md: allow re-add to failed arrays.

When an array is failed (some data inaccessible) then there is no
point attempting to add a spare as it could not possibly be recovered.

However that may be value in re-adding a recently removed device.
e.g. if there is a write-intent-bitmap and it is clear, then access
to the data could be restored by this action.

So don't reject a re-add to a failed array for RAID10 and RAID5 (the
only arrays  types that check for a failed array).

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

2 files changed, 2 insertions, 2 deletions

diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index 1a19c962f860..f4f3edcdaf8d 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -1483,7 +1483,7 @@ static int raid10_add_disk(struct mddev *mddev, struct md_rdev *rdev)
                  * very different from resync
                  */
                 return -EBUSY;
-        if (!enough(conf, -1))
+        if (rdev->saved_raid_disk < 0 && !enough(conf, -1))
                 return -EINVAL;
 
         if (rdev->raid_disk >= 0)
diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 99b2bbf8b5d8..d38d235cc39d 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -5361,7 +5361,7 @@ static int raid5_add_disk(struct mddev *mddev, struct md_rdev *rdev)
         if (mddev->recovery_disabled == conf->recovery_disabled)
                 return -EBUSY;
 
-        if (has_failed(conf))
+        if (rdev->saved_raid_disk < 0 && has_failed(conf))
                 /* no point adding a device */
                 return -EINVAL;