commit c5905afb0ee6550b42c49213da1c22d67316c194
author Ingo Molnar <mingo@elte.hu> Fri Feb 24 08:31:31 2012 +0100
committer Ingo Molnar <mingo@elte.hu> Fri Feb 24 10:05:59 2012 +0100
tree 253fdb322e6e5b257ffda3b9b66bce90a473a6f7
parent 1cfa60dc7d7c7cc774a44eee47ff135a644a1f31

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>

net/netfilter/core.c

diff --git a/net/netfilter/core.c b/net/netfilter/core.c
index b4e8ff0..e1b7e05 100644
--- a/net/netfilter/core.c
+++ b/net/netfilter/core.c
@@ -56,7 +56,7 @@
 EXPORT_SYMBOL(nf_hooks);
 
 #if defined(CONFIG_JUMP_LABEL)
-struct jump_label_key nf_hooks_needed[NFPROTO_NUMPROTO][NF_MAX_HOOKS];
+struct static_key nf_hooks_needed[NFPROTO_NUMPROTO][NF_MAX_HOOKS];
 EXPORT_SYMBOL(nf_hooks_needed);
 #endif
 
@@ -77,7 +77,7 @@
 	list_add_rcu(&reg->list, elem->list.prev);
 	mutex_unlock(&nf_hook_mutex);
 #if defined(CONFIG_JUMP_LABEL)
-	jump_label_inc(&nf_hooks_needed[reg->pf][reg->hooknum]);
+	static_key_slow_inc(&nf_hooks_needed[reg->pf][reg->hooknum]);
 #endif
 	return 0;
 }
@@ -89,7 +89,7 @@
 	list_del_rcu(&reg->list);
 	mutex_unlock(&nf_hook_mutex);
 #if defined(CONFIG_JUMP_LABEL)
-	jump_label_dec(&nf_hooks_needed[reg->pf][reg->hooknum]);
+	static_key_slow_dec(&nf_hooks_needed[reg->pf][reg->hooknum]);
 #endif
 	synchronize_net();
 }