selftests/bpf: Verify bpf_timer_cancel_async works

Add test that verifies that bpf_timer_cancel_async works: can cancel
callback successfully.

Signed-off-by: Mykyta Yatsenko <yatsenko@meta.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20260201025403.66625-7-alexei.starovoitov@gmail.com

Author: mykyta5

tools/testing/selftests/bpf/prog_tests/timer.c

@@ -99,6 +99,26 @@ static int timer(struct timer *timer_skel)
 	return 0;
 }
 
+static int timer_cancel_async(struct timer *timer_skel)
+{
+	int err, prog_fd;
+	LIBBPF_OPTS(bpf_test_run_opts, topts);
+
+	prog_fd = bpf_program__fd(timer_skel->progs.test_async_cancel_succeed);
+	err = bpf_prog_test_run_opts(prog_fd, &topts);
+	ASSERT_OK(err, "test_run");
+	ASSERT_EQ(topts.retval, 0, "test_run");
+
+	usleep(500);
+	/* check that there were no errors in timer execution */
+	ASSERT_EQ(timer_skel->bss->err, 0, "err");
+
+	/* check that code paths completed */
+	ASSERT_EQ(timer_skel->bss->ok, 1 | 2 | 4, "ok");
+
+	return 0;
+}
+
 static void test_timer(int (*timer_test_fn)(struct timer *timer_skel))
 {
 	struct timer *timer_skel = NULL;
@@ -134,6 +154,11 @@ void serial_test_timer_stress_async_cancel(void)
 	test_timer(timer_stress_async_cancel);
 }
 
+void serial_test_timer_async_cancel(void)
+{
+	test_timer(timer_cancel_async);
+}
+
 void test_timer_interrupt(void)
 {
 	struct timer_interrupt *skel = NULL;

tools/testing/selftests/bpf/progs/timer.c

@@ -169,6 +169,29 @@ int BPF_PROG2(test1, int, a)
 	return 0;
 }
 
+static int timer_error(void *map, int *key, struct bpf_timer *timer)
+{
+	err = 42;
+	return 0;
+}
+
+SEC("syscall")
+int test_async_cancel_succeed(void *ctx)
+{
+	struct bpf_timer *arr_timer;
+	int array_key = ARRAY;
+
+	arr_timer = bpf_map_lookup_elem(&array, &array_key);
+	if (!arr_timer)
+		return 0;
+	bpf_timer_init(arr_timer, &array, CLOCK_MONOTONIC);
+	bpf_timer_set_callback(arr_timer, timer_error);
+	bpf_timer_start(arr_timer, 100000 /* 100us */, 0);
+	bpf_timer_cancel_async(arr_timer);
+	ok = 7;
+	return 0;
+}
+
 /* callback for prealloc and non-prealloca hashtab timers */
 static int timer_cb2(void *map, int *key, struct hmap_elem *val)
 {