linux-kernel - Re: [PATCH v2 00/12] mm: page migration enhancement for thp

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Message-ID: <5890EB58.3050100@cs.rutgers.edu>
Date:   Tue, 31 Jan 2017 13:54:00 -0600
From:   Zi Yan <zi.yan@...rutgers.edu>
To:     Anshuman Khandual <khandual@...ux.vnet.ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
CC:     <linux-mm@...ck.org>, Hugh Dickins <hughd@...gle.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Michal Hocko <mhocko@...nel.org>,
        "Vlastimil Babka" <vbabka@...e.cz>,
        Pavel Emelyanov <xemul@...allels.com>,
        Balbir Singh <bsingharora@...il.com>,
        <linux-kernel@...r.kernel.org>,
        Naoya Horiguchi <nao.horiguchi@...il.com>
Subject: Re: [PATCH v2 00/12] mm: page migration enhancement for thp

I am also doing some tests on THP migration and discover that there are
some corner cases not handled in this patchset.

For example, in handle_mm_fault, without taking pmd_lock, the kernel may
see pmd_none(*pmd) during THP migrations, which leads to
handle_pte_fault or even deeper in the code path. At that moment,
pmd_trans_unstable() will treat a pmd_migration_entry as pmd_bad and
clear it. This leads to application crashing and page table leaks, since
a deposited PTE page is not released when the application crashes.

Even after I add is_pmd_migration_entry() into pmd_trans_unstable(), I
still see application data corruptions.

I hope someone can shed some light on how to debug this. Should I also
look into pmd_trans_huge() call sites where pmd_migration_entry should
be handled differently?

Thanks.

Anshuman Khandual wrote:
> On 11/08/2016 05:01 AM, Naoya Horiguchi wrote:
>> Hi everyone,
>>
>> I've updated thp migration patches for v4.9-rc2-mmotm-2016-10-27-18-27
>> with feedbacks for ver.1.
> 
> Hello Noaya,
> 
> I have been working with Zi Yan on the parallel huge page migration series
> (https://lkml.org/lkml/2016/11/22/457) and planning to post them on top of
> this THP migration enhancement series. Hence we were wondering if you have
> plans to post a new version of this series in near future ?
> 
> Regards
> Anshuman
> 

-- 
Best Regards,
Yan Zi

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