Comment # 19 on bug 1177973 from Bernhard Randolf

(In reply to Takashi Iwai from comment #18)
> I guess you might be able to trigger the bug by running like
>   xcmddc --i2c /dev/$I2C --identify
> where $I2C is i2c-0 or such existing device file.  Run the above from
> multiple places at the same time, and you might see the kernel warning again.

For the record: I did several more (more than 10) reboots with 5.9.0 in absence
of the xcm package, 100% of them successful. After reinstalling xcm, first boot
with 5.9.0 failed with the familiar kernel-panic. 5.9.1 with your fix still
works :-)

I was not able to reproduce the warnings with 3 concurrent xcmddc --i2c
/dev/i2c-0 --identify calls in a while true-loop from bash with your 5.9.1.
kernel (at least I did not find any warnings in dmesg or journal), but maybe
"same time" is not that easy to achieve (or i just did not manage to find the
warnings...)