Re: [PATCH] drivers/md/md.c: ignore recovery_offset if bitmap exists

[Neil Brown <neilb@suse.de>]

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On Sat, Oct 31 2015, Nate Dailey wrote:

> I first tested 4.3-rc6 that I already had laying around, and verified that the 
> bug still happens.
>
> Then I reverted 7eb418851f3278de67126ea0c427641ab4792c57, rebuilt & installed, 
> and tested again. Reverting this patch did indeed fix the bug.
>
> Thank you!
>
> Nate
>

Thanks a lot for testing.
The following with go to Linus soon, hopefully in time for 4.3-final.
It should then be picked up by stable.

If anyone wants to try their hand at the "future patch" I mentioned, I
wouldn't object. MD_FEATURE_RECOVERY_BITMAP is an important part of the
picture.  I won't have an opportunity to work on it until December.

Thanks,
NeilBrown


commit d01552a76d71f9879af448e9142389ee9be6e95b
Author: NeilBrown <neilb@suse.com>
Date:   Sat Oct 31 11:00:56 2015 +1100

    Revert "md: allow a partially recovered device to be hot-added to an array."
    
    This reverts commit 7eb418851f3278de67126ea0c427641ab4792c57.
    
    This commit is poorly justified, I can find not discusison in email,
    and it clearly causes a problem.
    
    If a device which is being recovered fails and is subsequently
    re-added to an array, there could easily have been changes to the
    array *before* the point where the recovery was up to.  So the
    recovery must start again from the beginning.
    
    If a spare is being recovered and fails, then when it is re-added we
    really should do a bitmap-based recovery up to the recovery-offset,
    and then a full recovery from there.  Before this reversion, we only
    did the "full recovery from there" which is not corect.  After this
    reversion with will do a full recovery from the start, which is safer
    but not ideal.
    
    It will be left to a future patch to arrange the two different styles
    of recovery.
    
    Reported-and-tested-by: Nate Dailey <nate.dailey@stratus.com>
    Signed-off-by: NeilBrown <neilb@suse.com>
    Cc: stable@vger.kernel.org (3.14+)
    Fixes: 7eb418851f32 ("md: allow a partially recovered device to be hot-added to an array.")

diff --git a/drivers/md/md.c b/drivers/md/md.c
index c702de18207a..3fe3d04a968a 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -8040,8 +8040,7 @@ static int remove_and_add_spares(struct mddev *mddev,
 		       !test_bit(Bitmap_sync, &rdev->flags)))
 			continue;
 
-		if (rdev->saved_raid_disk < 0)
-			rdev->recovery_offset = 0;
+		rdev->recovery_offset = 0;
 		if (mddev->pers->
 		    hot_add_disk(mddev, rdev) == 0) {
 			if (sysfs_link_rdev(mddev, rdev))

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