RE: [PATCH bpf-next v7 4/4] selftests/bpf: Add tests for bpf_rcu_read_lock()

[John Fastabend <john.fastabend@gmail.com>]

Yonghong Song wrote:
> Add a few positive/negative tests to test bpf_rcu_read_lock()
> and its corresponding verifier support. The new test will fail
> on s390x and aarch64, so an entry is added to each of their
> respective deny lists.
> 
> Signed-off-by: Yonghong Song <yhs@fb.com>

[...]

> +SEC("?fentry.s/" SYS_PREFIX "sys_nanosleep")
> +int nested_rcu_region(void *ctx)
> +{
> +	struct task_struct *task, *real_parent;
> +
> +	/* nested rcu read lock regions */
> +	task = bpf_get_current_task_btf();
> +	bpf_rcu_read_lock();
> +	bpf_rcu_read_lock();
> +	real_parent = task->real_parent;
> +	(void)bpf_task_storage_get(&map_a, real_parent, 0, 0);
> +	bpf_rcu_read_unlock();
> +	bpf_rcu_read_unlock();
> +	return 0;
> +}

I think you also need the nested imbalance case is this
handled? It looks like the active_rcu is just a bool?

 +SEC("?fentry.s/" SYS_PREFIX "sys_nanosleep")
 +int nested_rcu_region(void *ctx)
 +{
 +	struct task_struct *task, *real_parent;
 +
 +	/* nested rcu read lock regions */
 +	task = bpf_get_current_task_btf();
 +	bpf_rcu_read_lock();
 +	bpf_rcu_read_lock();
 +	real_parent = task->real_parent;
 +	(void)bpf_task_storage_get(&map_a, real_parent, 0, 0);
 +      // imbalance unlock()
 +	bpf_rcu_read_unlock();
 +	return 0;
 +}