Re: Oops in 3.7-rc8 isolate_free_pages_block()

[Linus Torvalds <torvalds@linux-foundation.org>]

On Thu, Dec 6, 2012 at 10:32 AM, Henrik Rydberg <rydberg@euromail.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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