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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 697FFC4167B for ; Wed, 1 Nov 2023 18:00:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1344277AbjKASAt (ORCPT ); Wed, 1 Nov 2023 14:00:49 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45480 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233842AbjKASAr (ORCPT ); Wed, 1 Nov 2023 14:00:47 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 49982C1 for ; Wed, 1 Nov 2023 10:59:59 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1698861598; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=KYk0tSjsrn4HcNFkcNV6IhBOk/uVrvqmA+02iLrYOnk=; b=i7UtwFj+4Q1PRmJxDIy5TGsz6Mbdmw1Z8+ZXCAHmqCNLcVH8k/T9TV7tJk8wwbxUakdxEb uHsS53ANOfZ+cEX9wOsr33oja4RPiGURWrSwKpnixbHDsYC0DD9CFHvuI2hdSOEO2ilCNW +2aLQ7wpjRQwFnkL9E1A9U/ygGxjmTA= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-222-O4ouqYOsNNaYX_05FZqvKQ-1; Wed, 01 Nov 2023 13:59:50 -0400 X-MC-Unique: O4ouqYOsNNaYX_05FZqvKQ-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.rdu2.redhat.com [10.11.54.5]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 22A57101A529; Wed, 1 Nov 2023 17:59:49 +0000 (UTC) Received: from [10.22.33.245] (unknown [10.22.33.245]) by smtp.corp.redhat.com (Postfix) with ESMTP id E15DA1A099; Wed, 1 Nov 2023 17:59:47 +0000 (UTC) Message-ID: <8e1b5497-d4ca-50a0-7cb1-ffa098e0a1c2@redhat.com> Date: Wed, 1 Nov 2023 13:59:47 -0400 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.14.0 Subject: Re: [PATCH v2] cgroup/cpuset: Change nr_deadline_tasks to an atomic_t value Content-Language: en-US To: =?UTF-8?Q?Michal_Koutn=c3=bd?= Cc: Tejun Heo , Zefan Li , Johannes Weiner , linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, Juri Lelli , Peter Zijlstra , Ingo Molnar , Qais Yousef , Hao Luo , Dietmar Eggemann , Steven Rostedt , Xia Fukun References: <20231024141834.4073262-1-longman@redhat.com> From: Waiman Long In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.5 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/1/23 12:34, Michal Koutný wrote: > On Tue, Oct 24, 2023 at 10:18:34AM -0400, Waiman Long wrote: >> The nr_deadline_tasks field in cpuset structure was introduced by >> commit 6c24849f5515 ("sched/cpuset: Keep track of SCHED_DEADLINE task >> in cpusets"). Unlike nr_migrate_dl_tasks which is only modified under >> cpuset_mutex, nr_deadline_tasks can be updated under two different >> locks - cpuset_mutex in most cases or css_set_lock in cgroup_exit(). As >> a result, data races can happen leading to incorrect nr_deadline_tasks >> value. > The effect is that dl_update_tasks_root_domain() processes tasks > unnecessarily or that it incorrectly skips dl_add_task_root_domain()? The effect is that dl_update_tasks_root_domain() may return incorrectly or it is doing unnecessary work. Will update the commit log to reflect that. > >> Since it is not practical to somehow take cpuset_mutex in cgroup_exit(), >> the easy way out to avoid this possible race condition is by making >> nr_deadline_tasks an atomic_t value. > If css_set_lock is useless for this fields and it's going to be atomic, > could you please add (presumably) a cleanup that moves dec_dl_tasks_cs() > from under css_set_lock in cgroup_exit() to a (new but specific) > cpuset_cgrp_subsys.exit() handler? But css_set_lock is needed for updating other css data. It is true that we can move dec_dl_tasks_cs() outside of the lock. I can do that in the next version. Cheers, Longman