md/raid5-cache: in r5l_do_submit_io(), submit io->split_bio first

In r5l_do_submit_io(), it is necessary to check io->split_bio before
submit io->current_bio. This is because, endio of current_bio may
free the whole IO unit, and thus change io->split_bio.
Signed-off-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Shaohua Li <shli@fb.com>

drivers/md/raid5-cache.c

@@ -622,20 +622,30 @@ static void r5l_do_submit_io(struct r5l_log *log, struct r5l_io_unit *io)
 	__r5l_set_io_unit_state(io, IO_UNIT_IO_START);
 	spin_unlock_irqrestore(&log->io_list_lock, flags);
 
-	if (io->has_flush)
-		io->current_bio->bi_opf |= REQ_PREFLUSH;
-	if (io->has_fua)
-		io->current_bio->bi_opf |= REQ_FUA;
-	submit_bio(io->current_bio);
-
-	if (!io->split_bio)
-		return;
-
+	/*
+	 * In case of journal device failures, submit_bio will get error
+	 * and calls endio, then active stripes will continue write
+	 * process. Therefore, it is not necessary to check Faulty bit
+	 * of journal device here.
+	 *
+	 * We can't check split_bio after current_bio is submitted. If
+	 * io->split_bio is null, after current_bio is submitted, current_bio
+	 * might already be completed and the io_unit is freed. We submit
+	 * split_bio first to avoid the issue.
+	 */
+	if (io->split_bio) {
 		if (io->has_flush)
 			io->split_bio->bi_opf |= REQ_PREFLUSH;
 		if (io->has_fua)
 			io->split_bio->bi_opf |= REQ_FUA;
 		submit_bio(io->split_bio);
+	}
+
+	if (io->has_flush)
+		io->current_bio->bi_opf |= REQ_PREFLUSH;
+	if (io->has_fua)
+		io->current_bio->bi_opf |= REQ_FUA;
+	submit_bio(io->current_bio);
 }
 
 /* deferred io_unit will be dispatched here */