Bug#1092103: Linux 6.12 freeze on small machine

[Salvatore Bonaccorso <carnil@debian.org>]

Control: tags -1 + moreinfo

Hi,

On Sat, Jan 04, 2025 at 11:08:41PM +0800, GMX wrote:
> Package: linux-image-6.12.6-amd64
> Version: 6.12.6-1
> 
> Found a case where cpu freeze(100% usage) will occur.
> 
> (Tested)Environment:
> CPU: 1 or 2 cores.
> Memory: <= 1GB
> 
> Only tested in Virtual Machine(KVM).
> 
> Procedure:
> 1. Start iperf3 as server on the test machine.
> 2. On any client machine, start a reversed(download) test to the test machine.
> To trigger the case, use 4 threads and 256k block size. Higer value slightly increase the chance.
> 3.Wait for iperf3 to run.
> (4). After a few iteration or at test end, the server will stop responding and completly locked.(no kernel panic log, console just freeze)
> 
> From monitoring platform , the process contained the already freezed vm uses 100% cpu(50% on 2 cores). Charts show the vm linearly increase memory usage to watermark point and never freed them(Because cpu is freezed ?).
> 
> Tested on vanilla debian 6.12 and xanmod(no debian patches) 6.12, both freezed.
> Tested on xanmod 6.6, no such problem.
> Tested on vanilla debian 6.1, no such problem.

Was unable here to reproduce the problem with a small VM.

Can you please describe in more details both the sizing of the choosen
VM ideally the full qemu commandline which is invoked as well when
starting and the vm description.

Additionally please the exact test setup which triggers the problem
for you with the iperf3 invocations.

Thanks already,

Regards,
Salvatore