Re: [PATCH 1/7] btrfs: Don't call readpage_end_io_hook for the btree inode

[David Sterba <dsterba@suse.cz>]

On Fri, Sep 18, 2020 at 04:34:33PM +0300, Nikolay Borisov wrote:
> Instead of relying on indirect calls to implement metadata buffer
> validation simply check if the inode whose page we are processing equals
> the btree inode. If it does call the necessary function.
> 
> This is an improvement in 2 directions:
> 1. We aren't paying the penalty of indirect calls in a post-speculation
>    attacks world.
> 
> 2. The function is now named more explicitly so it's obvious what's
>    going on

The new naming is not making things clear, btrfs_check_csum sounds very
generic while it does a very specific thing just by the number and type
of the parameters. Similar for btrfs_validate_metadata_buffer.

> --- a/fs/btrfs/extent_io.c
> +++ b/fs/btrfs/extent_io.c
> @@ -2851,9 +2851,12 @@ static void end_bio_extent_readpage(struct bio *bio)
>  
>  		mirror = io_bio->mirror_num;
>  		if (likely(uptodate)) {
> -			ret = tree->ops->readpage_end_io_hook(io_bio, offset,
> -							      page, start, end,
> -							      mirror);
> +			if (data_inode)
> +				ret = btrfs_check_csum(io_bio, offset, page,
> +						       start, end, mirror);
> +			else
> +				ret = btrfs_validate_metadata_buffer(io_bio,
> +					offset, page, start, end, mirror);

In the context where the functions are used I'd expect some symmetry,
data/metadata. Something like btrfs_validate_data_bio.