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From:   Guenter Roeck <linux@roeck-us.net>
Subject: Re: [PATCH 6.4 000/227] 6.4.7-rc1 review
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On 7/30/23 20:54, Paul E. McKenney wrote:
> 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?
> 

Not sure I understand the question. KVM is disabled in my systems.
The host CPUs are Ryzen 3900X and 5900X, but I don't really see why
that would matter.

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

Did you see the e-mail I sent about this problem earlier today ?

https://lore.kernel.org/lkml/3da81a5c-700b-8e21-1bde-27dd3a0b8945@roeck-us.net/

I think I'll declare this to be a problem with my test environment and disable
RCU debugging.

Thanks,
Guenter