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

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Message-ID: <20250408120318.65125876@kernel.org>
Date: Tue, 8 Apr 2025 12:03:18 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Matthieu Baerts <matttbe@...nel.org>
Cc: Stanislav Fomichev <sdf@...ichev.me>, netdev@...r.kernel.org,
 davem@...emloft.net, edumazet@...gle.com, pabeni@...hat.com,
 paulmck@...nel.org, joel@...lfernandes.org, steven.price@....com,
 akpm@...ux-foundation.org, anshuman.khandual@....com,
 linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH net-next] configs/debug: run and debug PREEMPT

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/20250402172305.1775226-1-sdf@fomichev.me/