linux-kernel - Re: [RFC][PATCH v1 02/11] mm: soft-offline: add missing error check of set_hwpoison_free_buddy

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Date:   Wed, 14 Nov 2018 14:23:52 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     Naoya Horiguchi <n-horiguchi@...jp.nec.com>
Cc:     "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Michal Hocko <mhocko@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        "xishi.qiuxishi@...baba-inc.com" <xishi.qiuxishi@...baba-inc.com>,
        Laurent Dufour <ldufour@...ux.vnet.ibm.com>
Subject: Re: [RFC][PATCH v1 02/11] mm: soft-offline: add missing error check
 of set_hwpoison_free_buddy_page()



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.