bpf: replace bpf_timer_set_callback with a generic helper

In the same way we have a generic __bpf_async_init(), we also need
to share code between timer and workqueue for the set_callback call.

We just add an unused flags parameter, as it will be used for workqueues.
Signed-off-by: Benjamin Tissoires <bentiss@kernel.org>
Link: https://lore.kernel.org/r/20240420-bpf_wq-v2-3-6c986a5a741f@kernel.orgSigned-off-by: Alexei Starovoitov <ast@kernel.org>

kernel/bpf/helpers.c

@@ -1262,22 +1262,23 @@ static const struct bpf_func_proto bpf_timer_init_proto = {
 	.arg3_type	= ARG_ANYTHING,
 };
 
-BPF_CALL_3(bpf_timer_set_callback, struct bpf_async_kern *, timer, void *, callback_fn,
-	   struct bpf_prog_aux *, aux)
+static int __bpf_async_set_callback(struct bpf_async_kern *async, void *callback_fn,
+				    struct bpf_prog_aux *aux, unsigned int flags,
+				    enum bpf_async_type type)
 {
 	struct bpf_prog *prev, *prog = aux->prog;
-	struct bpf_hrtimer *t;
+	struct bpf_async_cb *cb;
 	int ret = 0;
 
 	if (in_nmi())
 		return -EOPNOTSUPP;
-	__bpf_spin_lock_irqsave(&timer->lock);
-	t = timer->timer;
-	if (!t) {
+	__bpf_spin_lock_irqsave(&async->lock);
+	cb = async->cb;
+	if (!cb) {
 		ret = -EINVAL;
 		goto out;
 	}
-	if (!atomic64_read(&t->cb.map->usercnt)) {
+	if (!atomic64_read(&cb->map->usercnt)) {
 		/* maps with timers must be either held by user space
 		 * or pinned in bpffs. Otherwise timer might still be
 		 * running even when bpf prog is detached and user space
@@ -1286,7 +1287,7 @@ BPF_CALL_3(bpf_timer_set_callback, struct bpf_async_kern *, timer, void *, callb
 		ret = -EPERM;
 		goto out;
 	}
-	prev = t->cb.prog;
+	prev = cb->prog;
 	if (prev != prog) {
 		/* Bump prog refcnt once. Every bpf_timer_set_callback()
 		 * can pick different callback_fn-s within the same prog.
@@ -1299,14 +1300,20 @@ BPF_CALL_3(bpf_timer_set_callback, struct bpf_async_kern *, timer, void *, callb
 		if (prev)
 			/* Drop prev prog refcnt when swapping with new prog */
 			bpf_prog_put(prev);
-		t->cb.prog = prog;
+		cb->prog = prog;
 	}
-	rcu_assign_pointer(t->cb.callback_fn, callback_fn);
+	rcu_assign_pointer(cb->callback_fn, callback_fn);
 out:
-	__bpf_spin_unlock_irqrestore(&timer->lock);
+	__bpf_spin_unlock_irqrestore(&async->lock);
 	return ret;
 }
 
+BPF_CALL_3(bpf_timer_set_callback, struct bpf_async_kern *, timer, void *, callback_fn,
+	   struct bpf_prog_aux *, aux)
+{
+	return __bpf_async_set_callback(timer, callback_fn, aux, 0, BPF_ASYNC_TYPE_TIMER);
+}
+
 static const struct bpf_func_proto bpf_timer_set_callback_proto = {
 	.func		= bpf_timer_set_callback,
 	.gpl_only	= true,