Re: [PATCH bpf-next 11/18] bpf: wq: add bpf_wq_init

[Benjamin Tissoires]

On Apr 19 2024, Alexei Starovoitov wrote:
> On Fri, Apr 19, 2024 at 8:12 AM Benjamin Tissoires <bentiss@xxxxxxxxxx> wrote:
> >
> >
> > It's something I added while adding the tests. And some tests were passing
> > in case I was having a non sleepable callback. But if we have
> > bpf_rcu_read_lock(), we are all fine and can reduce the complexity.
> 
> Not quite following what was the issue.
> Since the verifier is unconditionally verifying such callback as sleepable
> the callback won't be able to access rcu pointers without doing
> explicit bpf_rcu_read_lock() first (and few other code patterns
> might be rejected), but that's a good thing.

Oh, I missed that. Well, given that the verifier enforces everything, I
guess we are good :)

> Maybe next to set_cb kfunc add a comment that wq callbacks are sleepable.
> I think bpf prog writers are often with kernel background,
> so it will be their natural assumption that cb is sleepable.

I assume so as well.

Cheers,
Benjamin