linux-kernel - Re: [mm 4.15-rc8] Random oopses under memory pressure.

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Message-ID: <4a6681a7-5ed6-ad9c-5d1d-73f1fcc82f3d@linux.intel.com>
Date:   Thu, 18 Jan 2018 06:38:10 -0800
From:   Dave Hansen <dave.hansen@...ux.intel.com>
To:     "Kirill A. Shutemov" <kirill@...temov.name>,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc:     torvalds@...ux-foundation.org, kirill.shutemov@...ux.intel.com,
        akpm@...ux-foundation.org, hannes@...xchg.org,
        iamjoonsoo.kim@....com, mgorman@...hsingularity.net,
        tony.luck@...el.com, vbabka@...e.cz, mhocko@...nel.org,
        aarcange@...hat.com, hillf.zj@...baba-inc.com, hughd@...gle.com,
        oleg@...hat.com, peterz@...radead.org, riel@...hat.com,
        srikar@...ux.vnet.ibm.com, vdavydov.dev@...il.com,
        mingo@...nel.org, linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        x86@...nel.org
Subject: Re: [mm 4.15-rc8] Random oopses under memory pressure.

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.

WARN_ON_ONCE(page_to_section(pvmw->page) !=
	     page_to_section(pte_page(*pvmw->pte));

Will detect that.