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>

6 files changed, 112 insertions, 92 deletions

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 7c3b9de..5e0f8bb 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -128,7 +128,7 @@ enum event_type_t {
  * perf_sched_events : >0 events exist
  * perf_cgroup_events: >0 per-cpu cgroup events exist on this cpu
  */
-struct jump_label_key_deferred perf_sched_events __read_mostly;
+struct static_key_deferred perf_sched_events __read_mostly;
 static DEFINE_PER_CPU(atomic_t, perf_cgroup_events);
 
 static atomic_t nr_mmap_events __read_mostly;
@@ -2769,7 +2769,7 @@ static void free_event(struct perf_event *event)
 
 	if (!event->parent) {
 		if (event->attach_state & PERF_ATTACH_TASK)
-			jump_label_dec_deferred(&perf_sched_events);
+			static_key_slow_dec_deferred(&perf_sched_events);
 		if (event->attr.mmap || event->attr.mmap_data)
 			atomic_dec(&nr_mmap_events);
 		if (event->attr.comm)
@@ -2780,7 +2780,7 @@ static void free_event(struct perf_event *event)
 			put_callchain_buffers();
 		if (is_cgroup_event(event)) {
 			atomic_dec(&per_cpu(perf_cgroup_events, event->cpu));
-			jump_label_dec_deferred(&perf_sched_events);
+			static_key_slow_dec_deferred(&perf_sched_events);
 		}
 	}
 
@@ -4982,7 +4982,7 @@ fail:
 	return err;
 }
 
-struct jump_label_key perf_swevent_enabled[PERF_COUNT_SW_MAX];
+struct static_key perf_swevent_enabled[PERF_COUNT_SW_MAX];
 
 static void sw_perf_event_destroy(struct perf_event *event)
 {
@@ -4990,7 +4990,7 @@ static void sw_perf_event_destroy(struct perf_event *event)
 
 	WARN_ON(event->parent);
 
-	jump_label_dec(&perf_swevent_enabled[event_id]);
+	static_key_slow_dec(&perf_swevent_enabled[event_id]);
 	swevent_hlist_put(event);
 }
 
@@ -5020,7 +5020,7 @@ static int perf_swevent_init(struct perf_event *event)
 		if (err)
 			return err;
 
-		jump_label_inc(&perf_swevent_enabled[event_id]);
+		static_key_slow_inc(&perf_swevent_enabled[event_id]);
 		event->destroy = sw_perf_event_destroy;
 	}
 
@@ -5843,7 +5843,7 @@ done:
 
 	if (!event->parent) {
 		if (event->attach_state & PERF_ATTACH_TASK)
-			jump_label_inc(&perf_sched_events.key);
+			static_key_slow_inc(&perf_sched_events.key);
 		if (event->attr.mmap || event->attr.mmap_data)
 			atomic_inc(&nr_mmap_events);
 		if (event->attr.comm)
@@ -6081,7 +6081,7 @@ SYSCALL_DEFINE5(perf_event_open,
 		 * - that may need work on context switch
 		 */
 		atomic_inc(&per_cpu(perf_cgroup_events, event->cpu));
-		jump_label_inc(&perf_sched_events.key);
+		static_key_slow_inc(&perf_sched_events.key);
 	}
 
 	/*
diff --git a/kernel/jump_label.c b/kernel/jump_label.c
index 543782e..bf9dcad 100644
--- a/kernel/jump_label.c
+++ b/kernel/jump_label.c
@@ -12,7 +12,7 @@
 #include <linux/slab.h>
 #include <linux/sort.h>
 #include <linux/err.h>
-#include <linux/jump_label.h>
+#include <linux/static_key.h>
 
 #ifdef HAVE_JUMP_LABEL
 
@@ -29,10 +29,11 @@ void jump_label_unlock(void)
 	mutex_unlock(&jump_label_mutex);
 }
 
-bool jump_label_enabled(struct jump_label_key *key)
+bool static_key_enabled(struct static_key *key)
 {
-	return !!atomic_read(&key->enabled);
+	return (atomic_read(&key->enabled) > 0);
 }
+EXPORT_SYMBOL_GPL(static_key_enabled);
 
 static int jump_label_cmp(const void *a, const void *b)
 {
@@ -58,22 +59,26 @@ jump_label_sort_entries(struct jump_entry *start, struct jump_entry *stop)
 	sort(start, size, sizeof(struct jump_entry), jump_label_cmp, NULL);
 }
 
-static void jump_label_update(struct jump_label_key *key, int enable);
+static void jump_label_update(struct static_key *key, int enable);
 
-void jump_label_inc(struct jump_label_key *key)
+void static_key_slow_inc(struct static_key *key)
 {
 	if (atomic_inc_not_zero(&key->enabled))
 		return;
 
 	jump_label_lock();
-	if (atomic_read(&key->enabled) == 0)
-		jump_label_update(key, JUMP_LABEL_ENABLE);
+	if (atomic_read(&key->enabled) == 0) {
+		if (!jump_label_get_branch_default(key))
+			jump_label_update(key, JUMP_LABEL_ENABLE);
+		else
+			jump_label_update(key, JUMP_LABEL_DISABLE);
+	}
 	atomic_inc(&key->enabled);
 	jump_label_unlock();
 }
-EXPORT_SYMBOL_GPL(jump_label_inc);
+EXPORT_SYMBOL_GPL(static_key_slow_inc);
 
-static void __jump_label_dec(struct jump_label_key *key,
+static void __static_key_slow_dec(struct static_key *key,
 		unsigned long rate_limit, struct delayed_work *work)
 {
 	if (!atomic_dec_and_mutex_lock(&key->enabled, &jump_label_mutex)) {
@@ -85,32 +90,35 @@ static void __jump_label_dec(struct jump_label_key *key,
 	if (rate_limit) {
 		atomic_inc(&key->enabled);
 		schedule_delayed_work(work, rate_limit);
-	} else
-		jump_label_update(key, JUMP_LABEL_DISABLE);
-
+	} else {
+		if (!jump_label_get_branch_default(key))
+			jump_label_update(key, JUMP_LABEL_DISABLE);
+		else
+			jump_label_update(key, JUMP_LABEL_ENABLE);
+	}
 	jump_label_unlock();
 }
-EXPORT_SYMBOL_GPL(jump_label_dec);
 
 static void jump_label_update_timeout(struct work_struct *work)
 {
-	struct jump_label_key_deferred *key =
-		container_of(work, struct jump_label_key_deferred, work.work);
-	__jump_label_dec(&key->key, 0, NULL);
+	struct static_key_deferred *key =
+		container_of(work, struct static_key_deferred, work.work);
+	__static_key_slow_dec(&key->key, 0, NULL);
 }
 
-void jump_label_dec(struct jump_label_key *key)
+void static_key_slow_dec(struct static_key *key)
 {
-	__jump_label_dec(key, 0, NULL);
+	__static_key_slow_dec(key, 0, NULL);
 }
+EXPORT_SYMBOL_GPL(static_key_slow_dec);
 
-void jump_label_dec_deferred(struct jump_label_key_deferred *key)
+void static_key_slow_dec_deferred(struct static_key_deferred *key)
 {
-	__jump_label_dec(&key->key, key->timeout, &key->work);
+	__static_key_slow_dec(&key->key, key->timeout, &key->work);
 }
+EXPORT_SYMBOL_GPL(static_key_slow_dec_deferred);
 
-
-void jump_label_rate_limit(struct jump_label_key_deferred *key,
+void jump_label_rate_limit(struct static_key_deferred *key,
 		unsigned long rl)
 {
 	key->timeout = rl;
@@ -153,7 +161,7 @@ void __weak __init_or_module arch_jump_label_transform_static(struct jump_entry
 	arch_jump_label_transform(entry, type);	
 }
 
-static void __jump_label_update(struct jump_label_key *key,
+static void __jump_label_update(struct static_key *key,
 				struct jump_entry *entry,
 				struct jump_entry *stop, int enable)
 {
@@ -170,27 +178,40 @@ static void __jump_label_update(struct jump_label_key *key,
 	}
 }
 
+static enum jump_label_type jump_label_type(struct static_key *key)
+{
+	bool true_branch = jump_label_get_branch_default(key);
+	bool state = static_key_enabled(key);
+
+	if ((!true_branch && state) || (true_branch && !state))
+		return JUMP_LABEL_ENABLE;
+
+	return JUMP_LABEL_DISABLE;
+}
+
 void __init jump_label_init(void)
 {
 	struct jump_entry *iter_start = __start___jump_table;
 	struct jump_entry *iter_stop = __stop___jump_table;
-	struct jump_label_key *key = NULL;
+	struct static_key *key = NULL;
 	struct jump_entry *iter;
 
 	jump_label_lock();
 	jump_label_sort_entries(iter_start, iter_stop);
 
 	for (iter = iter_start; iter < iter_stop; iter++) {
-		struct jump_label_key *iterk;
+		struct static_key *iterk;
 
-		iterk = (struct jump_label_key *)(unsigned long)iter->key;
-		arch_jump_label_transform_static(iter, jump_label_enabled(iterk) ?
-						 JUMP_LABEL_ENABLE : JUMP_LABEL_DISABLE);
+		iterk = (struct static_key *)(unsigned long)iter->key;
+		arch_jump_label_transform_static(iter, jump_label_type(iterk));
 		if (iterk == key)
 			continue;
 
 		key = iterk;
-		key->entries = iter;
+		/*
+		 * Set key->entries to iter, but preserve JUMP_LABEL_TRUE_BRANCH.
+		 */
+		*((unsigned long *)&key->entries) += (unsigned long)iter;
 #ifdef CONFIG_MODULES
 		key->next = NULL;
 #endif
@@ -200,8 +221,8 @@ void __init jump_label_init(void)
 
 #ifdef CONFIG_MODULES
 
-struct jump_label_mod {
-	struct jump_label_mod *next;
+struct static_key_mod {
+	struct static_key_mod *next;
 	struct jump_entry *entries;
 	struct module *mod;
 };
@@ -221,9 +242,9 @@ static int __jump_label_mod_text_reserved(void *start, void *end)
 				start, end);
 }
 
-static void __jump_label_mod_update(struct jump_label_key *key, int enable)
+static void __jump_label_mod_update(struct static_key *key, int enable)
 {
-	struct jump_label_mod *mod = key->next;
+	struct static_key_mod *mod = key->next;
 
 	while (mod) {
 		struct module *m = mod->mod;
@@ -254,11 +275,7 @@ void jump_label_apply_nops(struct module *mod)
 		return;
 
 	for (iter = iter_start; iter < iter_stop; iter++) {
-		struct jump_label_key *iterk;
-
-		iterk = (struct jump_label_key *)(unsigned long)iter->key;
-		arch_jump_label_transform_static(iter, jump_label_enabled(iterk) ?
-				JUMP_LABEL_ENABLE : JUMP_LABEL_DISABLE);
+		arch_jump_label_transform_static(iter, JUMP_LABEL_DISABLE);
 	}
 }
 
@@ -267,8 +284,8 @@ static int jump_label_add_module(struct module *mod)
 	struct jump_entry *iter_start = mod->jump_entries;
 	struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
 	struct jump_entry *iter;
-	struct jump_label_key *key = NULL;
-	struct jump_label_mod *jlm;
+	struct static_key *key = NULL;
+	struct static_key_mod *jlm;
 
 	/* if the module doesn't have jump label entries, just return */
 	if (iter_start == iter_stop)
@@ -277,28 +294,30 @@ static int jump_label_add_module(struct module *mod)
 	jump_label_sort_entries(iter_start, iter_stop);
 
 	for (iter = iter_start; iter < iter_stop; iter++) {
-		if (iter->key == (jump_label_t)(unsigned long)key)
-			continue;
+		struct static_key *iterk;
 
-		key = (struct jump_label_key *)(unsigned long)iter->key;
+		iterk = (struct static_key *)(unsigned long)iter->key;
+		if (iterk == key)
+			continue;
 
+		key = iterk;
 		if (__module_address(iter->key) == mod) {
-			atomic_set(&key->enabled, 0);
-			key->entries = iter;
+			/*
+			 * Set key->entries to iter, but preserve JUMP_LABEL_TRUE_BRANCH.
+			 */
+			*((unsigned long *)&key->entries) += (unsigned long)iter;
 			key->next = NULL;
 			continue;
 		}
-
-		jlm = kzalloc(sizeof(struct jump_label_mod), GFP_KERNEL);
+		jlm = kzalloc(sizeof(struct static_key_mod), GFP_KERNEL);
 		if (!jlm)
 			return -ENOMEM;
-
 		jlm->mod = mod;
 		jlm->entries = iter;
 		jlm->next = key->next;
 		key->next = jlm;
 
-		if (jump_label_enabled(key))
+		if (jump_label_type(key) == JUMP_LABEL_ENABLE)
 			__jump_label_update(key, iter, iter_stop, JUMP_LABEL_ENABLE);
 	}
 
@@ -310,14 +329,14 @@ static void jump_label_del_module(struct module *mod)
 	struct jump_entry *iter_start = mod->jump_entries;
 	struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
 	struct jump_entry *iter;
-	struct jump_label_key *key = NULL;
-	struct jump_label_mod *jlm, **prev;
+	struct static_key *key = NULL;
+	struct static_key_mod *jlm, **prev;
 
 	for (iter = iter_start; iter < iter_stop; iter++) {
 		if (iter->key == (jump_label_t)(unsigned long)key)
 			continue;
 
-		key = (struct jump_label_key *)(unsigned long)iter->key;
+		key = (struct static_key *)(unsigned long)iter->key;
 
 		if (__module_address(iter->key) == mod)
 			continue;
@@ -419,9 +438,10 @@ int jump_label_text_reserved(void *start, void *end)
 	return ret;
 }
 
-static void jump_label_update(struct jump_label_key *key, int enable)
+static void jump_label_update(struct static_key *key, int enable)
 {
-	struct jump_entry *entry = key->entries, *stop = __stop___jump_table;
+	struct jump_entry *stop = __stop___jump_table;
+	struct jump_entry *entry = jump_label_get_entries(key);
 
 #ifdef CONFIG_MODULES
 	struct module *mod = __module_address((unsigned long)key);
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 5255c9d..112c682 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -162,13 +162,13 @@ static int sched_feat_show(struct seq_file *m, void *v)
 
 #ifdef HAVE_JUMP_LABEL
 
-#define jump_label_key__true  jump_label_key_enabled
-#define jump_label_key__false jump_label_key_disabled
+#define jump_label_key__true  STATIC_KEY_INIT_TRUE
+#define jump_label_key__false STATIC_KEY_INIT_FALSE
 
 #define SCHED_FEAT(name, enabled)	\
 	jump_label_key__##enabled ,
 
-struct jump_label_key sched_feat_keys[__SCHED_FEAT_NR] = {
+struct static_key sched_feat_keys[__SCHED_FEAT_NR] = {
 #include "features.h"
 };
 
@@ -176,14 +176,14 @@ struct jump_label_key sched_feat_keys[__SCHED_FEAT_NR] = {
 
 static void sched_feat_disable(int i)
 {
-	if (jump_label_enabled(&sched_feat_keys[i]))
-		jump_label_dec(&sched_feat_keys[i]);
+	if (static_key_enabled(&sched_feat_keys[i]))
+		static_key_slow_dec(&sched_feat_keys[i]);
 }
 
 static void sched_feat_enable(int i)
 {
-	if (!jump_label_enabled(&sched_feat_keys[i]))
-		jump_label_inc(&sched_feat_keys[i]);
+	if (!static_key_enabled(&sched_feat_keys[i]))
+		static_key_slow_inc(&sched_feat_keys[i]);
 }
 #else
 static void sched_feat_disable(int i) { };
@@ -894,7 +894,7 @@ static void update_rq_clock_task(struct rq *rq, s64 delta)
 	delta -= irq_delta;
 #endif
 #ifdef CONFIG_PARAVIRT_TIME_ACCOUNTING
-	if (static_branch((&paravirt_steal_rq_enabled))) {
+	if (static_key_false((&paravirt_steal_rq_enabled))) {
 		u64 st;
 
 		steal = paravirt_steal_clock(cpu_of(rq));
@@ -2756,7 +2756,7 @@ void account_idle_time(cputime_t cputime)
 static __always_inline bool steal_account_process_tick(void)
 {
 #ifdef CONFIG_PARAVIRT
-	if (static_branch(&paravirt_steal_enabled)) {
+	if (static_key_false(&paravirt_steal_enabled)) {
 		u64 steal, st = 0;
 
 		steal = paravirt_steal_clock(smp_processor_id());
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 7c6414f..423547a 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1399,20 +1399,20 @@ entity_tick(struct cfs_rq *cfs_rq, struct sched_entity *curr, int queued)
 #ifdef CONFIG_CFS_BANDWIDTH
 
 #ifdef HAVE_JUMP_LABEL
-static struct jump_label_key __cfs_bandwidth_used;
+static struct static_key __cfs_bandwidth_used;
 
 static inline bool cfs_bandwidth_used(void)
 {
-	return static_branch(&__cfs_bandwidth_used);
+	return static_key_false(&__cfs_bandwidth_used);
 }
 
 void account_cfs_bandwidth_used(int enabled, int was_enabled)
 {
 	/* only need to count groups transitioning between enabled/!enabled */
 	if (enabled && !was_enabled)
-		jump_label_inc(&__cfs_bandwidth_used);
+		static_key_slow_inc(&__cfs_bandwidth_used);
 	else if (!enabled && was_enabled)
-		jump_label_dec(&__cfs_bandwidth_used);
+		static_key_slow_dec(&__cfs_bandwidth_used);
 }
 #else /* HAVE_JUMP_LABEL */
 static bool cfs_bandwidth_used(void)
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 98c0c26..b4cd6d8 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -611,7 +611,7 @@ static inline void __set_task_cpu(struct task_struct *p, unsigned int cpu)
  * Tunables that become constants when CONFIG_SCHED_DEBUG is off:
  */
 #ifdef CONFIG_SCHED_DEBUG
-# include <linux/jump_label.h>
+# include <linux/static_key.h>
 # define const_debug __read_mostly
 #else
 # define const_debug const
@@ -630,18 +630,18 @@ enum {
 #undef SCHED_FEAT
 
 #if defined(CONFIG_SCHED_DEBUG) && defined(HAVE_JUMP_LABEL)
-static __always_inline bool static_branch__true(struct jump_label_key *key)
+static __always_inline bool static_branch__true(struct static_key *key)
 {
-	return likely(static_branch(key)); /* Not out of line branch. */
+	return static_key_true(key); /* Not out of line branch. */
 }
 
-static __always_inline bool static_branch__false(struct jump_label_key *key)
+static __always_inline bool static_branch__false(struct static_key *key)
 {
-	return unlikely(static_branch(key)); /* Out of line branch. */
+	return static_key_false(key); /* Out of line branch. */
 }
 
 #define SCHED_FEAT(name, enabled)					\
-static __always_inline bool static_branch_##name(struct jump_label_key *key) \
+static __always_inline bool static_branch_##name(struct static_key *key) \
 {									\
 	return static_branch__##enabled(key);				\
 }
@@ -650,7 +650,7 @@ static __always_inline bool static_branch_##name(struct jump_label_key *key) \
 
 #undef SCHED_FEAT
 
-extern struct jump_label_key sched_feat_keys[__SCHED_FEAT_NR];
+extern struct static_key sched_feat_keys[__SCHED_FEAT_NR];
 #define sched_feat(x) (static_branch_##x(&sched_feat_keys[__SCHED_FEAT_##x]))
 #else /* !(SCHED_DEBUG && HAVE_JUMP_LABEL) */
 #define sched_feat(x) (sysctl_sched_features & (1UL << __SCHED_FEAT_##x))
diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
index f1539de..d96ba22 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);
 }