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=-2.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 C47D0C54FC9 for ; Tue, 21 Apr 2020 15:43:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 981912070B for ; Tue, 21 Apr 2020 15:43:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1587483794; bh=R/NUADyVb0jPVXUwpPx85cw01ErbiN3Dhg1JGLpE6VI=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:List-ID: From; b=vt7tPYOuB17eq4BwcMxwDo1Qor+gendckYBRZVNV7z/hLNlUKSgkzQvoMlIg1GCnd dt0921aPP6BIGfHFo0L7/e5NRhUPkUdY+Bw8OVr6FnvNZppG32bPGY/Mmb03bXj/hf p7I+PbRb6xjgUxuZSkzraZNu4rCPuDiJ4yfrrr3o= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729139AbgDUPnN (ORCPT ); Tue, 21 Apr 2020 11:43:13 -0400 Received: from mail.kernel.org ([198.145.29.99]:43578 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727023AbgDUPnN (ORCPT ); Tue, 21 Apr 2020 11:43:13 -0400 Received: from paulmck-ThinkPad-P72.home (50-39-105-78.bvtn.or.frontiernet.net [50.39.105.78]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id DB7D9206E9; Tue, 21 Apr 2020 15:43:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1587483792; bh=R/NUADyVb0jPVXUwpPx85cw01ErbiN3Dhg1JGLpE6VI=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=Ao8x/58ZZn7la+yBfyCFYFfuYED3lx9rg33fSVBDhbUeyu6r+7+Ru8Pj7mzLKt+0A WQZoZJcNG+1Trmv3u/3eNwm5VKgPLCpp/hykxPlpPatRLIpIXBaDlvOjE4T2qorEhn aiS5/YieEeUqadhHEYAdSPgVuKtxZs2IS4QheqKY= Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id C0ED33523432; Tue, 21 Apr 2020 08:43:12 -0700 (PDT) Date: Tue, 21 Apr 2020 08:43:12 -0700 From: "Paul E. McKenney" To: Peter Zijlstra Cc: Muchun Song , mingo@kernel.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, linux-kernel@vger.kernel.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, joel@joelfernandes.org Subject: Re: [PATCH] sched/fair: Fix call walk_tg_tree_from() without hold rcu_lock Message-ID: <20200421154312.GO17661@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <20200406121008.62903-1-songmuchun@bytedance.com> <20200421135258.GS20730@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200421135258.GS20730@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Apr 21, 2020 at 03:52:58PM +0200, Peter Zijlstra wrote: > On Mon, Apr 06, 2020 at 08:10:08PM +0800, Muchun Song wrote: > > The walk_tg_tree_from() caller must hold rcu_lock, > > Not quite; with the RCU unification done 'recently' having preemption > disabled is sufficient. AFAICT preemption is disabled. > > In fact; and I mentioned this to someone the other day, perhaps Joel; we > can go and delete a whole bunch of rcu_read_lock() from the scheduler -- > basically undo all the work we did after RCU was split many years ago. "If only I knew then what I know now..." Then again, I suspect that we all have ample opportunity to use that particular old phrase. ;-) Thanx, Paul