Re: md raid10 regression in 2.6.27.4 (possibly earlier) BISECTED

[Neil Brown <neilb@suse.de>]

On Thursday November 6, tmb@mandriva.org wrote:
> 
> But anyway...
> 
> This is the commit that breaks the raid10 rebuild/resync:

Awesome. Thanks!

> 
> --- cut ---
> 6c2fce2ef6b4821c21b5c42c7207cb9cf8c87eda is first bad commit
> commit 6c2fce2ef6b4821c21b5c42c7207cb9cf8c87eda
> Author: Neil Brown <neilb@notabene.brown>
                      ^^^^^^^^^^^^^^^^^^^^
Grown.  I hadn't noticed that.  Fixed now I hope.

> Date:   Sat Jun 28 08:31:31 2008 +1000
> 
>      Support adding a spare to a live md array with external metadata.
> 
>      i.e. extend the 'md/dev-XXX/slot' attribute so that you can
>      tell a device to fill an vacant slot in an and md array.
> 
>      Signed-off-by: Neil Brown <neilb@suse.de>
> --- cut ---
> 
> I have verified that adding this patch to a working 2.6.26 kernel breaks
> the rebuild/resync
> 
> I have not verified if reverting it on a 2.6.27 kernel restores the 
> rebuild/resync as it does not revert cleanly...
> 
> So...
> 
> Any suggestions of what to try next ?

You mean apart from hitting Neil with a clue-bat?

Maybe try this patch.  I haven't even compile tested it, but I'm
certain it'll fix your problem.

Thanks again,

NeilBrown

----------------------------------------------
From: NeilBrown <neilb@suse.de>
Date: Thu, 6 Nov 2008 17:14:31 +1100
Subject: [PATCH] md: fix bug in raid10 recovery.

Adding a spare to a raid10 doesn't cause recovery to start.
This is due to an silly type in
  commit 6c2fce2ef6b4821c21b5c42c7207cb9cf8c87eda
and so is a bug in 2.6.27 and .28-rc.

Thanks to Thomas Backlund for bisecting to find this.

Cc: Thomas Backlund <tmb@mandriva.org>
Cc: stable@kernel.org

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

diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index da5129a..970a96e 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -1137,7 +1137,7 @@ static int raid10_add_disk(mddev_t *mddev, mdk_rdev_t *rdev)
 	if (!enough(conf))
 		return -EINVAL;
 
-	if (rdev->raid_disk)
+	if (rdev->raid_disk >= 0)
 		first = last = rdev->raid_disk;
 
 	if (rdev->saved_raid_disk >= 0 &&
-- 
1.5.6.5