From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D8E35C33CB2 for ; Wed, 29 Jan 2020 12:13:57 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id A276920716 for ; Wed, 29 Jan 2020 12:13:57 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A276920716 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=I-love.SAKURA.ne.jp Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 270946B0005; Wed, 29 Jan 2020 07:13:57 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 220476B0006; Wed, 29 Jan 2020 07:13:57 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 0E9976B0007; Wed, 29 Jan 2020 07:13:57 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0035.hostedemail.com [216.40.44.35]) by kanga.kvack.org (Postfix) with ESMTP id E9C116B0005 for ; Wed, 29 Jan 2020 07:13:56 -0500 (EST) Received: from smtpin17.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id A3F9D4408 for ; Wed, 29 Jan 2020 12:13:56 +0000 (UTC) X-FDA: 76430563272.17.hour67_533c4743bc37 X-HE-Tag: hour67_533c4743bc37 X-Filterd-Recvd-Size: 3443 Received: from www262.sakura.ne.jp (www262.sakura.ne.jp [202.181.97.72]) by imf08.hostedemail.com (Postfix) with ESMTP for ; Wed, 29 Jan 2020 12:13:55 +0000 (UTC) Received: from fsav103.sakura.ne.jp (fsav103.sakura.ne.jp [27.133.134.230]) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTP id 00TCDiuQ097067; Wed, 29 Jan 2020 21:13:44 +0900 (JST) (envelope-from penguin-kernel@I-love.SAKURA.ne.jp) Received: from www262.sakura.ne.jp (202.181.97.72) by fsav103.sakura.ne.jp (F-Secure/fsigk_smtp/550/fsav103.sakura.ne.jp); Wed, 29 Jan 2020 21:13:44 +0900 (JST) X-Virus-Status: clean(F-Secure/fsigk_smtp/550/fsav103.sakura.ne.jp) Received: from [192.168.1.9] (softbank126040062084.bbtec.net [126.40.62.84]) (authenticated bits=0) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTPSA id 00TCDdNl097023 (version=TLSv1.2 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Wed, 29 Jan 2020 21:13:43 +0900 (JST) (envelope-from penguin-kernel@I-love.SAKURA.ne.jp) Subject: Re: [PATCH] mm/page_counter: fix various data races To: Qian Cai , Dmitry Vyukov Cc: Michal Hocko , akpm@linux-foundation.org, hannes@cmpxchg.org, elver@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20200129105224.4016-1-cai@lca.pw> <20200129120302.GJ24244@dhcp22.suse.cz> From: Tetsuo Handa Message-ID: <59f892d0-5fc4-ae32-ce65-5a688d9180c8@I-love.SAKURA.ne.jp> Date: Wed, 29 Jan 2020 21:13:37 +0900 User-Agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.4.2 MIME-Version: 1.0 In-Reply-To: <20200129120302.GJ24244@dhcp22.suse.cz> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit 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 2020/01/29 21:03, Michal Hocko wrote: >> Fixes: 3e32cb2e0a12 ("mm: memcontrol: lockless page counters") >> Signed-off-by: Qian Cai > > Acked-by: Michal Hocko Please include Reported-by: syzbot+f36cfe60b1006a94f9dc@syzkaller.appspotmail.com for https://syzkaller.appspot.com/bug?id=744097b8b91cecd8b035a6f746bb12e4efc7669f . By the way, can READ_ONCE()/WRITE_ONCE() really solve this warning? The link above says read/write on the same location ( mm/page_counter.c:129 ). I don't know how READ_ONCE()/WRITE_ONCE() can solve the race. > >> --- >> mm/page_counter.c | 8 ++++---- >> 1 file changed, 4 insertions(+), 4 deletions(-) >> >> diff --git a/mm/page_counter.c b/mm/page_counter.c >> index de31470655f6..a17841150906 100644 >> --- a/mm/page_counter.c >> +++ b/mm/page_counter.c >> @@ -82,8 +82,8 @@ void page_counter_charge(struct page_counter *counter, unsigned long nr_pages) >> * This is indeed racy, but we can live with some >> * inaccuracy in the watermark. >> */ >> - if (new > c->watermark) >> - c->watermark = new; >> + if (new > READ_ONCE(c->watermark)) >> + WRITE_ONCE(c->watermark, new); >> } >> } >> >> @@ -135,8 +135,8 @@ bool page_counter_try_charge(struct page_counter *counter, >> * Just like with failcnt, we can live with some >> * inaccuracy in the watermark. >> */ >> - if (new > c->watermark) >> - c->watermark = new; >> + if (new > READ_ONCE(c->watermark)) >> + WRITE_ONCE(c->watermark, new); >> } >> return true; >> >> -- >> 2.21.0 (Apple Git-122.2) >