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=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham 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 134D0C433E0 for ; Fri, 19 Jun 2020 21:59:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E92DE22243 for ; Fri, 19 Jun 2020 21:59:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728759AbgFSV7e (ORCPT ); Fri, 19 Jun 2020 17:59:34 -0400 Received: from mail-pl1-f193.google.com ([209.85.214.193]:42117 "EHLO mail-pl1-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728242AbgFSV7c (ORCPT ); Fri, 19 Jun 2020 17:59:32 -0400 Received: by mail-pl1-f193.google.com with SMTP id k6so4459880pll.9; Fri, 19 Jun 2020 14:59:32 -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=AV7sMf6DKdniuUMlAi+PCzyUcAZ8zYs0XbZP7OgqLvo=; b=EJRXZHIsW0P3yI0do5y+ISFK4xTQmy24IOFsz8Pr2L/5YZNh8lMwAf9keb3GtDmzHL Bzv8epY/zgnVtK7UqZMpbEyYo0d6/srGEfneSC8XqHb0n6jW/ONt85tlgmGFnyvrAe2g +qWsbgPqELk40tp8ab/xIaC6Zy01amTJgfQmTxek227pKyofBWP1WV6IFuEvWt28MXLB 99jjuK8XWPFibp+4G99EtHMGm/cD/h3TPD3W1Nbb7RQjr+mkm/efs2Dqd3Moax3Oeaye EZ0oD5W5vfnd6hfEXQNhJpf2z7T9hQ8ONCMqTRxd+yc2lV2OvLu+F8voIt7ZfScWRMMo TG5A== X-Gm-Message-State: AOAM531HHZfHRhRMUyaflb/6wqBheIZEz5OmtUR/qHqNm0OsodIrmhZV oA7VtC0EzJkl6WHxS3vnqwQJIZDG X-Google-Smtp-Source: ABdhPJx4OW9HYswSIJLZOwlHOxYK4xw7Rnvfy6NUwHa5lYL4TdK49UM/lZSvhmLbfdP9bmtLYJ83gg== X-Received: by 2002:a17:90a:d803:: with SMTP id a3mr5821475pjv.125.1592603971568; Fri, 19 Jun 2020 14:59:31 -0700 (PDT) Received: from [192.168.50.147] (c-73-241-217-19.hsd1.ca.comcast.net. [73.241.217.19]) by smtp.gmail.com with ESMTPSA id t201sm6757784pfc.104.2020.06.19.14.59.30 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 19 Jun 2020 14:59:30 -0700 (PDT) Subject: Re: [PATCH 2/2] block: only return started requests from blk_mq_tag_to_rq() To: Hannes Reinecke , Jens Axboe Cc: Christoph Hellwig , "Martin K. Petersen" , Keith Busch , Sagi Grimberg , James Bottomley , linux-block@vger.kernel.org, linux-scsi@vger.kernel.org References: <20200619140159.141905-1-hare@suse.de> <60e34dce-aea4-311f-22da-4cb130c5ba88@suse.de> 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: <3d073c18-50da-a4c8-2f1e-332a1e717efc@acm.org> Date: Fri, 19 Jun 2020 14:59:29 -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: <60e34dce-aea4-311f-22da-4cb130c5ba88@suse.de> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On 2020-06-19 07:09, Hannes Reinecke wrote: > On 6/19/20 4:01 PM, Hannes Reinecke wrote: >> blk_mq_tag_to_rq() is used from within the driver to map a tag >> to a request. As such it should only return requests which are >> already started (ie passed to the driver); otherwise the driver >> might trip over requests which it has never seen and random >> crashes will occur. >> >> Signed-off-by: Hannes Reinecke >> --- >>   block/blk-mq.c | 6 +++++- >>   1 file changed, 5 insertions(+), 1 deletion(-) >> >> diff --git a/block/blk-mq.c b/block/blk-mq.c >> index 4f57d27bfa73..f02d18113f9e 100644 >> --- a/block/blk-mq.c >> +++ b/block/blk-mq.c >> @@ -815,9 +815,13 @@ EXPORT_SYMBOL(blk_mq_delay_kick_requeue_list); >>     struct request *blk_mq_tag_to_rq(struct blk_mq_tags *tags, >> unsigned int tag) >>   { >> +    struct request *rq; >> + >>       if (tag < tags->nr_tags) { >>           prefetch(tags->rqs[tag]); >> -        return tags->rqs[tag]; >> +        rq = tags->rqs[tag]; >> +        if (blk_mq_request_started(rq)) >> +            return rq; >>       } >>         return NULL; >> > This becomes particularly obnoxious for SCSI drivers using > scsi_host_find_tag() for cleaning up stale commands (ie drivers like > qla4xxx, fnic, and snic). > All other drivers use it from the completion routine, so one can expect > a valid (and started) tag here. So for those it shouldn't matter. > > But still, if there are objections I could look at fixing it within the > SCSI stack; although that would most likely mean I'll have to implement > the above patch as an additional function. Hi Hannes, Will the above patch make the fast path of every block driver slightly slower? Shouldn't SCSI drivers (and other block drivers) use blk_mq_tagset_busy_iter() to clean up stale commands instead of iterating over all tags and calling blk_mq_tag_to_rq() directly? Thanks, Bart.