Date: Tue, 29 Aug 2017 14:04:26 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Laurent Dufour <ldufour@linux.vnet.ibm.com>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>,
        paulmck@linux.vnet.ibm.com, akpm@linux-foundation.org,
        ak@linux.intel.com, mhocko@kernel.org, dave@stgolabs.net, jack@suse.cz,
        Matthew Wilcox <willy@infradead.org>, benh@kernel.crashing.org,
        mpe@ellerman.id.au, paulus@samba.org,
        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
        hpa@zytor.com, Will Deacon <will.deacon@arm.com>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        haren@linux.vnet.ibm.com, khandual@linux.vnet.ibm.com,
        npiggin@gmail.com, bsingharora@gmail.com,
        Tim Chen <tim.c.chen@linux.intel.com>, linuxppc-dev@lists.ozlabs.org,
        x86@kernel.org
Subject: Re: [PATCH v2 14/20] mm: Provide speculative fault infrastructure
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On Tue, Aug 29, 2017 at 09:59:30AM +0200, Laurent Dufour wrote:
> On 27/08/2017 02:18, Kirill A. Shutemov wrote:
> >> +
> >> +	if (unlikely(!vma->anon_vma))
> >> +		goto unlock;
> > 
> > It deserves a comment.
> 
> You're right I'll add it in the next version.
> For the record, the root cause is that __anon_vma_prepare() requires the
> mmap_sem to be held because vm_next and vm_prev must be safe.

But should that test not be:

	if (unlikely(vma_is_anonymous(vma) && !vma->anon_vma))
		goto unlock;

Because !anon vmas will never have ->anon_vma set and you don't want to
exclude those.