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Subject: Re: [PATCH v2 1/2] mm: fix race on soft-offlining free huge pages
To:     Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc:     Michal Hocko <mhocko@kernel.org>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        "xishi.qiuxishi@alibaba-inc.com" <xishi.qiuxishi@alibaba-inc.com>,
        "zy.zhengyi@alibaba-inc.com" <zy.zhengyi@alibaba-inc.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
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 <773a2f4e-c420-e973-cadd-4144730d28e8@oracle.com>
 <20180718012817.GB12184@hori1.linux.bs1.fc.nec.co.jp>
From:   Mike Kravetz <mike.kravetz@oracle.com>
Message-ID: <161a4a4c-4311-9d68-fe05-b22d7e33dd61@oracle.com>
Date:   Tue, 17 Jul 2018 19:36:47 -0700
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On 07/17/2018 06:28 PM, Naoya Horiguchi wrote:
> On Tue, Jul 17, 2018 at 01:10:39PM -0700, Mike Kravetz wrote:
>> It seems that soft_offline_free_page can be called for in use pages.
>> Certainly, that is the case in the first workflow above.  With the
>> suggested changes, I think this is OK for huge pages.  However, it seems
>> that setting HWPoison on a in use non-huge page could cause issues?
> 
> Just after dissolve_free_huge_page() returns, the target page is just a
> free buddy page without PageHWPoison set. If this page is allocated
> immediately, that's "migration succeeded, but soft offline failed" case,
> so no problem.
> Certainly, there also is a race between cheking TestSetPageHWPoison and
> page allocation, so this issue is handled in patch 2/2.

Yes, the issue of calling soft_offline_free_page() for an 'in use' page
is handled in the new routine set_hwpoison_free_buddy_page() of patch 2/2.

Thanks,
-- 
Mike Kravetz