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=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS autolearn=unavailable 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 39071C43381 for ; Thu, 21 Feb 2019 23:06:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0CE8320838 for ; Thu, 21 Feb 2019 23:06:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727016AbfBUXGj (ORCPT ); Thu, 21 Feb 2019 18:06:39 -0500 Received: from cloudserver094114.home.pl ([79.96.170.134]:63179 "EHLO cloudserver094114.home.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726035AbfBUXGj (ORCPT ); Thu, 21 Feb 2019 18:06:39 -0500 Received: from 79.184.254.15.ipv4.supernova.orange.pl (79.184.254.15) (HELO aspire.rjw.lan) by serwer1319399.home.pl (79.96.170.134) with SMTP (IdeaSmtpServer 0.83.213) id ab686fc6f3bb911d; Fri, 22 Feb 2019 00:06:36 +0100 From: "Rafael J. Wysocki" To: "Joel Fernandes (Google)" Cc: linux-kernel@vger.kernel.org, Alexei Starovoitov , Christian Brauner , Daniel Borkmann , David Ahern , "David S. Miller" , Ido Schimmel , Ingo Molnar , "moderated list:INTEL ETHERNET DRIVERS" , Jakub Kicinski , Jeff Kirsher , Jesper Dangaard Brouer , John Fastabend , Josh Triplett , keescook@chromium.org, Lai Jiangshan , Martin KaFai Lau , Mathieu Desnoyers , netdev@vger.kernel.org, "Paul E. McKenney" , Peter Zijlstra , rcu@vger.kernel.org, Song Liu , Steven Rostedt , xdp-newbies@vger.kernel.org, Yonghong Song Subject: Re: [PATCH RFC 3/5] sched/cpufreq: Fix incorrect RCU API usage Date: Fri, 22 Feb 2019 00:05:08 +0100 Message-ID: <3194474.xhKMNsEZRq@aspire.rjw.lan> In-Reply-To: <20190221054942.132388-4-joel@joelfernandes.org> References: <20190221054942.132388-1-joel@joelfernandes.org> <20190221054942.132388-4-joel@joelfernandes.org> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thursday, February 21, 2019 6:49:40 AM CET Joel Fernandes (Google) wrote: > Recently I added an RCU annotation check to rcu_assign_pointer(). All > pointers assigned to RCU protected data are to be annotated with __rcu > inorder to be able to use rcu_assign_pointer() similar to checks in > other RCU APIs. > > This resulted in a sparse error: kernel//sched/cpufreq.c:41:9: sparse: > error: incompatible types in comparison expression (different address > spaces) > > Fix this by using the correct APIs for RCU accesses. This will > potentially avoid any future bugs in the code. If it is felt that RCU > protection is not needed here, then the rcu_assign_pointer call can be > dropped and replaced with, say, WRITE_ONCE or smp_store_release. Or, may > be we add a new API to do it. But calls rcu_assign_pointer seems an > abuse of the RCU API unless RCU is being used. > > Signed-off-by: Joel Fernandes (Google) > --- > kernel/sched/cpufreq.c | 8 ++++++-- > kernel/sched/sched.h | 2 +- > 2 files changed, 7 insertions(+), 3 deletions(-) > > diff --git a/kernel/sched/cpufreq.c b/kernel/sched/cpufreq.c > index 22bd8980f32f..c9aeb3bf5dc2 100644 > --- a/kernel/sched/cpufreq.c > +++ b/kernel/sched/cpufreq.c > @@ -7,7 +7,7 @@ > */ > #include "sched.h" > > -DEFINE_PER_CPU(struct update_util_data *, cpufreq_update_util_data); > +DEFINE_PER_CPU(struct update_util_data __rcu *, cpufreq_update_util_data); > > /** > * cpufreq_add_update_util_hook - Populate the CPU's update_util_data pointer. > @@ -34,8 +34,12 @@ void cpufreq_add_update_util_hook(int cpu, struct update_util_data *data, > if (WARN_ON(!data || !func)) > return; > > - if (WARN_ON(per_cpu(cpufreq_update_util_data, cpu))) > + rcu_read_lock(); > + if (WARN_ON(rcu_dereference(per_cpu(cpufreq_update_util_data, cpu)))) { > + rcu_read_unlock(); > return; > + } > + rcu_read_unlock(); As Steve said, this is not a read-side critical section, so the rcu_read_lock() and rcu_read_unlock() don't help. But rcu_access_pointer() should work here AFAICS. Cheers, Rafael