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[209.132.180.67]) by mx.google.com with ESMTP id f9si6265505pgq.347.2019.03.25.00.09.59; Mon, 25 Mar 2019 00:10:13 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; dkim=pass header.i=@oracle.com header.s=corp-2018-07-02 header.b="voopBjA/"; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=oracle.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729827AbfCYHIx (ORCPT + 99 others); Mon, 25 Mar 2019 03:08:53 -0400 Received: from userp2120.oracle.com ([156.151.31.85]:40682 "EHLO userp2120.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729230AbfCYHIx (ORCPT ); Mon, 25 Mar 2019 03:08:53 -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 x2P6wxHO075151; Mon, 25 Mar 2019 07:08:16 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=HWQ5kbHBQxWtPDAQ/NdzhYJ7OTSvXAsnNpX7vP3kHsY=; b=voopBjA/lA47y7J0CWliLDIa75VEDhs0tvraqbiUu+NWBYVRC4vUpVSSRlF8nA9MaQY7 OkxKdSAf88gUvnD7Ov+VpXgzPfo/oMis6OWMvtALlHxXJgH/Mr0yPjpFAqZzAhKFTUVr DvpBm8feJKLB5BXvKd3fqlBHu36MBEj6ePDDn63ftmbgVSOcHcYQi70yco4ifxvF6wde BFmvwx/NWuhUwShMttZ21892Gf7qi0f3eLXw3xlitofIyeOzwKJ0c6/mZzX6+Ih6HWqE kLrHD4FMNZ/lNavG0V8c9At08DX1+tPVL0rXqzgONxYVUG6LF2i21rMOgIBFch1dobaw wg== Received: from aserv0021.oracle.com (aserv0021.oracle.com [141.146.126.233]) by userp2120.oracle.com with ESMTP id 2re6dj27ac-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 25 Mar 2019 07:08:16 +0000 Received: from userv0121.oracle.com (userv0121.oracle.com [156.151.31.72]) by aserv0021.oracle.com (8.14.4/8.14.4) with ESMTP id x2P78Ej2022159 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 25 Mar 2019 07:08:14 GMT Received: from abhmp0013.oracle.com (abhmp0013.oracle.com [141.146.116.19]) by userv0121.oracle.com (8.14.4/8.13.8) with ESMTP id x2P78AEh015527; Mon, 25 Mar 2019 07:08:10 GMT Received: from [10.182.69.106] (/10.182.69.106) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Mon, 25 Mar 2019 00:08:10 -0700 Subject: Re: [PATCH V2 2/8] blk-mq: use static_rqs instead of rqs to iterate tags To: Jianchao Wang 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> From: Dongli Zhang Message-ID: <58796005-2f96-ad5c-fa21-b3a0071deb06@oracle.com> Date: Mon, 25 Mar 2019 15:12:18 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1 MIME-Version: 1.0 In-Reply-To: <1553492318-1810-3-git-send-email-jianchao.w.wang@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=1011 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=905 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1903250053 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. > -> bt_for_each > -> bt_iter > -> rq = taags->rqs[] %s/taags/tags/g > -> rq->q > -> blk_mq_rq_ctx_init > -> data->hctx->tags->rqs[rq->tag] = rq; > Thank you very much! Dongli Zhang