md: stop using for_each_mddev in md_do_sync

Just do a plain list_for_each that only grabs a mddev reference in
the case where the thread sleeps and restarts the list iteration.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Logan Gunthorpe <logang@deltatee.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Song Liu <song@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/md/md.c

@@ -8723,7 +8723,6 @@ void md_do_sync(struct md_thread *thread)
 	unsigned long update_time;
 	sector_t mark_cnt[SYNC_MARKS];
 	int last_mark,m;
-	struct list_head *tmp;
 	sector_t last_check;
 	int skipped = 0;
 	struct md_rdev *rdev;
@@ -8787,7 +8786,8 @@ void md_do_sync(struct md_thread *thread)
 	try_again:
 		if (test_bit(MD_RECOVERY_INTR, &mddev->recovery))
 			goto skip;
-		for_each_mddev(mddev2, tmp) {
+		spin_lock(&all_mddevs_lock);
+		list_for_each_entry(mddev2, &all_mddevs, all_mddevs) {
 			if (mddev2 == mddev)
 				continue;
 			if (!mddev->parallel_resync
@@ -8819,7 +8819,8 @@ void md_do_sync(struct md_thread *thread)
 							desc, mdname(mddev),
 							mdname(mddev2));
 					}
-					mddev_put(mddev2);
+					spin_unlock(&all_mddevs_lock);
+
 					if (signal_pending(current))
 						flush_signals(current);
 					schedule();
@@ -8829,6 +8830,7 @@ void md_do_sync(struct md_thread *thread)
 				finish_wait(&resync_wait, &wq);
 			}
 		}
+		spin_unlock(&all_mddevs_lock);
 	} while (mddev->curr_resync < MD_RESYNC_DELAYED);
 
 	j = 0;