[RFC] Tight check of pfn_valid on sparsemem

[Minchan Kim <minchan.kim@gmail.com>]

Kukjin, Could you test below patch?
I don't have any sparsemem system. Sorry. 

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Kukjin reported oops happen while he change min_free_kbytes
http://www.spinics.net/lists/arm-kernel/msg92894.html
It happen by memory map on sparsemem. 

The system has a memory map following as. 
     section 0             section 1              section 2
0x20000000-0x25000000, 0x40000000-0x50000000, 0x50000000-0x58000000
SECTION_SIZE_BITS 28(256M)

It means section 0 is an incompletely filled section.
Nontheless, current pfn_valid of sparsemem checks pfn loosely. 

It checks only mem_section's validation.
So in above case, pfn on 0x25000000 can pass pfn_valid's validation check.
It's not what we want. 

The Following patch adds check valid pfn range check on pfn_valid of sparsemem.

Signed-off-by: Minchan Kim <minchan.kim@gmail.com>
Reported-by: Kukjin Kim <kgene.kim@samsung.com>

P.S) 
It is just RFC. If we agree with this, I will make the patch on mmotm.

--

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index b4d109e..6c2147a 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -979,6 +979,8 @@ struct mem_section {
        struct page_cgroup *page_cgroup;
        unsigned long pad;
 #endif
+       unsigned long start_pfn;
+       unsigned long end_pfn;
 };
 
 #ifdef CONFIG_SPARSEMEM_EXTREME
@@ -1039,6 +1041,12 @@ static inline int valid_section(struct mem_section *section)
        return (section && (section->section_mem_map & SECTION_HAS_MEM_MAP));
 }
 
+static inline int valid_section_pfn(struct mem_section *section, unsigned long pfn)
+{
+       return ((section && (section->section_mem_map & SECTION_HAS_MEM_MAP)) &&
+               (section->start_pfn <= pfn && pfn < section->end_pfn));
+}
+
 static inline int valid_section_nr(unsigned long nr)
 {
        return valid_section(__nr_to_section(nr));
@@ -1053,7 +1061,7 @@ static inline int pfn_valid(unsigned long pfn)
 {
        if (pfn_to_section_nr(pfn) >= NR_MEM_SECTIONS)
                return 0;
-       return valid_section(__nr_to_section(pfn_to_section_nr(pfn)));
+       return valid_section_pfn(__nr_to_section(pfn_to_section_nr(pfn)), pfn);
 }

diff --git a/mm/sparse.c b/mm/sparse.c
index 95ac219..bde9090 100644
--- a/mm/sparse.c
+++ b/mm/sparse.c
@@ -195,6 +195,8 @@ void __init memory_present(int nid, unsigned long start, unsigned long end)
                if (!ms->section_mem_map)
                        ms->section_mem_map = sparse_encode_early_nid(nid) |
                                                        SECTION_MARKED_PRESENT;
+               ms->start_pfn = start;
+               ms->end_pfn = end;
        }
 }



-- 
Kind regards,
Minchan Kim