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Mon, 03 Oct 2022 14:32:32 -0700 (PDT) Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (Mac OS X Mail 16.0 \(3696.120.41.1.1\)) Subject: Re: [PATCH 1/3] mm/hugetlb: Fix race condition of uffd missing/minor handling From: Nadav Amit In-Reply-To: Date: Mon, 3 Oct 2022 14:32:31 -0700 Cc: LKML , Linux MM , Andrea Arcangeli , Mike Rapoport , David Hildenbrand , Andrew Morton , Axel Rasmussen , Mike Kravetz Content-Transfer-Encoding: quoted-printable Message-Id: <568C0BF2-28B9-438C-93D2-19130FAA3364@gmail.com> References: <20221003155630.469263-1-peterx@redhat.com> <20221003155630.469263-2-peterx@redhat.com> To: Peter Xu X-Mailer: Apple Mail (2.3696.120.41.1.1) ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1664832754; a=rsa-sha256; cv=none; b=t9vRMa67OmlSE4rUjh0E/E2Zj9cn2WL4khKhlRveslGGVCz/IEh1EMJaWY363VDWDUoCU1 DpWYZO/VPSQkqiI5lRm9Ou8HyK9zet4iaZCbZWgQ0Lxo/qsheCm9sSkN9IwyA4W7sfFH/3 B4ChELq9XZUMhry0IzVObTC42Di4BHY= ARC-Authentication-Results: i=1; imf07.hostedemail.com; dkim=pass header.d=gmail.com header.s=20210112 header.b=JjwHslh0; 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dmarc=pass (policy=none) header.from=gmail.com X-Stat-Signature: 96byytxhoyopkd7xujaehuthacx1amh4 X-HE-Tag: 1664832754-143209 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 Oct 3, 2022, at 2:16 PM, Peter Xu wrote: > On Mon, Oct 03, 2022 at 02:00:36PM -0700, Nadav Amit wrote: >> On Oct 3, 2022, at 8:56 AM, Peter Xu wrote: >>=20 >>> + */ >>> + if (hugetlb_pte_stable(h, mm, ptep, old_pte)) >>> + ret =3D hugetlb_handle_userfault( >>> + vma, mapping, idx, flags, haddr, >>> + address, VM_UFFD_MISSING); >>> + else >>> + /* Retry the fault */ >>> + ret =3D 0; >>=20 >> Might be unrelated, but at least for the sake of consistency if not >> potential GUP issues, don=E2=80=99t you want to return VM_FAULT_RETRY = ? >=20 > VM_FAULT_RETRY implies releasing of mmap sem, while we didn't? Of course. My bad.