sparsemem: record when a section has a valid mem_map

We have flags to indicate whether a section actually has a valid mem_map
associated with it.  This is never set and we rely solely on the present bit
to indicate a section is valid.  By definition a section is not valid if it
has no mem_map and there is a window during init where the present bit is set
but there is no mem_map, during which pfn_valid() will return true
incorrectly.

Use the existing SECTION_HAS_MEM_MAP flag to indicate the presence of a valid
mem_map.  Switch valid_section{,_nr} and pfn_valid() to this bit.  Add a new
present_section{,_nr} and pfn_present() interfaces for those users who care to
know that a section is going to be valid.

[akpm@linux-foundation.org: coding-syle fixes]
Signed-off-by: Andy Whitcroft <apw@shadowen.org>
Acked-by: Mel Gorman <mel@csn.ul.ie>
Cc: Christoph Lameter <clameter@sgi.com>
Cc: "Luck, Tony" <tony.luck@intel.com>
Cc: Andi Kleen <ak@suse.de>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 14 insertions, 2 deletions

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 4e5627379b09..f21e5951038b 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -771,12 +771,17 @@ static inline struct page *__section_mem_map_addr(struct mem_section *section)
         return (struct page *)map;
 }
 
-static inline int valid_section(struct mem_section *section)
+static inline int present_section(struct mem_section *section)
 {
         return (section && (section->section_mem_map & SECTION_MARKED_PRESENT));
 }
 
-static inline int section_has_mem_map(struct mem_section *section)
+static inline int present_section_nr(unsigned long nr)
+{
+        return present_section(__nr_to_section(nr));
+}
+
+static inline int valid_section(struct mem_section *section)
 {
         return (section && (section->section_mem_map & SECTION_HAS_MEM_MAP));
 }
@@ -798,6 +803,13 @@ static inline int pfn_valid(unsigned long pfn)
         return valid_section(__nr_to_section(pfn_to_section_nr(pfn)));
 }
 
+static inline int pfn_present(unsigned long pfn)
+{
+        if (pfn_to_section_nr(pfn) >= NR_MEM_SECTIONS)
+                return 0;
+        return present_section(__nr_to_section(pfn_to_section_nr(pfn)));
+}
+
 /*
  * These are _only_ used during initialisation, therefore they
  * can use __initdata ...  They could have names to indicate