diff --git a/fs/btrfs/raid56.c b/fs/btrfs/raid56.c
index 24a62224b24b1b5b307c84f38b07af31552729d7..cba5e7339462bc918d67a4e166ff4c6a87e53397 100644
--- a/fs/btrfs/raid56.c
+++ b/fs/btrfs/raid56.c
@@ -2231,12 +2231,18 @@ raid56_parity_alloc_scrub_rbio(struct btrfs_fs_info *fs_info, struct bio *bio,
 	ASSERT(!bio->bi_iter.bi_size);
 	rbio->operation = BTRFS_RBIO_PARITY_SCRUB;
 
-	for (i = 0; i < rbio->real_stripes; i++) {
+	/*
+	 * After mapping bbio with BTRFS_MAP_WRITE, parities have been sorted
+	 * to the end position, so this search can start from the first parity
+	 * stripe.
+	 */
+	for (i = rbio->nr_data; i < rbio->real_stripes; i++) {
 		if (bbio->stripes[i].dev == scrub_dev) {
 			rbio->scrubp = i;
 			break;
 		}
 	}
+	ASSERT(i < rbio->real_stripes);
 
 	/* Now we just support the sectorsize equals to page size */
 	ASSERT(fs_info->sectorsize == PAGE_SIZE);