linux-kernel - Re: [printk] b031a684bf: INFO:rcu_tasks_detected_stalls_on

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Date:   Wed, 27 Jan 2021 22:28:59 +0106
From:   John Ogness <john.ogness@...utronix.de>
To:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Petr Mladek <pmladek@...e.com>
Cc:     kernel test robot <oliver.sang@...el.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        LKML <linux-kernel@...r.kernel.org>, lkp@...ts.01.org,
        lkp@...el.com, zhengjun.xing@...ux.intel.com
Subject: Re: [printk]  b031a684bf: INFO:rcu_tasks_detected_stalls_on_tasks

On 2021-01-26, Sergey Senozhatsky <sergey.senozhatsky@...il.com> wrote:
> AFAIU this is just 'modprobe rcutorture'

I was finally able to trigger this by using my workstation:

    Intel(R) Core(TM) i5-8259U CPU @ 2.30GHz
    Debian/buster
    QEMU 3.1.0 (Debian 1:3.1+dfsg-8+deb10u8)

instead of my build server:

    Intel(R) Xeon(R) CPU E5-2697 v4 @ 2.30GHz
    Debian/bullseye
    QEMU 5.2.0 (Debian 1:5.2+dfsg-3)

I don't know what factors contributed, but I wanted to share my success
in reproducing the reported problem. Instead of using lkp, I am manually
booting with:

$ kvm -cpu host -smp 2 -m 8G -nographic \
      -kernel bzImage -append "console=ttyS0,115200 loglevel=6" \
      -initrd initrd

My initrd is a minimal busybox rootfs that runs:

# modprobe rcutorture onoff_interval=3 onoff_holdoff=30 torture_type=tasks

(Those are the same modprobe parameters used by the lkp job.)

After about a minute I see:

[   47.268292] tasks-torture: rcu_torture_read_exit: Start of episode
[   51.273365] tasks-torture: rcu_torture_read_exit: End of episode
[   55.823306] smpboot: do_boot_cpu failed(-1) to wakeup CPU#0
[   55.824350] tasks-torture:torture_onoff task: online 0 failed: errno -5
[   55.830661] tasks-torture:torture_onoff task: online 0 failed: errno -5
[   55.848524] tasks-torture:torture_onoff task: online 0 failed: errno -5

I will start to debug this now.

John Ogness