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[73.241.217.19]) by smtp.gmail.com with ESMTPSA id a30sm258527pfr.87.2020.06.29.09.56.50 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 29 Jun 2020 09:56:51 -0700 (PDT) Subject: Re: [PATCH] scsi: sd: add runtime pm to open / release To: Alan Stern , Martin Kepplinger Cc: jejb@linux.ibm.com, Can Guo , martin.petersen@oracle.com, linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org, kernel@puri.sm References: <20200623111018.31954-1-martin.kepplinger@puri.sm> <1379e21d-c51a-3710-e185-c2d7a9681fb7@acm.org> <20200626154441.GA296771@rowland.harvard.edu> <20200629161536.GA405175@rowland.harvard.edu> From: Bart Van Assche Autocrypt: addr=bvanassche@acm.org; prefer-encrypt=mutual; keydata= mQENBFSOu4oBCADcRWxVUvkkvRmmwTwIjIJvZOu6wNm+dz5AF4z0FHW2KNZL3oheO3P8UZWr LQOrCfRcK8e/sIs2Y2D3Lg/SL7qqbMehGEYcJptu6mKkywBfoYbtBkVoJ/jQsi2H0vBiiCOy fmxMHIPcYxaJdXxrOG2UO4B60Y/BzE6OrPDT44w4cZA9DH5xialliWU447Bts8TJNa3lZKS1 AvW1ZklbvJfAJJAwzDih35LxU2fcWbmhPa7EO2DCv/LM1B10GBB/oQB5kvlq4aA2PSIWkqz4 3SI5kCPSsygD6wKnbRsvNn2mIACva6VHdm62A7xel5dJRfpQjXj2snd1F/YNoNc66UUTABEB AAG0JEJhcnQgVmFuIEFzc2NoZSA8YnZhbmFzc2NoZUBhY20ub3JnPokBOQQTAQIAIwUCVI67 igIbAwcLCQgHAwIBBhUIAgkKCwQWAgMBAh4BAheAAAoJEHFcPTXFzhAJ8QkH/1AdXblKL65M Y1Zk1bYKnkAb4a98LxCPm/pJBilvci6boefwlBDZ2NZuuYWYgyrehMB5H+q+Kq4P0IBbTqTa jTPAANn62A6jwJ0FnCn6YaM9TZQjM1F7LoDX3v+oAkaoXuq0dQ4hnxQNu792bi6QyVdZUvKc macVFVgfK9n04mL7RzjO3f+X4midKt/s+G+IPr4DGlrq+WH27eDbpUR3aYRk8EgbgGKvQFdD CEBFJi+5ZKOArmJVBSk21RHDpqyz6Vit3rjep7c1SN8s7NhVi9cjkKmMDM7KYhXkWc10lKx2 RTkFI30rkDm4U+JpdAd2+tP3tjGf9AyGGinpzE2XY1K5AQ0EVI67igEIAKiSyd0nECrgz+H5 PcFDGYQpGDMTl8MOPCKw/F3diXPuj2eql4xSbAdbUCJzk2ETif5s3twT2ER8cUTEVOaCEUY3 eOiaFgQ+nGLx4BXqqGewikPJCe+UBjFnH1m2/IFn4T9jPZkV8xlkKmDUqMK5EV9n3eQLkn5g lco+FepTtmbkSCCjd91EfThVbNYpVQ5ZjdBCXN66CKyJDMJ85HVr5rmXG/nqriTh6cv1l1Js T7AFvvPjUPknS6d+BETMhTkbGzoyS+sywEsQAgA+BMCxBH4LvUmHYhpS+W6CiZ3ZMxjO8Hgc ++w1mLeRUvda3i4/U8wDT3SWuHcB3DWlcppECLkAEQEAAYkBHwQYAQIACQUCVI67igIbDAAK CRBxXD01xc4QCZ4dB/0QrnEasxjM0PGeXK5hcZMT9Eo998alUfn5XU0RQDYdwp6/kMEXMdmT oH0F0xB3SQ8WVSXA9rrc4EBvZruWQ+5/zjVrhhfUAx12CzL4oQ9Ro2k45daYaonKTANYG22y //x8dLe2Fv1By4SKGhmzwH87uXxbTJAUxiWIi1np0z3/RDnoVyfmfbbL1DY7zf2hYXLLzsJR mSsED/1nlJ9Oq5fALdNEPgDyPUerqHxcmIub+pF0AzJoYHK5punqpqfGmqPbjxrJLPJfHVKy goMj5DlBMoYqEgpbwdUYkH6QdizJJCur4icy8GUNbisFYABeoJ91pnD4IGei3MTdvINSZI5e Message-ID: Date: Mon, 29 Jun 2020 09:56:49 -0700 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: <20200629161536.GA405175@rowland.harvard.edu> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020-06-29 09:15, Alan Stern wrote: > Aha. Looking at this more closely, it's apparent that the code in > blk-core.c contains a logic bug: It assumes that if the BLK_MQ_REQ_PREEMPT > flag is set then the request can be issued regardless of the queue's > runtime status. That is not correct when the queue is suspended. Please clarify why this is not correct. > Index: usb-devel/block/blk-core.c > =================================================================== > --- usb-devel.orig/block/blk-core.c > +++ usb-devel/block/blk-core.c > @@ -423,7 +423,8 @@ int blk_queue_enter(struct request_queue > * responsible for ensuring that that counter is > * globally visible before the queue is unfrozen. > */ > - if (pm || !blk_queue_pm_only(q)) { > + if ((pm && q->rpm_status != RPM_SUSPENDED) || > + !blk_queue_pm_only(q)) { > success = true; > } else { > percpu_ref_put(&q->q_usage_counter); Does the above change make it impossible to bring a suspended device back to the RPM_ACTIVE state if the BLK_MQ_REQ_NOWAIT flag is set? > @@ -448,8 +449,7 @@ int blk_queue_enter(struct request_queue > > wait_event(q->mq_freeze_wq, > (!q->mq_freeze_depth && > - (pm || (blk_pm_request_resume(q), > - !blk_queue_pm_only(q)))) || > + blk_pm_resume_queue(pm, q)) || > blk_queue_dying(q)); > if (blk_queue_dying(q)) > return -ENODEV; > Index: usb-devel/block/blk-pm.h > =================================================================== > --- usb-devel.orig/block/blk-pm.h > +++ usb-devel/block/blk-pm.h > @@ -6,11 +6,14 @@ > #include > > #ifdef CONFIG_PM > -static inline void blk_pm_request_resume(struct request_queue *q) > +static inline int blk_pm_resume_queue(const bool pm, struct request_queue *q) > { > - if (q->dev && (q->rpm_status == RPM_SUSPENDED || > - q->rpm_status == RPM_SUSPENDING)) > - pm_request_resume(q->dev); > + if (!q->dev || !blk_queue_pm_only(q)) > + return 1; /* Nothing to do */ > + if (pm && q->rpm_status != RPM_SUSPENDED) > + return 1; /* Request allowed */ > + pm_request_resume(q->dev); > + return 0; > } Does the above change, especially the " && q->rpm_status != RPM_SUSPENDED" part, make it impossible to bring a suspended device back to the RPM_ACTIVE state? Thanks, Bart.