md: fix bug with re-adding of partially recovered device.

With v0.90 metadata, a hot-spare does not become a full member of the
array until recovery is complete.  So if we re-add such a device to
the array, we know that all of it is as up-to-date as the event count
would suggest, and so it a bitmap-based recovery is possible.

However with v1.x metadata, the hot-spare immediately becomes a full
member of the array, but it record how much of the device has been
recovered.  If the array is stopped and re-assembled recovery starts
from this point.

When such a device is hot-added to an array we currently lose the 'how
much is recovered' information and incorrectly included it as a full
in-sync member (after bitmap-based fixup).
This is wrong and unsafe and could corrupt data.

So be more careful about setting saved_raid_disk - which is what
guides the re-adding of devices back into an array.
The new code matches the code in slot_store which does a similar
thing, which is encouraging.

This is suitable for any -stable kernel.

Reported-by: "Dailey, Nate" <Nate.Dailey@stratus.com>
Cc: stable@kernel.org
Signed-off-by: NeilBrown <neilb@suse.de>

1 files changed, 5 insertions, 2 deletions

diff --git a/drivers/md/md.c b/drivers/md/md.c
index d66aaeddf95d..b757da175180 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -5159,7 +5159,7 @@ static int add_new_disk(mddev_t * mddev, mdu_disk_info_t *info)
                                 PTR_ERR(rdev));
                         return PTR_ERR(rdev);
                 }
-                /* set save_raid_disk if appropriate */
+                /* set saved_raid_disk if appropriate */
                 if (!mddev->persistent) {
                         if (info->state & (1<<MD_DISK_SYNC)  &&
                             info->raid_disk < mddev->raid_disks)
@@ -5169,7 +5169,10 @@ static int add_new_disk(mddev_t * mddev, mdu_disk_info_t *info)
                 } else
                         super_types[mddev->major_version].
                                 validate_super(mddev, rdev);
-                rdev->saved_raid_disk = rdev->raid_disk;
+                if (test_bit(In_sync, &rdev->flags))
+                        rdev->saved_raid_disk = rdev->raid_disk;
+                else
+                        rdev->saved_raid_disk = -1;
 
                 clear_bit(In_sync, &rdev->flags); /* just to be sure */
                 if (info->state & (1<<MD_DISK_WRITEMOSTLY))