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Date:   Tue, 15 Sep 2020 12:49:17 +1000
From:   Nicholas Piggin <npiggin@gmail.com>
Subject: Re: [PATCH v2 3/4] sparc64: remove mm_cpumask clearing to fix
 kthread_use_mm race
To:     Anatoly Pugachev <matorola@gmail.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        "Aneesh Kumar K . V" <aneesh.kumar@linux.ibm.com>,
        Jens Axboe <axboe@kernel.dk>,
        "David S . Miller" <davem@davemloft.net>,
        linux-arch@vger.kernel.org,
        Linux Kernel list <linux-kernel@vger.kernel.org>,
        linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org,
        Peter Zijlstra <peterz@infradead.org>,
        Sparc kernel list <sparclinux@vger.kernel.org>
References: <20200914045219.3736466-1-npiggin@gmail.com>
        <20200914045219.3736466-4-npiggin@gmail.com>
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        <CADxRZqxkB9tzO+nf56vFfvdYBooo1rqEbst=QGZQJA3jWhKLYw@mail.gmail.com>
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Excerpts from Anatoly Pugachev's message of September 14, 2020 8:23 pm:
> On Mon, Sep 14, 2020 at 10:00 AM Nicholas Piggin <npiggin@gmail.com> wrot=
e:
>>
>> Excerpts from Nicholas Piggin's message of September 14, 2020 2:52 pm:
>>
>> [...]
>>
>> > The basic fix for sparc64 is to remove its mm_cpumask clearing code. T=
he
>> > optimisation could be effectively restored by sending IPIs to mm_cpuma=
sk
>> > members and having them remove themselves from mm_cpumask. This is mor=
e
>> > tricky so I leave it as an exercise for someone with a sparc64 SMP.
>> > powerpc has a (currently similarly broken) example.
>>
>> So this compiles and boots on qemu, but qemu does not support any
>> sparc64 machines with SMP. Attempting some simple hacks doesn't get
>> me far because openbios isn't populating an SMP device tree, which
>> blows up everywhere.
>>
>> The patch is _relatively_ simple, hopefully it shouldn't explode, so
>> it's probably ready for testing on real SMP hardware, if someone has
>> a few cycles.
>=20
> Nick,
>=20
> applied this patch to over 'v5.9-rc5' tag , used my test VM (ldom)
> with 32 vcpus.
> Machine boot, stress-ng test ( run as
> "stress-ng --cpu 8 --io 8 --vm 8 --vm-bytes 2G --fork 8 --timeout 15m" )
> finishes without errors.
>=20

Thank you very much Anatoly.

Thanks,
Nick