linux-kernel - [PATCH 3.10 171/250] locking/static_keys: Add static_key

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Date:   Thu,  8 Jun 2017 00:59:17 +0200
From:   Willy Tarreau <w@....eu>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        linux@...ck-us.net
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>,
        Ingo Molnar <mingo@...nel.org>, Jiri Slaby <jslaby@...e.cz>,
        Willy Tarreau <w@....eu>
Subject: [PATCH 3.10 171/250] locking/static_keys: Add static_key_{en,dis}able() helpers

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

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>
[wt: only backported for use in next fix ;
     s/static_key_count(key)/atomic_read(&key->enabled)/]

Signed-off-by: Willy Tarreau <w@....eu>
---
 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 0976fc4..7f831b2 100644
--- a/include/linux/jump_label.h
+++ b/include/linux/jump_label.h
@@ -208,4 +208,20 @@ static inline bool static_key_enabled(struct static_key *key)
 	return (atomic_read(&key->enabled) > 0);
 }
 
+static inline void static_key_enable(struct static_key *key)
+{
+	int count = atomic_read(&key->enabled);
+
+	if (!count)
+		static_key_slow_inc(key);
+}
+
+static inline void static_key_disable(struct static_key *key)
+{
+	int count = atomic_read(&key->enabled);
+
+	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 6a366f9..506e56e 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) { };
-- 
2.8.0.rc2.1.gbe9624a