linux-kernel - Re: [patch 1/2] mm, mmu_notifier: annotate mmu notifiers with blockable invalidate callbacks

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Date:   Thu, 14 Dec 2017 01:19:20 -0800 (PST)
From:   David Rientjes <rientjes@...gle.com>
To:     Christian König <christian.koenig@....com>
cc:     Dimitri Sivanich <sivanich@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Oded Gabbay <oded.gabbay@...il.com>,
        Alex Deucher <alexander.deucher@....com>,
        David Airlie <airlied@...ux.ie>,
        Joerg Roedel <joro@...tes.org>,
        Doug Ledford <dledford@...hat.com>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Mike Marciniszyn <mike.marciniszyn@...el.com>,
        Sean Hefty <sean.hefty@...el.com>,
        Dimitri Sivanich <sivanich@....com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [patch 1/2] mm, mmu_notifier: annotate mmu notifiers with
 blockable invalidate callbacks

On Wed, 13 Dec 2017, Christian König wrote:

> > > > --- a/drivers/misc/sgi-gru/grutlbpurge.c
> > > > +++ b/drivers/misc/sgi-gru/grutlbpurge.c
> > > > @@ -298,6 +298,7 @@ struct gru_mm_struct
> > > > *gru_register_mmu_notifier(void)
> > > >   			return ERR_PTR(-ENOMEM);
> > > >   		STAT(gms_alloc);
> > > >   		spin_lock_init(&gms->ms_asid_lock);
> > > > +		gms->ms_notifier.flags = 0;
> > > >   		gms->ms_notifier.ops = &gru_mmuops;
> > > >   		atomic_set(&gms->ms_refcnt, 1);
> > > >   		init_waitqueue_head(&gms->ms_wait_queue);
> > > > diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
> > > There is a kzalloc() just above this:
> > > 	gms = kzalloc(sizeof(*gms), GFP_KERNEL);
> > > 
> > > Is that not sufficient to clear the 'flags' field?
> > > 
> > Absolutely, but whether it is better to explicitly document that the mmu
> > notifier has cleared flags, i.e. there are no blockable callbacks, is
> > another story.  I can change it if preferred.
> 
> Actually I would invert the new flag, in other words specify that an MMU
> notifier will never sleep.
> 

Very good idea, I'll do that.  I'll also move the flags member to ops as 
Paolo suggested.

Thanks both!