On Wed, 17 Feb 2010 16:45:54 -0800
Michael Bohan <mbohan@xxxxxxxxxxxxxx> wrote:
> Hi,
>
> I have encountered a kernel panic on the ARM/msm platform in the mm
> migration code on 2.6.29. My memory configuration has two discontiguous
> banks per our ATAG definition. These banks end up on addresses that
> are 1 MB aligned. I am using FLATMEM (not SPARSEMEM), but my
> understanding is that SPARSEMEM should not be necessary to support this
> configuration. Please correct me if I'm wrong.
>
> The crash occurs in mm/page_alloc.c:move_freepages() when being passed a
> start_page that corresponds to the last several megabytes of our first
> memory bank. The code in move_freepages_block() aligns the passed in
> page number to pageblock_nr_pages, which corresponds to 4 MB. It then
> passes that aligned pfn as the beginning of a 4 MB range to
> move_freepages(). The problem is that since our bank's end address is
> not 4 MB aligned, the range passed to move_freepages() exceeds the end
> of our memory bank. The code later blows up when trying to access
> uninitialized page structures.
>
That should be aligned, I think.
> As a temporary fix, I added some code to move_freepages_block() that
> inspects whether the range exceeds our first memory bank -- returning 0
> if it does. This is not a clean solution, since it requires exporting
> the ARM specific meminfo structure to extract the bank information.
>
Hmm, my first impression is...
- Using FLATMEM, memmap is created for the number of pages and memmap should
not have aligned size.
- Using SPARSEMEM, memmap is created for aligned number of pages.
Then, the range [zone->start_pfn ... zone->start_pfn + zone->spanned_pages]
should be checked always.
803 static int move_freepages_block(struct zone *zone, struct page *page,
804 int migratetype)
805 {
816 if (start_pfn < zone->zone_start_pfn)
817 start_page = page;
818 if (end_pfn >= zone->zone_start_pfn + zone->spanned_pages)
819 return 0;
820
821 return move_freepages(zone, start_page, end_page, migratetype);
822 }
"(end_pfn >= zone->zone_start_pfn + zone->spanned_pages)" is checked.
What zone->spanned_pages is set ? The zone's range is
[zone->start_pfn ... zone->start_pfn+zone->spanned_pages], so this
area should have initialized memmap. I wonder zone->spanned_pages is too big.
Could you check ? (maybe /proc/zoneinfo can show it.)
Dump of /proc/zoneinfo or dmesg will be helpful.
Thanks,
-Kame
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