[PATCH v2] static_key: WARN on usage before jump_label_init was called

[Hannes Frederic Sowa]

On Mon, Oct 07, 2013 at 11:51:52AM -0400, Steven Rostedt wrote:
> On Sun, 6 Oct 2013 20:29:19 +0200
> Hannes Frederic Sowa <hannes@xxxxxxxxxxxxxxxxxxx> wrote:
> 
> 
> > diff --git a/lib/jump_label_initialized.c b/lib/jump_label_initialized.c
> > new file mode 100644
> > index 0000000..a668a40
> > --- /dev/null
> > +++ b/lib/jump_label_initialized.c
> > @@ -0,0 +1,6 @@
> > +#include <linux/types.h>
> > +#include <linux/cache.h>
> > +
> > +bool static_key_initialized __read_mostly = false;
> > +EXPORT_SYMBOL_GPL(static_key_initialized);
> > +
> 
> So far, the only thing I don't like about this patch is the creation of
> this file for the sole purpose of adding this variable.
> 
> Perhaps it can just be added to init/main.c?

Yes, init/main.c seems to be a good fit. I also fixed some whitespace issues
and simplified the macro (as it is only one statement).

[PATCH v2] static_key: WARN on usage before jump_label_init was called

Based on a patch from Andi Kleen.

Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Cc: Andi Kleen <andi@xxxxxxxxxxxxxx>
Signed-off-by: Hannes Frederic Sowa <hannes@xxxxxxxxxxxxxxxxxxx>
---
 include/linux/jump_label.h           | 10 ++++++++++
 include/linux/jump_label_ratelimit.h |  2 ++
 init/main.c                          |  7 +++++++
 kernel/jump_label.c                  |  5 +++++
 4 files changed, 24 insertions(+)

diff --git a/include/linux/jump_label.h b/include/linux/jump_label.h
index a507907..e96be72 100644
--- a/include/linux/jump_label.h
+++ b/include/linux/jump_label.h
@@ -48,6 +48,13 @@
 
 #include <linux/types.h>
 #include <linux/compiler.h>
+#include <linux/bug.h>
+
+extern bool static_key_initialized;
+
+#define STATIC_KEY_CHECK_USE() WARN(!static_key_initialized,		      \
+				    "%s used before call to jump_label_init", \
+				    __func__)
 
 #if defined(CC_HAVE_ASM_GOTO) && defined(CONFIG_JUMP_LABEL)
 
@@ -128,6 +135,7 @@ struct static_key {
 
 static __always_inline void jump_label_init(void)
 {
+	static_key_initialized = true;
 }
 
 static __always_inline bool static_key_false(struct static_key *key)
@@ -146,11 +154,13 @@ static __always_inline bool static_key_true(struct static_key *key)
 
 static inline void static_key_slow_inc(struct static_key *key)
 {
+	STATIC_KEY_CHECK_USE();
 	atomic_inc(&key->enabled);
 }
 
 static inline void static_key_slow_dec(struct static_key *key)
 {
+	STATIC_KEY_CHECK_USE();
 	atomic_dec(&key->enabled);
 }
 
diff --git a/include/linux/jump_label_ratelimit.h b/include/linux/jump_label_ratelimit.h
index 1137883..089f70f 100644
--- a/include/linux/jump_label_ratelimit.h
+++ b/include/linux/jump_label_ratelimit.h
@@ -23,12 +23,14 @@ struct static_key_deferred {
 };
 static inline void static_key_slow_dec_deferred(struct static_key_deferred *key)
 {
+	STATIC_KEY_CHECK_USE();
 	static_key_slow_dec(&key->key);
 }
 static inline void
 jump_label_rate_limit(struct static_key_deferred *key,
 		unsigned long rl)
 {
+	STATIC_KEY_CHECK_USE();
 }
 #endif	/* HAVE_JUMP_LABEL */
 #endif	/* _LINUX_JUMP_LABEL_RATELIMIT_H */
diff --git a/init/main.c b/init/main.c
index af310af..6735b631 100644
--- a/init/main.c
+++ b/init/main.c
@@ -136,6 +136,13 @@ static char *execute_command;
 static char *ramdisk_execute_command;
 
 /*
+ * Used to generate warnings if static_key manipulation functions are used
+ * before boot
+ */
+bool static_key_initialized __read_mostly = false;
+EXPORT_SYMBOL_GPL(static_key_initialized);
+
+/*
  * If set, this is an indication to the drivers that reset the underlying
  * device before going ahead with the initialization otherwise driver might
  * rely on the BIOS and skip the reset operation.
diff --git a/kernel/jump_label.c b/kernel/jump_label.c
index 297a924..9019f15 100644
--- a/kernel/jump_label.c
+++ b/kernel/jump_label.c
@@ -58,6 +58,7 @@ static void jump_label_update(struct static_key *key, int enable);
 
 void static_key_slow_inc(struct static_key *key)
 {
+	STATIC_KEY_CHECK_USE();
 	if (atomic_inc_not_zero(&key->enabled))
 		return;
 
@@ -103,12 +104,14 @@ static void jump_label_update_timeout(struct work_struct *work)
 
 void static_key_slow_dec(struct static_key *key)
 {
+	STATIC_KEY_CHECK_USE();
 	__static_key_slow_dec(key, 0, NULL);
 }
 EXPORT_SYMBOL_GPL(static_key_slow_dec);
 
 void static_key_slow_dec_deferred(struct static_key_deferred *key)
 {
+	STATIC_KEY_CHECK_USE();
 	__static_key_slow_dec(&key->key, key->timeout, &key->work);
 }
 EXPORT_SYMBOL_GPL(static_key_slow_dec_deferred);
@@ -116,6 +119,7 @@ EXPORT_SYMBOL_GPL(static_key_slow_dec_deferred);
 void jump_label_rate_limit(struct static_key_deferred *key,
 		unsigned long rl)
 {
+	STATIC_KEY_CHECK_USE();
 	key->timeout = rl;
 	INIT_DELAYED_WORK(&key->work, jump_label_update_timeout);
 }
@@ -212,6 +216,7 @@ void __init jump_label_init(void)
 		key->next = NULL;
 #endif
 	}
+	static_key_initialized = true;
 	jump_label_unlock();
 }
 
-- 
1.8.3.1

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