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([2601:647:4000:d7:3f5a:7698:1b81:cc96]) by smtp.gmail.com with ESMTPSA id g23sm10805716pfh.133.2020.09.14.09.48.08 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 14 Sep 2020 09:48:08 -0700 (PDT) Subject: Re: [PATCH] blk-mq: fix hang issue in blk_queue_enter() To: Yang Yang , Jens Axboe , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org Cc: onlyfever@icloud.com References: <20200914071903.65704-1-yang.yang@vivo.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: <1f7aa460-6a6c-d200-786e-bfccf5fc2bff@acm.org> Date: Mon, 14 Sep 2020 09:48:07 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.12.0 MIME-Version: 1.0 In-Reply-To: <20200914071903.65704-1-yang.yang@vivo.com> 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 2020-09-14 00:19, Yang Yang wrote: > There is a race between blk_queue_enter() and block layer's runtime > suspend. > > CPU0 CPU1 > --------------------------------- ------------------------------- > blk_pre_runtime_suspend(q) { blk_queue_enter() { > /* q->rpm_status=RPM_ACTIVE */ > blk_set_pm_only(q) > /* q->pm_only=1 */ > blk_freeze_queue_start(q) > blk_mq_unfreeze_queue(q) > if (percpu_ref_tryget_live()) { > /* pm=0 && q->pm_only=1 */ > if (pm || !blk_queue_pm_only(q)) { > } else { > percpu_ref_put() > } > } > wait_event(q->mq_freeze_wq, > (!q->mq_freeze_depth && > /* q->rpm_status=RPM_ACTIVE > q->pm_only=1 */ > (pm || (blk_pm_request_resume(q), > !blk_queue_pm_only(q)))) || > blk_queue_dying(q)) > } > spin_lock_irq(&q->queue_lock) > q->rpm_status = RPM_SUSPENDING > spin_unlock_irq(&q->queue_lock) > } > > At this point blk_pm_request_resume() missed the chance to resume the > queue, so blk_queue_enter() may wait here forever. > The solution is to wake up the mq_freeze_wq after runtime suspend > completed, make blk_pm_request_resume() reexamine the q->rpm_status flag. > > Signed-off-by: Yang Yang > --- > block/blk-pm.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/block/blk-pm.c b/block/blk-pm.c > index b85234d758f7..dec7d0aef606 100644 > --- a/block/blk-pm.c > +++ b/block/blk-pm.c > @@ -132,6 +132,8 @@ void blk_post_runtime_suspend(struct request_queue *q, int err) > > if (err) > blk_clear_pm_only(q); > + else > + wake_up_all(&q->mq_freeze_wq); > } > EXPORT_SYMBOL(blk_post_runtime_suspend); Please verify whether the following patch series also fixes the reported hang: https://lore.kernel.org/linux-block/20200906012219.17893-1-bvanassche@acm.org/T/#t Thanks, Bart.