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    SubjectRe: Incorrect uses of get_driver()/put_driver()
    On Mon, 9 Jan 2012 12:35:09 -0500 (EST)
    Alan Stern <stern@rowland.harvard.edu> wrote:

    > drivers/s390/cio/device.c:1681: drv = get_driver(&cdrv->driver);
    > drivers/s390/cio/device.c:1687: put_driver(drv);
    >
    > Martin, these calls seem to be useless. The calls in ccwgroup.c are
    > definitely useless; there's no reason to take a reference to a driver
    > while it's being unregistered, since it can't go away until the
    > unregistration is finished.

    The get_driver/put_driver in ccwgroup.c are obviously useless, the caller
    passed ccwgroup_driver_unregister a ccwgroup_driver reference.
    I am not so sure about the code in device.c. get_ccwdev_by_busid() gets
    used e.g. by vmur like this:

    static struct ccw_driver ur_driver = { .. };

    static struct urdev *urdev_get_from_devno(u16 devno)
    {
    ..
    sprintf(bus_id, "0.0.%04x", devno);
    cdev = get_ccwdev_by_busid(&ur_driver, bus_id);
    ..
    }

    static int ur_open(struct inode *inode, struct file *file)
    {
    ..
    urd = urdev_get_from_devno(devno);
    ..
    }

    For vmur we should be safe by the fact that ur_open is only possible if
    a try_module_get has been successful and the ccw_driver is unregistered
    only in the module exit function. But we have to check if this is true
    for all users of the get_ccwdev_by_busid() function.

    --
    blue skies,
    Martin.

    "Reality continues to ruin my life." - Calvin.



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