Re: [PATCH v3 3/3] sched_ext: Guarantee rq lock on scx_bpf_cpu_rq()

[Tejun Heo <tj@kernel.org>]

Hello,

On Sun, Aug 10, 2025 at 11:18:52PM +0100, Christian Loehle wrote:
...
> > Yeah, this is not nice, but they would be still broken though, in PATCH 1/3
> > we force schedulers to check for NULL and, if they don't, the verifier
> > won't be happy, so this already breaks existing binaries.
> > 
> > Even if a scheduler performs the NULL check, this change might still cause
> > incorrect behaviors, which can be worse than triggering an error.

I'll revert that change. We shouldn't be introducing breaking changes
without grace period.

> > How about we introduce scx_bpf_locked_cpu_rq() and we still trigger an
> > error in scx_bpf_cpu_rq(), mentioning about the new locked kfunc and
> > scx_bpf_task_acquire_remote_curr()?
> 
> If we still trigger an error in scx_bpf_cpu_rq() what's the difference
> between scx_bpf_cpu_rq() and scx_bpf_cpu_rq_locked() then?
> Just the error message?

Let's add a warning to scx_bpf_cpu_rq() pointing to scx_bpf_cpu_rq_locked(),
update the schedulers, and drop scx_bpf_cpu_rq() in a couple releases.

Thanks.

-- 
tejun