linux-kernel - Re: [PATCH 3/7] mm/hmm: fix race between hmm_mirror_unregister() and mmu

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Date:   Fri, 31 Aug 2018 00:14:46 +1000
From:   Balbir Singh <bsingharora@...il.com>
To:     jglisse@...hat.com
Cc:     linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org,
        Ralph Campbell <rcampbell@...dia.com>, stable@...r.kernel.org
Subject: Re: [PATCH 3/7] mm/hmm: fix race between hmm_mirror_unregister() and
 mmu_notifier callback

On Fri, Aug 24, 2018 at 03:25:45PM -0400, jglisse@...hat.com wrote:
> From: Ralph Campbell <rcampbell@...dia.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@...dia.com>
> Reviewed-by: John Hubbard <jhubbard@...dia.com>
> Reviewed-by: Jérôme Glisse <jglisse@...hat.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: stable@...r.kernel.org

Reviewed-by: Balbir Singh <bsingharora@...il.com>