btrfs: tree-checker: Remove comprehensive root owner check

mainline inclusion
from mainline-5.2-rc1
commit ff2ac107
category: bugfix
bugzilla: NA
CVE: CVE-2019-19036
---------------------------

Commit 1ba98d08 ("Btrfs: detect corruption when non-root leaf has
zero item") introduced comprehensive root owner checker.

However it's pretty expensive tree search to locate the owner root,
especially when it get reused by mandatory read and write time
tree-checker.

This patch will remove that check, and completely rely on owner based
empty leaf check, which is much faster and still works fine for most
case.

And since we skip the old root owner check, now write time tree check
can be merged with btrfs_check_leaf_full().
Signed-off-by: NQu Wenruo <wqu@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>
Conflict:
	fs/btrfs/tree-checker.c
Signed-off-by: NYufen Yu <yuyufen@huawei.com>
Reviewed-by: Nzhangyi (F) <yi.zhang@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

fs/btrfs/tree-checker.c

@@ -495,7 +495,6 @@ static int check_leaf(struct btrfs_fs_info *fs_info, struct extent_buffer *leaf,
 	 */
 	if (nritems == 0 && !btrfs_header_flag(leaf, BTRFS_HEADER_FLAG_RELOC)) {
 		u64 owner = btrfs_header_owner(leaf);
-		struct btrfs_root *check_root;
 
 		/* These trees must never be empty */
 		if (owner == BTRFS_ROOT_TREE_OBJECTID ||
@@ -509,29 +508,6 @@ static int check_leaf(struct btrfs_fs_info *fs_info, struct extent_buffer *leaf,
 				    owner);
 			return -EUCLEAN;
 		}
-		key.objectid = owner;
-		key.type = BTRFS_ROOT_ITEM_KEY;
-		key.offset = (u64)-1;
-
-		check_root = btrfs_get_fs_root(fs_info, &key, false);
-		/*
-		 * The only reason we also check NULL here is that during
-		 * open_ctree() some roots has not yet been set up.
-		 */
-		if (!IS_ERR_OR_NULL(check_root)) {
-			struct extent_buffer *eb;
-
-			eb = btrfs_root_node(check_root);
-			/* if leaf is the root, then it's fine */
-			if (leaf != eb) {
-				generic_err(fs_info, leaf, 0,
-		"invalid nritems, have %u should not be 0 for non-root leaf",
-					nritems);
-				free_extent_buffer(eb);
-				return -EUCLEAN;
-			}
-			free_extent_buffer(eb);
-		}
 		return 0;
 	}