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=-19.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_GIT 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 AD5A6C4332E for ; Thu, 11 Feb 2021 16:03:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8B40464E92 for ; Thu, 11 Feb 2021 16:03:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231778AbhBKQDO (ORCPT ); Thu, 11 Feb 2021 11:03:14 -0500 Received: from mail.kernel.org ([198.145.29.99]:52620 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230337AbhBKPUh (ORCPT ); Thu, 11 Feb 2021 10:20:37 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id F1A6D64F2D; Thu, 11 Feb 2021 15:07:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1613056023; bh=C0DPekt7cQ22yF5PHlX2iRYj1NNUEKIwedTttxOIvXU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=n1sVoj93yPS0XtUl4IcQUaX11ss4FBIM4wB6rmcPO39jmZ6RZJu1wKvh8C7DtBWr0 7cufx56k4EfPkfns+X7q/NQG5U90yE2puCEjEiNNXZt1+JVK6U/+gcAKjQUUmlbwsw KOhpCnfxjVarI1dL9wAIFxNr2UuvcXRiyTjmFQOs= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Christoph Hellwig , Hannes Reinecke , Mike Snitzer , Bart Van Assche , Damien Le Moal , Ming Lei , Jens Axboe , Jack Wang Subject: [PATCH 4.19 20/24] block: dont hold q->sysfs_lock in elevator_init_mq Date: Thu, 11 Feb 2021 16:02:54 +0100 Message-Id: <20210211150148.637345944@linuxfoundation.org> X-Mailer: git-send-email 2.30.1 In-Reply-To: <20210211150147.743660073@linuxfoundation.org> References: <20210211150147.743660073@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Ming Lei commit c48dac137a62a5d6fa1ef3fa445cbd9c43655a76 upstream. The original comment says: q->sysfs_lock must be held to provide mutual exclusion between elevator_switch() and here. Which is simply wrong. elevator_init_mq() is only called from blk_mq_init_allocated_queue, which is always called before the request queue is registered via blk_register_queue(), for dm-rq or normal rq based driver. However, queue's kobject is only exposed and added to sysfs in blk_register_queue(). So there isn't such race between elevator_switch() and elevator_init_mq(). So avoid to hold q->sysfs_lock in elevator_init_mq(). Cc: Christoph Hellwig Cc: Hannes Reinecke Cc: Greg KH Cc: Mike Snitzer Cc: Bart Van Assche Cc: Damien Le Moal Reviewed-by: Bart Van Assche Signed-off-by: Ming Lei Signed-off-by: Jens Axboe Signed-off-by: Jack Wang Signed-off-by: Greg Kroah-Hartman --- block/elevator.c | 14 +++++--------- 1 file changed, 5 insertions(+), 9 deletions(-) --- a/block/elevator.c +++ b/block/elevator.c @@ -980,23 +980,19 @@ int elevator_init_mq(struct request_queu if (q->nr_hw_queues != 1) return 0; - /* - * q->sysfs_lock must be held to provide mutual exclusion between - * elevator_switch() and here. - */ - mutex_lock(&q->sysfs_lock); + WARN_ON_ONCE(test_bit(QUEUE_FLAG_REGISTERED, &q->queue_flags)); + if (unlikely(q->elevator)) - goto out_unlock; + goto out; e = elevator_get(q, "mq-deadline", false); if (!e) - goto out_unlock; + goto out; err = blk_mq_init_sched(q, e); if (err) elevator_put(e); -out_unlock: - mutex_unlock(&q->sysfs_lock); +out: return err; }