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

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Message-ID: <20190523193959.GA5658@redhat.com>
Date:   Thu, 23 May 2019 15:39:59 -0400
From:   Jerome Glisse <jglisse@...hat.com>
To:     Jason Gunthorpe <jgg@...pe.ca>
Cc:     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 Thu, May 23, 2019 at 04:10:38PM -0300, Jason Gunthorpe wrote:
> 
> On Thu, May 23, 2019 at 02:24:58PM -0400, Jerome Glisse wrote:
> > I can not take mmap_sem in range_register, the READ_ONCE is fine and
> > they are no race as we do take a reference on the hmm struct thus
> 
> Of course there are use after free races with a READ_ONCE scheme, I
> shouldn't have to explain this.

Well i can not think of anything again here the mm->hmm can not
change while driver is calling hmm_range_register() so if you
want i can remove the READ_ONCE() this does not change anything.


> If you cannot take the read mmap sem (why not?), then please use my
> version and push the update to the driver through -mm..

Please see previous threads on why it was a failure.

Cheers,
Jérôme