Date: Tue, 12 Dec 2017 13:28:01 -0800 (PST)
From: David Rientjes <rientjes@google.com>
To: Dimitri Sivanich <sivanich@hpe.com>
cc: Andrew Morton <akpm@linux-foundation.org>,
        Michal Hocko <mhocko@suse.com>, Andrea Arcangeli <aarcange@redhat.com>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>, Oded Gabbay <oded.gabbay@gmail.com>,
        Alex Deucher <alexander.deucher@amd.com>,
        =?UTF-8?Q?Christian_K=C3=B6nig?= <christian.koenig@amd.com>,
        David Airlie <airlied@linux.ie>, Joerg Roedel <joro@8bytes.org>,
        Doug Ledford <dledford@redhat.com>,
        Jani Nikula <jani.nikula@linux.intel.com>,
        Mike Marciniszyn <mike.marciniszyn@intel.com>,
        Sean Hefty <sean.hefty@intel.com>, Dimitri Sivanich <sivanich@sgi.com>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        =?UTF-8?Q?J=C3=A9r=C3=B4me_Glisse?= <jglisse@redhat.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        =?UTF-8?Q?Radim_Kr=C4=8Dm=C3=A1=C5=99?= <rkrcmar@redhat.com>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [patch 1/2] mm, mmu_notifier: annotate mmu notifiers with
 blockable invalidate callbacks
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On Tue, 12 Dec 2017, Dimitri Sivanich 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.