Re: [PATCH bpf-next v1 1/2] bpf: Fix sleepable context checks and remove in_sleepable helper

[Eduard Zingerman <eddyz87@gmail.com>]

On Thu, 2026-08-06 at 18:40 +0200, Kumar Kartikeya Dwivedi wrote:

...

> Several call sites incorrectly used in_sleepable() where
> in_sleepable_context() is required. This allowed sleepable programs
> in non-sleepable contexts (e.g., inside bpf_rcu_read_lock()) to
> incorrectly use sleepable iterators and kfuncs:
> 
>   - check_css_task_iter_allowlist() returned in_sleepable() and
>     therefore allowed css_task iterator in any sleepable program,
>     even inside RCU/preempt/lock/IRQ-disabled regions. Fix it to
>     use in_sleepable_context().

...

> @@ -12083,7 +12078,7 @@ static bool check_css_task_iter_allowlist(struct bpf_verifier_env *env)
>  			return true;
>  		fallthrough;
>  	default:
> -		return in_sleepable(env);
> +		return in_sleepable_context(env);
>  	}
>  }

I don't understand this change. The comment on top of the
check_css_task_iter_allowlist() says that it is about
cgroup.c:css_set_lock, not the current context per se.

The flags on bpf_iter_css_task_new() and bpf_iter_css_task_next()
is what should govern the decision regarding whether the function is
allowed within some kind of a critical section.

  BTF_ID_FLAGS(func, bpf_iter_css_task_new, KF_ITER_NEW)
  BTF_ID_FLAGS(func, bpf_iter_css_task_next, KF_ITER_NEXT | KF_RET_NULL)

Should these wield a KF_SLEEPABLE?

Looking at the bpf_iter_css_task_new() body, it uses bpf_mem_alloc()
which does not sleep and css_task_iter_start() which takes and
releases a spin lock.

Please elaborate.

...