md: Fix read balancing in RAID1 and RAID10 on drives > 2TB

read_balance uses a "unsigned long" for a sector number which
will get truncated beyond 2TB.
This will cause read-balancing to be non-optimal, and can cause
data to be read from the 'wrong' branch during a resync.  This has a
very small chance of returning wrong data.

Reported-by: Jordan Russell <jr-list-2010@quo.to>
Cc: stable@kernel.org
Signed-off-by: NeilBrown <neilb@suse.de>

1 files changed, 2 insertions, 2 deletions

diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
index 1db02c4955a9..a9b9972ff703 100644
--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -418,7 +418,7 @@ static void raid1_end_write_request(struct bio *bio, int error)
  */
 static int read_balance(conf_t *conf, r1bio_t *r1_bio)
 {
-        const unsigned long this_sector = r1_bio->sector;
+        const sector_t this_sector = r1_bio->sector;
         int new_disk = conf->last_used, disk = new_disk;
         int wonly_disk = -1;
         const int sectors = r1_bio->sectors;
@@ -434,7 +434,7 @@ static int read_balance(conf_t *conf, r1bio_t *r1_bio)
  retry:
         if (conf->mddev->recovery_cp < MaxSector &&
             (this_sector + sectors >= conf->next_resync)) {
-                /* Choose the first operation device, for consistancy */
+                /* Choose the first operational device, for consistancy */
                 new_disk = 0;
 
                 for (rdev = rcu_dereference(conf->mirrors[new_disk].rdev);