From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Date: Tue, 26 Oct 2010 21:22:08 +0000 (-0700)
Subject: mm: fix is_mem_section_removable() page_order BUG_ON check
X-Git-Tag: v2.6.27.57~37
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=6b5df7b78075c50f4918da9f4d7cdb99b145de23;p=thirdparty%2Fkernel%2Fstable.git

mm: fix is_mem_section_removable() page_order BUG_ON check

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@jp.fujitsu.com>
Acked-by: Wu Fengguang <fengguang.wu@intel.com>
Acked-by: Michal Hocko <mhocko@suse.cz>
Acked-by: Mel Gorman <mel@csn.ul.ie>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
---

diff --git a/mm/internal.h b/mm/internal.h
index 92729ea9dc8c9..362319a57eec6 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -49,7 +49,7 @@ extern void __free_pages_bootmem(struct page *page, unsigned int order);
  */
 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);
 }