selftests/bpf: add bpf_wq tests

We simply try in all supported map types if we can store/load a bpf_wq.
Signed-off-by: Benjamin Tissoires <bentiss@kernel.org>
Link: https://lore.kernel.org/r/20240420-bpf_wq-v2-10-6c986a5a741f@kernel.orgSigned-off-by: Alexei Starovoitov <ast@kernel.org>

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

+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2024 Benjamin Tissoires */
+#include <test_progs.h>
+#include "wq.skel.h"
+
+void serial_test_wq(void)
+{
+	LIBBPF_OPTS(bpf_test_run_opts, topts);
+
+	RUN_TESTS(wq);
+}

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

+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2024 Benjamin Tissoires
+ */
+
+#include "bpf_experimental.h"
+#include <bpf/bpf_helpers.h>
+#include "bpf_misc.h"
+#include "../bpf_testmod/bpf_testmod_kfunc.h"
+
+char _license[] SEC("license") = "GPL";
+
+struct hmap_elem {
+	int counter;
+	struct bpf_timer timer; /* unused */
+	struct bpf_spin_lock lock; /* unused */
+	struct bpf_wq work;
+};
+
+struct {
+	__uint(type, BPF_MAP_TYPE_HASH);
+	__uint(max_entries, 1000);
+	__type(key, int);
+	__type(value, struct hmap_elem);
+} hmap SEC(".maps");
+
+struct {
+	__uint(type, BPF_MAP_TYPE_HASH);
+	__uint(map_flags, BPF_F_NO_PREALLOC);
+	__uint(max_entries, 1000);
+	__type(key, int);
+	__type(value, struct hmap_elem);
+} hmap_malloc SEC(".maps");
+
+struct elem {
+	struct bpf_wq w;
+};
+
+struct {
+	__uint(type, BPF_MAP_TYPE_ARRAY);
+	__uint(max_entries, 2);
+	__type(key, int);
+	__type(value, struct elem);
+} array SEC(".maps");
+
+struct {
+	__uint(type, BPF_MAP_TYPE_LRU_HASH);
+	__uint(max_entries, 4);
+	__type(key, int);
+	__type(value, struct elem);
+} lru SEC(".maps");
+
+static int test_elem_callback(void *map, int *key)
+{
+	struct elem init = {}, *val;
+
+	if (map == &lru &&
+	    bpf_map_update_elem(map, key, &init, 0))
+		return -1;
+
+	val = bpf_map_lookup_elem(map, key);
+	if (!val)
+		return -2;
+
+	return 0;
+}
+
+static int test_hmap_elem_callback(void *map, int *key)
+{
+	struct hmap_elem init = {}, *val;
+
+	if (bpf_map_update_elem(map, key, &init, 0))
+		return -1;
+
+	val = bpf_map_lookup_elem(map, key);
+	if (!val)
+		return -2;
+
+	return 0;
+}
+
+SEC("tc")
+/* test that workqueues can be used from an array */
+__retval(0)
+long test_call_array_sleepable(void *ctx)
+{
+	int key = 0;
+
+	return test_elem_callback(&array, &key);
+}
+
+SEC("syscall")
+/* Same test than above but from a sleepable context. */
+__retval(0)
+long test_syscall_array_sleepable(void *ctx)
+{
+	int key = 1;
+
+	return test_elem_callback(&array, &key);
+}
+
+SEC("tc")
+/* test that workqueues can be used from a hashmap */
+__retval(0)
+long test_call_hash_sleepable(void *ctx)
+{
+	int key = 2;
+
+	return test_hmap_elem_callback(&hmap, &key);
+}
+
+SEC("tc")
+/* test that workqueues can be used from a hashmap with NO_PREALLOC. */
+__retval(0)
+long test_call_hash_malloc_sleepable(void *ctx)
+{
+	int key = 3;
+
+	return test_hmap_elem_callback(&hmap_malloc, &key);
+}
+
+SEC("tc")
+/* test that workqueues can be used from a LRU map */
+__retval(0)
+long test_call_lru_sleepable(void *ctx)
+{
+	int key = 4;
+
+	return test_elem_callback(&lru, &key);
+}