linux-kernel - [PATCH v2] sched/sysctl: Fix attributes of some extern declarations

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Date:   Mon, 30 Oct 2017 11:08:16 -0700
From:   Matthias Kaehlcke <mka@...omium.org>
To:     Ingo Molnar <mingo@...nel.org>,
        Shile Zhang <shile.zhang@...ia.com>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel@...r.kernel.org,
        Nick Desaulniers <nick.desaulniers@...il.com>,
        Douglas Anderson <dianders@...omium.org>,
        Guenter Roeck <groeck@...omium.org>,
        Matthias Kaehlcke <mka@...omium.org>
Subject: [PATCH v2] sched/sysctl: Fix attributes of some extern declarations

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 <mka@...omium.org>
Reviewed-by: Nick Desaulniers <nick.desaulniers@...il.com>
---
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;
 
 int sched_proc_update_handler(struct ctl_table *table, int write,
 		void __user *buffer, size_t *length,
-- 
2.15.0.rc2.357.g7e34df9404-goog