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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Thu, 18 Jan 2018 08:58:31 -0800
Message-ID: <CA+55aFzN5+S6c=J+nudHfcwidANejGQL9NkX2yF-hr5upM+gag@mail.gmail.com>
Subject: Re: [mm 4.15-rc8] Random oopses under memory pressure.
To:     Dave Hansen <dave.hansen@linux.intel.com>
Cc:     "Kirill A. Shutemov" <kirill@shutemov.name>,
        Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Mel Gorman <mgorman@techsingularity.net>,
        Tony Luck <tony.luck@intel.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        Michal Hocko <mhocko@kernel.org>,
        Andrea Arcangeli <aarcange@redhat.com>,
        "hillf.zj" <hillf.zj@alibaba-inc.com>,
        Hugh Dickins <hughd@google.com>,
        Oleg Nesterov <oleg@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Rik van Riel <riel@redhat.com>,
        Srikar Dronamraju <srikar@linux.vnet.ibm.com>,
        Vladimir Davydov <vdavydov.dev@gmail.com>,
        Ingo Molnar <mingo@kernel.org>,
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        linux-mm <linux-mm@kvack.org>,
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On Thu, Jan 18, 2018 at 6:38 AM, Dave Hansen
<dave.hansen@linux.intel.com> wrote:
> On 01/18/2018 05:12 AM, Kirill A. Shutemov wrote:
>> -             if (pte_page(*pvmw->pte) - pvmw->page >=
>> -                             hpage_nr_pages(pvmw->page)) {
>
> Is ->pte guaranteed to map a page which is within the same section as
> pvmw->page?  Otherwise, with sparsemem (non-vmemmap), the pointer
> arithmetic won't work.

Lovely.

Finally a reason for this bug that actually seems to make sense.

Thanks guys.

Tetsuo - does Kirill's latest patch fix this for you? The one with

    Subject: [PATCH] mm, page_vma_mapped: Fix pointer arithmetics in check_pte()

in the body of the email? I'm really hoping it does, since this seems
to make sense.

             Linus