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SubjectRe: Incorrect uses of get_driver()/put_driver()


On Tue, 10 Jan 2012, Martin Schwidefsky wrote:

> 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.

Done.
[PATCH] cio: remove {get,put}_driver

Remove useless {get,put}_driver - the caller of the functions
has to ensure valid driver pointers.

Signed-off-by: Sebastian Ott <sebott@linux.vnet.ibm.com>
---
drivers/s390/cio/ccwgroup.c | 2 --
drivers/s390/cio/device.c | 8 +-------
2 files changed, 1 insertion(+), 9 deletions(-)

--- a/drivers/s390/cio/ccwgroup.c
+++ b/drivers/s390/cio/ccwgroup.c
@@ -580,7 +580,6 @@ void ccwgroup_driver_unregister(struct c
struct device *dev;

/* We don't want ccwgroup devices to live longer than their driver. */
- get_driver(&cdriver->driver);
while ((dev = driver_find_device(&cdriver->driver, NULL, NULL,
__ccwgroup_match_all))) {
struct ccwgroup_device *gdev = to_ccwgroupdev(dev);
@@ -592,7 +591,6 @@ void ccwgroup_driver_unregister(struct c
mutex_unlock(&gdev->reg_mutex);
put_device(dev);
}
- put_driver(&cdriver->driver);
driver_unregister(&cdriver->driver);
}
EXPORT_SYMBOL(ccwgroup_driver_unregister);
--- a/drivers/s390/cio/device.c
+++ b/drivers/s390/cio/device.c
@@ -1676,15 +1676,9 @@ struct ccw_device *get_ccwdev_by_busid(s
const char *bus_id)
{
struct device *dev;
- struct device_driver *drv;

- drv = get_driver(&cdrv->driver);
- if (!drv)
- return NULL;
-
- dev = driver_find_device(drv, NULL, (void *)bus_id,
+ dev = driver_find_device(&cdrv->driver, NULL, (void *)bus_id,
__ccwdev_check_busid);
- put_driver(drv);

return dev ? to_ccwdev(dev) : NULL;
}


>
> --
> blue skies,
> Martin.
>
> "Reality continues to ruin my life." - Calvin.
>
> --
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