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From:   Qian Cai <cai@lca.pw>
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Subject: Re: [PATCH v2] sched/core: fix illegal RCU from offline CPUs
Date:   Thu, 2 Apr 2020 12:19:54 -0400
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References: <20200402155406.GP19865@paulmck-ThinkPad-P72>
Cc:     Michael Ellerman <mpe@ellerman.id.au>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>, juri.lelli@redhat.com,
        dietmar.eggemann@arm.com, vincent.guittot@linaro.org,
        rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de,
        tglx@linutronix.de,
        "James.Bottomley@hansenpartnership.com" 
        <James.Bottomley@hansenpartnership.com>, deller@gmx.de,
        linuxppc-dev@lists.ozlabs.org, linux-parisc@vger.kernel.org,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        Nicholas Piggin <npiggin@gmail.com>
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> On Apr 2, 2020, at 11:54 AM, Paul E. McKenney <paulmck@kernel.org> wrote:
>=20
> I do run this combination quite frequently, but only as part of
> rcutorture, which might not be a representative workload.  For one thing,
> it has a minimal userspace consisting only of a trivial init program.
> I don't recall having ever seen this.  (I have seen one recent complaint
> about an IPI being sent to an offline CPU, but I cannot prove that this
> was not due to RCU bugs that I was chasing at the time.)

Yes, a trivial init is tough while running systemd should be able to catch i=
t as it will use cgroup.=