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

[Tejun Heo <htejun@gmail.com>]

Tejun Heo wrote:
> Cornelia Huck wrote:
>> 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.
> 
> Yeah, exactly.  That's why any getting any kobject reference backed by a
> module must be accompanied by try_module_get().
> 
> int mydrv_get_dk(struct dk *dk)
> {
> 	rc = try_module_get(mydrv);
> 	if (rc)
> 		return rc;
> 	kobject_get(&dk->kobj);
> 	return 0;
> }

And one more thing just in case.  In the above code, try_module_get()
and kobject_get() must be and is atomic w.r.t. try_stop_module().
That's why we do the following.

  stop_machine_run(__try_stop_module, &sref, NR_CPUS);.

-- 
tejun