Subject: Re: [PATCH net-next] configs/debug: run and debug PREEMPT

From: Jakub Kicinski <[email-masked]>
Date: Tue, 8 Apr 2025 12:03:18 -0700

On Tue, 8 Apr 2025 20:18:26 +0200 Matthieu Baerts wrote:
> On 02/04/2025 19:23, Stanislav Fomichev wrote:
> > Recent change [0] resulted in a "BUG: using __this_cpu_read() in
> > preemptible" splat [1]. PREEMPT kernels have additional requirements
> > on what can and can not run with/without preemption enabled.
> > Expose those constrains in the debug kernels.  
> 
> Good idea to suggest this to find more bugs!
> 
> I did some quick tests on my side with our CI, and the MPTCP selftests
> seem to take a bit more time, but without impacting the results.
> Hopefully, there will be no impact in slower/busy environments :)

What kind of slow down do you see? I think we get up to 50% more time
spent in the longer tests. Not sure how bad is too bad.. I'm leaning
towards applying this to net-next and we can see if people running
on linux-next complain?

Let me CC kselftests, patch in question:
https://lore.kernel.org/all/[email-masked]/