selftests/bpf: Add test case for atomic htab update

Add a test case to verify the atomic update of existing element in hash
map. The test proceeds in three steps:
1) fill the map with keys in the range [0, 63]
2) create 8 threads to lookup these keys concurrently
3) create 2 threads to overwrite these keys concurrently

Without atomic update support, the lookup operation may return -ENOENT
error and the test will fail. After the atomic-update change, the lookup
operation will always return 0 and the test will succeed.

Signed-off-by: Hou Tao <[email protected]>

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

@@ -0,0 +1,130 @@
+// SPDX-License-Identifier: GPL-2.0
+#define _GNU_SOURCE
+#include <stdbool.h>
+#include <test_progs.h>
+#include "htab_lookup.skel.h"
+
+struct htab_op_ctx {
+	int fd;
+	int loop;
+	unsigned int entries;
+	bool stop;
+};
+
+static void *htab_lookup_fn(void *arg)
+{
+	struct htab_op_ctx *ctx = arg;
+	int i = 0;
+
+	while (i++ < ctx->loop && !ctx->stop) {
+		unsigned int j;
+
+		for (j = 0; j < ctx->entries; j++) {
+			unsigned long key = j, value;
+			int err;
+
+			err = bpf_map_lookup_elem(ctx->fd, &key, &value);
+			if (err) {
+				ctx->stop = true;
+				return (void *)(long)err;
+			}
+		}
+	}
+
+	return NULL;
+}
+
+static void *htab_update_fn(void *arg)
+{
+	struct htab_op_ctx *ctx = arg;
+	int i = 0;
+
+	while (i++ < ctx->loop && !ctx->stop) {
+		unsigned int j;
+
+		for (j = 0; j < ctx->entries; j++) {
+			unsigned long key = j, value = j;
+			int err;
+
+			err = bpf_map_update_elem(ctx->fd, &key, &value, BPF_EXIST);
+			if (err) {
+				if (err == -ENOMEM)
+					continue;
+				ctx->stop = true;
+				return (void *)(long)err;
+			}
+		}
+	}
+
+	return NULL;
+}
+
+static int setup_htab(int fd, unsigned int entries)
+{
+	unsigned int i;
+
+	for (i = 0; i < entries; i++) {
+		unsigned long key = i, value = i;
+		int err;
+
+		err = bpf_map_update_elem(fd, &key, &value, 0);
+		if (!ASSERT_OK(err, "init update"))
+			return -1;
+	}
+
+	return 0;
+}
+
+void test_htab_lookup(void)
+{
+	unsigned int i, wr_nr = 2, rd_nr = 8;
+	pthread_t tids[wr_nr + rd_nr];
+	struct htab_lookup *skel;
+	struct htab_op_ctx ctx;
+	int err;
+
+	skel = htab_lookup__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "htab_lookup__open_and_load"))
+		return;
+
+	ctx.fd = bpf_map__fd(skel->maps.htab);
+	ctx.loop = 50;
+	ctx.stop = false;
+	ctx.entries = 64;
+
+	err = setup_htab(ctx.fd, ctx.entries);
+	if (err)
+		goto destroy;
+
+	memset(tids, 0, sizeof(tids));
+	for (i = 0; i < wr_nr; i++) {
+		err = pthread_create(&tids[i], NULL, htab_update_fn, &ctx);
+		if (!ASSERT_OK(err, "pthread_create")) {
+			ctx.stop = true;
+			goto reap;
+		}
+	}
+	for (i = 0; i < rd_nr; i++) {
+		err = pthread_create(&tids[i + wr_nr], NULL, htab_lookup_fn, &ctx);
+		if (!ASSERT_OK(err, "pthread_create")) {
+			ctx.stop = true;
+			goto reap;
+		}
+	}
+
+reap:
+	for (i = 0; i < wr_nr + rd_nr; i++) {
+		void *ret = NULL;
+		char desc[32];
+
+		if (!tids[i])
+			continue;
+
+		snprintf(desc, sizeof(desc), "thread %u", i + 1);
+		err = pthread_join(tids[i], &ret);
+		ASSERT_OK(err, desc);
+		ASSERT_EQ(ret, NULL, desc);
+	}
+destroy:
+	htab_lookup__destroy(skel);
+}

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

@@ -0,0 +1,13 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+
+char _license[] SEC("license") = "GPL";
+
+struct {
+	__uint(type, BPF_MAP_TYPE_HASH);
+	__uint(max_entries, 64);
+	__type(key, unsigned long);
+	__type(value, unsigned long);
+	__uint(map_flags, BPF_F_NO_PREALLOC);
+} htab SEC(".maps");