Neil,
the patch worked fine in overnight test runs without the previous livelock.
No regressions have been triggered.
Yes, tidying up that optimization logic (e.g. in fetch_block()) is very
much appreciated :-)
Thanks,
Heinz
On 01/28/2015 01:03 PM, Heinz Mauelshagen wrote:
Neil,
thanks for providing the patch.
Test with it will take some hours in order to tell any success.
Regards,
Heinz
On 01/28/2015 03:37 AM, NeilBrown wrote:
On Sun, 25 Jan 2015 21:06:20 +0100 Heinz Mauelshagen <heinzm@xxxxxxxxxx>
wrote:
From: Heinz Mauelshagen <heinzm@xxxxxxxxxx>
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@xxxxxxxxxx>
Tested-by: Jon Brassow <jbrassow@xxxxxxxxxx>
Tested-by: Heinz Mauelshagen <heinzm@xxxxxxxxxx>
---
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
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