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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 82707C3A5A3 for ; Fri, 23 Aug 2019 16:46:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6527C21848 for ; Fri, 23 Aug 2019 16:46:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732939AbfHWQqu (ORCPT ); Fri, 23 Aug 2019 12:46:50 -0400 Received: from mail-pg1-f193.google.com ([209.85.215.193]:37797 "EHLO mail-pg1-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729659AbfHWQqu (ORCPT ); Fri, 23 Aug 2019 12:46:50 -0400 Received: by mail-pg1-f193.google.com with SMTP id d1so6072134pgp.4 for ; Fri, 23 Aug 2019 09:46:50 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=qM187xz+2+a1f+AI7u/OAtVFglgdVMWQOLdPSnLHvIY=; b=fLGJoSDiJMUmutHqhfaLBTU6hwcrQKyigi1RoAAbhSWzAIPtWlJxwvE/e7rSArMkPe GJ9msMnRWXJNy5fMiNU772Np6tnGPvcUDviLBeFmD3FeY4cvDPT6EbKGVKw91u5J2950 aipVq2DZU4N+HAghac3ZlTdoGiNHf+0Uq5o81YguX2bnI/zQTwJwWoVAzbVzYXMEQK7t 6o/d/KdvwGT6ZVnGh+HNzfTYs++esQRrkaWpEQej46FnpyiZAM7nJzo6tja5NKm1tvtM AJxZch1ZPo7BSxr3bP2dcsHXeGQlm0ncamXhmIQMy+gd09ddI4sekzedq7tOJwyNIfRd 5sIQ== X-Gm-Message-State: APjAAAXRKiTZAiCXJqurIRC69heGCx3YPIwakyntpFOmjygNgHkzXTRx 777Bi3cvVv9CYt0kpiUub+8= X-Google-Smtp-Source: APXvYqw8jgNMK4CZQs+No2nYxfTbHZwdVS0SUF7pU7e0DFOy0yykxLtcl9JLPl8EeRci7qOd9DlGmg== X-Received: by 2002:a63:6f41:: with SMTP id k62mr4845251pgc.32.1566578809756; Fri, 23 Aug 2019 09:46:49 -0700 (PDT) Received: from asus.site ([2601:647:4000:1349:56c2:95e9:3c7:9c11]) by smtp.gmail.com with ESMTPSA id z28sm3876936pfj.74.2019.08.23.09.46.48 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 23 Aug 2019 09:46:49 -0700 (PDT) Subject: Re: [PATCH V2 6/6] block: split .sysfs_lock into two locks To: Ming Lei , Jens Axboe Cc: linux-block@vger.kernel.org, Christoph Hellwig , Hannes Reinecke , Greg KH , Mike Snitzer References: <20190821091506.21196-1-ming.lei@redhat.com> <20190821091506.21196-7-ming.lei@redhat.com> From: Bart Van Assche Message-ID: Date: Fri, 23 Aug 2019 09:46:48 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <20190821091506.21196-7-ming.lei@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On 8/21/19 2:15 AM, Ming Lei wrote: > @@ -966,7 +966,7 @@ int blk_register_queue(struct gendisk *disk) > return ret; > > /* Prevent changes through sysfs until registration is completed. */ > - mutex_lock(&q->sysfs_lock); > + mutex_lock(&q->sysfs_dir_lock); > > ret = kobject_add(&q->kobj, kobject_get(&dev->kobj), "%s", "queue"); > if (ret < 0) { > @@ -987,26 +987,37 @@ int blk_register_queue(struct gendisk *disk) > blk_mq_debugfs_register(q); > } > > - kobject_uevent(&q->kobj, KOBJ_ADD); > - > - wbt_enable_default(q); > - > - blk_throtl_register_queue(q); > - > + /* > + * The queue's kobject ADD uevent isn't sent out, also the > + * flag of QUEUE_FLAG_REGISTERED isn't set yet, so elevator > + * switch won't happen at all. > + */ > if (q->elevator) { > - ret = elv_register_queue(q); > + ret = elv_register_queue(q, false); > if (ret) { The above changes seems risky to me. In contrast with what the comment suggests, user space code is not required to wait for KOBJ_ADD event to start using sysfs attributes. I think user space code *can* write into the request queue I/O scheduler sysfs attribute after the kobject_add() call has finished and before kobject_uevent(&q->kobj, KOBJ_ADD) is called. Bart.