in LVM raid4/5 tests.
>
> Test scenarios:
> the tests wait for full initial array resynchronization before making a
> filesystem
> on the raid4/5 logical volume, mounting it, writing to the filesystem
> and failing
> one physical volume holding a raiddev.
>
> In short, we're seeing livelocks on fully synchronized raid4/5 arrays
> with a failed device.
>
> This patch fixes the issue but likely in a suboptimnal way.
>
> Do you think there is a better solution to avoid livelocks on
> reconstruct writes?
>
> Regards,
> Heinz
>
> Signed-off-by: Heinz Mauelshagen <heinzm at redhat.com>
> Tested-by: Jon Brassow <jbrassow at redhat.com>
> Tested-by: Heinz Mauelshagen <heinzm at redhat.com>
>
> ---
> 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 c1b0d52..0fc8737 100644
> --- a/drivers/md/raid5.c
> +++ b/drivers/md/raid5.c
> @@ -2915,7 +2915,7 @@ static int fetch_block(struct stripe_head *sh,
> struct stripe_head_state *s,
> (s->failed >= 1 && fdev[0]->toread) ||
> (s->failed >= 2 && fdev[1]->toread) ||
> (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_Insync, &dev->flags) ||
> test_bit(STRIPE_PREREAD_ACTIVE, &sh->state) || s->non_overwrite) &&
> !test_bit(R5_OVERWRITE, &fdev[0]->flags)) ||
> ((sh->raid_conf->level == 6 ||
> sh->sector >= sh->raid_conf->mddev->recovery_cp)
That is a bit heavy handed, but knowing that fixes the problem helps a lot.
I think the problem happens when processes a non-overwrite write to a failed
device.
fetch_block() should, in that case, pre-read all of the working device, but
since
(!test_bit(R5_Insync, &dev->flags) || test_bit(STRIPE_PREREAD_ACTIVE, &sh->state)) &&
was added, it sometimes doesn't. The root problem is that
handle_stripe_dirtying is getting confused because neither rmw or rcw seem to
work, so it doesn't start the chain of events to set STRIPE_PREREAD_ACTIVE.
The following (which is against mainline) might fix it. Can you test?
Thanks,
NeilBrown
diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index c1b0d52bfcb0..793cf2861e97 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -3195,6 +3195,10 @@ static void handle_stripe_dirtying(struct r5conf *conf,
(unsigned long long)sh->sector,
rcw, qread, test_bit(STRIPE_DELAYED, &sh->state));
}
+ if (rcw > disks && rmw > disks &&
+ !test_bit(STRIPE_PREREAD_ACTIVE, &sh->state))
+ set_bit(STRIPE_DELAYED, &sh->state);
+
/* now if nothing is locked, and if we have enough data,
* we can start a write request
*/
This code really really needs to be tidied up and commented better!!!
Thanks,
NeilBrown
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 811 bytes
Desc: OpenPGP digital signature
URL: <http://listman.redhat.com/archives/dm-devel/attachments/20150128/f20bc212/attachment.sig>
More information about the dm-devel
mailing list