linux-kernel - Re: Oops in 3.7-rc8 isolate_free_pages

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Message-ID: <CA+55aFzievpA_b5p-bXwW11a89eC-ucpzKUuSqb2PNQOLrqaPg@mail.gmail.com>
Date:	Thu, 6 Dec 2012 10:41:14 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Henrik Rydberg <rydberg@...omail.se>
Cc:	Mel Gorman <mgorman@...e.de>, Jan Kara <jack@...e.cz>,
	linux-mm <linux-mm@...ck.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Oops in 3.7-rc8 isolate_free_pages_block()

On Thu, Dec 6, 2012 at 10:32 AM, Henrik Rydberg <rydberg@...omail.se> wrote:
>>
>> 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.

Actually, looking at it some more, I think that two-liner patch had
*ANOTHER* bug.

Because the other line seems buggy as well.

Instead of

        end_pfn = ALIGN(pfn + pageblock_nr_pages, pageblock_nr_pages);

I think it should be

        end_pfn = ALIGN(pfn+1, pageblock_nr_pages);

instead. ALIGN() already aligns upwards (but the "+1" is needed in
case pfn is already at a pageblock_nr_pages boundary, at which point
ALIGN() would have just returned that same boundary.

Hmm? Mel, please confirm. And Henrik, it might be good to test that
doubly-fixed patch. Because reading the patch and trying to fix bugs
in it that way is *not* the same as actually verifying it ;)

                 Linus
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