From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754243AbdKAIfC (ORCPT ); Wed, 1 Nov 2017 04:35:02 -0400 Received: from mail-wr0-f196.google.com ([209.85.128.196]:44102 "EHLO mail-wr0-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751721AbdKAIe7 (ORCPT ); Wed, 1 Nov 2017 04:34:59 -0400 X-Google-Smtp-Source: ABhQp+QEMutCbSX59fIqAZZYw+ZCl95EDhOjFyT/5KcTGWhHYY2PVa3wk46DKdWuNlo+j+vhXzdIWA== Date: Wed, 1 Nov 2017 09:34:55 +0100 From: Ingo Molnar To: Matthias Kaehlcke Cc: Masahiro Yamada , Shile Zhang , Peter Zijlstra , linux-kernel@vger.kernel.org, Nick Desaulniers , Douglas Anderson , Guenter Roeck Subject: Re: [PATCH v2] sched/sysctl: Fix attributes of some extern declarations Message-ID: <20171101083455.v42vqrcjsphhzkmw@gmail.com> References: <20171030180816.170850-1-mka@chromium.org> <20171031095758.wsgbrsdz7hzn5o2n@gmail.com> <20171031223157.GF96615@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20171031223157.GF96615@google.com> User-Agent: NeoMutt/20170609 (1.8.3) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Matthias Kaehlcke wrote: > El Tue, Oct 30, 2017 at 10:57:58AM +0100 Ingo Molnar ha dit: > > > * Matthias Kaehlcke wrote: > > > > > The definition of sysctl_sched_migration_cost, sysctl_sched_nr_migrate > > > and sysctl_sched_time_avg includes the attribute const_debug. This > > > attribute is not part of the extern declaration of these variables in > > > include/linux/sched/sysctl.h, as a result clang generates warnings like > > > this: > > > > > > kernel/sched/sched.h:1618:33: warning: section attribute is specified on > > > redeclared variable [-Wsection] > > > extern const_debug unsigned int sysctl_sched_time_avg; > > > ^ > > > ./include/linux/sched/sysctl.h:42:21: note: previous declaration is here > > > extern unsigned int sysctl_sched_time_avg; > > > > > > The header only declares the variables when CONFIG_SCHED_DEBUG is defined, > > > therefore it is not necessary to duplicate the definition of const_debug. > > > Instead we can use the attribute __read_mostly, which is the expansion of > > > const_debug when CONFIG_SCHED_DEBUG is set. > > > > > > Signed-off-by: Matthias Kaehlcke > > > Reviewed-by: Nick Desaulniers > > > --- > > > Changes in v2: > > > - removed pointless include of linux/static_key.h > > > - added Reviewed-by tag > > > > > > include/linux/sched/sysctl.h | 6 +++--- > > > 1 file changed, 3 insertions(+), 3 deletions(-) > > > > > > diff --git a/include/linux/sched/sysctl.h b/include/linux/sched/sysctl.h > > > index 0f5ecd4d298e..d34c823f3d36 100644 > > > --- a/include/linux/sched/sysctl.h > > > +++ b/include/linux/sched/sysctl.h > > > @@ -37,9 +37,9 @@ extern unsigned int sysctl_numa_balancing_scan_period_max; > > > extern unsigned int sysctl_numa_balancing_scan_size; > > > > > > #ifdef CONFIG_SCHED_DEBUG > > > -extern unsigned int sysctl_sched_migration_cost; > > > -extern unsigned int sysctl_sched_nr_migrate; > > > -extern unsigned int sysctl_sched_time_avg; > > > +extern __read_mostly unsigned int sysctl_sched_migration_cost; > > > +extern __read_mostly unsigned int sysctl_sched_nr_migrate; > > > +extern __read_mostly unsigned int sysctl_sched_time_avg; > > > > So I hate this change, because it pointlessly duplicates an attribute that should > > only matter at the definition site. > > It's certainly not ideal, and then again essentially the same is done > in kernel/sched/sched.h, just that here the specific attribute is > hidden behind const_debug. Ok - and that indeed is a problem and makes the Clang build warning useful, as there are two conflicting prototypes and one definition. I'll apply your fix. Thanks, Ingo