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SubjectRe: Incorrect uses of get_driver()/put_driver()
On Mon, 9 Jan 2012 12:35:09 -0500 (EST)
Alan Stern <> 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,

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

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