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=-9.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,UNPARSEABLE_RELAY,USER_AGENT_GIT 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 B8343C43381 for ; Fri, 15 Mar 2019 09:07:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 87A43218C3 for ; Fri, 15 Mar 2019 09:07:03 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=oracle.com header.i=@oracle.com header.b="VQ0ttMj3" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726468AbfCOJHC (ORCPT ); Fri, 15 Mar 2019 05:07:02 -0400 Received: from aserp2130.oracle.com ([141.146.126.79]:44886 "EHLO aserp2130.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728640AbfCOJGx (ORCPT ); Fri, 15 Mar 2019 05:06:53 -0400 Received: from pps.filterd (aserp2130.oracle.com [127.0.0.1]) by aserp2130.oracle.com (8.16.0.27/8.16.0.27) with SMTP id x2F8xIDk057534; Fri, 15 Mar 2019 09:06:16 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=OC/PdQhEPXLumSdNoF/bK0ObwxgKZgaL5SrQOG5BdtQ=; b=VQ0ttMj3Q7gxdNh6WbdeF8gSVgCqxu3LVd0I/9nmYWAQe3vhHatIxpvaD9DlR8X+4EnZ 7vADoSf7Mj7ap5cYxRjRjAcw+JPnECYGvdKDOl9/VpGy6jWpPqm2PjAmUnJeXxTXnXKE tnINDT5W6J5EM0Zn0HNjxaXxsJsw8R5F8pFOZb92izlwyKDdq8Dnxn/oO95IlZQKzKkD XiLtC/YuIAxe/FpjZK100Ytej5FMArnFsmU4bcuWttxycvP/ofhQJl56wEj4kHoelSQ5 fxh25m6AUmKmJSEPOjaSCIhtMEk668z8udyd9m4DDxbhPyqqpyqDfBQnXF4FxdbheuxI Ow== Received: from userv0021.oracle.com (userv0021.oracle.com [156.151.31.71]) by aserp2130.oracle.com with ESMTP id 2r430f61hs-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Fri, 15 Mar 2019 09:06:15 +0000 Received: from userv0122.oracle.com (userv0122.oracle.com [156.151.31.75]) by userv0021.oracle.com (8.14.4/8.14.4) with ESMTP id x2F96D9K022654 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Fri, 15 Mar 2019 09:06:13 GMT Received: from abhmp0015.oracle.com (abhmp0015.oracle.com [141.146.116.21]) by userv0122.oracle.com (8.14.4/8.14.4) with ESMTP id x2F96CLJ021411; Fri, 15 Mar 2019 09:06:12 GMT Received: from will-ThinkCentre-M93p.cn.oracle.com (/10.182.71.12) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Fri, 15 Mar 2019 09:06:11 +0000 From: Jianchao Wang To: axboe@kernel.dk Cc: hch@lst.de, jthumshirn@suse.de, hare@suse.de, josef@toxicpanda.com, bvanassche@acm.org, sagi@grimberg.me, keith.busch@intel.com, jsmart2021@gmail.com, linux-block@vger.kernel.org, linux-nvme@lists.infradead.org, linux-kernel@vger.kernel.org Subject: [PATCH 1/8] blk-mq: get rid of the synchronize_rcu in __blk_mq_update_nr_hw_queues Date: Fri, 15 Mar 2019 16:57:37 +0800 Message-Id: <1552640264-26101-2-git-send-email-jianchao.w.wang@oracle.com> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1552640264-26101-1-git-send-email-jianchao.w.wang@oracle.com> References: <1552640264-26101-1-git-send-email-jianchao.w.wang@oracle.com> X-Proofpoint-Virus-Version: vendor=nai engine=5900 definitions=9195 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 priorityscore=1501 malwarescore=0 suspectscore=1 phishscore=0 bulkscore=0 spamscore=0 clxscore=1011 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1903150067 Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org In commit 530ca2c (blk-mq: Allow blocking queue tag iter callbacks), we try to get a non-zero q_usage_counter to avoid access hctxs that being modified. So the synchronize_rcu is useless and should be removed. Signed-off-by: Jianchao Wang --- block/blk-mq-tag.c | 4 +--- block/blk-mq.c | 4 ---- 2 files changed, 1 insertion(+), 7 deletions(-) diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c index 2089c6c..b792537 100644 --- a/block/blk-mq-tag.c +++ b/block/blk-mq-tag.c @@ -384,9 +384,7 @@ void blk_mq_queue_tag_busy_iter(struct request_queue *q, busy_iter_fn *fn, /* * __blk_mq_update_nr_hw_queues() updates nr_hw_queues and queue_hw_ctx * while the queue is frozen. So we can use q_usage_counter to avoid - * racing with it. __blk_mq_update_nr_hw_queues() uses - * synchronize_rcu() to ensure this function left the critical section - * below. + * racing with it. */ if (!percpu_ref_tryget(&q->q_usage_counter)) return; diff --git a/block/blk-mq.c b/block/blk-mq.c index 9437a5e..07584a9 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -3208,10 +3208,6 @@ 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. -- 2.7.4