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    Subject[PATCH AUTOSEL 5.13 174/219] btrfs: subpage: fix false alert when relocating partial preallocated data extents
    Date
    From: Qu Wenruo <wqu@suse.com>

    [ Upstream commit e3c62324e470c0a89df966603156b34fccd01708 ]

    [BUG]
    When relocating partial preallocated data extents (part of the
    preallocated extent is written) for subpage, it can cause the following
    false alert and make the relocation to fail:

    BTRFS info (device dm-3): balance: start -d
    BTRFS info (device dm-3): relocating block group 13631488 flags data
    BTRFS warning (device dm-3): csum failed root -9 ino 257 off 4096 csum 0x98757625 expected csum 0x00000000 mirror 1
    BTRFS error (device dm-3): bdev /dev/mapper/arm_nvme-test errs: wr 0, rd 0, flush 0, corrupt 1, gen 0
    BTRFS warning (device dm-3): csum failed root -9 ino 257 off 4096 csum 0x98757625 expected csum 0x00000000 mirror 1
    BTRFS error (device dm-3): bdev /dev/mapper/arm_nvme-test errs: wr 0, rd 0, flush 0, corrupt 2, gen 0
    BTRFS info (device dm-3): balance: ended with status: -5

    The minimal script to reproduce looks like this:

    mkfs.btrfs -f -s 4k $dev
    mount $dev -o nospace_cache $mnt
    xfs_io -f -c "falloc 0 8k" $mnt/file
    xfs_io -f -c "pwrite 0 4k" $mnt/file
    btrfs balance start -d $mnt

    [CAUSE]
    Function btrfs_verify_data_csum() checks if the full range has
    EXTENT_NODATASUM bit for data reloc inode, if *all* bytes of the range
    have EXTENT_NODATASUM bit, then it skip the range.

    This works pretty well for regular sectorsize, as in that case
    btrfs_verify_data_csum() is called for each sector, thus no problem at
    all.

    But for subpage case, btrfs_verify_data_csum() is called on each bvec,
    which can contain several sectors, and since it checks *all* bytes for
    EXTENT_NODATASUM bit, if we have some range with csum, then we will
    continue checking all the sectors.

    For the preallocated sectors, it doesn't have any csum, thus obviously
    the csum won't match and cause the false alert.

    [FIX]
    Move the EXTENT_NODATASUM check into the main loop, so that we can check
    each sector for EXTENT_NODATASUM bit for subpage case.

    Signed-off-by: Qu Wenruo <wqu@suse.com>
    Signed-off-by: David Sterba <dsterba@suse.com>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    fs/btrfs/inode.c | 17 +++++++++++------
    1 file changed, 11 insertions(+), 6 deletions(-)

    diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
    index f1fd88137003..1477cd4f3eac 100644
    --- a/fs/btrfs/inode.c
    +++ b/fs/btrfs/inode.c
    @@ -3276,19 +3276,24 @@ int btrfs_verify_data_csum(struct btrfs_io_bio *io_bio, u32 bio_offset,
    if (!root->fs_info->csum_root)
    return 0;

    - if (root->root_key.objectid == BTRFS_DATA_RELOC_TREE_OBJECTID &&
    - test_range_bit(io_tree, start, end, EXTENT_NODATASUM, 1, NULL)) {
    - clear_extent_bits(io_tree, start, end, EXTENT_NODATASUM);
    - return 0;
    - }
    -
    ASSERT(page_offset(page) <= start &&
    end <= page_offset(page) + PAGE_SIZE - 1);
    for (pg_off = offset_in_page(start);
    pg_off < offset_in_page(end);
    pg_off += sectorsize, bio_offset += sectorsize) {
    + u64 file_offset = pg_off + page_offset(page);
    int ret;

    + if (root->root_key.objectid == BTRFS_DATA_RELOC_TREE_OBJECTID &&
    + test_range_bit(io_tree, file_offset,
    + file_offset + sectorsize - 1,
    + EXTENT_NODATASUM, 1, NULL)) {
    + /* Skip the range without csum for data reloc inode */
    + clear_extent_bits(io_tree, file_offset,
    + file_offset + sectorsize - 1,
    + EXTENT_NODATASUM);
    + continue;
    + }
    ret = check_data_csum(inode, io_bio, bio_offset, page, pg_off,
    page_offset(page) + pg_off);
    if (ret < 0)
    --
    2.30.2
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