Index: linux-3.10.0-799.el7.x86_64/drivers/md/raid5.c
===================================================================
--- linux-3.10.0-799.el7.x86_64.orig/drivers/md/raid5.c
+++ linux-3.10.0-799.el7.x86_64/drivers/md/raid5.c
@@ -3096,7 +3096,9 @@ static int add_stripe_bio(struct stripe_
 		bi->bi_next = *bip;
 	*bip = bi;
 	raid5_inc_bi_active_stripes(bi);
	md_write_inc(conf->mddev, 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 */
@@ -5548,6 +5550,9 @@ static void raid5_make_request(struct md
 					 bi, 0);
 		bio_endio(bi, 0);
 	}
+
+	if (bi->bi_rw & REQ_SYNC)
+		md_wakeup_thread(mddev->thread);
 }
 
 static sector_t raid5_size(struct mddev *mddev, sector_t sectors, int raid_disks);