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Wed, 16 Jun 2021 08:41:04 +0800 (CST) Subject: Re: [PATCH v1 2/6] mm/hwpoison: remove race consideration To: =?UTF-8?B?SE9SSUdVQ0hJIE5BT1lBKOWggOWPoyDnm7TkuZ8p?= Cc: Naoya Horiguchi , "linux-mm@kvack.org" , Andrew Morton , David Hildenbrand , Oscar Salvador , Michal Hocko , Tony Luck , "Aneesh Kumar K.V" , "linux-kernel@vger.kernel.org" References: <20210614021212.223326-1-nao.horiguchi@gmail.com> <20210614021212.223326-3-nao.horiguchi@gmail.com> <25c69dc8-0ce2-8330-dfb0-506481dc9a53@sangfor.com.cn> <20210616001141.GA1924716@hori.linux.bs1.fc.nec.co.jp> From: Ding Hui Message-ID: <7b8f576b-b61b-ad68-c84b-476c96f89156@sangfor.com.cn> Date: Wed, 16 Jun 2021 08:40:58 +0800 User-Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <20210616001141.GA1924716@hori.linux.bs1.fc.nec.co.jp> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US X-HM-Spam-Status: e1kfGhgUHx5ZQUtXWQgYFAkeWUFZS1VLWVdZKFlBSE83V1ktWUFJV1kPCR oVCBIfWUFZQh1JGFYeTU4dTx5PQ0hPGktVEwETFhoSFyQUDg9ZV1kWGg8SFR0UWUFZT0tIVUpKS0 hKQ1VLWQY+ X-HM-Sender-Digest: e1kMHhlZQR0aFwgeV1kSHx4VD1lBWUc6OFE6Qgw4HT8LTk8QKkw2EwI3 KxgwFENVSlVKTUlIQ0tPS01MSENCVTMWGhIXVR8SFRwTDhI7CBoVHB0UCVUYFBZVGBVFWVdZEgtZ QVlKSk1VSU9VTk1VTE1ZV1kIAVlBSEJCQjcG X-HM-Tid: 0a7a1243bd0f2c17kusn944cee0193 Content-Transfer-Encoding: quoted-printable Authentication-Results: imf01.hostedemail.com; dkim=none; spf=pass (imf01.hostedemail.com: domain of dinghui@sangfor.com.cn designates 115.236.118.208 as permitted sender) smtp.mailfrom=dinghui@sangfor.com.cn; dmarc=pass (policy=none) header.from=sangfor.com.cn X-Stat-Signature: x1sx4xfty3ujfbjuhjqeh91r3wkpocsh X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 486495001533 X-HE-Tag: 1623804061-103380 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 2021/6/16 8:11, HORIGUCHI NAOYA(=E5=A0=80=E5=8F=A3 =E7=9B=B4=E4=B9=9F)= wrote: > On Tue, Jun 15, 2021 at 08:57:06PM +0800, Ding Hui wrote: >> On 2021/6/14 10:12, Naoya Horiguchi wrote: >>> @@ -1956,17 +1938,6 @@ int unpoison_memory(unsigned long pfn) >>> goto unlock_mutex; >>> } >>> - /* >>> - * unpoison_memory() can encounter thp only when the thp is being >>> - * worked by memory_failure() and the page lock is not held yet. >>> - * In such case, we yield to memory_failure() and make unpoison fai= l. >>> - */ >>> - if (!PageHuge(page) && PageTransHuge(page)) { >>> - unpoison_pr_info("Unpoison: Memory failure is now running on %#lx\= n", >>> - pfn, &unpoison_rs); >>> - goto unlock_mutex; >>> - } >>> - >> >> if a huge page is in process of alloc or free, HUGETLB_PAGE_DTOR can b= e set >> after __SetPageHead() or be cleared before __ClearPageHead(), so this >> condition may be true in racy. >=20 > Hi Ding, >=20 > We confirm PageHWPoison() before reaching this if-block and hwpoisoned = pages > are prohibited from allocation, so it seems to me that this check never > races with hugetlb allocation. >=20 > And according to the original patch introduced this if-block (0cea3fdc4= 16d: > "mm/hwpoison: fix race against poison thp"), this if-block intended to = close > the race between memory_failure() and unpoison_memory(), so that's no l= onger > necessary due to mf_mutex. >=20 I got it and thanks for your explanation. >> Do we need the racy test for this situation? >=20 > I'm not sure, but I think that we need more stress/fuzz testing focusin= g on > this subsystem, and "unpoison vs allocation" race can be covered in the= topic. >=20 > Thank you, > Naoya Horiguchi >=20 --=20 Thanks, - Ding Hui