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[156.34.55.100]) by smtp.gmail.com with ESMTPSA id b1sm15328088qkk.8.2019.08.08.06.05.26 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Thu, 08 Aug 2019 06:05:26 -0700 (PDT) Received: from jgg by mlx.ziepe.ca with local (Exim 4.90_1) (envelope-from ) id 1hvi6f-0003Ih-LV; Thu, 08 Aug 2019 10:05:25 -0300 Date: Thu, 8 Aug 2019 10:05:25 -0300 From: Jason Gunthorpe To: Jason Wang Cc: mst@redhat.com, kvm@vger.kernel.org, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH V4 7/9] vhost: do not use RCU to synchronize MMU notifier with worker Message-ID: <20190808130525.GA1989@ziepe.ca> References: <20190807070617.23716-1-jasowang@redhat.com> <20190807070617.23716-8-jasowang@redhat.com> <20190807120738.GB1557@ziepe.ca> <1000f8a3-19a9-0383-61e5-ba08ddc9fcba@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <1000f8a3-19a9-0383-61e5-ba08ddc9fcba@redhat.com> User-Agent: Mutt/1.9.4 (2018-02-28) 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 Thu, Aug 08, 2019 at 08:54:54PM +0800, Jason Wang wrote: > I don't have any objection to convert  to spinlock() but just want to > know if any case that the above smp_mb() + counter looks good to you? This email is horribly mangled, but I don't think mixing smb_mb() and smp_load_acquire() would be considerd a best-practice, and using smp_store_release() instead would be the wrong barrier. spinlock does seem to be the only existing locking primitive that does what is needed here. Jason