Re: [PATCH] btrfs: pass a valid btrfs_tree_parent_check when possible

[Boris Burkov <boris@bur.io>]

On Fri, Apr 10, 2026 at 08:46:40AM +0930, Qu Wenruo wrote:
> Commit 6e181cfe2409 ("btrfs: revalidate cached tree blocks on the
> uptodate path") introduced the @check parameter for
> btrfs_buffer_uptodate() to allow re-validation of a cached extent
> buffer.
> 
> But there are still call sites that doesn't utilize this parameter,
> which exposes them to possible corrupted tree blocks, e.g. an empty
> child leaf of a parent node, which should be rejected by
> btrfs_verify_level_key() but if @check is NULL such check will be
> skipped and cause problems.
> 
> Thankfully for a lot of cases there is already an existing @check
> structure around and we can pass it directly to btrfs_buffer_uptodate().
> 
Reviewed-by: Boris Burkov <boris@bur.io>
> Signed-off-by: Qu Wenruo <wqu@suse.com>
> ---
>  fs/btrfs/ctree.c       | 16 +++++-----------
>  fs/btrfs/extent-tree.c | 11 ++++++++---
>  fs/btrfs/extent_io.c   |  2 +-
>  3 files changed, 14 insertions(+), 15 deletions(-)
> 
> diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
> index d70da290bedf..829d8be7f423 100644
> --- a/fs/btrfs/ctree.c
> +++ b/fs/btrfs/ctree.c
> @@ -1497,17 +1497,11 @@ read_block_for_search(struct btrfs_root *root, struct btrfs_path *p,
>  		if (p->reada == READA_FORWARD_ALWAYS)
>  			reada_for_search(fs_info, p, parent_level, slot, key->objectid);
>  
> -		/* first we do an atomic uptodate check */
> -		if (btrfs_buffer_uptodate(tmp, check.transid, NULL) > 0) {
> -			/*
> -			 * Do extra check for first_key, eb can be stale due to
> -			 * being cached, read from scrub, or have multiple
> -			 * parents (shared tree blocks).
> -			 */
> -			if (unlikely(btrfs_verify_level_key(tmp, &check))) {
> -				ret = -EUCLEAN;
> -				goto out;
> -			}
> +		/* Check if the cached eb is uptodate. */
> +		ret = btrfs_buffer_uptodate(tmp, check.transid, &check);
> +		if (unlikely(ret < 0))
> +			goto out;
> +		if (ret > 0) {
>  			*eb_ret = tmp;
>  			tmp = NULL;
>  			ret = 0;
> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
> index 391fad41c3b6..5d5b42ea4ade 100644
> --- a/fs/btrfs/extent-tree.c
> +++ b/fs/btrfs/extent-tree.c
> @@ -5781,16 +5781,21 @@ static int check_next_block_uptodate(struct btrfs_trans_handle *trans,
>  
>  	generation = btrfs_node_ptr_generation(path->nodes[level], path->slots[level]);
>  
> -	if (btrfs_buffer_uptodate(next, generation, NULL))
> -		return 0;
> -
>  	check.level = level - 1;
>  	check.transid = generation;
>  	check.owner_root = btrfs_root_id(root);
>  	check.has_first_key = true;
>  	btrfs_node_key_to_cpu(path->nodes[level], &check.first_key, path->slots[level]);
>  
> +	ret = btrfs_buffer_uptodate(next, generation, &check);
> +	if (ret > 0)
> +		return 0;
>  	btrfs_tree_unlock(next);
> +	if (ret < 0) {
> +		free_extent_buffer(next);
> +		return ret;
> +	}
> +
>  	if (level == 1)
>  		reada_walk_down(trans, root, wc, path);
>  	ret = btrfs_read_extent_buffer(next, &check);
> diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
> index a8887285deda..3f59fb0a9ee5 100644
> --- a/fs/btrfs/extent_io.c
> +++ b/fs/btrfs/extent_io.c
> @@ -4648,7 +4648,7 @@ void btrfs_readahead_tree_block(struct btrfs_fs_info *fs_info,
>  	if (IS_ERR(eb))
>  		return;
>  
> -	if (btrfs_buffer_uptodate(eb, gen, NULL)) {
> +	if (btrfs_buffer_uptodate(eb, gen, &check)) {
>  		free_extent_buffer(eb);
>  		return;
>  	}
> -- 
> 2.53.0
>