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=-0.6 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, 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 BD6B0C54FC9 for ; Tue, 21 Apr 2020 13:53:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9B2A320644 for ; Tue, 21 Apr 2020 13:53:38 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="NvpZkEOh" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729137AbgDUNxh (ORCPT ); Tue, 21 Apr 2020 09:53:37 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43072 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1728884AbgDUNxg (ORCPT ); Tue, 21 Apr 2020 09:53:36 -0400 Received: from merlin.infradead.org (unknown [IPv6:2001:8b0:10b:1231::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8AF17C061A10 for ; Tue, 21 Apr 2020 06:53:35 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=Cm++CYMcsoHl8cG3ue51rLtk5CV6sBkxw+kso6vgYGo=; b=NvpZkEOh9d9dZ42Sx/O1xfgNtp bGhF2PkYFUNGYKyFrPHeKINYmNp/MsvFY+rbz6szP/KJaMGQzie1f0eKsYHzF1pB+ZLxn0wpQLCGq foadxUdbwgobnwwB9t2aRe7Xt3vLRV/nwxtjCguJcO0HQUxTR02Svg7IbTacCpJ1d+8qUZwaWZu+k vfnXtQIBTCmZwPWZFeeLDXFJscCcbuHoiOB1uO1cdu9pQTykRikutnxu6+rWOYgh9Uq8pg7GEypUw giW6Eqsy44ErQHhRHEC8LvPrbs1EqXMxeYaZZzRFKdFJq1Un7Dil+ahaV8QdLcDdI4udyfgaGseHC TsRuwD6g==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1jQtKe-00008i-S5; Tue, 21 Apr 2020 13:53:01 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id B518030275A; Tue, 21 Apr 2020 15:52:58 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 9861C2BAC7929; Tue, 21 Apr 2020 15:52:58 +0200 (CEST) Date: Tue, 21 Apr 2020 15:52:58 +0200 From: Peter Zijlstra To: Muchun Song Cc: 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, paulmck@kernel.org, joel@joelfernandes.org Subject: Re: [PATCH] sched/fair: Fix call walk_tg_tree_from() without hold rcu_lock Message-ID: <20200421135258.GS20730@hirez.programming.kicks-ass.net> References: <20200406121008.62903-1-songmuchun@bytedance.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200406121008.62903-1-songmuchun@bytedance.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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.