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=-6.7 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED 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 2CEEDC3A5A3 for ; Tue, 27 Aug 2019 11:02:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0DD2620656 for ; Tue, 27 Aug 2019 11:02:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727380AbfH0LCO (ORCPT ); Tue, 27 Aug 2019 07:02:14 -0400 Received: from mx1.redhat.com ([209.132.183.28]:53322 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726059AbfH0LCO (ORCPT ); Tue, 27 Aug 2019 07:02:14 -0400 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 14D92307D915; Tue, 27 Aug 2019 11:02:14 +0000 (UTC) Received: from localhost (ovpn-8-27.pek2.redhat.com [10.72.8.27]) by smtp.corp.redhat.com (Postfix) with ESMTP id 1AC155D6B0; Tue, 27 Aug 2019 11:02:07 +0000 (UTC) From: Ming Lei To: Jens Axboe Cc: linux-block@vger.kernel.org, Ming Lei , Christoph Hellwig , Hannes Reinecke , Greg KH , Mike Snitzer , Bart Van Assche , Damien Le Moal Subject: [PATCH V4 2/5] block: don't hold q->sysfs_lock in elevator_init_mq Date: Tue, 27 Aug 2019 19:01:45 +0800 Message-Id: <20190827110148.808-3-ming.lei@redhat.com> In-Reply-To: <20190827110148.808-1-ming.lei@redhat.com> References: <20190827110148.808-1-ming.lei@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.48]); Tue, 27 Aug 2019 11:02:14 +0000 (UTC) Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org 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 --- block/elevator.c | 14 +++++--------- 1 file changed, 5 insertions(+), 9 deletions(-) diff --git a/block/elevator.c b/block/elevator.c index 2f17d66d0e61..33c15fb54ed1 100644 --- a/block/elevator.c +++ b/block/elevator.c @@ -607,23 +607,19 @@ int elevator_init_mq(struct request_queue *q) 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; } -- 2.20.1