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From: "Henrik Rydberg" <rydberg@euromail.se>
Date: Thu, 6 Dec 2012 19:32:59 +0100
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mel Gorman <mgorman@suse.de>, Jan Kara <jack@suse.cz>,
        linux-mm <linux-mm@kvack.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: Oops in 3.7-rc8 isolate_free_pages_block()
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On Thu, Dec 06, 2012 at 10:19:35AM -0800, Linus Torvalds wrote:
> 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?

Yes - I can no longer trigger the failpath, so it seems to work. Mel,
enjoy the rest of the talk. ;-)

Generally, I am a bit surprised that noone hit this before, given that
it was quite easy to trigger. I will check 3.6 as well.

Thanks,
Henrik