[PATCH v2 1/4] jump_label: remove bug.h, atomic.h dependencies for HAVE_JUMP_LABEL

[Jason Baron]

The current jump_label.h includes bug.h for things such as WARN_ON(). This
makes the header problematic for inclusion by kernel.h or any headers that
kernel.h includes, since bug.h includes kernel.h (circular dependency). The
inclusion of atomic.h is similarly problematic. Thus, this should make
jump_label.h 'includable' from most places.

Signed-off-by: Jason Baron <jbaron@xxxxxxxxxx>
---
 include/linux/jump_label.h | 50 +++++++++++++++++++++++++++-------------------
 kernel/jump_label.c        | 48 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 78 insertions(+), 20 deletions(-)

diff --git a/include/linux/jump_label.h b/include/linux/jump_label.h
index 0536524..3b9ebb9 100644
--- a/include/linux/jump_label.h
+++ b/include/linux/jump_label.h
@@ -76,7 +76,6 @@
 
 #include <linux/types.h>
 #include <linux/compiler.h>
-#include <linux/bug.h>
 
 extern bool static_key_initialized;
 
@@ -115,13 +114,6 @@ enum jump_label_type {
 
 struct module;
 
-#include <linux/atomic.h>
-
-static inline int static_key_count(struct static_key *key)
-{
-	return atomic_read(&key->enabled);
-}
-
 #ifdef HAVE_JUMP_LABEL
 
 #define JUMP_TYPE_FALSE	0UL
@@ -152,16 +144,34 @@ extern int jump_label_text_reserved(void *start, void *end);
 extern void static_key_slow_inc(struct static_key *key);
 extern void static_key_slow_dec(struct static_key *key);
 extern void jump_label_apply_nops(struct module *mod);
+extern int static_key_count(struct static_key *key);
+extern void static_key_enable(struct static_key *key);
+extern void static_key_disable(struct static_key *key);
 
-#define STATIC_KEY_INIT_TRUE					\
-	{ .enabled = ATOMIC_INIT(1),				\
+/*
+ * We should be using ATOMIC_INIT() for initializing .enabled, but
+ * the inclusion of atomic.h is problematic for inclusion of jump_label.h
+ * in 'low-level' headers. Thus, we are initializing .enabled with a
+ * raw value, but have added a BUILD_BUG_ON() to catch any issues in
+ * jump_label_init() see: kernel/jump_label.c.
+ */
+#define STATIC_KEY_INIT_TRUE			\
+	{ .enabled = { 1 },			\
 	  .entries = (void *)JUMP_TYPE_TRUE }
-#define STATIC_KEY_INIT_FALSE					\
-	{ .enabled = ATOMIC_INIT(0),				\
+#define STATIC_KEY_INIT_FALSE			\
+	{ .enabled = { 0 },			\
 	  .entries = (void *)JUMP_TYPE_FALSE }
 
 #else  /* !HAVE_JUMP_LABEL */
 
+#include <linux/atomic.h>
+#include <linux/bug.h>
+
+static inline int static_key_count(struct static_key *key)
+{
+	return atomic_read(&key->enabled);
+}
+
 static __always_inline void jump_label_init(void)
 {
 	static_key_initialized = true;
@@ -206,14 +216,6 @@ static inline int jump_label_apply_nops(struct module *mod)
 	return 0;
 }
 
-#define STATIC_KEY_INIT_TRUE	{ .enabled = ATOMIC_INIT(1) }
-#define STATIC_KEY_INIT_FALSE	{ .enabled = ATOMIC_INIT(0) }
-
-#endif	/* HAVE_JUMP_LABEL */
-
-#define STATIC_KEY_INIT STATIC_KEY_INIT_FALSE
-#define jump_label_enabled static_key_enabled
-
 static inline void static_key_enable(struct static_key *key)
 {
 	int count = static_key_count(key);
@@ -234,6 +236,14 @@ static inline void static_key_disable(struct static_key *key)
 		static_key_slow_dec(key);
 }
 
+#define STATIC_KEY_INIT_TRUE	{ .enabled = ATOMIC_INIT(1) }
+#define STATIC_KEY_INIT_FALSE	{ .enabled = ATOMIC_INIT(0) }
+
+#endif	/* HAVE_JUMP_LABEL */
+
+#define STATIC_KEY_INIT STATIC_KEY_INIT_FALSE
+#define jump_label_enabled static_key_enabled
+
 /* -------------------------------------------------------------------------- */
 
 /*
diff --git a/kernel/jump_label.c b/kernel/jump_label.c
index 05254ee..3c67e5e 100644
--- a/kernel/jump_label.c
+++ b/kernel/jump_label.c
@@ -14,6 +14,7 @@
 #include <linux/err.h>
 #include <linux/static_key.h>
 #include <linux/jump_label_ratelimit.h>
+#include <linux/bug.h>
 
 #ifdef HAVE_JUMP_LABEL
 
@@ -56,6 +57,44 @@ jump_label_sort_entries(struct jump_entry *start, struct jump_entry *stop)
 
 static void jump_label_update(struct static_key *key);
 
+/*
+ * There is a similar definition for the !HAVE_JUMP_LABEL case in jump_label.h.
+ * The reason for the copying is that the use of 'atomic_read()' requires
+ * atomic.h and its problematic for some kernel headers such as kernel.h and
+ * others. Since static_key_count() is not used in the branch statements as it
+ * is for the !HAVE_JUMP_LABEL case its ok to have it be a function here.
+ * Similarly, for 'static_key_enable()' and 'static_key_disable()', which
+ * require bug.h. This should allow jump_label.h to be included from most/all
+ * places for HAVE_JUMP_LABEL.
+ */
+int static_key_count(struct static_key *key)
+{
+	return atomic_read(&key->enabled);
+}
+EXPORT_SYMBOL_GPL(static_key_count);
+
+void static_key_enable(struct static_key *key)
+{
+	int count = static_key_count(key);
+
+	WARN_ON_ONCE(count < 0 || count > 1);
+
+	if (!count)
+		static_key_slow_inc(key);
+}
+EXPORT_SYMBOL_GPL(static_key_enable);
+
+void static_key_disable(struct static_key *key)
+{
+	int count = static_key_count(key);
+
+	WARN_ON_ONCE(count < 0 || count > 1);
+
+	if (count)
+		static_key_slow_dec(key);
+}
+EXPORT_SYMBOL_GPL(static_key_disable);
+
 void static_key_slow_inc(struct static_key *key)
 {
 	STATIC_KEY_CHECK_USE();
@@ -205,6 +244,15 @@ void __init jump_label_init(void)
 	struct static_key *key = NULL;
 	struct jump_entry *iter;
 
+	/*
+	 * Since we are initializing the static_key.enabled field with
+	 * with the 'raw' int values (to avoid pulling in atomic.h), let's make
+	 * sure that is safe. There are only two cases to check since we
+	 * initialize to 0 or 1.
+	 */
+	BUILD_BUG_ON((int)ATOMIC_INIT(0) != 0);
+	BUILD_BUG_ON((int)ATOMIC_INIT(1) != 1);
+
 	jump_label_lock();
 	jump_label_sort_entries(iter_start, iter_stop);
 
-- 
2.6.1