From patchwork Tue Aug 21 07:15:04 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "jianchao.wang" X-Patchwork-Id: 10571109 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id D6B99921 for ; Tue, 21 Aug 2018 07:14:34 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id C1D9429CB7 for ; Tue, 21 Aug 2018 07:14:34 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id B62B929CB9; Tue, 21 Aug 2018 07:14:34 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.0 required=2.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,RCVD_IN_DNSWL_HI, UNPARSEABLE_RELAY autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 562A229CB7 for ; Tue, 21 Aug 2018 07:14:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726315AbeHUKda (ORCPT ); Tue, 21 Aug 2018 06:33:30 -0400 Received: from userp2120.oracle.com ([156.151.31.85]:45968 "EHLO userp2120.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726253AbeHUKda (ORCPT ); Tue, 21 Aug 2018 06:33:30 -0400 Received: from pps.filterd (userp2120.oracle.com [127.0.0.1]) by userp2120.oracle.com (8.16.0.22/8.16.0.22) with SMTP id w7L78xel056050; Tue, 21 Aug 2018 07:13:29 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.com; h=from : to : cc : subject : date : message-id : in-reply-to : references; s=corp-2018-07-02; bh=znaTFbEDOmUEg8O+aRKk96aenhOx02Xvk1T4VRvWen4=; b=bJ5wC+CPPvArS3RBMTMh8iTiF0U6RpciJw9yd+mWWxi9wxIdyC/UIxoYDDZW97IZaw5/ W2AkX9NL3BRy2wfEZIy39GtTlbSQ/chsiPOTpn5D02r18hwXG55ku6dOTgOcqpb8VljJ 9bCfIGVoUWkYdmdn/8AtcU2Iywp0JS1twv6nmEglMeDlIsMxQ0MICC4kMRiWw/SkLRU2 DqsebSbqbTLcYnyB+rr8X4WL/keRczlNHxHz5KALTrkUIx3zG/q5D8MdASj4LH4sYDxw tOb3PYVs8OcPbZa2QnY/XNtpv6VF3iuupgw8D3a9LtAmwLYhQbP18dzn1ag+Z4C4cx9q xQ== Received: from userv0022.oracle.com (userv0022.oracle.com [156.151.31.74]) by userp2120.oracle.com with ESMTP id 2kxc3qjfu3-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 21 Aug 2018 07:13:29 +0000 Received: from aserv0121.oracle.com (aserv0121.oracle.com [141.146.126.235]) by userv0022.oracle.com (8.14.4/8.14.4) with ESMTP id w7L7DSqY010418 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 21 Aug 2018 07:13:29 GMT Received: from abhmp0015.oracle.com (abhmp0015.oracle.com [141.146.116.21]) by aserv0121.oracle.com (8.14.4/8.13.8) with ESMTP id w7L7DS3N021343; Tue, 21 Aug 2018 07:13:28 GMT Received: from will-ThinkCentre-M910s.cn.oracle.com (/10.182.70.254) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Tue, 21 Aug 2018 00:13:28 -0700 From: Jianchao Wang To: axboe@kernel.dk Cc: tom.leiming@gmail.com, bart.vanassche@wdc.com, keith.busch@linux.intel.com, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH V4 2/2] blk-mq: sync the update nr_hw_queues with blk_mq_queue_tag_busy_iter Date: Tue, 21 Aug 2018 15:15:04 +0800 Message-Id: <1534835704-3607-3-git-send-email-jianchao.w.wang@oracle.com> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1534835704-3607-1-git-send-email-jianchao.w.wang@oracle.com> References: <1534835704-3607-1-git-send-email-jianchao.w.wang@oracle.com> X-Proofpoint-Virus-Version: vendor=nai engine=5900 definitions=8991 signatures=668707 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=1 malwarescore=0 phishscore=0 bulkscore=0 spamscore=0 mlxscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1807170000 definitions=main-1808210076 Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP For blk-mq, part_in_flight/rw will invoke blk_mq_in_flight/rw to account the inflight requests. It will access the queue_hw_ctx and nr_hw_queues w/o any protection. When updating nr_hw_queues and blk_mq_in_flight/rw occur concurrently, panic comes up. Before update nr_hw_queues, the q will be frozen. So we could use q_usage_counter to avoid the race. percpu_ref_is_zero is used here so that we will not miss any in-flight request. The access to nr_hw_queues and queue_hw_ctx in blk_mq_queue_tag_busy_iter are under rcu critical section, __blk_mq_update_nr_hw_queues could use synchronize_rcu to ensure the zeroed q_usage_counter to be globally visible. Signed-off-by: Jianchao Wang Reviewed-by: Ming Lei --- block/blk-mq-tag.c | 14 +++++++++++++- block/blk-mq.c | 4 ++++ 2 files changed, 17 insertions(+), 1 deletion(-) diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c index c0c4e63..8c5cc11 100644 --- a/block/blk-mq-tag.c +++ b/block/blk-mq-tag.c @@ -320,6 +320,18 @@ void blk_mq_queue_tag_busy_iter(struct request_queue *q, busy_iter_fn *fn, struct blk_mq_hw_ctx *hctx; int i; + /* + * __blk_mq_update_nr_hw_queues will update the nr_hw_queues and + * queue_hw_ctx after freeze the queue. So we could use q_usage_counter + * to avoid race with it. __blk_mq_update_nr_hw_queues will users + * synchronize_rcu to ensure all of the users go out of the critical + * section below and see zeroed q_usage_counter. + */ + rcu_read_lock(); + if (percpu_ref_is_zero(&q->q_usage_counter)) { + rcu_read_unlock(); + return; + } queue_for_each_hw_ctx(q, hctx, i) { struct blk_mq_tags *tags = hctx->tags; @@ -335,7 +347,7 @@ void blk_mq_queue_tag_busy_iter(struct request_queue *q, busy_iter_fn *fn, bt_for_each(hctx, &tags->breserved_tags, fn, priv, true); bt_for_each(hctx, &tags->bitmap_tags, fn, priv, false); } - + rcu_read_unlock(); } static int bt_alloc(struct sbitmap_queue *bt, unsigned int depth, diff --git a/block/blk-mq.c b/block/blk-mq.c index 9c8c8c7..81cb84b 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -2977,6 +2977,10 @@ static void __blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set, list_for_each_entry(q, &set->tag_list, tag_set_list) blk_mq_freeze_queue(q); /* + * Sync with blk_mq_queue_tag_busy_iter. + */ + synchronize_rcu(); + /* * Switch IO scheduler to 'none', cleaning up the data associated * with the previous scheduler. We will switch back once we are done * updating the new sw to hw queue mappings.