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=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 0E1DEC43381 for ; Mon, 25 Mar 2019 05:37:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C349F2075D for ; Mon, 25 Mar 2019 05:37:04 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=oracle.com header.i=@oracle.com header.b="sK+4ZZVA" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729568AbfCYFhD (ORCPT ); Mon, 25 Mar 2019 01:37:03 -0400 Received: from userp2120.oracle.com ([156.151.31.85]:59446 "EHLO userp2120.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729327AbfCYFhC (ORCPT ); Mon, 25 Mar 2019 01:37:02 -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 x2P5Y5vs005446; Mon, 25 Mar 2019 05:36:33 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=B16cFUfS6yD+xn3VK8ZrKe+BmymbY5Q0EdsbbXhicUo=; b=sK+4ZZVAOksYvXgHt9jhsfEpVy84xvxZbE8OoGulW2marKlomEGPYt7l8IWTJ8swj/p3 l3KOL6D4ve11bFNb26pYuBAqIR/y9zKl0Fv/g5NttvEcd4d7CO5ZZ5kno/EyBmQEynuC wT4KxJZz+HtFmTDDoLb5crioGgWt+esi0FrNGVI24hAsWKnyt3Sil4joR4bIjwAsiIs5 8+LtizSA/kgZUX86RXnF4XraTXaFLe+ODeC9CxR+h8FeCtekTKuF3jpJJuj2Eu0FJ9p9 AH0sjBQvre/HCAIJY44hgLYnveXj9Q+meYg7zuCguRZyfTBiPpvaXqy0o6FiaK4aee1A VA== Received: from aserv0022.oracle.com (aserv0022.oracle.com [141.146.126.234]) by userp2120.oracle.com with ESMTP id 2re6dj1tpy-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 25 Mar 2019 05:36:32 +0000 Received: from userv0122.oracle.com (userv0122.oracle.com [156.151.31.75]) by aserv0022.oracle.com (8.14.4/8.14.4) with ESMTP id x2P5aVoC021084 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 25 Mar 2019 05:36:31 GMT Received: from abhmp0012.oracle.com (abhmp0012.oracle.com [141.146.116.18]) by userv0122.oracle.com (8.14.4/8.14.4) with ESMTP id x2P5aUFA027811; Mon, 25 Mar 2019 05:36:30 GMT Received: from will-ThinkCentre-M93p.cn.oracle.com (/10.182.71.12) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Sun, 24 Mar 2019 22:36:30 -0700 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-nvme@lists.infradead.org, linux-kernel@vger.kernel.org Subject: [PATCH V2 1/8] blk-mq: get rid of the synchronize_rcu in __blk_mq_update_nr_hw_queues Date: Mon, 25 Mar 2019 13:28:02 +0800 Message-Id: <1553491689-1730-2-git-send-email-jianchao.w.wang@oracle.com> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1553491689-1730-1-git-send-email-jianchao.w.wang@oracle.com> References: <1553491689-1730-1-git-send-email-jianchao.w.wang@oracle.com> 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=1 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 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-1903250043 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@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. Reviewed-by: Ming Lei 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 a4931fc..5f28002 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 a9c1816..2102d91 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -3211,10 +3211,6 @@ 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