Re: kernel locks due to USB I/O

[Alan Stern <stern@rowland.harvard.edu>]

On Tue, Nov 10, 2020 at 06:42:17PM -0500, Alberto Sentieri wrote:
> 1) The current Ubuntu Kernel is 5.4.0-53. Do you want me to upgrade it to
> 5.9, from kernel.org? Or is there a Ubuntu 5.9 package that I can use? It
> would be easy to do it If there is a Ubuntu package with 5.9, which I would
> install and, after the tests, uninstall.

If you want to know what Ubuntu packages are available, you should ask 
on an Ubuntu mailing list instead of the linux-usb mailing list.

> 2) Why do you believe that 5.9 would solve the problem? I am asking that
> because I cannot change the production machine for a test if I cannot go
> back to the original state. There is always a risk involved.

We do not believe that 5.9 will solve the problem -- we have no reason 
to believe this -- but we could be wrong.  In any case it is always 
best to test with the most up-to-date software available, and 5.9 is the 
version closest to what we are working on now.

> 3) It is one single thread dealing with all 36 devices. Each device has its
> own co-routine (not preemptive), but all co-routines are executed by a
> unique thread.

If everything runs within a single thread, how can adding a semaphore 
or mutex make any difference?

> 4) By network console, do you mean ssh? It dies as well when it locks. The
> screen is the regular GNOME3 screen and nothing can be seen there. Every
> time it locks they send a picture, and I cannot see anything meaningful
> there. I am thinking about disabling GNOME3, but I need their blessing for
> that.

See https://www.kernel.org/doc/Documentation/networking/netconsole.txt
for instructions on netconsole.  And when you use it for testing, be 
sure to set the console log level to a high value.

Alan Stern