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=-14.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 20BC8C433F5 for ; Mon, 13 Sep 2021 18:35:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 06362610D2 for ; Mon, 13 Sep 2021 18:35:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1345116AbhIMSgZ (ORCPT ); Mon, 13 Sep 2021 14:36:25 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:43687 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241450AbhIMSgX (ORCPT ); Mon, 13 Sep 2021 14:36:23 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1631558107; 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=5isvOFNgXlqIatGmtfTkUEKNgVy1/GCmO2C5vtiGe3M=; b=Q+ko2pgeWQHh2iiOUPgfH+DXQia+fIJvRzuTgMBQTO3oGX/8zjL1K2U6aKTm3YI0JQjUbG 2WqG8QwCRKRVQi8TSph+vvAZdDw3K3+CjGJdxjOdfjXffcIU/VjW2z47yMvYELgA8VwsfQ Pxded/YSPX+xNV7uTbd3FrPv1BpefKo= Received: from mail-qk1-f200.google.com (mail-qk1-f200.google.com [209.85.222.200]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-212-5WdFyACgPrmh2q2auVp8cg-1; Mon, 13 Sep 2021 14:35:06 -0400 X-MC-Unique: 5WdFyACgPrmh2q2auVp8cg-1 Received: by mail-qk1-f200.google.com with SMTP id x19-20020a05620a099300b003f64d79cbbaso41869185qkx.7 for ; Mon, 13 Sep 2021 11:35:06 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:from:subject:to:cc:references:message-id:date :user-agent:mime-version:in-reply-to:content-transfer-encoding :content-language; bh=5isvOFNgXlqIatGmtfTkUEKNgVy1/GCmO2C5vtiGe3M=; b=P36a5R3I2VgXmGD/GkdrztdGFq29VxYSz42CS61/AqEAnWKj/V/BhLwCu9+oLayoiT pBp8YXI/wtr3ENZ8GPSOm6+Ma0HlEWMZgdh+NdK/nwk8IXCphMS29LMXJ/zRIhLDLTeb UdeTi1g9Pbl2zaUfgawV00RpdTZsd0NLjeGeIOWYRbuKJavLEFR16w6CIFeQHKOB91nl H7zSrqcjxzo5sXUJ6EWrGXnQ1YUHc3H941CiqX1hLtA6SWvtSzmemIfQHf3zwHTUOtmY IPE6suc/6PcTj6/P0AN7tja+s5l7Gdi3K/MNHSvteIC0kwsU3tJqfvnjo0rypvXHH2W3 nj/A== X-Gm-Message-State: AOAM532C6qAPGmgGQgeB+wHy6Z91+PeNfcFHZhKpTvV+7HiWtNOYovdp me+ylrthYQ38AvkP+frp1r71q+shIZ9F8cAeJ/PwNsY8leKEuCmOwWmM1u1Cndejw7BgqDXe1Rn pyYZ2e5qkuSX6PG0aceAC8XfkYy1J3Z2PSxbzmcJV3Pu0zQbU+ZQuAQVlyAftUUSXhtR3uDlC X-Received: by 2002:a0c:9046:: with SMTP id o64mr932413qvo.47.1631558105406; Mon, 13 Sep 2021 11:35:05 -0700 (PDT) X-Google-Smtp-Source: ABdhPJw1BG3KBsCosg0JD7e56jd8qkejQSMVo43bSnz3aaYPBYSfqDJsr5X6s1a3atd41gOJN0ooJg== X-Received: by 2002:a0c:9046:: with SMTP id o64mr932378qvo.47.1631558105055; Mon, 13 Sep 2021 11:35:05 -0700 (PDT) Received: from llong.remote.csb ([2601:191:8500:76c0::cdbc]) by smtp.gmail.com with ESMTPSA id x27sm4623407qtm.23.2021.09.13.11.35.04 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 13 Sep 2021 11:35:04 -0700 (PDT) From: Waiman Long X-Google-Original-From: Waiman Long Subject: Re: [PATCH 1/2] cgroup: Fix incorrect warning from cgroup_apply_control_disable() To: Tejun Heo Cc: Zefan Li , Johannes Weiner , Juri Lelli , cgroups@vger.kernel.org, linux-kernel@vger.kernel.org References: <20210910024256.7615-1-longman@redhat.com> Message-ID: <125c4202-68d1-1a4e-03d6-2b18f0794ba4@redhat.com> Date: Mon, 13 Sep 2021 14:35:03 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 9/13/21 2:05 PM, Tejun Heo wrote: > Hello, > > On Thu, Sep 09, 2021 at 10:42:55PM -0400, Waiman Long wrote: >> diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c >> index 881ce1470beb..e31bca9fcd46 100644 >> --- a/kernel/cgroup/cgroup.c >> +++ b/kernel/cgroup/cgroup.c >> @@ -3140,7 +3140,16 @@ static void cgroup_apply_control_disable(struct cgroup *cgrp) >> if (!css) >> continue; >> >> - WARN_ON_ONCE(percpu_ref_is_dying(&css->refcnt)); >> + /* >> + * A kill_css() might have been called previously, but >> + * the css may still linger for a while before being >> + * removed. Skip it in this case. >> + */ >> + if (percpu_ref_is_dying(&css->refcnt)) { >> + WARN_ON_ONCE(css->parent && >> + cgroup_ss_mask(dsct) & (1 << ss->id)); >> + continue; >> + } > This warning did help me catch some gnarly bugs. Any chance we can keep it > for normal cases and elide it just for remounting? The problem with percpu_ref_is_dying() is the fact that it becomes true after percpu_ref_exit() is called in css_free_rwork_fn() which has an RCU delay. If you want to catch the fact that kill_css() has been called, we can check the CSS_DYING flag which is set in kill_css() by commit 33c35aa481786 ("cgroup: Prevent kill_css() from being called more than once"). Will that be an acceptable alternative? Cheers, Longman