Don't unconditionally set in_sync on newly added device in raid5_reshape

When a reshape finds that it can add spare devices into the array,
those devices might already be 'in_sync' if they are beyond the old
size of the array, or they might not if they are within the array.

The first case happens when we change an N-drive RAID5 to an
N+1-drive RAID5.
The second happens when we convert an N-drive RAID5 to an
N+1-drive RAID6.

So set the flag more carefully.
Also, ->recovery_offset is only meaningful when the flag is clear,
so only set it in that case.

This change needs the preceding two to ensure that the non-in_sync
device doesn't get evicted from the array when it is stopped, in the
case where v0.90 metadata is used.

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

drivers/md/raid5.c

@@ -5361,9 +5361,11 @@ static int raid5_start_reshape(mddev_t *mddev)
 		    !test_bit(Faulty, &rdev->flags)) {
 			if (raid5_add_disk(mddev, rdev) == 0) {
 				char nm[20];
-				set_bit(In_sync, &rdev->flags);
+				if (rdev->raid_disk >= conf->previous_raid_disks)
+					set_bit(In_sync, &rdev->flags);
+				else
+					rdev->recovery_offset = 0;
 				added_devices++;
-				rdev->recovery_offset = 0;
 				sprintf(nm, "rd%d", rdev->raid_disk);
 				if (sysfs_create_link(&mddev->kobj,
 						      &rdev->kobj, nm))