[023/127] mm: fix is_mem_section_removable() page_order BUG_ON check

[Greg KH]

2.6.32-stable review patch.  If anyone has any objections, please let us know.

------------------

From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>

commit 572438f9b52236bd8938b1647cc15e027d27ef55 upstream.

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@xxxxxxxxxxxxxx>
Acked-by: Wu Fengguang <fengguang.wu@xxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxx>
Acked-by: Mel Gorman <mel@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>

---
 mm/internal.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/mm/internal.h
+++ b/mm/internal.h
@@ -59,7 +59,7 @@ extern void prep_compound_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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