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    Subject[PATCH AUTOSEL 4.14 50/57] s390/dasd/cio: Interpret ccw_device_get_mdc return value correctly
    Date
    From: Jan Höppner <hoeppner@linux.ibm.com>

    [ Upstream commit dd4b3c83b9efac10d48a94c61372119fc555a077 ]

    The max data count (mdc) is an unsigned 16-bit integer value as per AR
    documentation and is received via ccw_device_get_mdc() for a specific
    path mask from the CIO layer. The function itself also always returns a
    positive mdc value or 0 in case mdc isn't supported or couldn't be
    determined.

    Though, the comment for this function describes a negative return value
    to indicate failures.

    As a result, the DASD device driver interprets the return value of
    ccw_device_get_mdc() incorrectly. The error case is essentially a dead
    code path.

    To fix this behaviour, check explicitly for a return value of 0 and
    change the comment for ccw_device_get_mdc() accordingly.

    This fix merely enables the error code path in the DASD functions
    get_fcx_max_data() and verify_fcx_max_data(). The actual functionality
    stays the same and is still correct.

    Reviewed-by: Cornelia Huck <cohuck@redhat.com>
    Signed-off-by: Jan Höppner <hoeppner@linux.ibm.com>
    Acked-by: Peter Oberparleiter <oberpar@linux.ibm.com>
    Reviewed-by: Stefan Haberland <sth@linux.ibm.com>
    Signed-off-by: Stefan Haberland <sth@linux.ibm.com>
    Signed-off-by: Jens Axboe <axboe@kernel.dk>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    drivers/s390/block/dasd_eckd.c | 9 +++++----
    drivers/s390/cio/device_ops.c | 2 +-
    2 files changed, 6 insertions(+), 5 deletions(-)

    diff --git a/drivers/s390/block/dasd_eckd.c b/drivers/s390/block/dasd_eckd.c
    index 0d5e2d92e05b..81359312a987 100644
    --- a/drivers/s390/block/dasd_eckd.c
    +++ b/drivers/s390/block/dasd_eckd.c
    @@ -1133,7 +1133,8 @@ static u32 get_fcx_max_data(struct dasd_device *device)
    {
    struct dasd_eckd_private *private = device->private;
    int fcx_in_css, fcx_in_gneq, fcx_in_features;
    - int tpm, mdc;
    + unsigned int mdc;
    + int tpm;

    if (dasd_nofcx)
    return 0;
    @@ -1147,7 +1148,7 @@ static u32 get_fcx_max_data(struct dasd_device *device)
    return 0;

    mdc = ccw_device_get_mdc(device->cdev, 0);
    - if (mdc < 0) {
    + if (mdc == 0) {
    dev_warn(&device->cdev->dev, "Detecting the maximum supported data size for zHPF requests failed\n");
    return 0;
    } else {
    @@ -1158,12 +1159,12 @@ static u32 get_fcx_max_data(struct dasd_device *device)
    static int verify_fcx_max_data(struct dasd_device *device, __u8 lpm)
    {
    struct dasd_eckd_private *private = device->private;
    - int mdc;
    + unsigned int mdc;
    u32 fcx_max_data;

    if (private->fcx_max_data) {
    mdc = ccw_device_get_mdc(device->cdev, lpm);
    - if ((mdc < 0)) {
    + if (mdc == 0) {
    dev_warn(&device->cdev->dev,
    "Detecting the maximum data size for zHPF "
    "requests failed (rc=%d) for a new path %x\n",
    diff --git a/drivers/s390/cio/device_ops.c b/drivers/s390/cio/device_ops.c
    index b22922ec32d1..474afec9ab87 100644
    --- a/drivers/s390/cio/device_ops.c
    +++ b/drivers/s390/cio/device_ops.c
    @@ -595,7 +595,7 @@ EXPORT_SYMBOL(ccw_device_tm_start_timeout);
    * @mask: mask of paths to use
    *
    * Return the number of 64K-bytes blocks all paths at least support
    - * for a transport command. Return values <= 0 indicate failures.
    + * for a transport command. Return value 0 indicates failure.
    */
    int ccw_device_get_mdc(struct ccw_device *cdev, u8 mask)
    {
    --
    2.20.1
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