[makedumpfile][patch] handle !SPARSEMEM_EX properly

[Ken'ichi Ohmichi]

Hi Nishimura-san,

Thank you for the patch.

Daisuke Nishimura wrote:
> In !SPARSEMEM_EX case, the symbol mem_section points a array of struct mem_section,
> doesn't point a array of pointer to mem_section[], so I think the check:
> 
> 	if (!is_kvaddr(mem_sec[SECTION_NR_TO_ROOT(nr)]))
> 		return NOT_KV_ADDR;
> 
> in nr_to_section() is not a valid check in this case.
> 
> To make the matters worse, if CONFIG_CGROUP_MEM_RES_CTLR is enabled, the end of
> struct mem_section is padded with 0.
> 
> So, reading mem_section by "rd" of crash will look like:
> 
> 	crash> rd mem_section 128
> 	c08b71e0:  c9002003 c9001200 f7000000 00000000   . ..............
> 	c08b71f0:  c9002003 c9001260 f6980000 00000000   . ..`...........
> 	c08b7200:  c9002003 c90012c0 f6300000 00000000   . ........0.....
> 	c08b7210:  c9002003 c9001320 f5c80000 00000000   . .. ...........
> 	...

I see.

In !SPARSEMEM_EX case, nr_to_section() checked invalid area
(pageblock_flags, page_cgroup, and pad) as section_mem_map.

linux-2.6.33/include/linux/mmzone.h:
  struct mem_section {
        unsigned long section_mem_map;
        unsigned long *pageblock_flags;
  #ifdef CONFIG_CGROUP_MEM_RES_CTLR
        struct page_cgroup *page_cgroup;
        unsigned long pad;
  #endif
  };

> This means nr_to_section() will return 0 when "nr" is 3,7,11,... because it meets
> the condition(mem_sec[SECTION_NR_TO_ROOT(nr)] == mem_sec[nr] == 0 == !is_kvaddr).
> 
> As a result, mem_map for section 3,7,11,... cannot be handled properly.
> 
> This patch is a fix for this problem. nr_to_section() will check "addr" by
> is_kvaddr() later anyway, so this patch just removes the problematic check.
> 
> Signed-off-by: Masayuki Igawa <igawa at mxs.nes.nec.co.jp>
> Signed-off-by: Daisuke Nishimura <nishimura at mxp.nes.nec.co.jp>
> ---
> diff --git a/makedumpfile.c b/makedumpfile.c
> index 855c718..73fa94f 100644
> --- a/makedumpfile.c
> +++ b/makedumpfile.c
> @@ -3547,9 +3547,6 @@ nr_to_section(unsigned long nr, unsigned long *mem_sec)
>  {
>  	unsigned long addr;
>  
> -	if (!is_kvaddr(mem_sec[SECTION_NR_TO_ROOT(nr)]))
> -		return NOT_KV_ADDR;
> -
>  	if (is_sparsemem_extreme())
>  		addr = mem_sec[SECTION_NR_TO_ROOT(nr)] +
>  		    (nr & SECTION_ROOT_MASK()) * SIZE(mem_section);

The patch is good, and it has been merged to git tree of makedumpfile:

http://makedumpfile.git.sourceforge.net/git/gitweb.cgi?p=makedumpfile/makedumpfile;a=commit;h=27b71566ec11128c5b061a350e467546f2d26be6


Thanks
Ken'ichi Ohmichi