[PATCH 2/4] btrfs-progs: lowmem check: Fix function call stack overflow caused by wrong tree reloc tree detection

[Qu Wenruo <wqu@suse.com>]

For tree reloc tree root, its backref points to it self.
So for such case, we should finish the lookup.

Previous end condition is to ensure it's tree reloc tree *and* needs its
root bytenr to match the bytenr passed in.

However the @root passed in can be other tree, e.g. other tree reloc
tree which shares the node/leaf.
This makes any check based on @root passed in invalid.

The patch removes the unreliable root objectid detection, and only use
root->bytenr check.
For the possibility of invalid self-pointing backref, extent tree
checker should have already handled it, so we don't need to bother in
fs tree checker.

Fixes: 54c8f9152fd9 ("btrfs-progs: check: Fix lowmem mode stack overflow caused by fsck/023")
Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 cmds-check.c | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/cmds-check.c b/cmds-check.c
index b9943a0d3a0f..36e4a91b7e17 100644
--- a/cmds-check.c
+++ b/cmds-check.c
@@ -10251,15 +10251,10 @@ static int check_tree_block_ref(struct btrfs_root *root,
 	u32 nodesize = root->fs_info->nodesize;
 	u32 item_size;
 	u64 offset;
-	int tree_reloc_root = 0;
 	int found_ref = 0;
 	int err = 0;
 	int ret;
 
-	if (root->root_key.objectid == BTRFS_TREE_RELOC_OBJECTID &&
-	    btrfs_header_bytenr(root->node) == bytenr)
-		tree_reloc_root = 1;
-
 	btrfs_init_path(&path);
 	key.objectid = bytenr;
 	if (btrfs_fs_incompat(root->fs_info, SKINNY_METADATA))
@@ -10350,8 +10345,12 @@ static int check_tree_block_ref(struct btrfs_root *root,
 			/*
 			 * Backref of tree reloc root points to itself, no need
 			 * to check backref any more.
+			 *
+			 * This may be an error of loop backref, but extent tree
+			 * checker should have already handled it.
+			 * Here we only need to avoid infinite iteration.
 			 */
-			if (tree_reloc_root)
+			if (offset == bytenr)
 				found_ref = 1;
 			else
 			/* Check if the backref points to valid referencer */
-- 
2.15.0