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[73.241.217.19]) by smtp.gmail.com with ESMTPSA id fs12sm403898pjb.21.2020.08.25.19.58.12 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 25 Aug 2020 19:58:13 -0700 (PDT) Subject: Re: [PATCH] block: Fix a race in the runtime power management code To: Stanley Chu Cc: Jens Axboe , linux-block@vger.kernel.org, Christoph Hellwig , Alan Stern , Ming Lei , stable , Can Guo References: <20200824030607.19357-1-bvanassche@acm.org> <1598346681.10649.8.camel@mtkswgap22> 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: Tue, 25 Aug 2020 19:58:11 -0700 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: <1598346681.10649.8.camel@mtkswgap22> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On 2020-08-25 02:11, Stanley Chu wrote: >> diff --git a/block/blk-pm.c b/block/blk-pm.c >> index b85234d758f7..17bd020268d4 100644 >> --- a/block/blk-pm.c >> +++ b/block/blk-pm.c >> @@ -67,6 +67,10 @@ int blk_pre_runtime_suspend(struct request_queue *q) >> >> WARN_ON_ONCE(q->rpm_status != RPM_ACTIVE); >> >> + spin_lock_irq(&q->queue_lock); >> + q->rpm_status = RPM_SUSPENDING; >> + spin_unlock_irq(&q->queue_lock); >> + > > Has below alternative way been considered that RPM_SUSPENDING is set > after blk_freeze_queue_start()? > > blk_freeze_queue_start(q); > > + spin_lock_irq(&q->queue_lock); > + q->rpm_status = RPM_SUSPENDING; > + spin_unlock_irq(&q->queue_lock); > > > Otherwise requests can enter queue while rpm_status is RPM_SUSPENDING > during a small window, i.e., before blk_set_pm_only() is invoked. This > would make the definition of rpm_status ambiguous. > > In this way, the racing could be also solved: > > - Before blk_freeze_queue_start(), any requests shall be allowed to > enter queue > - blk_freeze_queue_start() freezes the queue and blocks all upcoming > requests (make them wait_event(q->mq_freeze_wq)) > - rpm_status is set as RPM_SUSPENDING > - blk_mq_unfreeze_queue() wakes up q->mq_freeze_wq and then > blk_pm_request_resume() can be executed Hi Stanley, I prefer the order from the patch. I think it is important to change q->rpm_status into RPM_SUSPENDING before blk_queue_enter() calls blk_queue_pm_only(). Otherwise it could happen that blk_queue_enter() calls blk_pm_request_resume() while q->rpm_status == RPM_ACTIVE, resulting in blk_queue_enter() not resuming a queue although that queue should be resumed. Thanks, Bart.