md/raid10: allow removal of failed replacement devices.

Enhance raid10_remove_disk to be able to remove ->replacement
as well as ->rdev
Signed-off-by: NNeilBrown <neilb@suse.de>

drivers/md/raid10.c

@@ -1429,16 +1429,23 @@ static int raid10_remove_disk(struct mddev *mddev, struct md_rdev *rdev)
 	struct r10conf *conf = mddev->private;
 	int err = 0;
 	int number = rdev->raid_disk;
-	struct mirror_info *p = conf->mirrors+ number;
+	struct md_rdev **rdevp;
+	struct mirror_info *p = conf->mirrors + number;
 
 	print_conf(conf);
-	if (rdev == p->rdev) {
+	if (rdev == p->rdev)
+		rdevp = &p->rdev;
+	else if (rdev == p->replacement)
+		rdevp = &p->replacement;
+	else
+		return 0;
+
 	if (test_bit(In_sync, &rdev->flags) ||
 	    atomic_read(&rdev->nr_pending)) {
 		err = -EBUSY;
 		goto abort;
 	}
-		/* Only remove faulty devices in recovery
+	/* Only remove faulty devices if recovery
 	 * is not possible.
 	 */
 	if (!test_bit(Faulty, &rdev->flags) &&
@@ -1447,16 +1454,16 @@ static int raid10_remove_disk(struct mddev *mddev, struct md_rdev *rdev)
 		err = -EBUSY;
 		goto abort;
 	}
-		p->rdev = NULL;
+	*rdevp = NULL;
 	synchronize_rcu();
 	if (atomic_read(&rdev->nr_pending)) {
 		/* lost the race, try later */
 		err = -EBUSY;
-			p->rdev = rdev;
+		*rdevp = rdev;
 		goto abort;
 	}
 	err = md_integrity_register(mddev);
-	}
+
 abort:
 
 	print_conf(conf);