linux-kernel - [patch added to 3.12-stable] locking/static_keys: Add static_key

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Message-Id: <20170327073617.2664-1-jslaby@suse.cz>
Date:   Mon, 27 Mar 2017 09:36:02 +0200
From:   Jiri Slaby <jslaby@...e.cz>
To:     stable@...r.kernel.org
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
        Jiri Slaby <jslaby@...e.cz>
Subject: [patch added to 3.12-stable] locking/static_keys: Add static_key_{en,dis}able() helpers

From: Peter Zijlstra <peterz@...radead.org>

This patch has been added to the 3.12 stable tree. If you have any
objections, please let us know.

===============

commit e33886b38cc82a9fc3b2d655dfc7f50467594138 upstream.

Add two helpers to make it easier to treat the refcount as boolean.

[js] do not involve WARN_ON_ONCE as it causes build failures

Suggested-by: Jason Baron <jasonbaron0@...il.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: linux-kernel@...r.kernel.org
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 include/linux/jump_label.h | 16 ++++++++++++++++
 kernel/sched/core.c        |  6 ++----
 2 files changed, 18 insertions(+), 4 deletions(-)

diff --git a/include/linux/jump_label.h b/include/linux/jump_label.h
index 9216e465289a..6fdea8105f45 100644
--- a/include/linux/jump_label.h
+++ b/include/linux/jump_label.h
@@ -188,4 +188,20 @@ static inline bool static_key_enabled(struct static_key *key)
 	return static_key_count(key) > 0;
 }
 
+static inline void static_key_enable(struct static_key *key)
+{
+	int count = static_key_count(key);
+
+	if (!count)
+		static_key_slow_inc(key);
+}
+
+static inline void static_key_disable(struct static_key *key)
+{
+	int count = static_key_count(key);
+
+	if (count)
+		static_key_slow_dec(key);
+}
+
 #endif	/* _LINUX_JUMP_LABEL_H */
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 426193802b1f..602b6c08c47d 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -179,14 +179,12 @@ struct static_key sched_feat_keys[__SCHED_FEAT_NR] = {
 
 static void sched_feat_disable(int i)
 {
-	if (static_key_enabled(&sched_feat_keys[i]))
-		static_key_slow_dec(&sched_feat_keys[i]);
+	static_key_disable(&sched_feat_keys[i]);
 }
 
 static void sched_feat_enable(int i)
 {
-	if (!static_key_enabled(&sched_feat_keys[i]))
-		static_key_slow_inc(&sched_feat_keys[i]);
+	static_key_enable(&sched_feat_keys[i]);
 }
 #else
 static void sched_feat_disable(int i) { };
-- 
2.12.2