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

From: Zi Yan
Date: Tue Jan 31 2017 - 15:11:46 EST

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?


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
> ( 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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