debug: add notifier chain debugging, v2

- unbreak ia64 (and powerpc) where function pointers dont
  point at code but at data (reported by Tony Luck)

[ mingo@elte.hu: various cleanups ]
Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

include/linux/kernel.h

@@ -187,6 +187,9 @@ extern unsigned long long memparse(char *ptr, char **retptr);
 extern int core_kernel_text(unsigned long addr);
 extern int __kernel_text_address(unsigned long addr);
 extern int kernel_text_address(unsigned long addr);
+extern int func_ptr_is_kernel_text(void *ptr);
+extern void *dereference_function_descriptor(void *ptr);
+
 struct pid;
 extern struct pid *session_of_pgrp(struct pid *pgrp);
 

kernel/extable.c

@@ -66,3 +66,19 @@ int kernel_text_address(unsigned long addr)
 		return 1;
 	return module_text_address(addr) != NULL;
 }
+
+/*
+ * On some architectures (PPC64, IA64) function pointers
+ * are actually only tokens to some data that then holds the
+ * real function address. As a result, to find if a function
+ * pointer is part of the kernel text, we need to do some
+ * special dereferencing first.
+ */
+int func_ptr_is_kernel_text(void *ptr)
+{
+	unsigned long addr;
+	addr = (unsigned long) dereference_function_descriptor(ptr);
+	if (core_kernel_text(addr))
+		return 1;
+	return module_text_address(addr) != NULL;
+}

kernel/notifier.c

@@ -21,10 +21,6 @@ BLOCKING_NOTIFIER_HEAD(reboot_notifier_list);
 static int notifier_chain_register(struct notifier_block **nl,
 		struct notifier_block *n)
 {
-	if (!kernel_text_address((unsigned long)n->notifier_call)) {
-		WARN(1, "Invalid notifier registered!");
-		return 0;
-	}
 	while ((*nl) != NULL) {
 		if (n->priority > (*nl)->priority)
 			break;
@@ -38,10 +34,6 @@ static int notifier_chain_register(struct notifier_block **nl,
 static int notifier_chain_cond_register(struct notifier_block **nl,
 		struct notifier_block *n)
 {
-	if (!kernel_text_address((unsigned long)n->notifier_call)) {
-		WARN(1, "Invalid notifier registered!");
-		return 0;
-	}
 	while ((*nl) != NULL) {
 		if ((*nl) == n)
 			return 0;
@@ -92,7 +84,7 @@ static int __kprobes notifier_call_chain(struct notifier_block **nl,
 		next_nb = rcu_dereference(nb->next);
 
 #ifdef CONFIG_DEBUG_NOTIFIERS
-		if (!kernel_text_address((unsigned long)nb->notifier_call)) {
+		if (unlikely(!func_ptr_is_kernel_text(nb->notifier_call))) {
 			WARN(1, "Invalid notifier called!");
 			nb = next_nb;
 			continue;

lib/vsprintf.c

@@ -513,7 +513,7 @@ static char *string(char *buf, char *end, char *s, int field_width, int precisio
 	return buf;
 }
 
-static inline void *dereference_function_descriptor(void *ptr)
+void *dereference_function_descriptor(void *ptr)
 {
 #if defined(CONFIG_IA64) || defined(CONFIG_PPC64)
 	void *p;