btrfs: handle unexpected exact match in btrfs_set_inode_index_count()

We search with offset (u64)-1 which should never match exactly.
Previously the code silently returned success without setting the index
count. Now logs an error and return -EUCLEAN instead.

Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Adarsh Das <adarshdas950@gmail.com>
Reviewed-by: David Sterba <dsterba@suse.com>,
Signed-off-by: David Sterba <dsterba@suse.com>

Author: Saphereye

fs/btrfs/inode.c

@@ -6149,9 +6149,18 @@ static int btrfs_set_inode_index_count(struct btrfs_inode *inode)
 	ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
 	if (ret < 0)
 		return ret;
-	/* FIXME: we should be able to handle this */
-	if (ret == 0)
-		return ret;
+
+	if (unlikely(ret == 0)) {
+		/*
+		 * Key with offset -1 found, there would have to exist a dir
+		 * index item with such offset, but this is out of the valid
+		 * range.
+		 */
+		btrfs_err(root->fs_info,
+			  "unexpected exact match for DIR_INDEX key, inode %llu",
+			  btrfs_ino(inode));
+		return -EUCLEAN;
+	}
 
 	if (path->slots[0] == 0) {
 		inode->index_cnt = BTRFS_DIR_START_INDEX;