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([2001:b07:6468:f312:75e3:aaa7:77d6:f4e4]) by smtp.gmail.com with ESMTPSA id 189sm3961554wmb.3.2020.09.30.10.46.33 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 30 Sep 2020 10:46:35 -0700 (PDT) Subject: Re: [PATCH 08/10] scsi/scsi_bus: Add scsi_device_get To: Maxim Levitsky , qemu-devel@nongnu.org References: <20200925172604.2142227-1-pbonzini@redhat.com> <20200925172604.2142227-9-pbonzini@redhat.com> <0d124b6991e607e496da4afa39027320e617aa0e.camel@redhat.com> From: Paolo Bonzini Message-ID: <67859d7f-5293-a11e-add3-f93893dfa7af@redhat.com> Date: Wed, 30 Sep 2020 19:46:32 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.11.0 MIME-Version: 1.0 In-Reply-To: <0d124b6991e607e496da4afa39027320e617aa0e.camel@redhat.com> Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=pbonzini@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=63.128.21.124; envelope-from=pbonzini@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/09/30 00:31:59 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -25 X-Spam_score: -2.6 X-Spam_bar: -- X-Spam_report: (-2.6 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.469, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, 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: Stefan Hajnoczi , stefanha@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 30/09/20 16:32, Maxim Levitsky wrote: >> Compared to Maxim's patch, I am avoiding the extra argument >> to do_scsi_device_find by moving the RCU_READ_LOCK_GUARD() >> out of do_scsi_device_find itself. > Which is a good idea, although my mindset was like, I got a device, > lets just grab a ref to it before it disappears and then do > whatever I want. Understood, but "I got a device, I know I'm under RCU so it can't disappear" is more efficient and just as common. This also explains the difference in patch 7. Paolo