Index: linux-4.4.21-64/drivers/md/raid5.c
===================================================================
--- linux-4.4.21-64.orig/drivers/md/raid5.c
+++ linux-4.4.21-64/drivers/md/raid5.c
@@ -2991,6 +2991,8 @@ static int add_stripe_bio(struct stripe_
 		bi->bi_next = *bip;
 	*bip = bi;
 	raid5_inc_bi_active_stripes(bi);
+	if ((bi->bi_rw & REQ_SYNC) && !forwrite)
+		clear_bit(R5_UPTODATE, &sh->dev[dd_idx].flags);	/* force to read from disk. */
 
 	if (forwrite) {
 		/* check if page is covered */
@@ -5136,6 +5138,9 @@ static void make_discard_request(struct
 		md_write_end(mddev);
 		bio_endio(bi);
 	}
+
+	if (bi->bi_rw & REQ_SYNC)
+		md_wakeup_thread(mddev->thread);
 }
 
 static void raid5_make_request(struct mddev *mddev, struct bio * bi)