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=-2.5 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, 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 CF11AC47404 for ; Thu, 12 Sep 2019 13:13:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9FF9B2084D for ; Thu, 12 Sep 2019 13:13:56 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=kernel-dk.20150623.gappssmtp.com header.i=@kernel-dk.20150623.gappssmtp.com header.b="IkOmuc8t" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731749AbfILNN4 (ORCPT ); Thu, 12 Sep 2019 09:13:56 -0400 Received: from mail-pf1-f196.google.com ([209.85.210.196]:36655 "EHLO mail-pf1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731283AbfILNNz (ORCPT ); Thu, 12 Sep 2019 09:13:55 -0400 Received: by mail-pf1-f196.google.com with SMTP id y22so16025815pfr.3 for ; Thu, 12 Sep 2019 06:13:52 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel-dk.20150623.gappssmtp.com; s=20150623; h=subject:to:cc:references:from:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=+Q1W0kNNUr5cIkEJ99a/uCvT7A7Ngx5Y71tVQcQVETA=; b=IkOmuc8tdiJhGS1NMxy+Idj96CRlUBl9Mo+odPgaT0msmISZ1V51UhpGui+1ygllrV dn3u6n45xsE30kQBn/lt/Q5q9p3hLHIYWLCd6NshvdRQ14aDhWl3LJyflx7Hsr5bUB3p X7x9E5XH3T7rBhjPOBKDefGJHOfMQh/GeCAvxyb2uEqpQC/RVH6IsivdJrgnfKcnRCkg sRFRYdwMJwQTO/6spOTYgTUa6IMUXrt4NUKyLnhCA0uNtdDT17aJYVatb9GbOtrjgvR9 53fSiiziIiwm8FFPAfz9x4+1rkgDatjDT0TyrYOAy21RDOvMbmGzkiRipPYBRorb8suE 406g== 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=+Q1W0kNNUr5cIkEJ99a/uCvT7A7Ngx5Y71tVQcQVETA=; b=rEBElUGxR2tXrK/smIpR1KJ61IjHviViVN7b7rEhjcFHXYZUj6cSFctyr2N+dH39b0 VxA+tf3tIccAt0M2f9nAJ+YEZURygu0Ie1rII0Gt/MjCS61h/pQroG6O6FkXgOtIWaRB RfwJe63Sxw6HUjJkyr21fwZUWRqziTCGpjrjUiQHFE2UiAIEM4g1YT0E2Ey/wGeqPp+S 2cz6IJCJf+LbXiQx2zDI2bLrDKEHl+WnlMNlnVRqpedcBe3V55+rvofrHNPtGZ8Benis egJ+RkSh2jZu0kIByOLbm2e/boiMJRUbERPIQEZHWk5CiqnovQ8z0MTQJNg0WxWfyv0I ipZQ== X-Gm-Message-State: APjAAAX86/YHQlJNjRaow4Bsd/lIxhWVJZ3aLEfQqCA7XSqOJfnoNCOc 8NAw0pzttNaknuF3WooFRYSqhx7BNCiv7g== X-Google-Smtp-Source: APXvYqy0UZBE/+dRwqZxY6Zz3y78Ej/WoGg0v+49e9/oqIqvn5m7wBIi80Rp3LhBsoLMIIDdqz8wEw== X-Received: by 2002:a63:2b0c:: with SMTP id r12mr37950896pgr.206.1568294031658; Thu, 12 Sep 2019 06:13:51 -0700 (PDT) Received: from ?IPv6:2600:380:4b2e:3b64:29ff:2f14:b019:100? ([2600:380:4b2e:3b64:29ff:2f14:b019:100]) by smtp.gmail.com with ESMTPSA id l72sm6425648pjb.7.2019.09.12.06.13.49 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 12 Sep 2019 06:13:50 -0700 (PDT) Subject: Re: [PATCH] block: fix race between switching elevator and removing queues To: Ming Lei Cc: linux-block@vger.kernel.org, Christoph Hellwig , Hannes Reinecke , Greg KH , Mike Snitzer , Bart Van Assche References: <20190912040224.7554-1-ming.lei@redhat.com> From: Jens Axboe Message-ID: <5e27cc85-d6ec-b77b-3584-648fb1a88c58@kernel.dk> Date: Thu, 12 Sep 2019 07:13:48 -0600 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: <20190912040224.7554-1-ming.lei@redhat.com> Content-Type: text/plain; charset=utf-8 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 9/11/19 10:02 PM, Ming Lei wrote: > cecf5d87ff20 ("block: split .sysfs_lock into two locks") starts to > release & actuire sysfs_lock again during switching elevator. So it > isn't enough to prevent switching elevator from happening by simply > clearing QUEUE_FLAG_REGISTERED with holding sysfs_lock, because > in-progress switch still can move on after re-acquiring the lock, > meantime the flag of QUEUE_FLAG_REGISTERED won't get checked. > > Fixes this issue by checking 'q->elevator' directly & locklessly after > q->kobj is removed in blk_unregister_queue(), this way is safe because > q->elevator can't be changed at that time. Thanks Ming, looks good to me and cleaner than before too. -- Jens Axboe