linux-kernel - [PATCH 4.9 62/63] sched/sysctl: Fix attributes of some extern declarations

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Message-Id: <20190225195040.553659307@linuxfoundation.org>
Date:   Mon, 25 Feb 2019 22:12:02 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Matthias Kaehlcke <mka@...omium.org>,
        Nick Desaulniers <nick.desaulniers@...il.com>,
        Douglas Anderson <dianders@...omium.org>,
        Guenter Roeck <groeck@...omium.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Shile Zhang <shile.zhang@...ia.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        Nathan Chancellor <natechancellor@...il.com>
Subject: [PATCH 4.9 62/63] sched/sysctl: Fix attributes of some extern declarations

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Matthias Kaehlcke <mka@...omium.org>

commit a9903f04e0a4ea522d959c2f287cdf0ab029e324 upstream.

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, while it is in kernel/sched/sched.h,
and 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=y is set.

Signed-off-by: Matthias Kaehlcke <mka@...omium.org>
Reviewed-by: Nick Desaulniers <nick.desaulniers@...il.com>
Cc: Douglas Anderson <dianders@...omium.org>
Cc: Guenter Roeck <groeck@...omium.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Shile Zhang <shile.zhang@...ia.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Link: http://lkml.kernel.org/r/20171030180816.170850-1-mka@chromium.org
Signed-off-by: Ingo Molnar <mingo@...nel.org>
[nc: Backport to 4.9]
Signed-off-by: Nathan Chancellor <natechancellor@...il.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 include/linux/sched/sysctl.h |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

--- a/include/linux/sched/sysctl.h
+++ b/include/linux/sched/sysctl.h
@@ -33,9 +33,9 @@ extern unsigned int sysctl_numa_balancin
 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;
 extern unsigned int sysctl_sched_shares_window;
 
 int sched_proc_update_handler(struct ctl_table *table, int write,