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([2001:b07:6468:f312:5e2c:eb9a:a8b6:fd3e]) by smtp.googlemail.com with ESMTPSA id h2sm1906975edq.61.2021.05.28.04.01.23 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 28 May 2021 04:01:24 -0700 (PDT) Subject: Re: [PATCH v2 7/7] block-copy: protect BlockCopyState .method fields From: Paolo Bonzini To: Vladimir Sementsov-Ogievskiy , Emanuele Giuseppe Esposito , qemu-block@nongnu.org References: <20210518100757.31243-1-eesposit@redhat.com> <20210518100757.31243-8-eesposit@redhat.com> <404e2891-9c03-bc7d-2c69-a572422d7804@virtuozzo.com> <4403ee17-0c12-c545-7f64-683bb9057b91@redhat.com> <47ae4243-5a4b-e3a5-44fb-48c689f8bc77@virtuozzo.com> <867d0357-1032-f56d-dbed-bd646ce8ec00@redhat.com> Message-ID: Date: Fri, 28 May 2021 13:01:23 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.10.1 MIME-Version: 1.0 In-Reply-To: <867d0357-1032-f56d-dbed-bd646ce8ec00@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=2a00:1450:4864:20::62b; envelope-from=paolo.bonzini@gmail.com; helo=mail-ej1-x62b.google.com X-Spam_score_int: -14 X-Spam_score: -1.5 X-Spam_bar: - X-Spam_report: (-1.5 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_EF=-0.1, FREEMAIL_FORGED_FROMDOMAIN=0.25, FREEMAIL_FROM=0.001, HEADER_FROM_DIFFERENT_DOMAINS=0.25, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Kevin Wolf , John Snow , qemu-devel@nongnu.org, Stefan Hajnoczi , Max Reitz Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 28/05/21 12:24, Paolo Bonzini wrote: > > It's still more complicated, because you need to add some kind of > >     method = s->method; This would even have to be a separate, one-line critical section... Paolo >     ret = block_copy_do_copy(..., method); >     if (ret < 0 && method <= COPY_RANGE_SMALL) { >         method = COPY_RANGE_READ_WRITE; >         ret = block_copy_do_copy(..., method); >         } >     lock(); >         if (method == s->method) { >             /* compute new method */ >         } > > which makes it more complicated than this patch IMO.  But yeah at least > it's a viable alternative to the atomics.