bpf: add bpf_wq_start

again, copy/paste from bpf_timer_start().
Signed-off-by: Benjamin Tissoires <bentiss@kernel.org>
Link: https://lore.kernel.org/r/20240420-bpf_wq-v2-15-6c986a5a741f@kernel.orgSigned-off-by: Alexei Starovoitov <ast@kernel.org>

kernel/bpf/helpers.c

@@ -2711,6 +2711,23 @@ __bpf_kfunc int bpf_wq_init(struct bpf_wq *wq, void *p__map, unsigned int flags)
 	return __bpf_async_init(async, map, flags, BPF_ASYNC_TYPE_WQ);
 }
 
+__bpf_kfunc int bpf_wq_start(struct bpf_wq *wq, unsigned int flags)
+{
+	struct bpf_async_kern *async = (struct bpf_async_kern *)wq;
+	struct bpf_work *w;
+
+	if (in_nmi())
+		return -EOPNOTSUPP;
+	if (flags)
+		return -EINVAL;
+	w = READ_ONCE(async->work);
+	if (!w || !READ_ONCE(w->cb.prog))
+		return -EINVAL;
+
+	schedule_work(&w->work);
+	return 0;
+}
+
 __bpf_kfunc int bpf_wq_set_callback_impl(struct bpf_wq *wq,
 					 int (callback_fn)(void *map, int *key, struct bpf_wq *wq),
 					 unsigned int flags,
@@ -2804,6 +2821,7 @@ BTF_ID_FLAGS(func, bpf_dynptr_clone)
 BTF_ID_FLAGS(func, bpf_modify_return_test_tp)
 BTF_ID_FLAGS(func, bpf_wq_init)
 BTF_ID_FLAGS(func, bpf_wq_set_callback_impl)
+BTF_ID_FLAGS(func, bpf_wq_start)
 BTF_KFUNCS_END(common_btf_ids)
 
 static const struct btf_kfunc_id_set common_kfunc_set = {