From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.5 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9D7A9C433E3 for ; Thu, 27 Aug 2020 03:35:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7C6C820737 for ; Thu, 27 Aug 2020 03:35:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726820AbgH0Dfr (ORCPT ); Wed, 26 Aug 2020 23:35:47 -0400 Received: from mail-pj1-f68.google.com ([209.85.216.68]:53802 "EHLO mail-pj1-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726802AbgH0Dfq (ORCPT ); Wed, 26 Aug 2020 23:35:46 -0400 Received: by mail-pj1-f68.google.com with SMTP id nv17so1902481pjb.3; Wed, 26 Aug 2020 20:35:46 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:autocrypt :message-id:date:user-agent:mime-version:in-reply-to :content-language:content-transfer-encoding; bh=DLj4W2vhUepXhNqbwxvkKgKcWXo+LmOht5KSU3PyXno=; b=CNDuEBG3TZeebeFRiiITJUHlIIvyzkH1AJVox26BEl4Fz7DTRoOz2YsBVZajxz6x7H 31XHwgDCNnCbhy8TrDR8e7lIRahN4CJZtzNAThIi2ESfAn5WSFn1omZAcY3rojqB+ntj P6/NJtqPKAJB9k7jI6X6QhJG3vLeClGE06TUE3Z7fUxKhcpAYlSWwLq/lD0Ki9kJOjHZ keWfOAfkfzlhyZ8xtBo6KzA1NgNtijR4OtallNuy6eQijg7L2gUBPbZinQetHZZzC5BN TAXcHxvjKCZkKLkTvpfLN165W9/5vTNCL8TkNPOEqvlxbY5gNdXEzu6Mg0jLVy6Z9JzP WFkw== X-Gm-Message-State: AOAM532pBPKAtwKUJcjDy18fmwloiNCFtH7bP317iEPIbU5mDldhbjKz AqbjyULq+BG9W4LoNgNJ/p4= X-Google-Smtp-Source: ABdhPJyklio1mpgzNgrsrCHSPZvogO3jiJOroyEAHY0jOBex6B9DucFvtYvn85NN5Ors5xumTTcubg== X-Received: by 2002:a17:90b:18e:: with SMTP id t14mr7740779pjs.69.1598499345718; Wed, 26 Aug 2020 20:35:45 -0700 (PDT) Received: from [192.168.3.217] (c-73-241-217-19.hsd1.ca.comcast.net. [73.241.217.19]) by smtp.gmail.com with ESMTPSA id d23sm504620pjz.44.2020.08.26.20.35.43 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 26 Aug 2020 20:35:44 -0700 (PDT) Subject: Re: [PATCH] block: Fix a race in the runtime power management code To: Alan Stern Cc: Stanley Chu , Jens Axboe , linux-block@vger.kernel.org, Christoph Hellwig , Ming Lei , stable , Can Guo , "Martin K. Petersen" References: <20200824030607.19357-1-bvanassche@acm.org> <1598346681.10649.8.camel@mtkswgap22> <20200825182423.GB375466@rowland.harvard.edu> <1f798c21-241f-59f8-5298-a32fffe2ff01@acm.org> <20200826015159.GA387575@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: Wed, 26 Aug 2020 20:35:42 -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: <20200826015159.GA387575@rowland.harvard.edu> 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 18:51, Alan Stern wrote: > Ah, perfect. So in blk_queue_enter(), pm should be defined in terms of > RQF_PM rather than BLK_MQ_REQ_PREEMPT. > > The difficulty is that the flags argument is the wrong type; RQF_PM is > defined as req_flags_t, not blk_mq_req_flags_t. It is associated with a > particular request after the request has been created, so after > blk_queue_enter() has been called. > > How can we solve this? The current code looks a bit weird because my focus when modifying the PM code has been on not breaking any existing code. scsi_device_quiesce() relies on blk_queue_enter() processing all PREEMPT requests. A difficulty is that scsi_device_quiesce() is used for two separate purposes: * Runtime power management. * SCSI domain validation. See e.g. https://lwn.net/Articles/75917/. I think that modifying blk_queue_enter() such that it only accepts PM requests will require to split scsi_device_quiesce() into two functions: one function that is used by the runtime power management code and another function that is used by the SCSI domain validation code. This may require to introduce new SCSI device states. If new SCSI device states are introduced, that should be done without modifying the state that is reported to user space. See also sdev_states[] and show_state_field in scsi_sysfs.c. Thanks, Bart.