selftests/bpf: Add test cases for htab update

One test demonstrates the reentrancy of hash map update on the same
bucket should fail, and another one shows concureently updates of
the same hash map bucket should succeed and not fail due to
the reentrancy checking for bucket lock.

There is no trampoline support on s390x, so move htab_update to
denylist.
Signed-off-by: Hou Tao <houtao1@huawei.com>
Link: https://lore.kernel.org/r/20220831042629.130006-4-houtao@huaweicloud.comSigned-off-by: Martin KaFai Lau <martin.lau@kernel.org>

tools/testing/selftests/bpf/DENYLIST.s390x

@@ -68,3 +68,4 @@ unpriv_bpf_disabled                      # fentry
 setget_sockopt                           # attach unexpected error: -524                                               (trampoline)
 cb_refs                                  # expected error message unexpected error: -524                               (trampoline)
 cgroup_hierarchical_stats                # JIT does not support calling kernel function                                (kfunc)
+htab_update                              # failed to attach: ERROR: strerror_r(-524)=22                                (trampoline)

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

+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (C) 2022. Huawei Technologies Co., Ltd */
+#define _GNU_SOURCE
+#include <sched.h>
+#include <stdbool.h>
+#include <test_progs.h>
+#include "htab_update.skel.h"
+
+struct htab_update_ctx {
+	int fd;
+	int loop;
+	bool stop;
+};
+
+static void test_reenter_update(void)
+{
+	struct htab_update *skel;
+	unsigned int key, value;
+	int err;
+
+	skel = htab_update__open();
+	if (!ASSERT_OK_PTR(skel, "htab_update__open"))
+		return;
+
+	/* lookup_elem_raw() may be inlined and find_kernel_btf_id() will return -ESRCH */
+	bpf_program__set_autoload(skel->progs.lookup_elem_raw, true);
+	err = htab_update__load(skel);
+	if (!ASSERT_TRUE(!err || err == -ESRCH, "htab_update__load") || err)
+		goto out;
+
+	skel->bss->pid = getpid();
+	err = htab_update__attach(skel);
+	if (!ASSERT_OK(err, "htab_update__attach"))
+		goto out;
+
+	/* Will trigger the reentrancy of bpf_map_update_elem() */
+	key = 0;
+	value = 0;
+	err = bpf_map_update_elem(bpf_map__fd(skel->maps.htab), &key, &value, 0);
+	if (!ASSERT_OK(err, "add element"))
+		goto out;
+
+	ASSERT_EQ(skel->bss->update_err, -EBUSY, "no reentrancy");
+out:
+	htab_update__destroy(skel);
+}
+
+static void *htab_update_thread(void *arg)
+{
+	struct htab_update_ctx *ctx = arg;
+	cpu_set_t cpus;
+	int i;
+
+	/* Pinned on CPU 0 */
+	CPU_ZERO(&cpus);
+	CPU_SET(0, &cpus);
+	pthread_setaffinity_np(pthread_self(), sizeof(cpus), &cpus);
+
+	i = 0;
+	while (i++ < ctx->loop && !ctx->stop) {
+		unsigned int key = 0, value = 0;
+		int err;
+
+		err = bpf_map_update_elem(ctx->fd, &key, &value, 0);
+		if (err) {
+			ctx->stop = true;
+			return (void *)(long)err;
+		}
+	}
+
+	return NULL;
+}
+
+static void test_concurrent_update(void)
+{
+	struct htab_update_ctx ctx;
+	struct htab_update *skel;
+	unsigned int i, nr;
+	pthread_t *tids;
+	int err;
+
+	skel = htab_update__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "htab_update__open_and_load"))
+		return;
+
+	ctx.fd = bpf_map__fd(skel->maps.htab);
+	ctx.loop = 1000;
+	ctx.stop = false;
+
+	nr = 4;
+	tids = calloc(nr, sizeof(*tids));
+	if (!ASSERT_NEQ(tids, NULL, "no mem"))
+		goto out;
+
+	for (i = 0; i < nr; i++) {
+		err = pthread_create(&tids[i], NULL, htab_update_thread, &ctx);
+		if (!ASSERT_OK(err, "pthread_create")) {
+			unsigned int j;
+
+			ctx.stop = true;
+			for (j = 0; j < i; j++)
+				pthread_join(tids[j], NULL);
+			goto out;
+		}
+	}
+
+	for (i = 0; i < nr; i++) {
+		void *thread_err = NULL;
+
+		pthread_join(tids[i], &thread_err);
+		ASSERT_EQ(thread_err, NULL, "update error");
+	}
+
+out:
+	if (tids)
+		free(tids);
+	htab_update__destroy(skel);
+}
+
+void test_htab_update(void)
+{
+	if (test__start_subtest("reenter_update"))
+		test_reenter_update();
+	if (test__start_subtest("concurrent_update"))
+		test_concurrent_update();
+}

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

+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (C) 2022. Huawei Technologies Co., Ltd */
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+char _license[] SEC("license") = "GPL";
+
+struct {
+	__uint(type, BPF_MAP_TYPE_HASH);
+	__uint(max_entries, 1);
+	__uint(key_size, sizeof(__u32));
+	__uint(value_size, sizeof(__u32));
+} htab SEC(".maps");
+
+int pid = 0;
+int update_err = 0;
+
+SEC("?fentry/lookup_elem_raw")
+int lookup_elem_raw(void *ctx)
+{
+	__u32 key = 0, value = 1;
+
+	if ((bpf_get_current_pid_tgid() >> 32) != pid)
+		return 0;
+
+	update_err = bpf_map_update_elem(&htab, &key, &value, 0);
+	return 0;
+}