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=-1.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS autolearn=unavailable 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 DC477C10F03 for ; Mon, 25 Mar 2019 07:14:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id AB95C20830 for ; Mon, 25 Mar 2019 07:14:35 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=oracle.com header.i=@oracle.com header.b="DuU0UdwI" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729835AbfCYHOe (ORCPT ); Mon, 25 Mar 2019 03:14:34 -0400 Received: from userp2120.oracle.com ([156.151.31.85]:46070 "EHLO userp2120.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729720AbfCYHOe (ORCPT ); Mon, 25 Mar 2019 03:14:34 -0400 Received: from pps.filterd (userp2120.oracle.com [127.0.0.1]) by userp2120.oracle.com (8.16.0.27/8.16.0.27) with SMTP id x2P7Dgre086555; Mon, 25 Mar 2019 07:14:12 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.com; h=subject : to : cc : references : from : message-id : date : mime-version : in-reply-to : content-type : content-transfer-encoding; s=corp-2018-07-02; bh=gn1J2mfFH9tzliczQIqyF3ccwE8byCWrg5+JR27iD+g=; b=DuU0UdwIw1da4YPnkUKCikH64YmCRNul62tod0HUuObhDSI1b/ZwZ2cWmzfOhA7H9L8b jzsME7gwRgbutJu5Jnr3Xa7bnvJXEc7t6g0Hbo1LdCWO0uHFMYyETWM2KJbxkV8F2EsG 8qnY4aB6+RqvNFA8L7AJtuVuo0YszWpdzf/Fvw9+cG43MH13/t1K7wrBGdPbASOW44pv YHzdDaqVVVFbx4ltxMY74eTSyw9x1aVGbUOqicKx8HB9EOG1KJ1QIFFmI4Reo58j81lX EtcvB2UvelQRKBbxVGej27Ie8cG4G3MtPg3AQpuNeFM1+R5tK/ssES09HLiD5SdNq97R 2Q== Received: from userv0021.oracle.com (userv0021.oracle.com [156.151.31.71]) by userp2120.oracle.com with ESMTP id 2re6dj2806-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 25 Mar 2019 07:14:12 +0000 Received: from userv0121.oracle.com (userv0121.oracle.com [156.151.31.72]) by userv0021.oracle.com (8.14.4/8.14.4) with ESMTP id x2P7EBbb000383 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 25 Mar 2019 07:14:11 GMT Received: from abhmp0004.oracle.com (abhmp0004.oracle.com [141.146.116.10]) by userv0121.oracle.com (8.14.4/8.13.8) with ESMTP id x2P7EAmW018083; Mon, 25 Mar 2019 07:14:10 GMT Received: from [10.182.71.8] (/10.182.71.8) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Mon, 25 Mar 2019 00:14:10 -0700 Subject: Re: [PATCH V2 2/8] blk-mq: use static_rqs instead of rqs to iterate tags To: Dongli Zhang Cc: axboe@kernel.dk, linux-block@vger.kernel.org, jsmart2021@gmail.com, sagi@grimberg.me, josef@toxicpanda.com, linux-nvme@lists.infradead.org, linux-kernel@vger.kernel.org, keith.busch@intel.com, hare@suse.de, jthumshirn@suse.de, hch@lst.de, bvanassche@acm.org References: <1553492318-1810-1-git-send-email-jianchao.w.wang@oracle.com> <1553492318-1810-3-git-send-email-jianchao.w.wang@oracle.com> <58796005-2f96-ad5c-fa21-b3a0071deb06@oracle.com> From: "jianchao.wang" Message-ID: Date: Mon, 25 Mar 2019 15:14:08 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.5.1 MIME-Version: 1.0 In-Reply-To: <58796005-2f96-ad5c-fa21-b3a0071deb06@oracle.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Proofpoint-Virus-Version: vendor=nai engine=5900 definitions=9205 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 priorityscore=1501 malwarescore=0 suspectscore=2 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=929 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1903250055 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Dongli Thanks for your kindly response. On 3/25/19 3:12 PM, Dongli Zhang wrote: > Hi Jianchao, > > On 3/25/19 1:38 PM, Jianchao Wang wrote: >> tags->rqs[] will not been cleaned when free driver tag to avoid >> an extra store on a shared area in the per io path. But there >> is a window between get driver tag and write tags->rqs[], so we >> may see stale rq in tags->rqs[] which may have been freed, as >> following case, >> blk_mq_get_request blk_mq_queue_tag_busy_iter >> -> blk_mq_get_tag > > Sorry I forgot to mention below when I was studying the v1 patchset. > > If there is further review iteration, I would suggest clarify here that > blk_mq_get_tag() would set the bit in sbitmap (e.g., via __sbitmap_get_word()) > that bt_for_each() would iterate. Otherwise, please ignore my message. > > E.g., > > blk_mq_get_request > -> blk_mq_get_tag > -> taint sbitmap tag bit > without setting tags->rqs[tag] > > -> bt_for_each > -> iterate all dirty bit... > > This would be much more friendly for people not working on block layer and when > they are looking for the potential fix for a bug by simply searching over the > commit messages. People not working on this would be able to quickly understand > there is a window between setting bit and setting data. Yes, I will do that. > > >> -> bt_for_each >> -> bt_iter >> -> rq = taags->rqs[] > > %s/taags/tags/g Yes. Thanks Jianchao > >> -> rq->q >> -> blk_mq_rq_ctx_init >> -> data->hctx->tags->rqs[rq->tag] = rq; >> > > Thank you very much! > > Dongli Zhang >