md/raid1: call free_r1bio() before allow_barrier() in raid_end_bio_io()

After allow_barrier, a concurrent raid1_reshape() will replace old mempool
and r1conf::raid_disks. Move allow_barrier() to the end of raid_end_bio_io(),
so that r1bio can be freed safely.

Reviewed-by: Yu Kuai <yukuai3@huawei.com>
Signed-off-by: Xueshi Hu <xueshi.hu@smartx.com>
Link: https://lore.kernel.org/r/20230814135356.1113639-2-xueshi.hu@smartx.com
Signed-off-by: Song Liu <song@kernel.org>

drivers/md/raid1.c

@@ -311,6 +311,7 @@ static void raid_end_bio_io(struct r1bio *r1_bio)
 {
 	struct bio *bio = r1_bio->master_bio;
 	struct r1conf *conf = r1_bio->mddev->private;
+	sector_t sector = r1_bio->sector;
 
 	/* if nobody has done the final endio yet, do it now */
 	if (!test_and_set_bit(R1BIO_Returned, &r1_bio->state)) {
@@ -321,13 +322,13 @@ static void raid_end_bio_io(struct r1bio *r1_bio)
 
 		call_bio_endio(r1_bio);
 	}
+
+	free_r1bio(r1_bio);
 	/*
 	 * Wake up any possible resync thread that waits for the device
 	 * to go idle.  All I/Os, even write-behind writes, are done.
 	 */
-	allow_barrier(conf, r1_bio->sector);
-
-	free_r1bio(r1_bio);
+	allow_barrier(conf, sector);
 }
 
 /*