debug: move WARN_ON() out of line

A quick grep shows that there are currently 1145 instances of WARN_ON
in the kernel. Currently, WARN_ON is pretty much entirely inlined,
which makes it hard to enhance it without growing the size of the kernel
(and getting Andrew unhappy).

This patch build on top of Olof's patch that introduces __WARN,
and places the slowpath out of line. It also uses Ingo's suggestion
to not use __FUNCTION__ but to use kallsyms to do the lookup;
this saves a ton of extra space since gcc doesn't need to store the function
string twice now:

3936367  833603  624736 5394706  525112 vmlinux.before
3917508  833603  624736 5375847  520767 vmlinux-slowpath

15Kb savings...

Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
CC: Andrew Morton <akpm@linux-foundation.org>
CC: Olof Johansson <olof@lixom.net>
Acked-by: Matt Meckall <mpm@selenic.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

include/asm-generic/bug.h

@@ -32,11 +32,11 @@ struct bug_entry {
 #endif
 
 #ifndef __WARN
-#define __WARN() do {							\
-	printk("WARNING: at %s:%d %s()\n", __FILE__,			\
-		__LINE__, __FUNCTION__);				\
-	dump_stack();							\
-} while (0)
+#ifndef __ASSEMBLY__
+extern void warn_on_slowpath(const char *file, const int line);
+#define WANT_WARN_ON_SLOWPATH
+#endif
+#define __WARN() warn_on_slowpath(__FILE__, __LINE__)
 #endif
 
 #ifndef WARN_ON

kernel/panic.c

@@ -20,6 +20,7 @@
 #include <linux/kexec.h>
 #include <linux/debug_locks.h>
 #include <linux/random.h>
+#include <linux/kallsyms.h>
 
 int panic_on_oops;
 int tainted;
@@ -292,6 +293,20 @@ void oops_exit(void)
 		(unsigned long long)oops_id);
 }
 
+#ifdef WANT_WARN_ON_SLOWPATH
+void warn_on_slowpath(const char *file, int line)
+{
+	char function[KSYM_SYMBOL_LEN];
+	unsigned long caller = (unsigned long) __builtin_return_address(0);
+
+	sprint_symbol(function, caller);
+	printk(KERN_WARNING "WARNING: at %s:%d %s()\n", file,
+		line, function);
+	dump_stack();
+}
+EXPORT_SYMBOL(warn_on_slowpath);
+#endif
+
 #ifdef CONFIG_CC_STACKPROTECTOR
 /*
  * Called when gcc's -fstack-protector feature is used, and