Re: [PATCH] mm/page_alloc: fix memmap_init_zone pageblock alignment
From: Michal Hocko
Date: Thu Mar 01 2018 - 10:29:26 EST
On Thu 01-03-18 16:09:35, Daniel Vacek wrote:
[...]
> $ grep 7b7ff000 /proc/iomem
> 7b7ff000-7b7fffff : System RAM
[...]
> After commit b92df1de5d28 machine eventually crashes with:
>
> BUG at mm/page_alloc.c:1913
>
> > VM_BUG_ON(page_zone(start_page) != page_zone(end_page));
This is an important information that should be in the changelog.
> >From registers and stack I digged start_page points to
> ffffe31d01ed8000 (note that this is
> page ffffe31d01edffc0 aligned to pageblock) and I can see this in memory dump:
>
> crash> kmem -p 77fff000 78000000 7b5ff000 7b600000 7b7fe000 7b7ff000
> 7b800000 7ffff000 80000000
> PAGE PHYSICAL MAPPING INDEX CNT FLAGS
> ffffe31d01e00000 78000000 0 0 0 0
> ffffe31d01ed7fc0 7b5ff000 0 0 0 0
> ffffe31d01ed8000 7b600000 0 0 0 0 <<<< note
Are those ranges covered by the System RAM as well?
> that nodeid and zonenr are encoded in top bits of page flags which are
> not initialized here, hence the crash :-(
> ffffe31d01edff80 7b7fe000 0 0 0 0
> ffffe31d01edffc0 7b7ff000 0 0 1 1fffff00000000
> ffffe31d01ee0000 7b800000 0 0 1 1fffff00000000
> ffffe31d01ffffc0 7ffff000 0 0 1 1fffff00000000
It is still not clear why not to do the alignment in
memblock_next_valid_pfn rahter than its caller.
--
Michal Hocko
SUSE Labs