arm64 torture test hotplug failures (offlining causes -EBUSY)

[Joel Fernandes]

Hi Marc,
Thanks a lot for taking a look.

On Mon, Jan 16, 2023 at 1:03 PM Marc Zyngier <maz at kernel.org> wrote:
>
> Hi Joel,
>
> On Mon, 16 Jan 2023 17:03:31 +0000,
> Joel Fernandes <joel at 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've taken your kernel for a ride as a KVM guest (probably similar to
> what you are doing), and saw the same thing (CPU0 not offlining):
>
> [   64.555845] Detected VIPT I-cache on CPU4
> [   64.556146] GICv3: CPU4: found redistributor 4 region 0:0x000000003ff70000
> [   64.556689] CPU4: Booted secondary processor 0x0000000004 [0x612f0290]
> [   69.823670] rcu-torture:torture_onoff task: offline 0 failed: errno -16
> [   73.991960] psci: CPU7 killed (polled 0 ms)
> [   74.239626] rcu-torture: rcu_torture_read_exit: Start of episode
> [   74.243863] rcu-torture: rcu_torture_read_exit: End of episode
>
> I then tried v6.2-rc4 with defconfig + RCU_TORTURE and your command
> line, and CPU0 does seem to hotplug off correctly:

Interesting, can you try the Config fragment of the failing config on
the 6.2-rc4 [1] ?

[1] 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/ConfigFragment

Notable, it has the following which Zhoui said he was able to repro
with on another arch as well:
CONFIG_NO_HZ_IDLE=n
CONFIG_NO_HZ_FULL=y

> [   47.217109] psci: CPU3 killed (polled 0 ms)
> [   52.241009] Detected VIPT I-cache on CPU3
> [   52.241227] cacheinfo: Unable to detect cache hierarchy for CPU 3
> [   52.241481] GICv3: CPU3: found redistributor 3 region 0:0x000000003ff50000
> [   52.241849] CPU3: Booted secondary processor 0x0000000003 [0x612f0290]
> [   56.337011] psci: CPU0 killed (polled 0 ms)
> [...]
> [  121.090339] rcu-torture: Free-Block Circulation:  922 920 919 918 917 916 914 913 912 911 0
> [  125.574311] Detected VIPT I-cache on CPU0
> [  125.574557] cacheinfo: Unable to detect cache hierarchy for CPU 0
> [  125.574901] GICv3: CPU0: found redistributor 0 region 0:0x000000003fef0000
> [  125.575322] CPU0: Booted secondary processor 0x0000000000 [0x612f0290]
> [  130.176893] rcu-torture: rcu_torture_read_exit: Start of episode
> [  130.317001] psci: CPU0 killed (polled 0 ms)
> [...]
> [  225.588999] Detected VIPT I-cache on CPU0
> [  225.589224] cacheinfo: Unable to detect cache hierarchy for CPU 0
> [  225.589535] GICv3: CPU0: found redistributor 0 region 0:0x000000003fef0000
> [  225.589946] CPU0: Booted secondary processor 0x0000000000 [0x612f0290]
>
> No such error is being reported.
>
> Is there anything special in your config that would help triggering
> this with the current tip of tree?

Perhaps, your config needs the options in the config fragment I mentioned above.

Thanks!

 - Joel