Re: [PATCH 1/6] mmput: use notifier chain to call subsystem exit handler.

["Gabbay, Oded" <Oded.Gabbay@amd.com>]

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On Fri, 2014-07-04 at 01:15 +0200, Joerg Roedel wrote:
> Hi Jerome,
> 
> On Thu, Jul 03, 2014 at 02:30:26PM -0400, Jerome Glisse wrote:
> > Joerg do you still object to this patch ?
> 
> Yes.
> 
> > Again the natural place to call this is from mmput and the fact that many
> > other subsystem already call in from there to cleanup there own per mm data
> > structure is a testimony that this is a valid use case and valid design.
> 
> Device drivers are something different than subsystems. 
I think that hsa (kfd) and hmm _are_ subsystems, if not in definition
than in practice. Our model is not a classic device-driver model in the
sense that our ioctl's are more like syscalls than traditional
device-driver ioctls. e.g our kfd_open() doesn't open a kfd device or
even a gpu device, it *binds* a *process* to a device. So basically, our
ioctls are not related to a specific H/W instance (specific GPU in case
of kfd) but more related to a specific process.

Once we can agree on that, than I think we can agree that kfd and hmm
can and should be bounded to mm struct and not file descriptors.

	Oded

> I think the
> point that the mmu_notifier struct can not be freed in the .release
> call-back is a weak reason for introducing a new notifier. In the end
> every user of mmu_notifiers has to call mmu_notifier_register somewhere
> (file-open/ioctl path or somewhere else where the mm<->device binding is
>  set up) and can call mmu_notifier_unregister in a similar path which
> destroys the binding.
> 
> > You pointed out that the cleanup should be done from the device driver file
> > close call. But as i stressed some of the new user will not necessarily have
> > a device file open hence no way for them to free the associated structure
> > except with hackish delayed job.
> 
> Please tell me more about these 'new users', how does mm<->device binding
> is set up there if no fd is used?
> 
> 
> 	Joerg
> 
> 

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