Re: Stalls when starting a VSOCK listening socket: soft lockups, RCU stalls, timeout

[Matthieu Baerts <matttbe@kernel.org>]

Hi Thomas,

On 09/03/2026 09:43, Thomas Gleixner wrote:
> On Sun, Mar 08 2026 at 18:23, Matthieu Baerts wrote:
>> 08 Mar 2026 17:58:26 Thomas Gleixner <tglx@kernel.org>:
>>> So I'm back to square one. I go and do what I should have done in the
>>> first place. Write a debug patch with trace_printks and let the people
>>> who can actually trigger the problem run with it.
>>
>> Happy to test such debug patches!
> 
> See below.
> 
> Enable the tracepoints either on the kernel command line:
> 
>     trace_event=sched_switch,mmcid:*
> 
> or before starting the test case:
> 
>     echo 1 >/sys/kernel/tracing/events/sched/sched_switch/enable
>     echo 1 >/sys/kernel/tracing/events/mmcid/enable
> 
> I added a 50ms timeout into mm_cid_get() which freezes the trace and
> emits a warning. If you enable panic_on_warn and ftrace_dump_on_oops,
> then it dumps the trace buffer once it hits the warning.
> 
> Either kernel command line:
> 
>    panic_on_warn ftrace_dump_on_oops
> 
> or
> 
>   echo 1 >/proc/sys/kernel/panic_on_warn
>   echo 1 >/proc/sys/kernel/ftrace_dump_on_oops
> 
> That should provide enough information to decode this mystery.

Thank you for the debug patch and the clear instructions. I managed to
reproduce the issue with the extra debug. The ouput is available here:

  https://github.com/user-attachments/files/25841808/issue-617-debug.txt.gz

Just in case, the kernel config file that was used:


https://github.com/user-attachments/files/25841873/issue-617-debug.config.gz

Please tell me if it is an issue to download these files from GitHub.
The output file has 10k+ lines.

Cheers,
Matt
-- 
Sponsored by the NGI0 Core fund.