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([2601:647:4000:d7:8ef:746a:4fe7:1df]) by smtp.gmail.com with ESMTPSA id j14sm5054162pjm.27.2020.05.09.07.07.56 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 09 May 2020 07:07:57 -0700 (PDT) Subject: Re: [PATCH V10 11/11] block: deactivate hctx when the hctx is actually inactive To: Ming Lei , Jens Axboe Cc: linux-block@vger.kernel.org, John Garry , Hannes Reinecke , Christoph Hellwig , Thomas Gleixner , Hannes Reinecke References: <20200505020930.1146281-1-ming.lei@redhat.com> <20200505020930.1146281-12-ming.lei@redhat.com> 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: <954b942e-3b06-4be7-9f2f-23f87ff514f0@acm.org> Date: Sat, 9 May 2020 07:07:55 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: <20200505020930.1146281-12-ming.lei@redhat.com> 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 2020-05-04 19:09, Ming Lei wrote: > @@ -1373,28 +1375,16 @@ static void __blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx) > int srcu_idx; > [ ... ] > if (!cpumask_test_cpu(raw_smp_processor_id(), hctx->cpumask) && > - cpu_online(hctx->next_cpu)) { > - printk(KERN_WARNING "run queue from wrong CPU %d, hctx %s\n", > - raw_smp_processor_id(), > - cpumask_empty(hctx->cpumask) ? "inactive": "active"); > - dump_stack(); > + cpumask_next_and(-1, hctx->cpumask, cpu_online_mask) >= > + nr_cpu_ids) { > + blk_mq_hctx_deactivate(hctx); > + return; > } The blk_mq_hctx_deactivate() function calls blk_mq_resubmit_rq() indirectly. From blk_mq_resubmit_rq(): + /* avoid allocation failure by clearing NOWAIT */ + nrq = blk_get_request(rq->q, rq->cmd_flags & ~REQ_NOWAIT, flags); blk_get_request() calls blk_mq_alloc_request(). blk_mq_alloc_request() calls blk_queue_enter(). blk_queue_enter() waits until a queue is unfrozen if freezing of a queue has started. As one can see freezing a queue triggers a queue run: void blk_freeze_queue_start(struct request_queue *q) { mutex_lock(&q->mq_freeze_lock); if (++q->mq_freeze_depth == 1) { percpu_ref_kill(&q->q_usage_counter); mutex_unlock(&q->mq_freeze_lock); if (queue_is_mq(q)) blk_mq_run_hw_queues(q, false); } else { mutex_unlock(&q->mq_freeze_lock); } } Does this mean that if queue freezing happens after hot unplugging started that a deadlock will occur because the blk_mq_run_hw_queues() call in blk_freeze_queue_start() will wait forever? Bart.