linux-kernel - [PATCH] [73/223] mm: fix is_mem_section_removable() page_order BUG

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Date:	Mon, 13 Dec 2010 00:46:11 +0100 (CET)
From:	Andi Kleen <andi@...stfloor.org>
To:	kamezawa.hiroyu@...fujitsu.com, fengguang.wu@...el.com,
	mhocko@...e.cz, mel@....ul.ie, akpm@...ux-foundation.org,
	torvalds@...ux-foundation.org, gregkh@...e.de, ak@...ux.intel.com,
	linux-kernel@...r.kernel.org, stable@...nel.org
Subject: [PATCH] [73/223] mm: fix is_mem_section_removable() page_order BUG_ON check

2.6.35-longterm review patch.  If anyone has any objections, please let me know.

------------------
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>

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@...fujitsu.com>
Acked-by: Wu Fengguang <fengguang.wu@...el.com>
Acked-by: Michal Hocko <mhocko@...e.cz>
Acked-by: Mel Gorman <mel@....ul.ie>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>
Signed-off-by: Andi Kleen <ak@...ux.intel.com>

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

Index: linux/mm/internal.h
===================================================================
--- linux.orig/mm/internal.h
+++ linux/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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