Btrfs: fix repair code for RAID10

btrfs_map_block sets mirror_num, so that the repair code knows eventually
which device gave us the read error. For RAID10, mirror_num must be 1 or 2.
Before this fix mirror_num was incorrectly related to our stripe index.

Signed-off-by: Jan Schmidt <list.btrfs@jan-o-sch.net>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 2 insertions, 1 deletions

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 3b984173d25b..1411b99555a4 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -3807,10 +3807,11 @@ static int __btrfs_map_block(struct btrfs_mapping_tree *map_tree, int rw,
                 else if (mirror_num)
                         stripe_index += mirror_num - 1;
                 else {
+                        int old_stripe_index = stripe_index;
                         stripe_index = find_live_mirror(map, stripe_index,
                                               map->sub_stripes, stripe_index +
                                               current->pid % map->sub_stripes);
-                        mirror_num = stripe_index + 1;
+                        mirror_num = stripe_index - old_stripe_index + 1;
                 }
         } else {
                 /*