RE: [RFC] Tight check of pfn_valid on sparsemem

[Kukjin Kim <kgene.kim@samsung.com>]

Minchan Kim wrote:
> 
Hi :-)

> Kukjin, Could you test below patch?

Sure.

> I don't have any sparsemem system. Sorry.

No problem...
And in the same test, there was no problem ;-)

It means has no kernel panic with your this patch.

If you need other test on sparsemem system, please let me know.

Thanks.

Best regards,
Kgene.
--
Kukjin Kim <kgene.kim@samsung.com>, Senior Engineer,
SW Solution Development Team, Samsung Electronics Co., Ltd.
> 
> -- CUT DOWN HERE --
> 
> 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

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