kobj->state_initialized is never set to 0

kobj->state_initialized is never set to 0

[Helen Koike]

Hi,

I am simulating hotplugging a platform device (to the
media/platform/vimc driver), so I register it using
platform_device_register, then I unregister it with
platform_device_unregister, then I register it again, but the code
doesn't allow me to register something that was registered before due
to this line:

    https://github.com/torvalds/linux/blob/master/lib/kobject.c#L334

The variable kobj->state_initialized is set to 1 at

    https://github.com/torvalds/linux/blob/master/lib/kobject.c#L194

but it is never set to 0 again.

Is this how it is supposed to work? Or kobj->state_initialized is set
to 0 somewhere else I couldn't find?

Thanks
Helen

kobj->state_initialized is never set to 0

[Greg KH]

On Fri, Jul 20, 2018 at 03:33:22PM -0300, Helen Koike wrote:
> Hi,
> 
> I am simulating hotplugging a platform device (to the
> media/platform/vimc driver), so I register it using
> platform_device_register, then I unregister it with
> platform_device_unregister, then I register it again, but the code
> doesn't allow me to register something that was registered before due
> to this line:
> 
>     https://github.com/torvalds/linux/blob/master/lib/kobject.c#L334
> 
> The variable kobj->state_initialized is set to 1 at
> 
>     https://github.com/torvalds/linux/blob/master/lib/kobject.c#L194
> 
> but it is never set to 0 again.

Yes, do not do that, that is why we wrote that code.  Never "recycle" a
struct device, or a kobject, as you never really know if it is still in
use or not.  That is why it needs to be dynamically created, not
statically created.

> Is this how it is supposed to work? Or kobj->state_initialized is set
> to 0 somewhere else I couldn't find?

Nope, don't do this please.  Again, never recycle these objects, bad
things will happen as the code is not designed to do that for good
reasons (think object lifetimes, you do not control them fully, other
things do which you have no control over.)

hope this helps,

greg k-h

kobj->state_initialized is never set to 0

[Helen Koike]

On Fri, Jul 20, 2018 at 3:39 PM, Greg KH <greg@kroah.com> wrote:
> On Fri, Jul 20, 2018 at 03:33:22PM -0300, Helen Koike wrote:
>> Hi,
>>
>> I am simulating hotplugging a platform device (to the
>> media/platform/vimc driver), so I register it using
>> platform_device_register, then I unregister it with
>> platform_device_unregister, then I register it again, but the code
>> doesn't allow me to register something that was registered before due
>> to this line:
>>
>>     https://github.com/torvalds/linux/blob/master/lib/kobject.c#L334
>>
>> The variable kobj->state_initialized is set to 1 at
>>
>>     https://github.com/torvalds/linux/blob/master/lib/kobject.c#L194
>>
>> but it is never set to 0 again.
>
> Yes, do not do that, that is why we wrote that code.  Never "recycle" a
> struct device, or a kobject, as you never really know if it is still in
> use or not.  That is why it needs to be dynamically created, not
> statically created.
>
>> Is this how it is supposed to work? Or kobj->state_initialized is set
>> to 0 somewhere else I couldn't find?
>
> Nope, don't do this please.  Again, never recycle these objects, bad
> things will happen as the code is not designed to do that for good
> reasons (think object lifetimes, you do not control them fully, other
> things do which you have no control over.)
>
> hope this helps,
>
> greg k-h

Yes, this helps a lot, thank you!

Helen