Re: [RFD driver-core] Lifetime problems of the current driver model

Cornelia Huck
2007-03-30T19:31:01Z

On Sat, 31 Mar 2007 00:08:19 +0900,
Tejun Heo <htejun@gmail.com> wrote:

> (3) make sure all existing kobjects are released by module exit function.
>
> For example, let's say there is a hypothetical disk device /dev/dk0
> driven by a hypothetical driver mydrv. /dev/dk0 is represented like the
> following in the sysfs tree.
>
> /sys/devices/pci0000:00/0000:00:1f.0/dk0/{myknob0,myknob1}
>
> Owner of both attrs myknob0 and myknob1 is mydrv and opening either
> increases the reference counts of dk0 and mydrv and closing does the
> opposite.
>
> * When there is no opener of either knob and the /dev/dk0 isn't used by
> anyone. Reference count of dk0 is 1, mydrv 0.

Hm, but as long as dk0 is registered, it can be looked up and someone
could get a reference on it.

>
> * User issues rmmod mydrv. As mydrv's reference count is zero, unload
> proceeds and mydrv's exit function is called.
>
> * mydrv's exit function looks like the following.
>
> mydrv_exit()
> {
> sysfs_remove_file(dk0, myknob0);
> sysfs_remove_file(dk1, myknob1);
> device_del(dk0);
> deinit controller;
> release all resources;
> }
>
> The device_del(dk0) drops dk0's reference count to zero and its
> ->release is invoked immediately.

And here is the problem if someone else still has a reference. The
module will be unloaded, but ->release will not be called until the
"someone else" gives up the reference...