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From:   Anatoly Pugachev <matorola@gmail.com>
Date:   Mon, 14 Sep 2020 13:23:58 +0300
Message-ID: <CADxRZqxkB9tzO+nf56vFfvdYBooo1rqEbst=QGZQJA3jWhKLYw@mail.gmail.com>
Subject: Re: [PATCH v2 3/4] sparc64: remove mm_cpumask clearing to fix
 kthread_use_mm race
To:     Nicholas Piggin <npiggin@gmail.com>
Cc:     linux-mm@kvack.org, 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>,
        linuxppc-dev@lists.ozlabs.org,
        Peter Zijlstra <peterz@infradead.org>,
        Sparc kernel list <sparclinux@vger.kernel.org>
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On Mon, Sep 14, 2020 at 10:00 AM Nicholas Piggin <npiggin@gmail.com> wrote:
>
> 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. The
> > optimisation could be effectively restored by sending IPIs to mm_cpumask
> > members and having them remove themselves from mm_cpumask. This is more
> > 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.

Nick,

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.