md: update superblock after changing rdev flags in state_store

When the in memory flag is changed, we need to persist the change in the
rdev superblock flags. This is needed for "writemostly" and "failfast".
Reviewed-by: Li Feng <fengli@smartx.com>
Signed-off-by: Xiao Ni <xni@redhat.com>
Signed-off-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/md/md.c

@@ -2976,7 +2976,11 @@ state_store(struct md_rdev *rdev, const char *buf, size_t len)
 	 *  -write_error - clears WriteErrorSeen
 	 *  {,-}failfast - set/clear FailFast
 	 */
+
+	struct mddev *mddev = rdev->mddev;
 	int err = -EINVAL;
+	bool need_update_sb = false;
+
 	if (cmd_match(buf, "faulty") && rdev->mddev->pers) {
 		md_error(rdev->mddev, rdev);
 		if (test_bit(Faulty, &rdev->flags))
@@ -2991,7 +2995,6 @@ state_store(struct md_rdev *rdev, const char *buf, size_t len)
 		if (rdev->raid_disk >= 0)
 			err = -EBUSY;
 		else {
-			struct mddev *mddev = rdev->mddev;
 			err = 0;
 			if (mddev_is_clustered(mddev))
 				err = md_cluster_ops->remove_disk(mddev, rdev);
@@ -3008,10 +3011,12 @@ state_store(struct md_rdev *rdev, const char *buf, size_t len)
 	} else if (cmd_match(buf, "writemostly")) {
 		set_bit(WriteMostly, &rdev->flags);
 		mddev_create_serial_pool(rdev->mddev, rdev, false);
+		need_update_sb = true;
 		err = 0;
 	} else if (cmd_match(buf, "-writemostly")) {
 		mddev_destroy_serial_pool(rdev->mddev, rdev, false);
 		clear_bit(WriteMostly, &rdev->flags);
+		need_update_sb = true;
 		err = 0;
 	} else if (cmd_match(buf, "blocked")) {
 		set_bit(Blocked, &rdev->flags);
@@ -3037,9 +3042,11 @@ state_store(struct md_rdev *rdev, const char *buf, size_t len)
 		err = 0;
 	} else if (cmd_match(buf, "failfast")) {
 		set_bit(FailFast, &rdev->flags);
+		need_update_sb = true;
 		err = 0;
 	} else if (cmd_match(buf, "-failfast")) {
 		clear_bit(FailFast, &rdev->flags);
+		need_update_sb = true;
 		err = 0;
 	} else if (cmd_match(buf, "-insync") && rdev->raid_disk >= 0 &&
 		   !test_bit(Journal, &rdev->flags)) {
@@ -3118,6 +3125,8 @@ state_store(struct md_rdev *rdev, const char *buf, size_t len)
 		clear_bit(ExternalBbl, &rdev->flags);
 		err = 0;
 	}
+	if (need_update_sb)
+		md_update_sb(mddev, 1);
 	if (!err)
 		sysfs_notify_dirent_safe(rdev->sysfs_state);
 	return err ? err : len;