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Darwish" CC: , Peter Xu , Linus Torvalds , Andrea Arcangeli , Andrew Morton , Aneesh Kumar K.V , Christoph Hellwig , Hugh Dickins , Jan Kara , Jann Horn , John Hubbard , Kirill Shutemov , Kirill Tkhai , Leon Romanovsky , Linux-MM , Michal Hocko , Oleg Nesterov , Peter Zijlstra , "Sebastian A. Siewior" , Thomas Gleixner Subject: Re: [PATCH v3 2/2] mm: prevent gup_fast from racing with COW during fork Message-ID: <20201106175746.GX2620339@nvidia.com> References: <0-v3-7358966cab09+14e9-gup_fork_jgg@nvidia.com> <2-v3-7358966cab09+14e9-gup_fork_jgg@nvidia.com> <20201106171716.GA91138@lx-t490> Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <20201106171716.GA91138@lx-t490> X-ClientProxiedBy: BL1PR13CA0132.namprd13.prod.outlook.com (2603:10b6:208:2bb::17) To DM6PR12MB3834.namprd12.prod.outlook.com (2603:10b6:5:14a::12) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from mlx.ziepe.ca (156.34.48.30) by BL1PR13CA0132.namprd13.prod.outlook.com (2603:10b6:208:2bb::17) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3541.10 via Frontend Transport; Fri, 6 Nov 2020 17:57:48 +0000 Received: from jgg by mlx with local (Exim 4.94) (envelope-from ) id 1kb5ze-000zjP-KK; Fri, 06 Nov 2020 13:57:46 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=nvidia.com; s=n1; t=1604685468; bh=184A0uGen3xJsMOZmccGj5t8ejNJlm+rWx4fnc4CqoQ=; h=ARC-Seal:ARC-Message-Signature:ARC-Authentication-Results:Date: From:To:CC:Subject:Message-ID:References:Content-Type: Content-Disposition:In-Reply-To:X-ClientProxiedBy:MIME-Version: X-MS-Exchange-MessageSentRepresentingType; b=WoKyQ0hD11UFDKnq9UfSuicd+r05JgeaD60wIOQrr19Qdr0eMBoVg9XBSIdnoEry9 x0DITrVDuxGalkms//MnzkUUa2XjAOLBpMP03KSNvz3zaYfS6OkOb12QME1AolW6cs BGNa/0pfS4Ft2qmCUvNfvUX/ODnfn6Bykorg6CT1fEEZCzQxcx5LWbDaJyEYuIVERH RtLqJ9BugzB8OcaJDSx/QT7hnYZQHujoPXHCXiHlaG24rQ1/j6gxPvNmIyU9EqZmfz 2ORlJpnB1sp9du1SrQTgmoOCI5Tz6XKUp2levc42pJ5X6GiywsvlYCP6N8FweVBdTG YfGp15/5+FraQ== 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 Fri, Nov 06, 2020 at 06:17:16PM +0100, Ahmed S. Darwish wrote: > Hi Jason, > > On Fri, Nov 06, 2020 at 11:55:14AM -0400, Jason Gunthorpe wrote: > ... > > + if (gup_flags & FOLL_PIN) { > > + seq = raw_read_seqcount(¤t->mm->write_protect_seq); > > + if (seq & 1) > > + return 0; > > + } > > + > ... > > + if (gup_flags & FOLL_PIN) { > > + if (read_seqcount_t_retry(¤t->mm->write_protect_seq, > > + seq)) { > > + unpin_user_pages(pages, nr_pinned); > > + return 0; > > + } > > + } > > From seqlock.h: > > /** > * raw_read_seqcount() - read the raw seqcount_t counter value > * ... > * Return: count to be passed to read_seqcount_retry() > */ > #define raw_read_seqcount(s) > > Please avoid using the internal API (read_seqcount_*t*_retry) and just > use read_seqcount_retry() as the documentation suggests. Oh, yes I didn't notice this one in all the discussion that spawned from the first thread. Thanks Jason