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Date:   Fri, 13 May 2022 14:01:41 -0700
From:   Andrew Morton <akpm@linux-foundation.org>
To:     Rei Yamamoto <yamamoto.rei@jp.fujitsu.com>
Cc:     aquini@redhat.com, ddutile@redhat.com, linmiaohe@huawei.com,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        mgorman@techsingularity.net, vvghjk1234@gmail.com
Subject: Re: [PATCH] mm, compaction: fast_find_migrateblock() should return
 pfn in the target zone
Message-Id: <20220513140141.3b2accfc8fbae08ec4177781@linux-foundation.org>
In-Reply-To: <20220513041112.31609-1-yamamoto.rei@jp.fujitsu.com>
References: <20220512134945.fe74df5e322b98ae4046ce15@linux-foundation.org>
        <20220513041112.31609-1-yamamoto.rei@jp.fujitsu.com>
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On Fri, 13 May 2022 13:11:12 +0900 Rei Yamamoto <yamamoto.rei@jp.fujitsu.com> wrote:

> On Thu, 12 May 2022 13:49:45 -0700 Andrew Morton <akpm@linux-foundation.org> wrote:
> > On Thu, 12 May 2022 13:27:33 +0900 Rei Yamamoto <yamamoto.rei@jp.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, I added the above to the changelog.

The patch applies OK to older kernels (I tried v5.10).  So I guess we
put a cc:stable in this, so it gets backported?