dm raid: set MD_CHANGE_DEVS when rebuilding

The 'rebuild' parameter is used to rebuild individual devices in an
array (e.g. resynchronize a RAID1 device or recalculate a parity device
in higher RAID).  The MD_CHANGE_DEVS flag must be set when this
parameter is given in order to write out the superblocks and make the
change take immediate effect.  The code that handles new devices in
super_load already sets MD_CHANGE_DEVS and 'FirstUse'.  (The 'FirstUse'
flag was being set as a special case for rebuilds in
super_init_validation.)

Add a condition for rebuilds in super_load to take care of both flags
without the special case in 'super_init_validation'.
Signed-off-by: Jonathan Brassow <jbrassow@redhat.com>
Cc: stable@kernel.org
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

drivers/md/dm-raid.c

@@ -668,7 +668,14 @@ static int super_load(struct md_rdev *rdev, struct md_rdev *refdev)
 		return ret;
 
 	sb = page_address(rdev->sb_page);
-	if (sb->magic != cpu_to_le32(DM_RAID_MAGIC)) {
+
+	/*
+	 * Two cases that we want to write new superblocks and rebuild:
+	 * 1) New device (no matching magic number)
+	 * 2) Device specified for rebuild (!In_sync w/ offset == 0)
+	 */
+	if ((sb->magic != cpu_to_le32(DM_RAID_MAGIC)) ||
+	    (!test_bit(In_sync, &rdev->flags) && !rdev->recovery_offset)) {
 		super_sync(rdev->mddev, rdev);
 
 		set_bit(FirstUse, &rdev->flags);
@@ -745,11 +752,8 @@ static int super_init_validation(struct mddev *mddev, struct md_rdev *rdev)
 	 */
 	rdev_for_each(r, t, mddev) {
 		if (!test_bit(In_sync, &r->flags)) {
-			if (!test_bit(FirstUse, &r->flags))
-				DMERR("Superblock area of "
-				      "rebuild device %d should have been "
-				      "cleared.", r->raid_disk);
-			set_bit(FirstUse, &r->flags);
+			DMINFO("Device %d specified for rebuild: "
+			       "Clearing superblock", r->raid_disk);
 			rebuilds++;
 		} else if (test_bit(FirstUse, &r->flags))
 			new_devs++;