Re: Kernel panic in __migrate_swap_task() under stress-ng

[Jirka Hladky]

Thank you, Abhigyan!

>often crashing around test 30+ out of 41,
This is not relevant. We run 41 different benchmarks from Libmicro and
order them alphabetically, so test #30 has no special meaning.

 Let’s see if I can narrow it down further. If I get a hit, I’ll share
the trace.
Keeping my fingers crossed!

Jirka


On Thu, Jun 19, 2025 at 7:14 AM Abhigyan ghosh
<zscript.team.zs@xxxxxxxxx> wrote:
>
>
>
> Hi Jirka,
>
> Thanks again for the detailed logs and clarification.
>
> Based on your trace and timing (often crashing around test 30+ out of 41, after long runtime), I suspect it could be a use-after-free or delayed wake-up race in the CPU stopper thread handling.
>
> In particular, I noticed:
>
> The RIP __migrate_swap_task+0x2f attempts to dereference +0x4c8 from a NULL task_struct pointer.
>
> That offset is near task->se.cfs_rq or task->sched_info on some architectures — which makes me wonder if the task was already de-queued from its CPU’s rq during swap or sem cleanup.
>
> Since stress-ng uses short timed sem/fork loops with varying threads, maybe the task was migrated mid-finalization?
>
>
> As an experiment, I’ll try:
>
> Looping stress-ng --sem --taskset 0-15
>
> Watching perf top and tracing with ftrace on migrate_swap_stop and task_rq_lock
>
>
> Let’s see if I can narrow it down further. If I get a hit, I’ll share the trace.
>
> Thanks again —
> Best regards,
> Abhigyan Ghosh
> zsml.zscript.org
>
> aghosh
>


-- 
-Jirka