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From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Thu, 6 Dec 2012 10:19:35 -0800
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Subject: Re: Oops in 3.7-rc8 isolate_free_pages_block()
To: Mel Gorman <mgorman@suse.de>
Cc: Jan Kara <jack@suse.cz>, Henrik Rydberg <rydberg@euromail.se>,
        linux-mm <linux-mm@kvack.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Thu, Dec 6, 2012 at 9:55 AM, Mel Gorman <mgorman@suse.de> wrote:
>
> Yeah. I was listening to a talk while I was writing it, a bit cranky and
> didn't see why I should suffer alone.

Makes sense.

> Quasimoto strikes again

Is that Quasimodo's Japanese cousin?

> -               end_pfn = min(pfn + pageblock_nr_pages, zone_end_pfn);
> +
> +               /*
> +                * As pfn may not start aligned, pfn+pageblock_nr_page
> +                * may cross a MAX_ORDER_NR_PAGES boundary and miss
> +                * a pfn_valid check. Ensure isolate_freepages_block()
> +                * only scans within a pageblock.
> +                */
> +               end_pfn = ALIGN(pfn + pageblock_nr_pages, pageblock_nr_pages);
> +               end_pfn = min(end_pfn, end_pfn);

Ok, this looks much nicer, except it's obviously buggy. The
min(end_pfn, end_pfn) thing is insane, and I'm sure you meant for that
line to be

+               end_pfn = min(end_pfn, zone_end_pfn);

Henrik, does that - corrected - patch (*instead* of the previous one,
not in addition to) also fix your issue?

                  Linus