From: Yu Kuai <yukuai3@huawei.com>

Currently, if reshape is interrupted, echo "reshape" to sync_action will
restart reshape from scratch, for example:

echo frozen > sync_action
echo reshape > sync_action

This will corrupt data before reshape_position if the array is growing,
fix the problem by continue reshape from reshape_position.

Reported-by: Peter Neuwirth <reddunur@online.de>
Link: https://lore.kernel.org/linux-raid/e2f96772-bfbc-f43b-6da1-f520e5164536@online.de/
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
---
 drivers/md/md.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index e1bc223d58b3..cf60d4b5356d 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -4827,11 +4827,21 @@ action_store(struct mddev *mddev, const char *page, size_t len)
 			return -EINVAL;
 		err = mddev_lock(mddev);
 		if (!err) {
-			if (test_bit(MD_RECOVERY_RUNNING, &mddev->recovery))
+			if (test_bit(MD_RECOVERY_RUNNING, &mddev->recovery)) {
 				err =  -EBUSY;
-			else {
+			} 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);
 		}
-- 
2.39.2