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[209.85.208.169]) by smtp.gmail.com with ESMTPSA id m2sm294633lfo.194.2020.11.11.10.27.45 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 11 Nov 2020 10:27:45 -0800 (PST) Received: by mail-lj1-f169.google.com with SMTP id y16so3189410ljk.1 for ; Wed, 11 Nov 2020 10:27:45 -0800 (PST) X-Received: by 2002:a2e:8092:: with SMTP id i18mr10549600ljg.314.1605119265247; Wed, 11 Nov 2020 10:27:45 -0800 (PST) MIME-Version: 1.0 References: <0-v4-908497cf359a+4782-gup_fork_jgg@nvidia.com> In-Reply-To: <0-v4-908497cf359a+4782-gup_fork_jgg@nvidia.com> From: Linus Torvalds Date: Wed, 11 Nov 2020 10:27:29 -0800 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH v4 0/2] Add a seqcount between gup_fast and copy_page_range() To: Jason Gunthorpe Cc: Linux Kernel Mailing List , Peter Xu , "Ahmed S. Darwish" , 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 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 Tue, Nov 10, 2020 at 3:44 PM Jason Gunthorpe wrote: > > As discussed and suggested by Linus use a seqcount to close the small race > between gup_fast and copy_page_range(). > > Ahmed confirms that raw_write_seqcount_begin() is the correct API to use > in this case and it doesn't trigger any lockdeps. > > I was able to test it using two threads, one forking and the other using > ibv_reg_mr() to trigger GUP fast. Modifying copy_page_range() to sleep > made the window large enough to reliably hit to test the logic. Looks all good to me. Linus