Re: [PATCH v2] btrfs: inode: Don't compress if NODATASUM or NODATACOW set

[David Sterba <dsterba@suse.cz>]

On Mon, Jul 01, 2019 at 05:12:46AM +0000, Qu Wenruo wrote:
> As btrfs(5) specified:
> 
> 	Note
> 	If nodatacow or nodatasum are enabled, compression is disabled.
> 
> If NODATASUM or NODATACOW set, we should not compress the extent.
> 
> Normally NODATACOW is detected properly in run_delalloc_range() so
> compression won't happen for NODATACOW.
> 
> However for NODATASUM we don't have any check, and it can cause
> compressed extent without csum pretty easily, just by:
>   mkfs.btrfs -f $dev
>   mount $dev $mnt -o nodatasum
>   touch $mnt/foobar
>   mount -o remount,datasum,compress $mnt
>   xfs_io -f -c "pwrite 0 128K" $mnt/foobar
> 
> And in fact, we have a bug report about corrupted compressed extent
> without proper data checksum so even RAID1 can't recover the corruption.
> (https://bugzilla.kernel.org/show_bug.cgi?id=199707)
> 
> Running compression without proper checksum could cause more damage when
> corruption happens, as compressed data could make the whole extent
> unreadable, so there is no need to allow compression for
> NODATACSUM.
> 
> The fix will refactor the inode compression check into two parts:
> - inode_can_compress()
>   As the hard requirement, checked at btrfs_run_delalloc_range(), so no
>   compression will happen for NODATASUM inode at all.
> 
> - inode_need_compress()
>   As the soft requirement, checked at btrfs_run_delalloc_range() and
>   compress_file_range().
> 
> Reported-by: James Harvey <jamespharvey20@gmail.com>
> Signed-off-by: Qu Wenruo <wqu@suse.com>
> ---
> Changelog:
> v2:
> - Refactor inode_need_compress() into two functions
> - Refactor inode_need_compress() to return bool
> ---
>  fs/btrfs/inode.c | 38 ++++++++++++++++++++++++++++++++------
>  1 file changed, 32 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> index a2aabdb85226..be1cabf35680 100644
> --- a/fs/btrfs/inode.c
> +++ b/fs/btrfs/inode.c
> @@ -394,24 +394,49 @@ static noinline int add_async_extent(struct async_chunk *cow,
>  	return 0;
>  }
>  
> -static inline int inode_need_compress(struct inode *inode, u64 start, u64 end)
> +/*
> + * Check if the inode can accept compression.
> + *
> + * This checks for the hard requirement of compression, including CoW and
> + * checksum requirement.
> + */
> +static inline bool inode_can_compress(struct inode *inode)
> +{
> +	if (BTRFS_I(inode)->flags & BTRFS_INODE_NODATACOW ||
> +	    BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM)
> +		return false;
> +	return true;
> +}
> +
> +/*
> + * Check if the inode need compression.
> + *
> + * This checks for the soft requirement of compression.
> + */
> +static inline bool inode_need_compress(struct inode *inode, u64 start, u64 end)
>  {
>  	struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
>  
> +	if (!inode_can_compress(inode)) {
> +		WARN(IS_ENABLED(CONFIG_BTRFS_DEBUG),
> +			KERN_ERR "BTRFS: unexpected compression for ino %llu\n",
> +			btrfs_ino(BTRFS_I(inode)));
> +		return false;
> +	}
>  	/* force compress */
>  	if (btrfs_test_opt(fs_info, FORCE_COMPRESS))
> -		return 1;
> +		return true;
>  	/* defrag ioctl */
>  	if (BTRFS_I(inode)->defrag_compress)
> -		return 1;
> +		return true;
>  	/* bad compression ratios */
>  	if (BTRFS_I(inode)->flags & BTRFS_INODE_NOCOMPRESS)
> -		return 0;
> +		return false;
>  	if (btrfs_test_opt(fs_info, COMPRESS) ||
>  	    BTRFS_I(inode)->flags & BTRFS_INODE_COMPRESS ||
>  	    BTRFS_I(inode)->prop_compress)
>  		return btrfs_compress_heuristic(inode, start, end);
> -	return 0;
> +	return false;
>  }
>  
>  static inline void inode_should_defrag(struct btrfs_inode *inode,
> @@ -1630,7 +1655,8 @@ int btrfs_run_delalloc_range(struct inode *inode, struct page *locked_page,
>  	} else if (BTRFS_I(inode)->flags & BTRFS_INODE_PREALLOC && !force_cow) {
>  		ret = run_delalloc_nocow(inode, locked_page, start, end,
>  					 page_started, 0, nr_written);
> -	} else if (!inode_need_compress(inode, start, end)) {
> +	} else if (!inode_can_compress(inode) ||
> +		   !inode_need_compress(inode, start, end)) {

Well, that's not excatly what I expected, but because this is an
important fix I won't object now and add it to 5.3 queue.