From db36a46113e101a8aa2d6ede41e78f2eaabed3f1 Mon Sep 17 00:00:00 2001
From: Gavin Shan <shangw@linux.vnet.ibm.com>
Date: Tue, 31 Jul 2012 16:46:04 -0700
Subject: [PATCH] mm/sparse: more checks on mem_section number

__section_nr() was implemented to retrieve the corresponding memory
section number according to its descriptor.  It's possible that the
specified memory section descriptor doesn't exist in the global array.  So
add more checking on that and report an error for a wrong case.

Signed-off-by: Gavin Shan <shangw@linux.vnet.ibm.com>
Acked-by: David Rientjes <rientjes@google.com>
Cc: Michal Hocko <mhocko@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
 mm/sparse.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/sparse.c b/mm/sparse.c
index fa933f43b2c9..42ca0ea9af1b 100644
--- a/mm/sparse.c
+++ b/mm/sparse.c
@@ -130,6 +130,8 @@ int __section_nr(struct mem_section* ms)
 		     break;
 	}
 
+	VM_BUG_ON(root_nr == NR_SECTION_ROOTS);
+
 	return (root_nr * SECTIONS_PER_ROOT) + (ms - root);
 }
 
-- 
2.20.1