linux-kernel - Re: [PATCH] mm, compaction: fast_find_migrateblock() should return pfn in the target zone

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Date:   Fri, 13 May 2022 13:11:12 +0900
From:   Rei Yamamoto <yamamoto.rei@...fujitsu.com>
To:     akpm@...ux-foundation.org
Cc:     aquini@...hat.com, ddutile@...hat.com, linmiaohe@...wei.com,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        mgorman@...hsingularity.net, vvghjk1234@...il.com,
        yamamoto.rei@...fujitsu.com
Subject: Re: [PATCH] mm, compaction: fast_find_migrateblock() should return pfn in the target zone

On Thu, 12 May 2022 13:49:45 -0700 Andrew Morton <akpm@...ux-foundation.org> wrote:
> On Thu, 12 May 2022 13:27:33 +0900 Rei Yamamoto <yamamoto.rei@...fujitsu.com> wrote:
>
>> >> Thank you for your review.
>> >> The runtime effect is that compaction become unintended behavior.
>> >> For example, pages not in the target zone are added to cc->migratepages list in isolate_migratepages_block().
>> >> As a result, pages migrate between nodes unintentionally.
>> >
>> > Many thanks for clarifying. :) Is this worth a Fixes tag or even CC stable?
>> >
>> > Thanks!
>> 
>> Thank you for your reply.
>> 
>> If add a Fixes tag, I think the following commit:
>>   Fixes: 70b4459 ("mm, compaction: use free lists to quickly locate a migration source")
>> 
>> Andrew, how do you think about this? 
>
> Thanks, I added that and also a paragraph describing the effect of the bug:
>
> https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-compaction-fast_find_migrateblock-should-return-pfn-in-the-target-zone.patch
>
> I assume this problem isn't sufficiently serious to require a -stable
> backport of the fix?

This would be a serious problem for older kernels without commit a984226, 
because it can corrupt the lru list by handling pages in list without holding proper lru_lock.

Thanks,
Rei