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From:   Qian Cai <cai@lca.pw>
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Subject: Re: [PATCH] locking/osq_lock: fix a data race in osq_wait_next
Date:   Tue, 28 Jan 2020 05:10:06 -0500
Message-Id: <E65D0BFC-719A-4CF9-A934-55ACFF663F98@lca.pw>
References: <CANpmjNMzvcrQWpGWVgNRxvZroecAEZYYa2yYAtm5+ekcK=H3OQ@mail.gmail.com>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Will Deacon <will@kernel.org>, Ingo Molnar <mingo@redhat.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        "paul E. McKenney" <paulmck@kernel.org>
In-Reply-To: <CANpmjNMzvcrQWpGWVgNRxvZroecAEZYYa2yYAtm5+ekcK=H3OQ@mail.gmail.com>
To:     Marco Elver <elver@google.com>
Sender: linux-kernel-owner@vger.kernel.org
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> On Jan 28, 2020, at 3:18 AM, Marco Elver <elver@google.com> wrote:
>=20
> This should be an instance of same-value-store, since the node->cpu is
> per-CPU and smp_processor_id() should always be the same, at least
> once it's published. I believe the data race I observed here before
> KCSAN had KCSAN_REPORT_VALUE_CHANGE_ONLY on syzbot, and hasn't been
> observed since. For the most part, that should deal with this case.

Are you sure? I had KCSAN_REPORT_VALUE_CHANGE_ONLY=3Dy here and saw somethin=
g similar a splat. I=E2=80=99ll also double check on my side and provide the=
 decoding.=