md: factor out helper to start reshape from action_store()

There are no functional changes, just to make code cleaner and prepare
for following refactor.
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Signed-off-by: Song Liu <song@kernel.org>
Link: https://lore.kernel.org/r/20240611132251.1967786-5-yukuai1@huaweicloud.com

drivers/md/md.c

@@ -5071,6 +5071,45 @@ static void frozen_sync_thread(struct mddev *mddev)
 	mutex_unlock(&mddev->sync_mutex);
 }
 
+static int mddev_start_reshape(struct mddev *mddev)
+{
+	int ret;
+
+	if (mddev->pers->start_reshape == NULL)
+		return -EINVAL;
+
+	ret = mddev_lock(mddev);
+	if (ret)
+		return ret;
+
+	if (test_bit(MD_RECOVERY_RUNNING, &mddev->recovery)) {
+		mddev_unlock(mddev);
+		return -EBUSY;
+	}
+
+	if (mddev->reshape_position == MaxSector ||
+	    mddev->pers->check_reshape == NULL ||
+	    mddev->pers->check_reshape(mddev)) {
+		clear_bit(MD_RECOVERY_FROZEN, &mddev->recovery);
+		ret = mddev->pers->start_reshape(mddev);
+		if (ret) {
+			mddev_unlock(mddev);
+			return ret;
+		}
+	} else {
+		/*
+		 * If reshape is still in progress, and md_check_recovery() can
+		 * continue to reshape, don't restart reshape because data can
+		 * be corrupted for raid456.
+		 */
+		clear_bit(MD_RECOVERY_FROZEN, &mddev->recovery);
+	}
+
+	mddev_unlock(mddev);
+	sysfs_notify_dirent_safe(mddev->sysfs_degraded);
+	return 0;
+}
+
 static ssize_t
 action_store(struct mddev *mddev, const char *page, size_t len)
 {
@@ -5090,32 +5129,10 @@ action_store(struct mddev *mddev, const char *page, size_t len)
 		clear_bit(MD_RECOVERY_FROZEN, &mddev->recovery);
 		set_bit(MD_RECOVERY_RECOVER, &mddev->recovery);
 	} else if (cmd_match(page, "reshape")) {
-		int err;
-		if (mddev->pers->start_reshape == NULL)
-			return -EINVAL;
-		err = mddev_lock(mddev);
-		if (!err) {
-			if (test_bit(MD_RECOVERY_RUNNING, &mddev->recovery)) {
-				err =  -EBUSY;
-			} else if (mddev->reshape_position == MaxSector ||
-				   mddev->pers->check_reshape == NULL ||
-				   mddev->pers->check_reshape(mddev)) {
-				clear_bit(MD_RECOVERY_FROZEN, &mddev->recovery);
-				err = mddev->pers->start_reshape(mddev);
-			} else {
-				/*
-				 * If reshape is still in progress, and
-				 * md_check_recovery() can continue to reshape,
-				 * don't restart reshape because data can be
-				 * corrupted for raid456.
-				 */
-				clear_bit(MD_RECOVERY_FROZEN, &mddev->recovery);
-			}
-			mddev_unlock(mddev);
-		}
+		int err = mddev_start_reshape(mddev);
+
 		if (err)
 			return err;
-		sysfs_notify_dirent_safe(mddev->sysfs_degraded);
 	} else {
 		if (cmd_match(page, "check"))
 			set_bit(MD_RECOVERY_CHECK, &mddev->recovery);