Re: [PATCH 1/8] mmput: use notifier chain to call subsystem exit handler.

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

On Wed, 2014-07-09 at 18:21 +0200, Joerg Roedel wrote:
> On Tue, Jul 08, 2014 at 05:59:58PM -0400, j.glisse@gmail.com wrote:
> >  +int mmput_register_notifier(struct notifier_block *nb)
> >  +{
> >  +        return blocking_notifier_chain_register(&mmput_notifier, nb);
> >  +}
> >  +EXPORT_SYMBOL_GPL(mmput_register_notifier);
> >  +
> >  +int mmput_unregister_notifier(struct notifier_block *nb)
> >  +{
> >  +        return blocking_notifier_chain_unregister(&mmput_notifier, nb);
> >  +}
> >  +EXPORT_SYMBOL_GPL(mmput_unregister_notifier);
>  
> I am still not convinced that this is required. For core code that 
> needs
> to hook into mmput (like aio or uprobes) it really improves code
> readability if their teardown functions are called explicitly in 
> mmput.
>  
> And drivers that deal with the mm can use the already existing
> mmu_notifers. That works at least for the AMD-IOMMUv2 and KFD 
> drivers.
>  
> Maybe HMM is different here, but then you should explain why and how 
> it
> is different and why you can't add an explicit teardown function for
> HMM.
>  
>  
>         Joerg
>  
>  
Joerg, 

It's true I'm using the callback from AMD-IOMMUv2 when it is called 
from the release notifier, but I only use that to destroy queues that 
are related to the pasid that is being unbound.
KFD driver still needs either this patch, or an explicit call to 
kfd_process_exit from mmput to release kfd_process object, which can't 
be released in the callback. I went for the explicit call but Andrew 
Morton said that this begs for converting into notifier chain. Jerome 
and I followed his advice and hence this patch.

        Oded