[PATCH V2] printk: pr_debug_ratelimited: check state first to reduce "callbacks suppressed" messages

[Joe Perches <joe@perches.com>]

pr_debug_ratelimited should be coded similarly to dev_dbg_ratelimited
to reduce the "callbacks suppressed" messages.

Add #include <linux/dynamic_debug.h> to printk.h. Unfortunately, this
new #include must be after the prototype/declaration of function printk.

It may be better to split out these _ratelimited declarations into
a separate file one day.

Any use of these pr_<foo>_ratelimited functions must also have another
specific #include <ratelimited.h>.  Most users have this done indirectly
via #include <linux/kernel.h>

printk.h may not #include <linux/ratelimit.h> as it causes circular
dependencies and compilation failures.

Signed-off-by: Joe Perches <joe@perches.com>
---
V2: Fix #include dependencies and typos.

Compile tested with and without CONFIG_DYNAMIC_DEBUG

It looks to me as if device.h should also have #include <dynamic_debug.h>
It currently gets the #include indirectly via kobject.h -> kernel.h.

 include/linux/printk.h | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/include/linux/printk.h b/include/linux/printk.h
index e6131a78..6949258 100644
--- a/include/linux/printk.h
+++ b/include/linux/printk.h
@@ -233,6 +233,8 @@ extern asmlinkage void dump_stack(void) __cold;
 	no_printk(KERN_DEBUG pr_fmt(fmt), ##__VA_ARGS__)
 #endif
 
+#include <linux/dynamic_debug.h>
+
 /* If you are writing a driver, please use dev_dbg instead */
 #if defined(CONFIG_DYNAMIC_DEBUG)
 /* dynamic_pr_debug() uses pr_fmt() internally so we don't need it here */
@@ -343,7 +345,19 @@ extern asmlinkage void dump_stack(void) __cold;
 #endif
 
 /* If you are writing a driver, please use dev_dbg instead */
-#if defined(DEBUG)
+#if defined(CONFIG_DYNAMIC_DEBUG)
+/* descriptor check is first to prevent flooding with "callbacks suppressed" */
+#define pr_debug_ratelimited(fmt, ...)					\
+do {									\
+	static DEFINE_RATELIMIT_STATE(_rs,				\
+				      DEFAULT_RATELIMIT_INTERVAL,	\
+				      DEFAULT_RATELIMIT_BURST);		\
+	DEFINE_DYNAMIC_DEBUG_METADATA(descriptor, fmt);			\
+	if (unlikely(descriptor.flags & _DPRINTK_FLAGS_PRINT) &&	\
+	    __ratelimit(&_rs))						\
+		__dynamic_pr_debug(&descriptor, fmt, ##__VA_ARGS__);	\
+} while (0)
+#elif defined(DEBUG)
 #define pr_debug_ratelimited(fmt, ...)					\
 	printk_ratelimited(KERN_DEBUG pr_fmt(fmt), ##__VA_ARGS__)
 #else