selftests/bpf: Add test case for element reuse in htab map

The reinitialization of spin-lock in map value after immediate reuse may
corrupt lookup with BPF_F_LOCK flag and result in hard lock-up, so add
one test case to demonstrate the problem.
Signed-off-by: Hou Tao <houtao1@huawei.com>
Link: https://lore.kernel.org/r/20230215082132.3856544-3-houtao@huaweicloud.comSigned-off-by: Alexei Starovoitov <ast@kernel.org>

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

+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (C) 2023. Huawei Technologies Co., Ltd */
+#define _GNU_SOURCE
+#include <sched.h>
+#include <stdbool.h>
+#include <test_progs.h>
+#include "htab_reuse.skel.h"
+
+struct htab_op_ctx {
+	int fd;
+	int loop;
+	bool stop;
+};
+
+struct htab_val {
+	unsigned int lock;
+	unsigned int data;
+};
+
+static void *htab_lookup_fn(void *arg)
+{
+	struct htab_op_ctx *ctx = arg;
+	int i = 0;
+
+	while (i++ < ctx->loop && !ctx->stop) {
+		struct htab_val value;
+		unsigned int key;
+
+		/* Use BPF_F_LOCK to use spin-lock in map value. */
+		key = 7;
+		bpf_map_lookup_elem_flags(ctx->fd, &key, &value, BPF_F_LOCK);
+	}
+
+	return NULL;
+}
+
+static void *htab_update_fn(void *arg)
+{
+	struct htab_op_ctx *ctx = arg;
+	int i = 0;
+
+	while (i++ < ctx->loop && !ctx->stop) {
+		struct htab_val value;
+		unsigned int key;
+
+		key = 7;
+		value.lock = 0;
+		value.data = key;
+		bpf_map_update_elem(ctx->fd, &key, &value, BPF_F_LOCK);
+		bpf_map_delete_elem(ctx->fd, &key);
+
+		key = 24;
+		value.lock = 0;
+		value.data = key;
+		bpf_map_update_elem(ctx->fd, &key, &value, BPF_F_LOCK);
+		bpf_map_delete_elem(ctx->fd, &key);
+	}
+
+	return NULL;
+}
+
+void test_htab_reuse(void)
+{
+	unsigned int i, wr_nr = 1, rd_nr = 4;
+	pthread_t tids[wr_nr + rd_nr];
+	struct htab_reuse *skel;
+	struct htab_op_ctx ctx;
+	int err;
+
+	skel = htab_reuse__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "htab_reuse__open_and_load"))
+		return;
+
+	ctx.fd = bpf_map__fd(skel->maps.htab);
+	ctx.loop = 500;
+	ctx.stop = false;
+
+	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++) {
+		if (!tids[i])
+			continue;
+		pthread_join(tids[i], NULL);
+	}
+	htab_reuse__destroy(skel);
+}

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

+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (C) 2023. Huawei Technologies Co., Ltd */
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+
+char _license[] SEC("license") = "GPL";
+
+struct htab_val {
+	struct bpf_spin_lock lock;
+	unsigned int data;
+};
+
+struct {
+	__uint(type, BPF_MAP_TYPE_HASH);
+	__uint(max_entries, 64);
+	__type(key, unsigned int);
+	__type(value, struct htab_val);
+	__uint(map_flags, BPF_F_NO_PREALLOC);
+} htab SEC(".maps");