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[209.85.167.42]) by smtp.gmail.com with ESMTPSA id 78sm2797001lfe.196.2020.11.02.14.40.05 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 02 Nov 2020 14:40:06 -0800 (PST) Received: by mail-lf1-f42.google.com with SMTP id 184so19560573lfd.6 for ; Mon, 02 Nov 2020 14:40:05 -0800 (PST) X-Received: by 2002:ac2:52ad:: with SMTP id r13mr6025281lfm.534.1604356805454; Mon, 02 Nov 2020 14:40:05 -0800 (PST) MIME-Version: 1.0 References: <0-v2-dfe9ecdb6c74+2066-gup_fork_jgg@nvidia.com> <20201102221945.GA48454@lx-t490> In-Reply-To: <20201102221945.GA48454@lx-t490> From: Linus Torvalds Date: Mon, 2 Nov 2020 14:39:49 -0800 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH v2 0/2] Add a seqcount between gup_fast and copy_page_range() To: "Ahmed S. Darwish" Cc: Jason Gunthorpe , Linux Kernel Mailing List , Peter Xu , 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 , Ingo Molnar , Will Deacon , Thomas Gleixner , Sebastian Siewior Content-Type: text/plain; charset="UTF-8" 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 Mon, Nov 2, 2020 at 2:19 PM Ahmed S. Darwish wrote: > > Disabling preemption for seqcount_t write-side critical sections was > never a new requirement. It has always been this way, for the reasons > explained at Documentation/locking/seqlock.rst, "Introduction" section. Note that that is only true if you spin on the reading side (either of the two kinds of spinning: (a) spinning to wait for it to become even, or (b) repeating if they don't match) Which this code doesn't do, it just fails. I'm not sure how to perhaps document that. Linus