Re: [RFT] sched_ext: Skip stack trace capture in NMI context

[Tejun Heo]

Hello,

On Mon, Dec 22, 2025 at 07:50:37PM -0500, Joel Fernandes wrote:
> stack_trace_save() is not guaranteed to be NMI-safe on all
> architectures.
> 
> The hardlockup detector calls into sched_ext via the following call
> chain when an NMI occurs:
> 
>   watchdog_overflow_callback()
>     watchdog_hardlockup_check()
>       scx_hardlockup()
>         stack_trace_save()
> 
> Skip stack trace capture when in_nmi() returns true to prevent
> potential deadlocks.
> 
> Fixes: 582f700e1bdc ("sched_ext: Hook up hardlockup detector")
> Signed-off-by: Joel Fernandes <joelagnelf@xxxxxxxxxx>

This does work on x86 (right?) and is useful in understanding what the
underlying problem is. It'd be great if there's a config flag we can test
but if not can we specifically exclude archs which are known to not work?

Thanks.

-- 
tejun