md: raid1: check rdev before reference in raid1_sync_request func

BugLink: https://bugs.launchpad.net/bugs/1859640

[ Upstream commit 028288df ]

In raid1_sync_request func, rdev should be checked before reference.
Signed-off-by: Zhiqiang Liu <liuzhiqiang26@huawei.com>
Signed-off-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Connor Kuehl <connor.kuehl@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

drivers/md/raid1.c

@@ -2630,7 +2630,7 @@ static sector_t sync_request(struct mddev *mddev, sector_t sector_nr, int *skipp
 				write_targets++;
 			}
 		}
-		if (bio->bi_end_io) {
+		if (rdev && bio->bi_end_io) {
 			atomic_inc(&rdev->nr_pending);
 			bio->bi_iter.bi_sector = sector_nr + rdev->data_offset;
 			bio->bi_bdev = rdev->bdev;