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Date:   Sun, 30 Jul 2023 20:54:46 -0700
From:   "Paul E. McKenney" <paulmck@kernel.org>
To:     Guenter Roeck <linux@roeck-us.net>
Cc:     Joel Fernandes <joel@joelfernandes.org>,
        Pavel Machek <pavel@denx.de>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
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        akpm@linux-foundation.org, shuah@kernel.org, patches@kernelci.org,
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        rcu@vger.kernel.org
Subject: Re: [PATCH 6.4 000/227] 6.4.7-rc1 review
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On Thu, Jul 27, 2023 at 09:22:52PM -0700, Guenter Roeck wrote:
> On 7/27/23 13:33, Paul E. McKenney wrote:
> [ ... ]
> 
> > So which of the following Kconfig options is defined in your .config?
> > CONFIG_TASKS_RCU, CONFIG_TASKS_RUDE_RCU, and CONFIG_TASKS_TRACE_RCU.
> > 
> 
> Only CONFIG_TASKS_RCU. I added another log message after call_rcu_tasks().
> It never returns from that function.
> 
> [    1.168993] Running RCU synchronous self tests
> [    1.169219] Running RCU synchronous self tests
> [    1.285795] smpboot: CPU0: Intel Xeon Processor (Cascadelake) (family: 0x6, model: 0x55, stepping: 0x6)
> [    1.302827] RCU Tasks: Setting shift to 0 and lim to 1 rcu_task_cb_adjust=1.
> [    1.304526] Running RCU Tasks wait API self tests
> 
> ... and then nothing for at least 10 minutes (then I gave up and stopped the test).
> 
> Qemu command line:
> 
> qemu-system-x86_64 -kernel \
>      arch/x86/boot/bzImage -M q35 -cpu Cascadelake-Server -no-reboot \
>      -snapshot -device e1000e,netdev=net0 -netdev user,id=net0 -m 256 \
>      -drive file=rootfs.iso,format=raw,if=ide,media=cdrom \
>      --append "earlycon=uart8250,io,0x3f8,9600n8 panic=-1 slub_debug=FZPUA root=/dev/sr0 rootwait console=ttyS0 noreboot" \
>      -d unimp,guest_errors -nographic -monitor none
> 
> Again, this doesn't happen all the time. With Cascadelake-Server
> I see it maybe once every 5 boot attempts. I tried with qemu v8.0
> and v8.1. Note that it does seem to happen with various CPU types,
> only for some it seems to me more likely to happen (so maybe the
> CPU type was a red herring). It does seem to depend on the system
> load, and happen more often if the system is under heavy load.

Hmmm...  What kernel are you using as your qemu/KVM hypervisor?

And I echo Joel's requests for your .config file.

							Thanx, Paul