Re: arm64 torture test hotplug failures (offlining causes -EBUSY)

From: Zhouyi Zhou <zhouzhouyi@gmail.com>
To: Joel Fernandes <joel@joelfernandes.org>
Cc: "moderated list:ARM/STM32 ARCHITECTURE"
	<linux-arm-kernel@lists.infradead.org>,
	Will Deacon <will@kernel.org>,  Marc Zyngier <maz@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	 Catalin Marinas <catalin.marinas@arm.com>,
	rcu <rcu@vger.kernel.org>,
	 "Paul E. McKenney" <paulmck@kernel.org>
Subject: Re: arm64 torture test hotplug failures (offlining causes -EBUSY)
Date: Tue, 17 Jan 2023 02:32:57 +0800	[thread overview]
Message-ID: <CAABZP2xnCCfCf5DLQuiTXBVbpEgsoedqxA8JsWBLs4SyLOLuFw@mail.gmail.com> (raw)
In-Reply-To: <CAEXW_YQB1Wm3YhgUP8S9a4drgvDasu3s+zyt3j9Wwpt83W=W=Q@mail.gmail.com>

Hi Joel

On Tue, Jan 17, 2023 at 1:27 AM Joel Fernandes <joel@joelfernandes.org> wrote:
>
> Hello,
> I am seeing -EBUSY returned a lot during torture_onoff() when running
> rcutorture on arm64. This causes hotplug failure 30% of the time. I am
> also seeing this in 6.1-rc kernels. I believe see this only for CPU0.
>
> This causes warnings in torture tests:
> [  217.582290] rcu-torture:torture_onoff task: offline 0 failed: errno -16
> [  221.866362] rcu-torture:torture_onoff task: offline 0 failed: errno -16
>
> Full kernel log here:
> http://box.joelfernandes.org:9080/job/rcutorture_stable_arm/job/linux-5.15.y/7/artifact/tools/testing/selftests/rcutorture/res/2023.01.15-14.51.11/TREE04/console.log
>
> Any ideas on why this is happening and only for CPU 0 (presumably the
> boot CPU)? I'd personally need these warnings to go away for my tests
> as this causes rcutorture's tests to not cleanly pass for me. It
> appears remove_cpu() -> device_offline() is what returns the error.
>
I guess this probably because CPU 0 is the tick_do_timer_cpu in
nohz_full mode, which prevent that cpu from
going offline [1]. We have discussed this topic, but there is no
agreement on how to solve it yet.

[1] https://lore.kernel.org/lkml/20221127175317.GF4001@paulmck-ThinkPad-P17-Gen-1/T/

Thanks
Zhouyi
> You can browse through all the torture test artifacts here which
> contains everything (build logs, vmlinux, etc).
> http://box.joelfernandes.org:9080/job/rcutorture_stable_arm/job/linux-5.15.y/7/artifact/tools/testing/selftests/rcutorture/res/2023.01.15-14.51.11/
>
> Thanks for your help!
>
>  - Joel

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