linux-kernel - Re: [PATCH v4 0/1] Use HMM for ODP v4

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Date:   Wed, 22 May 2019 18:06:49 -0400
From:   Jerome Glisse <jglisse@...hat.com>
To:     Ralph Campbell <rcampbell@...dia.com>
Cc:     Jason Gunthorpe <jgg@...pe.ca>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, linux-rdma@...r.kernel.org,
        Leon Romanovsky <leonro@...lanox.com>,
        Doug Ledford <dledford@...hat.com>,
        Artemy Kovalyov <artemyko@...lanox.com>,
        Moni Shoua <monis@...lanox.com>,
        Mike Marciniszyn <mike.marciniszyn@...el.com>,
        Kaike Wan <kaike.wan@...el.com>,
        Dennis Dalessandro <dennis.dalessandro@...el.com>
Subject: Re: [PATCH v4 0/1] Use HMM for ODP v4

On Wed, May 22, 2019 at 02:12:31PM -0700, Ralph Campbell wrote:
> 
> On 5/22/19 1:12 PM, Jason Gunthorpe wrote:
> > On Wed, May 22, 2019 at 01:48:52PM -0400, Jerome Glisse wrote:
> > 
> > >   static void put_per_mm(struct ib_umem_odp *umem_odp)
> > >   {
> > >   	struct ib_ucontext_per_mm *per_mm = umem_odp->per_mm;
> > > @@ -325,9 +283,10 @@ static void put_per_mm(struct ib_umem_odp *umem_odp)
> > >   	up_write(&per_mm->umem_rwsem);
> > >   	WARN_ON(!RB_EMPTY_ROOT(&per_mm->umem_tree.rb_root));
> > > -	mmu_notifier_unregister_no_release(&per_mm->mn, per_mm->mm);
> > > +	hmm_mirror_unregister(&per_mm->mirror);
> > >   	put_pid(per_mm->tgid);
> > > -	mmu_notifier_call_srcu(&per_mm->rcu, free_per_mm);
> > > +
> > > +	kfree(per_mm);
> > 
> > Notice that mmu_notifier only uses SRCU to fence in-progress ops
> > callbacks, so I think hmm internally has the bug that this ODP
> > approach prevents.
> > 
> > hmm should follow the same pattern ODP has and 'kfree_srcu' the hmm
> > struct, use container_of in the mmu_notifier callbacks, and use the
> > otherwise vestigal kref_get_unless_zero() to bail:
> 
> You might also want to look at my patch where
> I try to fix some of these same issues (5/5).
> 
> https://marc.info/?l=linux-mm&m=155718572908765&w=2

I need to review the patchset but i do not want to invert referencing
ie having mm hold reference on hmm. Will review tommorrow. I wanted to
do that today but did not had time.