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Subject: Re: [PATCH v4] mm/ksm: Fix NULL pointer dereference when KSM zero
 page is enabled
From:   Joe Perches <joe@perches.com>
To:     Kirill Tkhai <ktkhai@virtuozzo.com>,
        Markus Elfring <Markus.Elfring@web.de>,
        Andrew Morton <akpm@linux-foundation.org>,
        Muchun Song <songmuchun@bytedance.com>,
        Xiongchun Duan <duanxiongchun@bytedance.com>
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        David Hildenbrand <david@redhat.com>,
        Yang Shi <yang.shi@linux.alibaba.com>
Date:   Thu, 16 Apr 2020 13:05:54 -0700
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         <20200415195841.da4361916f662a0136a271a5@linux-foundation.org>
         <516df5d7-b514-11dc-130e-f1a2edce0108@web.de>
         <e620f913-d0fb-7d48-b6b2-d4c6b433b563@virtuozzo.com>
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On Thu, 2020-04-16 at 14:20 +0300, Kirill Tkhai wrote:
> On 16.04.2020 09:14, Markus Elfring wrote:
> > …
> > > > +++ b/mm/ksm.c
> > > > @@ -2112,8 +2112,15 @@ static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item)
> > …
> > > > +		if (vma)
> > > > +			err = try_to_merge_one_page(vma, page,
> > > > +					ZERO_PAGE(rmap_item->address));
> > > > +		else
> > > > +			/**
> > > > +			 * If the vma is out of date, we do not need to
> > > > +			 * continue.

trivia:

It's generally better to not use "/**" as that's used for kernel-doc
and this could be a single line like

+			/* If the vma is out of date, no need to continue */

> > > It's conventional to put braces around multi-line blocks such as this.

true

> > Are there different views to consider around the usage of single statements
> > together with curly brackets in if branches?

no