md/raid10: fix bug which causes all RAID10 reshapes to move no data.

The recent comment:
commit 7e83ccbecd608b971f340e951c9e84cd0343002f
    md/raid10: Allow skipping recovery when clean arrays are assembled

Causes raid10 to skip a recovery in certain cases where it is safe to
do so.  Unfortunately it also causes a reshape to be skipped which is
never safe.  The result is that an attempt to reshape a RAID10 will
appear to complete instantly, but no data will have been moves so the
array will now contain garbage.
(If nothing is written, you can recovery by simple performing the
reverse reshape which will also complete instantly).

Bug was introduced in 3.10, so this is suitable for 3.10-stable.

Cc: stable@vger.kernel.org (3.10)
Cc: Martin Wilck <mwilck@arcor.de>
Signed-off-by: NeilBrown <neilb@suse.de>

1 files changed, 4 insertions, 5 deletions

diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index 3480bf7c20d4..cd066b63bdaf 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -2931,14 +2931,13 @@ static sector_t sync_request(struct mddev *mddev, sector_t sector_nr,
          */
         if (mddev->bitmap == NULL &&
             mddev->recovery_cp == MaxSector &&
+            mddev->reshape_position == MaxSector &&
+            !test_bit(MD_RECOVERY_SYNC, &mddev->recovery) &&
             !test_bit(MD_RECOVERY_REQUESTED, &mddev->recovery) &&
+            !test_bit(MD_RECOVERY_RESHAPE, &mddev->recovery) &&
             conf->fullsync == 0) {
                 *skipped = 1;
-                max_sector = mddev->dev_sectors;
-                if (test_bit(MD_RECOVERY_SYNC, &mddev->recovery) ||
-                    test_bit(MD_RECOVERY_RESHAPE, &mddev->recovery))
-                        max_sector = mddev->resync_max_sectors;
-                return max_sector - sector_nr;
+                return mddev->dev_sectors - sector_nr;
         }
 
  skipped: