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Subject: Re: [RFC][PATCH v1 02/11] mm: soft-offline: add missing error check
 of set_hwpoison_free_buddy_page()
To:     Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc:     "linux-mm@kvack.org" <linux-mm@kvack.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Michal Hocko <mhocko@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        "xishi.qiuxishi@alibaba-inc.com" <xishi.qiuxishi@alibaba-inc.com>,
        Laurent Dufour <ldufour@linux.vnet.ibm.com>
References: <1541746035-13408-1-git-send-email-n-horiguchi@ah.jp.nec.com>
 <1541746035-13408-3-git-send-email-n-horiguchi@ah.jp.nec.com>
 <9ea93154-4843-231d-d72b-bf12c8807c24@arm.com>
 <20181113001652.GA5945@hori1.linux.bs1.fc.nec.co.jp>
From:   Anshuman Khandual <anshuman.khandual@arm.com>
Message-ID: <ffbc7a7e-58c3-742c-2bae-8cd4cf1e6aa8@arm.com>
Date:   Wed, 14 Nov 2018 14:23:52 +0530
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On 11/13/2018 05:46 AM, Naoya Horiguchi wrote:
> Hi Anshuman,
> 
> On Fri, Nov 09, 2018 at 03:50:41PM +0530, Anshuman Khandual wrote:
>>
>> On 11/09/2018 12:17 PM, Naoya Horiguchi wrote:
>>> set_hwpoison_free_buddy_page() could fail, then the target page is
>>> finally not isolated, so it's better to report -EBUSY for userspace
>>> to know the failure and chance of retry.
>>>
>> IIUC set_hwpoison_free_buddy_page() could only fail if the page is not
>> free in the buddy. At least for soft_offline_huge_page() that wont be
>> the case otherwise dissolve_free_huge_page() would have returned non
>> zero -EBUSY. Is there any other reason set_hwpoison_free_buddy_page()
>> would not succeed ?
> There is a race window between page freeing (after successful soft-offline
> -> page migration case) and the containment by set_hwpoison_free_buddy_page().
> Or a target page can be allocated just after get_any_page() decided that
> the target page is a free page.
> So set_hwpoison_free_buddy_page() would safely fail in such cases.

Makes sense. Thanks.