[BUGFIX][PATCH] fix is_mem_section_removable() page_order BUG_ON check.

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

I wonder this should be for stable tree...but want to hear opinions before.
==
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

page_order() is called by memory hotplug's user interface to check 
the section is removable or not. (is_mem_section_removable())

It calls page_order() withoug holding zone->lock.
So, even if the caller does

	if (PageBuddy(page))
		ret = page_order(page) ...
The caller may hit BUG_ON().

For fixing this, there are 2 choices.
  1. add zone->lock.
  2. remove BUG_ON().

is_mem_section_removable() is used for some "advice" and doesn't need
to be 100% accurate. This is_removable() can be called via user program..
We don't want to take this important lock for long by user's request.
So, this patch removes BUG_ON().

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
---
 mm/internal.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Index: mmotm-1024/mm/internal.h
===================================================================
--- mmotm-1024.orig/mm/internal.h
+++ mmotm-1024/mm/internal.h
@@ -62,7 +62,7 @@ extern bool is_free_buddy_page(struct pa
  */
 static inline unsigned long page_order(struct page *page)
 {
-	VM_BUG_ON(!PageBuddy(page));
+	/* PageBuddy() must be checked by the caller */
 	return page_private(page);
 }
 

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