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Date:   Sat, 2 Oct 2021 18:15:58 +0100
From:   Matthew Wilcox <willy@infradead.org>
To:     Eric Dumazet <edumazet@google.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Eric Dumazet <eric.dumazet@gmail.com>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        linux-mm <linux-mm@kvack.org>,
        syzbot <syzkaller@googlegroups.com>,
        "Huang, Ying" <ying.huang@intel.com>, Mel Gorman <mgorman@suse.de>
Subject: Re: [PATCH v2] mm/mempolicy: do not allow illegal
 MPOL_F_NUMA_BALANCING | MPOL_LOCAL in mbind()
Message-ID: <YViTzvQII8al8HYW@casper.infradead.org>
References: <20211001215630.810592-1-eric.dumazet@gmail.com>
 <20211001154949.98956c092734590e781ce672@linux-foundation.org>
 <CANn89i+diZ9cmMo+y3KhBK3xiWbzAsC_RF86=hN4KJ1Kxg1SwA@mail.gmail.com>
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On Fri, Oct 01, 2021 at 04:37:40PM -0700, Eric Dumazet wrote:
> > > Issue came with commit bda420b98505 ("numa balancing: migrate on
> > > fault among multiple bound nodes")
> >
> > No cc:stable?  What's the worst-case user-visible impact here?
> 
> I added the more precise tag  :  Fixes: bda420b98505 ("numa balancing:
> migrate on fault among multiple bound nodes")
> I only put Fixes: tag, so that stable teams can use their automation just fine.
> 
> worst-case impact, I am not sure if any application ever used this
> undocumented combinations of flags ?
> Also, it is generally advised that accessing garbage values has
> undocumented behavior.
> A host could for example crash (it certainly does with KMSAN)

mm has special stable rules; fixes only get backported if explicitly
requested instead of automatically like most of the rest of the kernel.