trace: Add a CONFIG_DISABLE_TRACE_PRINTK option.

 * Poorly made kernel trees often use trace_printk() without
   properly guarding them in a #ifdef macro.

 * Such usage of trace_printk() causes a warning at
   boot and additional memory allocation.

This option serves to disable those all at once with ease.

include/linux/kernel.h

@@ -713,6 +713,9 @@ do {									\
  * let gcc optimize the rest.
  */
 
+#ifdef CONFIG_DISABLE_TRACE_PRINTK
+#define trace_printk pr_debug
+#else
 #define trace_printk(fmt, ...)				\
 do {							\
 	char _______STR[] = __stringify((__VA_ARGS__));	\
@@ -735,6 +738,7 @@ do {									\
 	else								\
 		__trace_printk(_THIS_IP_, fmt, ##args);			\
 } while (0)
+#endif
 
 extern __printf(2, 3)
 int __trace_bprintk(unsigned long ip, const char *fmt, ...);

kernel/trace/Kconfig

@@ -146,6 +146,20 @@ config GENERIC_TRACER
 	bool
 	select TRACING
 
+if TRACING
+
+config DISABLE_TRACE_PRINTK
+	bool "Force disable trace_printk() usage"
+	default y
+	help
+	  When trace_printk() is used in any of the kernel source, it enables
+	  debugging functions which are not desired for production kernel.
+	  Enabling this option will replace trace_printk() with pr_debug().
+
+	  If in doubt, say Y.
+
+endif
+
 #
 # Minimum requirements an architecture has to meet for us to
 # be able to offer generic tracing facilities: