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Date:   Sun, 30 Jul 2023 20:56:26 -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>,
        stable@vger.kernel.org, patches@lists.linux.dev,
        linux-kernel@vger.kernel.org, torvalds@linux-foundation.org,
        akpm@linux-foundation.org, shuah@kernel.org, patches@kernelci.org,
        lkft-triage@lists.linaro.org, jonathanh@nvidia.com,
        f.fainelli@gmail.com, sudipm.mukherjee@gmail.com,
        srw@sladewatkins.net, rwarsow@gmx.de, conor@kernel.org,
        rcu@vger.kernel.org
Subject: Re: [PATCH 6.4 000/227] 6.4.7-rc1 review
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On Sun, Jul 30, 2023 at 08:54:46PM -0700, 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?

Never mind, I now see your bisection result.  Good show, thank you!!!

						Thanx, Paul

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