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    Subject[PATCH 4.19 080/276] Btrfs: fix data bytes_may_use underflow with fallocate due to failed quota reserve
    Date
    [ Upstream commit 39ad317315887c2cb9a4347a93a8859326ddf136 ]

    When doing fallocate, we first add the range to the reserve_list and
    then reserve the quota. If quota reservation fails, we'll release all
    reserved parts of reserve_list.

    However, cur_offset is not updated to indicate that this range is
    already been inserted into the list. Therefore, the same range is freed
    twice. Once at list_for_each_entry loop, and once at the end of the
    function. This will result in WARN_ON on bytes_may_use when we free the
    remaining space.

    At the end, under the 'out' label we have a call to:

    btrfs_free_reserved_data_space(inode, data_reserved, alloc_start, alloc_end - cur_offset);

    The start offset, third argument, should be cur_offset.

    Everything from alloc_start to cur_offset was freed by the
    list_for_each_entry_safe_loop.

    Fixes: 18513091af94 ("btrfs: update btrfs_space_info's bytes_may_use timely")
    Reviewed-by: Filipe Manana <fdmanana@suse.com>
    Signed-off-by: Robbie Ko <robbieko@synology.com>
    Signed-off-by: David Sterba <dsterba@suse.com>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    fs/btrfs/file.c | 3 ++-
    1 file changed, 2 insertions(+), 1 deletion(-)

    diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
    index de4d3baec1616..e24c0a69ff5d4 100644
    --- a/fs/btrfs/file.c
    +++ b/fs/btrfs/file.c
    @@ -3161,6 +3161,7 @@ static long btrfs_fallocate(struct file *file, int mode,
    ret = btrfs_qgroup_reserve_data(inode, &data_reserved,
    cur_offset, last_byte - cur_offset);
    if (ret < 0) {
    + cur_offset = last_byte;
    free_extent_map(em);
    break;
    }
    @@ -3210,7 +3211,7 @@ static long btrfs_fallocate(struct file *file, int mode,
    /* Let go of our reservation. */
    if (ret != 0 && !(mode & FALLOC_FL_ZERO_RANGE))
    btrfs_free_reserved_data_space(inode, data_reserved,
    - alloc_start, alloc_end - cur_offset);
    + cur_offset, alloc_end - cur_offset);
    extent_changeset_free(data_reserved);
    return ret;
    }
    --
    2.20.1


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