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Date:   Wed, 24 Oct 2018 16:10:47 -0700
From:   Andrew Morton <akpm@linux-foundation.org>
To:     jglisse@redhat.com
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        Ralph Campbell <rcampbell@nvidia.com>, stable@vger.kernel.org
Subject: Re: [PATCH 3/6] mm/hmm: fix race between hmm_mirror_unregister()
 and mmu_notifier callback
Message-Id: <20181024161047.cd979d1c3da115844182de3b@linux-foundation.org>
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        <20181019160442.18723-4-jglisse@redhat.com>
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On Fri, 19 Oct 2018 12:04:39 -0400 jglisse@redhat.com wrote:

> From: Ralph Campbell <rcampbell@nvidia.com>
> 
> In hmm_mirror_unregister(), mm->hmm is set to NULL and then
> mmu_notifier_unregister_no_release() is called. That creates a small
> window where mmu_notifier can call mmu_notifier_ops with mm->hmm equal
> to NULL. Fix this by first unregistering mmu notifier callbacks and
> then setting mm->hmm to NULL.
> 
> Similarly in hmm_register(), set mm->hmm before registering mmu_notifier
> callbacks so callback functions always see mm->hmm set.
> 
> Signed-off-by: Ralph Campbell <rcampbell@nvidia.com>
> Reviewed-by: John Hubbard <jhubbard@nvidia.com>
> Reviewed-by: Jérôme Glisse <jglisse@redhat.com>
> Reviewed-by: Balbir Singh <bsingharora@gmail.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: stable@vger.kernel.org

I added your Signed-off-by: to this one.  It's required since you were
on the patch delivery path.