Btrfs: fix btrfs_search_slot_for_read backwards iteration

If the current path's leaf slot is 0, we do search for the previous
leaf (via btrfs_prev_leaf) and set the new path's leaf slot to a
value corresponding to the number of items - 1 of the former leaf.
Fix this by using the slot set by btrfs_prev_leaf, decrementing it
by 1 if it's equal to the leaf's number of items.

Use of btrfs_search_slot_for_read() for backward iteration is used in
particular by the send feature, which could miss items when the input
leaf has less items than its previous leaf.

This could be reproduced by running btrfs/007 from xfstests in a loop.

Signed-off-by: Filipe David Borba Manana <fdmanana@gmail.com>
Signed-off-by: Chris Mason <clm@fb.com>

diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
index 30f5b11d7dd35cb34cd1bae5b02a208f466460cf..cbd3a7d6fa681acfc0b00cb515fcddbcf8880f49 100644 (file)
--- a/fs/btrfs/ctree.c
+++ b/fs/btrfs/ctree.c
@@ -3142,7 +3142,9 @@ again:
                        if (ret < 0)
                                return ret;
                        if (!ret) {
-                               p->slots[0] = btrfs_header_nritems(leaf) - 1;
+                               leaf = p->nodes[0];
+                               if (p->slots[0] == btrfs_header_nritems(leaf))
+                                       p->slots[0]--;
                                return 0;
                        }
                        if (!return_any)