context_tracking: Switch to new static_branch API

This is much less error-prone than the old code.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/812df7e64f120c5c7c08481f36a8caa9f53b2199.1447361906.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
diff --git a/kernel/context_tracking.c b/kernel/context_tracking.c
index d8560ee..9ad37b9 100644
--- a/kernel/context_tracking.c
+++ b/kernel/context_tracking.c
@@ -24,7 +24,7 @@
 #define CREATE_TRACE_POINTS
 #include <trace/events/context_tracking.h>
 
-struct static_key context_tracking_enabled = STATIC_KEY_INIT_FALSE;
+DEFINE_STATIC_KEY_FALSE(context_tracking_enabled);
 EXPORT_SYMBOL_GPL(context_tracking_enabled);
 
 DEFINE_PER_CPU(struct context_tracking, context_tracking);
@@ -191,7 +191,7 @@
 
 	if (!per_cpu(context_tracking.active, cpu)) {
 		per_cpu(context_tracking.active, cpu) = true;
-		static_key_slow_inc(&context_tracking_enabled);
+		static_branch_inc(&context_tracking_enabled);
 	}
 
 	if (initialized)