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=-4.1 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS 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 3D30CC433E0 for ; Fri, 7 Aug 2020 15:37:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 16C8F20866 for ; Fri, 7 Aug 2020 15:37:37 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=joelfernandes.org header.i=@joelfernandes.org header.b="fnVygkK2" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726393AbgHGPhf (ORCPT ); Fri, 7 Aug 2020 11:37:35 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55960 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726061AbgHGPhf (ORCPT ); Fri, 7 Aug 2020 11:37:35 -0400 Received: from mail-qk1-x743.google.com (mail-qk1-x743.google.com [IPv6:2607:f8b0:4864:20::743]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E7DE5C061756 for ; Fri, 7 Aug 2020 08:37:34 -0700 (PDT) Received: by mail-qk1-x743.google.com with SMTP id p4so2109582qkf.0 for ; Fri, 07 Aug 2020 08:37:34 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=joelfernandes.org; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=eLwi9oVvNS2LpmnHVpeAiCa4eD/S6H9JAq2fjvFA1xU=; b=fnVygkK2zJ1EV5RXMiYReFaLv63tH+QLUWn0SQ+rrEUEe8AMGkZeFGVzS7y8A/Vrvx V/nDGc/jSKVHLRTdFIWawRhjfSCcBTdIwQJAJk9CUUyJ3yi0keYeZhnh6EmMbrjTtqcd 8fEWD2Xryc/nDKOFA4AxWW6OYfVqVia6ym+Zs= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=eLwi9oVvNS2LpmnHVpeAiCa4eD/S6H9JAq2fjvFA1xU=; b=mdTQxyoyld9mU+cPZL6XkI0/BsVYWNEd8NwJp1TVlLUXJ1Nql1DE2DNNci9HNqkL0U 1t79oJ2xZJknsmuaCiAqEIirP7mYoVDEp5+SMJ1YTU7yxTKYJMKOOdrD3oeCveglSJHM mJLY85RIz0Zgo2YMCV4H1cXn/KBLi+hVcZdMpYlTTMhroJpD3Kkj8ddbr5LOQVpoDmpg kpUcnZIPuC8BHCXzOrYXLKWI3LfMd5Vpfo6I7eP1/ddpMACtR/QTyA7Y6qp9pOYDvXpI RMmq+QhxURPKyp1XBJK4LMDVk537wH8/WUp3xdqqrNZnyZ69Vyfo2RKnwsmfG7FVdOua BmfA== X-Gm-Message-State: AOAM532wbV/jAa62CJUvCBmQbF9muu300fC+KF7TzHsJ8z6BVS1sagNX ciJr+uesXEQ70DGRIQHEUcYu0Q== X-Google-Smtp-Source: ABdhPJxoa5G4OLetc65+xiFpl7TElfCRJSoj+NnB2mbtwFg1wgoPiF63XLC9Ov1yQG+ajwcdrF64Jg== X-Received: by 2002:a37:8107:: with SMTP id c7mr14316099qkd.22.1596814654004; Fri, 07 Aug 2020 08:37:34 -0700 (PDT) Received: from localhost ([2620:15c:6:12:cad3:ffff:feb3:bd59]) by smtp.gmail.com with ESMTPSA id q34sm8125956qtk.32.2020.08.07.08.37.33 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 07 Aug 2020 08:37:33 -0700 (PDT) Date: Fri, 7 Aug 2020 11:37:32 -0400 From: Joel Fernandes To: "Paul E. McKenney" Cc: linux-kernel@vger.kernel.org, Neeraj Upadhyay , Josh Triplett , Lai Jiangshan , Mathieu Desnoyers , rcu@vger.kernel.org, Steven Rostedt Subject: Re: [PATCH 1/2] rcu/tree: Add a warning if CPU being onlined did not report QS already Message-ID: <20200807153732.GA2865655@google.com> References: <20200730030221.705255-1-joel@joelfernandes.org> <20200730162159.GZ9247@paulmck-ThinkPad-P72> <20200731014222.GA2349603@google.com> <20200731034825.GI9247@paulmck-ThinkPad-P72> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200731034825.GI9247@paulmck-ThinkPad-P72> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Paul, On Thu, Jul 30, 2020 at 08:48:25PM -0700, Paul E. McKenney wrote: [...] > > And I could make the comment here as: > > /* > > * Delete QS reporting from here, by June 2021, if the warning does not > > * fire. Leave the warning indefinitely. Check RCU design requirements > > * in Documentation/RCU/ about CPU hotplug requirements. > > */ > > Rather than decide for our future selves, could we please just suggest > reviewing this on June 2021? Or, given enterprise distro schedules, > 2024. :-/ I am replacing it with the following, let me know if any objections, thanks: + * XXX: The following rcu_report_qs_rnp() is redundant. If the below + * warning does not fire, consider replacing it with the "else" block, + * by June 2021 or so. The rationale for this is as follows: The CPU + * onlining path does not need to report QS for an offline CPU. Either + * the QS should have reported during CPU offlining, or during + * rcu_gp_init() if it detected a race with either CPU offlining or + * task unblocking on previously offlined CPUs. To avoid deadlocks + * related to waiting on timers or cpu hotplug locks, only those paths + * do the QS reporting for offline CPUs. thanks, - Joel > > Thanx, Paul > > > I will post my v3 with changes to the requirements document. > > > > Let me know any other comments, thanks, > > > > - Joel > >