md: fix two raid10 bugs

1/ When resyncing a degraded raid10 which has more than 2 copies of each block,
  garbage can get synced on top of good data.

2/ We round the wrong way in part of the device size calculation, which
  can cause confusion.
Signed-off-by: NNeil Brown <neilb@suse.de>
Cc: <stable@kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

drivers/md/raid10.c

@@ -1867,6 +1867,7 @@ static sector_t sync_request(mddev_t *mddev, sector_t sector_nr, int *skipped, i
 			int d = r10_bio->devs[i].devnum;
 			bio = r10_bio->devs[i].bio;
 			bio->bi_end_io = NULL;
+			clear_bit(BIO_UPTODATE, &bio->bi_flags);
 			if (conf->mirrors[d].rdev == NULL ||
 			    test_bit(Faulty, &conf->mirrors[d].rdev->flags))
 				continue;
@@ -2037,6 +2038,11 @@ static int run(mddev_t *mddev)
 	/* 'size' is now the number of chunks in the array */
 	/* calculate "used chunks per device" in 'stride' */
 	stride = size * conf->copies;
+
+	/* We need to round up when dividing by raid_disks to
+	 * get the stride size.
+	 */
+	stride += conf->raid_disks - 1;
 	sector_div(stride, conf->raid_disks);
 	mddev->size = stride  << (conf->chunk_shift-1);