Btrfs: fix locking issue in btrfs_find_next_key

When walking up the tree, btrfs_find_next_key assumes the upper level tree
block is properly locked. This isn't always true even path->keep_locks is 1.
This is because btrfs_find_next_key may advance path->slots[] several times
instead of only once.

When 'path->slots[level] >= btrfs_header_nritems(path->nodes[level])' is found,
we can't guarantee the original value of 'path->slots[level]' is
'btrfs_header_nritems(path->nodes[level]) - 1'. If it's not, the tree block at
'level + 1' isn't locked.

This patch fixes the issue by explicitly checking the locking state,
re-searching the tree if it's not locked.

Signed-off-by: Yan Zheng <zheng.yan@oracle.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
index 008397934778..e71264d1c2c9 100644
--- a/fs/btrfs/relocation.c
+++ b/fs/btrfs/relocation.c
@@ -670,6 +670,8 @@ again:
                         err = ret;
                         goto out;
                 }
+                if (ret > 0 && path2->slots[level] > 0)
+                        path2->slots[level]--;
 
                 eb = path2->nodes[level];
                 WARN_ON(btrfs_node_blockptr(eb, path2->slots[level]) !=
@@ -1609,6 +1611,7 @@ static noinline_for_stack int merge_reloc_root(struct reloc_control *rc,
                 BUG_ON(level == 0);
                 path->lowest_level = level;
                 ret = btrfs_search_slot(NULL, reloc_root, &key, path, 0, 0);
+                path->lowest_level = 0;
                 if (ret < 0) {
                         btrfs_free_path(path);
                         return ret;