Re: [PATCH bpf-next v4 3/5] selftests/bpf: Add ksock kfunc test

[Jiayuan Chen <jiayuan.chen@linux.dev>]

On 8/7/26 2:22 AM, Mahe Tardy wrote:
> Add
[...]
> +
> +SEC("lsm.s/socket_bind")
> +int BPF_PROG(ksock_socket_bind, struct socket *sock, struct sockaddr *address,
> +	     int addrlen, int ret)
> +{
> +	struct __ksock_ctx_value *v;
> +	struct bpf_ksock *ks, *tmp;
> +	u32 pid = bpf_get_current_pid_tgid() >> 32;
> +
> +	if (ret || pid != target_pid)
> +		return ret;
> +
> +	v = ksock_ctx_value_lookup();
> +	if (!v) {
> +		send_ret = -ENOENT;
> +		return ret;
> +	}
> +
> +	ks = NULL;
> +	bpf_rcu_read_lock();
> +	tmp = v->ctx;
> +	if (tmp)
> +		ks = bpf_ksock_acquire(tmp);
> +	bpf_rcu_read_unlock();
> +
> +	if (!ks) {
> +		send_ret = -ENOENT;
> +		return ret;
> +	}
> +


Since bpf_ksock_send() is sleepable, every consumer of the kptr is
necessarily a sleepable program and thus has to open-code the same
bpf_rcu_read_lock()/acquire/unlock sequence before each send.

Given ksock_common.h already wraps the insert side, how about also
providing the get side, e.g.:

static inline struct bpf_ksock *ksock_ctx_get(void)
{
     struct __ksock_ctx_value *v = ksock_ctx_value_lookup();
     struct bpf_ksock *ks = NULL, *tmp;

     if (!v)
             return NULL;
     bpf_rcu_read_lock();
     tmp = v->ctx;
     if (tmp)
             ks = bpf_ksock_acquire(tmp);
     bpf_rcu_read_unlock();
     return ks;
}

These selftests will be the reference everyone copies from, so
encapsulating the RCU dance here also documents the correct usage.