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

David Sterba
2019-07-04T16:03:27Z

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.