md: integrate spares into array at earliest opportunity.

As v1.x metadata can record that a member of the array is
not completely recovered, it make sense to record that a
spare has become a regular member of the array at the earliest
opportunity.
So remove the tests on "recovery_offset > 0" in super_1_sync
as they really aren't needed, and schedule a metadata update
immediately after adding spares to a degraded array.

This means that if a crash happens immediately after a recovery
starts, the new device will be included in the array and recovery will
continue from wherever it was up to.  Previously this didn't happen
unless recovery was at least 1/16 of the way through.
Signed-off-by: NeilBrown <neilb@suse.de>

drivers/md/md.c

@@ -1508,12 +1508,10 @@ static void super_1_sync(mddev_t *mddev, mdk_rdev_t *rdev)
 
 	if (rdev->raid_disk >= 0 &&
 	    !test_bit(In_sync, &rdev->flags)) {
-		if (rdev->recovery_offset > 0) {
-			sb->feature_map |=
-				cpu_to_le32(MD_FEATURE_RECOVERY_OFFSET);
-			sb->recovery_offset =
-				cpu_to_le64(rdev->recovery_offset);
-		}
+		sb->feature_map |=
+			cpu_to_le32(MD_FEATURE_RECOVERY_OFFSET);
+		sb->recovery_offset =
+			cpu_to_le64(rdev->recovery_offset);
 	}
 
 	if (mddev->reshape_position != MaxSector) {
@@ -1547,7 +1545,7 @@ static void super_1_sync(mddev_t *mddev, mdk_rdev_t *rdev)
 			sb->dev_roles[i] = cpu_to_le16(0xfffe);
 		else if (test_bit(In_sync, &rdev2->flags))
 			sb->dev_roles[i] = cpu_to_le16(rdev2->raid_disk);
-		else if (rdev2->raid_disk >= 0 && rdev2->recovery_offset > 0)
+		else if (rdev2->raid_disk >= 0)
 			sb->dev_roles[i] = cpu_to_le16(rdev2->raid_disk);
 		else
 			sb->dev_roles[i] = cpu_to_le16(0xffff);
@@ -6786,6 +6784,7 @@ static int remove_and_add_spares(mddev_t *mddev)
 						       nm, mdname(mddev));
 					spares++;
 					md_new_event(mddev);
+					set_bit(MD_CHANGE_DEVS, &mddev->flags);
 				} else
 					break;
 			}