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([2001:b07:6468:f312:51ad:9349:1ff0:923e]) by smtp.gmail.com with ESMTPSA id h14sm9590112wml.30.2020.08.13.08.54.34 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 13 Aug 2020 08:54:34 -0700 (PDT) Subject: Re: What is bs->reqs_lock for? To: Vladimir Sementsov-Ogievskiy , qemu block References: From: Paolo Bonzini Message-ID: <2c237be3-7e28-f61a-d339-5765089fe65c@redhat.com> Date: Thu, 13 Aug 2020 17:54:33 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.9.0 MIME-Version: 1.0 In-Reply-To: Content-Language: en-US Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=pbonzini@redhat.com X-Mimecast-Spam-Score: 0.001 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=207.211.31.120; envelope-from=pbonzini@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/08/13 03:45:42 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -30 X-Spam_score: -3.1 X-Spam_bar: --- X-Spam_report: (-3.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=-0.01, RCVD_IN_MSPIKE_WL=-0.01, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham 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 , qemu-devel , Stefan Hajnoczi , Max Reitz Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 13/08/20 16:57, Vladimir Sementsov-Ogievskiy wrote: > Hi! > > Sorry my stupid question, but which kind of concurrent access > bs->reqs_lock prevents? > > In my understanding the whole logic of request tracking for the bs is > going in the coroutine, so, we don't have parallel access anyway? How > can parallel access to bs->tracked_requests happen? Different iothreads can access the same BlockDriverState, and block/io.c is not protected by the AioContext lock (in fact almost nothing, or nothing, needs it in the I/O path). Paolo