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    Subject[PATCH 4.20 44/88] direct-io: allow direct writes to empty inodes
    Date
    4.20-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    [ Upstream commit 8b9433eb4de3c26a9226c981c283f9f4896ae030 ]

    On a DIO_SKIP_HOLES filesystem, the ->get_block() method is currently
    not allowed to create blocks for an empty inode. This confusion comes
    from trying to bit shift a negative number, so check the size of the
    inode first.

    The problem is most visible for hfsplus, because the fallback to
    buffered I/O doesn't happen and the write fails with EIO. This is in
    part the fault of the module, because it gives a wrong return value on
    ->get_block(); that will be fixed in a separate patch.

    Reviewed-by: Jeff Moyer <jmoyer@redhat.com>
    Reviewed-by: Jan Kara <jack@suse.cz>
    Signed-off-by: Ernesto A. Fernández <ernesto.mnd.fernandez@gmail.com>
    Signed-off-by: Jens Axboe <axboe@kernel.dk>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    fs/direct-io.c | 5 +++--
    1 file changed, 3 insertions(+), 2 deletions(-)

    diff --git a/fs/direct-io.c b/fs/direct-io.c
    index 41a0e97252aed..7d3f2c1d141dc 100644
    --- a/fs/direct-io.c
    +++ b/fs/direct-io.c
    @@ -679,6 +679,7 @@ static int get_more_blocks(struct dio *dio, struct dio_submit *sdio,
    unsigned long fs_count; /* Number of filesystem-sized blocks */
    int create;
    unsigned int i_blkbits = sdio->blkbits + sdio->blkfactor;
    + loff_t i_size;

    /*
    * If there was a memory error and we've overwritten all the
    @@ -708,8 +709,8 @@ static int get_more_blocks(struct dio *dio, struct dio_submit *sdio,
    */
    create = dio->op == REQ_OP_WRITE;
    if (dio->flags & DIO_SKIP_HOLES) {
    - if (fs_startblk <= ((i_size_read(dio->inode) - 1) >>
    - i_blkbits))
    + i_size = i_size_read(dio->inode);
    + if (i_size && fs_startblk <= (i_size - 1) >> i_blkbits)
    create = 0;
    }

    --
    2.19.1


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