[PATCH] md: abort the resync of raid1 there is only one device.

If raid1 decides it needs to resync it will do so even if there is only one
working device.  This is pointless.

With this patch we abort resync if there is nowhere to write to.
Signed-off-by: Neil Brown <neilb@cse.unsw.edu.au>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

drivers/md/md.c

@@ -3284,7 +3284,7 @@ static void md_do_sync(mddev_t *mddev)
 		j += sectors;
 		if (j>1) mddev->curr_resync = j;
 
-		if (last_check + window > j)
+		if (last_check + window > j || j == max_sectors)
 			continue;
 
 		last_check = j;

drivers/md/raid1.c

@@ -979,6 +979,7 @@ static int sync_request(mddev_t *mddev, sector_t sector_nr, int go_faster)
 	sector_t max_sector, nr_sectors;
 	int disk;
 	int i;
+	int write_targets = 0;
 
 	if (!conf->r1buf_pool)
 		if (init_resync(conf))
@@ -1055,12 +1056,24 @@ static int sync_request(mddev_t *mddev, sector_t sector_nr, int go_faster)
 			    sector_nr + RESYNC_SECTORS > mddev->recovery_cp)) {
 			bio->bi_rw = WRITE;
 			bio->bi_end_io = end_sync_write;
+			write_targets ++;
 		} else
 			continue;
 		bio->bi_sector = sector_nr + conf->mirrors[i].rdev->data_offset;
 		bio->bi_bdev = conf->mirrors[i].rdev->bdev;
 		bio->bi_private = r1_bio;
 	}
+	if (write_targets == 0) {
+		/* There is nowhere to write, so all non-sync
+		 * drives must be failed - so we are finished
+		 */
+		int rv = max_sector - sector_nr;
+		md_done_sync(mddev, rv, 1);
+		put_buf(r1_bio);
+		atomic_dec(&conf->mirrors[disk].rdev->nr_pending);
+		return rv;
+	}
+
 	nr_sectors = 0;
 	do {
 		struct page *page;