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[71.184.117.43]) by smtp.gmail.com with ESMTPSA id j30sm2612022qki.96.2020.02.21.21.23.45 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 21 Feb 2020 21:23:46 -0800 (PST) Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable From: Qian Cai Mime-Version: 1.0 (1.0) Date: Sat, 22 Feb 2020 00:23:44 -0500 Subject: Re: [PATCH v2] mm/hugetlb: fix a addressing exception caused by huge_pte_offset() Message-Id: Cc: akpm@linux-foundation.org, mike.kravetz@oracle.com, kirill.shutemov@linux.intel.com, linux-kernel@vger.kernel.org, arei.gonglei@huawei.com, weidong.huang@huawei.com, weifuqiang@huawei.com, kvm@vger.kernel.org, linux-mm@kvack.org, Matthew Wilcox , Sean Christopherson , stable@vger.kernel.org To: "Longpeng(Mike)" X-Mailer: iPhone Mail (17D50) 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 Feb 21, 2020, at 10:34 PM, Longpeng(Mike) wrote:= >=20 > 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; >=20 > 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; What=E2=80=99s the point of READ_ONCE() on those two places?=