--- linux-3.10.0-685.el7.x86_64/drivers/md/raid5.c.orig	2017-06-28 14:06:00.627299582 -0700
+++ linux-3.10.0-685.el7.x86_64/drivers/md/raid5.c	2017-06-28 14:08:01.564618793 -0700
@@ -3090,6 +3090,8 @@ 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 */
@@ -5538,6 +5540,9 @@ static bool raid5_make_request(struct md
 					 bi, 0);
 		bio_endio(bi, 0);
 	}
+
+	if (bi->bi_rw & REQ_SYNC)
+		md_wakeup_thread(mddev->thread);
 	return true;
 }