Re: [PATCH v6] can: virtio: Add virtio CAN driver

[Francesco Valla <francesco@valla.it>]

Hi Matias,

On Mon, Dec 29, 2025 at 07:53:48PM +0100, Matias Ezequiel Vara Larsen wrote:
> > While stress testing this, I noticed that flooding the virtio-can
> > interface with packets leads to an hang of the interface itself.
> > I am seeing this issuing, at host side:
> > 
> > 	while true; do cansend can0 123#00; done
> > 
> > with:
> > 
> >  - QEMU: the tip of the master branch plus [2]
> >  - vhost-device: the tip of the main branch
> > 
> > and the following QEMU invocation:
> > 
> > qemu-system-x86_64 -serial mon:stdio \
> >     -m 2G -smp 2 \
> >     -kernel $(pwd)/BUILD.bin/arch/x86/boot/bzImage \
> >     -initrd /home/francesco/SRC/LINUX_KERNEL/initramfs.gz \
> >     -append "loglevel=7 console=ttyS0" \
> >     -machine memory-backend=pc.ram \
> >     -object memory-backend-file,id=pc.ram,size=2G,mem-path=/tmp/pc.ram,share=on \
> >     -chardev socket,id=can0,path=/tmp/sock-can0 \
> >     -device vhost-user-can-pci,chardev=can0
> > 
> > 
> > Restarting the interface (i.e.: ip link set down and the up) does not
> > fix the situation.
> > 
> > I'll try to do some more testing during the next days.
> 
> I tried this and I could not reproduce it. [2] requires a minimal change
> to apply, i.e., qdev-properties.h has changed to /core. I'll send a v2
> for that. I used latest vhost-device-can. I run `candump can0` in the
> guest and `while true; do cangen vcan0; done` in the host. Am I missing
> something?

With the plain 'cangen' you are not really flooding the interface, since
you are only sending a random CAN frame every 200ms. The only way I can
reproduce this behaviour in a consistent manner is running from the host:

    while true; do cansend vcan0 134#00; done

which seems to generate the maximum amount of traffic.

This is not of course a realistic bus load, but is leading the system
(at least on my setup) to a corner case somewhere.

> 
> Thanks,
> 
> Matias
> 
> 

Thank you for this effort!

Regards,
Francesco