static keys: Introduce 'struct static_key', static_key_true()/false() and static_key_slow_[inc|dec]()

So here's a boot tested patch on top of Jason's series that does
all the cleanups I talked about and turns jump labels into a
more intuitive to use facility. It should also address the
various misconceptions and confusions that surround jump labels.

Typical usage scenarios:

        #include <linux/static_key.h>

        struct static_key key = STATIC_KEY_INIT_TRUE;

        if (static_key_false(&key))
                do unlikely code
        else
                do likely code

Or:

        if (static_key_true(&key))
                do likely code
        else
                do unlikely code

The static key is modified via:

        static_key_slow_inc(&key);
        ...
        static_key_slow_dec(&key);

The 'slow' prefix makes it abundantly clear that this is an
expensive operation.

I've updated all in-kernel code to use this everywhere. Note
that I (intentionally) have not pushed through the rename
blindly through to the lowest levels: the actual jump-label
patching arch facility should be named like that, so we want to
decouple jump labels from the static-key facility a bit.

On non-jump-label enabled architectures static keys default to
likely()/unlikely() branches.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Acked-by: Jason Baron <jbaron@redhat.com>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Cc: a.p.zijlstra@chello.nl
Cc: mathieu.desnoyers@efficios.com
Cc: davem@davemloft.net
Cc: ddaney.cavm@gmail.com
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/20120222085809.GA26397@elte.hu
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 10 insertions, 10 deletions

diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
index f1539decd99..d96ba22dabf 100644
--- a/kernel/tracepoint.c
+++ b/kernel/tracepoint.c
@@ -25,7 +25,7 @@
 #include <linux/err.h>
 #include <linux/slab.h>
 #include <linux/sched.h>
-#include <linux/jump_label.h>
+#include <linux/static_key.h>
 
 extern struct tracepoint * const __start___tracepoints_ptrs[];
 extern struct tracepoint * const __stop___tracepoints_ptrs[];
@@ -256,9 +256,9 @@ static void set_tracepoint(struct tracepoint_entry **entry,
 {
 	WARN_ON(strcmp((*entry)->name, elem->name) != 0);
 
-	if (elem->regfunc && !jump_label_enabled(&elem->key) && active)
+	if (elem->regfunc && !static_key_enabled(&elem->key) && active)
 		elem->regfunc();
-	else if (elem->unregfunc && jump_label_enabled(&elem->key) && !active)
+	else if (elem->unregfunc && static_key_enabled(&elem->key) && !active)
 		elem->unregfunc();
 
 	/*
@@ -269,10 +269,10 @@ static void set_tracepoint(struct tracepoint_entry **entry,
 	 * is used.
 	 */
 	rcu_assign_pointer(elem->funcs, (*entry)->funcs);
-	if (active && !jump_label_enabled(&elem->key))
-		jump_label_inc(&elem->key);
-	else if (!active && jump_label_enabled(&elem->key))
-		jump_label_dec(&elem->key);
+	if (active && !static_key_enabled(&elem->key))
+		static_key_slow_inc(&elem->key);
+	else if (!active && static_key_enabled(&elem->key))
+		static_key_slow_dec(&elem->key);
 }
 
 /*
@@ -283,11 +283,11 @@ static void set_tracepoint(struct tracepoint_entry **entry,
  */
 static void disable_tracepoint(struct tracepoint *elem)
 {
-	if (elem->unregfunc && jump_label_enabled(&elem->key))
+	if (elem->unregfunc && static_key_enabled(&elem->key))
 		elem->unregfunc();
 
-	if (jump_label_enabled(&elem->key))
-		jump_label_dec(&elem->key);
+	if (static_key_enabled(&elem->key))
+		static_key_slow_dec(&elem->key);
 	rcu_assign_pointer(elem->funcs, NULL);
 }