mm: use 'const char *' insted of 'char *' for reason in dump_page()

I tried to use 'dump_page(page, __func__)' for debugging, but it triggers
warning:

  warning: passing argument 2 of `dump_page' discards `const' qualifier from pointer target type [enabled by default]

Let's convert 'reason' to 'const char *' in dump_page() and friends: we
shouldn't modify it anyway.
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/mmdebug.h

@@ -3,8 +3,8 @@
 
 struct page;
 
-extern void dump_page(struct page *page, char *reason);
-extern void dump_page_badflags(struct page *page, char *reason,
+extern void dump_page(struct page *page, const char *reason);
+extern void dump_page_badflags(struct page *page, const char *reason,
 			       unsigned long badflags);
 
 #ifdef CONFIG_DEBUG_VM

mm/page_alloc.c

@@ -295,7 +295,8 @@ static inline int bad_range(struct zone *zone, struct page *page)
 }
 #endif
 
-static void bad_page(struct page *page, char *reason, unsigned long bad_flags)
+static void bad_page(struct page *page, const char *reason,
+		unsigned long bad_flags)
 {
 	static unsigned long resume;
 	static unsigned long nr_shown;
@@ -623,7 +624,7 @@ static inline void __free_one_page(struct page *page,
 
 static inline int free_pages_check(struct page *page)
 {
-	char *bad_reason = NULL;
+	const char *bad_reason = NULL;
 	unsigned long bad_flags = 0;
 
 	if (unlikely(page_mapcount(page)))
@@ -859,7 +860,7 @@ static inline void expand(struct zone *zone, struct page *page,
  */
 static inline int check_new_page(struct page *page)
 {
-	char *bad_reason = NULL;
+	const char *bad_reason = NULL;
 	unsigned long bad_flags = 0;
 
 	if (unlikely(page_mapcount(page)))
@@ -6545,7 +6546,8 @@ static void dump_page_flags(unsigned long flags)
 	printk(")\n");
 }
 
-void dump_page_badflags(struct page *page, char *reason, unsigned long badflags)
+void dump_page_badflags(struct page *page, const char *reason,
+		unsigned long badflags)
 {
 	printk(KERN_ALERT
 	       "page:%p count:%d mapcount:%d mapping:%p index:%#lx\n",
@@ -6561,7 +6563,7 @@ void dump_page_badflags(struct page *page, char *reason, unsigned long badflags)
 	mem_cgroup_print_bad_page(page);
 }
 
-void dump_page(struct page *page, char *reason)
+void dump_page(struct page *page, const char *reason)
 {
 	dump_page_badflags(page, reason, 0);
 }