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=-5.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham 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 6E609C35671 for ; Sat, 22 Feb 2020 06:33:28 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id CC3CE208C3 for ; Sat, 22 Feb 2020 06:33:27 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org CC3CE208C3 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=huawei.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 355016B0003; Sat, 22 Feb 2020 01:33:27 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 305A96B0006; Sat, 22 Feb 2020 01:33:27 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 21AB26B0007; Sat, 22 Feb 2020 01:33:27 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0028.hostedemail.com [216.40.44.28]) by kanga.kvack.org (Postfix) with ESMTP id 092066B0003 for ; Sat, 22 Feb 2020 01:33:27 -0500 (EST) Received: from smtpin03.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id 9C726181AEF10 for ; Sat, 22 Feb 2020 06:33:26 +0000 (UTC) X-FDA: 76516796412.03.women63_1ddc0c8474228 X-HE-Tag: women63_1ddc0c8474228 X-Filterd-Recvd-Size: 2592 Received: from huawei.com (szxga07-in.huawei.com [45.249.212.35]) by imf34.hostedemail.com (Postfix) with ESMTP for ; Sat, 22 Feb 2020 06:33:25 +0000 (UTC) Received: from DGGEMS409-HUB.china.huawei.com (unknown [172.30.72.60]) by Forcepoint Email with ESMTP id 315C9FA8F813A2B4B96F; Sat, 22 Feb 2020 14:33:20 +0800 (CST) Received: from [127.0.0.1] (10.177.246.209) by DGGEMS409-HUB.china.huawei.com (10.3.19.209) with Microsoft SMTP Server id 14.3.439.0; Sat, 22 Feb 2020 14:33:11 +0800 Subject: Re: [PATCH v2] mm/hugetlb: fix a addressing exception caused by huge_pte_offset() To: Qian Cai CC: , , , , , , , , , "Matthew Wilcox" , Sean Christopherson , References: From: "Longpeng (Mike)" Message-ID: Date: Sat, 22 Feb 2020 14:33:10 +0800 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.7.2 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8" X-Originating-IP: [10.177.246.209] X-CFilter-Loop: Reflected Content-Transfer-Encoding: quoted-printable 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: =E5=9C=A8 2020/2/22 13:23, Qian Cai =E5=86=99=E9=81=93: >=20 >=20 >> On Feb 21, 2020, at 10:34 PM, Longpeng(Mike) wr= ote: >> >> diff --git a/mm/hugetlb.c b/mm/hugetlb.c >> index dd8737a..90daf37 100644 >> --- a/mm/hugetlb.c >> +++ b/mm/hugetlb.c >> @@ -4910,28 +4910,30 @@ pte_t *huge_pte_offset(struct mm_struct *mm, >> { >> pgd_t *pgd; >> p4d_t *p4d; >> - pud_t *pud; >> - pmd_t *pmd; >> + pud_t *pud, pud_entry; >> + pmd_t *pmd, pmd_entry; >> >> pgd =3D pgd_offset(mm, addr); >> - if (!pgd_present(*pgd)) >> + if (!pgd_present(READ_ONCE(*pgd))) >> return NULL; >> p4d =3D p4d_offset(pgd, addr); >> - if (!p4d_present(*p4d)) >> + if (!p4d_present(READ_ONCE(*p4d))) >> return NULL; >=20 > What=E2=80=99s the point of READ_ONCE() on those two places? >=20 As explained in the commit messages, it's for safe(e.g. avoid the compili= er mischief). You can also find the same usage in the ARM64's huge_pte_offse= t() in arch/arm64/mm/hugetlbpage.c --=20 Regards, Longpeng(Mike)