linux-kernel - Re: [PATCHv2 1/2] mm: Fix vma_is

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Message-ID: <20180712163916.pzewd3nhane7af3u@kshutemo-mobl1>
Date:   Thu, 12 Jul 2018 19:39:16 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Oleg Nesterov <oleg@...hat.com>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Andrea Arcangeli <aarcange@...hat.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCHv2 1/2] mm: Fix vma_is_anonymous() false-positives

On Thu, Jul 12, 2018 at 06:20:39PM +0200, Oleg Nesterov wrote:
> Kirill, I am not trying to review this change (but it looks good to me),
> just a silly question...
> 
> On 07/12, Kirill A. Shutemov wrote:
> >
> > This can be fixed by assigning anonymous VMAs own vm_ops and not relying
> > on it being NULL.
> 
> I agree, this makes sense, but...
> 
> > If ->mmap() failed to set ->vm_ops, mmap_region() will set it to
> > dummy_vm_ops.
> 
> Shouldn't this change alone fix the problem?

Unfortunately, no. I've tried it before. Mapping /dev/zero with
MAP_PRIVATE hast to produce anonymous VMA. The trick with dummy_vm_ops
wouldn't be able to handle the situation.

-- 
 Kirill A. Shutemov