[PATCH] Add debugging boundary check to pfn_to_page

[Eric B Munson]

Bugzilla 36192 showed a problem where pages were being accessed outside of
a node boundary.  It would be helpful in diagnosing this kind of problem to
have pfn_to_page complain when a page is accessed outside of the node boundary.
This patch adds a new debug config option which adds a WARN_ON in pfn_to_page
that will complain when pages are accessed outside of the node boundary.

Signed-of-by: Eric B Munson <emunson@xxxxxxxxx>
---
 include/asm-generic/memory_model.h |   19 +++++++++++++++----
 lib/Kconfig.debug                  |   10 ++++++++++
 2 files changed, 25 insertions(+), 4 deletions(-)

diff --git a/include/asm-generic/memory_model.h b/include/asm-generic/memory_model.h
index fb2d63f..a0f1d19 100644
--- a/include/asm-generic/memory_model.h
+++ b/include/asm-generic/memory_model.h
@@ -62,11 +62,22 @@
 	(unsigned long)(__pg - __section_mem_map_addr(__nr_to_section(__sec)));	\
 })
 
-#define __pfn_to_page(pfn)				\
-({	unsigned long __pfn = (pfn);			\
-	struct mem_section *__sec = __pfn_to_section(__pfn);	\
-	__section_mem_map_addr(__sec) + __pfn;		\
+#ifdef CONFIG_DEBUG_MEMORY_MODEL
+#define __pfn_to_page(pfn)						\
+({	unsigned long __pfn = (pfn);					\
+	struct mem_section *__sec = __pfn_to_section(__pfn);		\
+	struct page *__page = __section_mem_map_addr(__sec) + __pfn;	\
+	WARN_ON(__page->flags == 0);					\
+	__page;								\
 })
+#else
+#define __pfn_to_page(pfn)						\
+({	unsigned long __pfn = (pfn);					\
+	struct mem_section *__sec = __pfn_to_section(__pfn);		\
+	__section_mem_map_addr(__sec) + __pfn;	\
+})
+#endif /* CONFIG_DEBUG_MEMORY_MODEL */
+
 #endif /* CONFIG_FLATMEM/DISCONTIGMEM/SPARSEMEM */
 
 #define page_to_pfn __page_to_pfn
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index dd373c8..d932cbf 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -777,6 +777,16 @@ config DEBUG_MEMORY_INIT
 
 	  If unsure, say Y
 
+config DEBUG_MEMORY_MODEL
+	bool "Debug memory model" if SPARSEMEM || DISCONTIGMEM
+	depends on SPARSEMEM || DISCONTIGMEM
+	help
+	  Enable this to check that page accesses are done within node
+	  boundaries.  The check will warn each time a page is requested
+	  outside node boundaries.
+
+	  If unsure, say N
+
 config DEBUG_LIST
 	bool "Debug linked list manipulation"
 	depends on DEBUG_KERNEL
-- 
1.7.4.1

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