selftests/bpf: Test preemption between bpf_obj_new() and bpf_obj_drop()

The test case creates 4 threads and then pins these 4 threads in CPU 0.
These 4 threads will run different bpf program through
bpf_prog_test_run_opts() and these bpf program will use bpf_obj_new()
and bpf_obj_drop() to allocate and free local kptrs concurrently.

Under preemptible kernel, bpf_obj_new() and bpf_obj_drop() may preempt
each other, bpf_obj_new() may return NULL and the test will fail before
applying these fixes as shown below:

test_preempted_bpf_ma_op:PASS:open_and_load 0 nsec
test_preempted_bpf_ma_op:PASS:attach 0 nsec
test_preempted_bpf_ma_op:PASS:no test prog 0 nsec
test_preempted_bpf_ma_op:PASS:no test prog 0 nsec
test_preempted_bpf_ma_op:PASS:no test prog 0 nsec
test_preempted_bpf_ma_op:PASS:no test prog 0 nsec
test_preempted_bpf_ma_op:PASS:pthread_create 0 nsec
test_preempted_bpf_ma_op:PASS:pthread_create 0 nsec
test_preempted_bpf_ma_op:PASS:pthread_create 0 nsec
test_preempted_bpf_ma_op:PASS:pthread_create 0 nsec
test_preempted_bpf_ma_op:PASS:run prog err 0 nsec
test_preempted_bpf_ma_op:PASS:run prog err 0 nsec
test_preempted_bpf_ma_op:PASS:run prog err 0 nsec
test_preempted_bpf_ma_op:PASS:run prog err 0 nsec
test_preempted_bpf_ma_op:FAIL:ENOMEM unexpected ENOMEM: got TRUE
#168 preempted_bpf_ma_op:FAIL
Summary: 0/0 PASSED, 0 SKIPPED, 1 FAILED

Signed-off-by: Hou Tao <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Alexei Starovoitov <[e-mail]>

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

···
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (C) 2023. Huawei Technologies Co., Ltd */
+#define _GNU_SOURCE
+#include <sched.h>
+#include <pthread.h>
+#include <stdbool.h>
+#include <test_progs.h>
+
+#include "preempted_bpf_ma_op.skel.h"
+
+#define ALLOC_THREAD_NR 4
+#define ALLOC_LOOP_NR 512
+
+struct alloc_ctx {
+	/* output */
+	int run_err;
+	/* input */
+	int fd;
+	bool *nomem_err;
+};
+
+static void *run_alloc_prog(void *data)
+{
+	struct alloc_ctx *ctx = data;
+	cpu_set_t cpu_set;
+	int i;
+
+	CPU_ZERO(&cpu_set);
+	CPU_SET(0, &cpu_set);
+	pthread_setaffinity_np(pthread_self(), sizeof(cpu_set), &cpu_set);
+
+	for (i = 0; i < ALLOC_LOOP_NR && !*ctx->nomem_err; i++) {
+		LIBBPF_OPTS(bpf_test_run_opts, topts);
+		int err;
+
+		err = bpf_prog_test_run_opts(ctx->fd, &topts);
+		ctx->run_err |= err | topts.retval;
+	}
+
+	return NULL;
+}
+
+void test_preempted_bpf_ma_op(void)
+{
+	struct alloc_ctx ctx[ALLOC_THREAD_NR];
+	struct preempted_bpf_ma_op *skel;
+	pthread_t tid[ALLOC_THREAD_NR];
+	int i, err;
+
+	skel = preempted_bpf_ma_op__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "open_and_load"))
+		return;
+
+	err = preempted_bpf_ma_op__attach(skel);
+	if (!ASSERT_OK(err, "attach"))
+		goto out;
+
+	for (i = 0; i < ARRAY_SIZE(ctx); i++) {
+		struct bpf_program *prog;
+		char name[8];
+
+		snprintf(name, sizeof(name), "test%d", i);
+		prog = bpf_object__find_program_by_name(skel->obj, name);
+		if (!ASSERT_OK_PTR(prog, "no test prog"))
+			goto out;
+
+		ctx[i].run_err = 0;
+		ctx[i].fd = bpf_program__fd(prog);
+		ctx[i].nomem_err = &skel->bss->nomem_err;
+	}
+
+	memset(tid, 0, sizeof(tid));
+	for (i = 0; i < ARRAY_SIZE(tid); i++) {
+		err = pthread_create(&tid[i], NULL, run_alloc_prog, &ctx[i]);
+		if (!ASSERT_OK(err, "pthread_create"))
+			break;
+	}
+
+	for (i = 0; i < ARRAY_SIZE(tid); i++) {
+		if (!tid[i])
+			break;
+		pthread_join(tid[i], NULL);
+		ASSERT_EQ(ctx[i].run_err, 0, "run prog err");
+	}
+
+	ASSERT_FALSE(skel->bss->nomem_err, "ENOMEM");
+out:
+	preempted_bpf_ma_op__destroy(skel);
+}

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

···
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (C) 2023. Huawei Technologies Co., Ltd */
+#include <vmlinux.h>
+#include <bpf/bpf_tracing.h>
+#include <bpf/bpf_helpers.h>
+
+#include "bpf_experimental.h"
+
+struct bin_data {
+	char data[256];
+	struct bpf_spin_lock lock;
+};
+
+struct map_value {
+	struct bin_data __kptr * data;
+};
+
+struct {
+	__uint(type, BPF_MAP_TYPE_ARRAY);
+	__type(key, int);
+	__type(value, struct map_value);
+	__uint(max_entries, 2048);
+} array SEC(".maps");
+
+char _license[] SEC("license") = "GPL";
+
+bool nomem_err = false;
+
+static int del_array(unsigned int i, int *from)
+{
+	struct map_value *value;
+	struct bin_data *old;
+
+	value = bpf_map_lookup_elem(&array, from);
+	if (!value)
+		return 1;
+
+	old = bpf_kptr_xchg(&value->data, NULL);
+	if (old)
+		bpf_obj_drop(old);
+
+	(*from)++;
+	return 0;
+}
+
+static int add_array(unsigned int i, int *from)
+{
+	struct bin_data *old, *new;
+	struct map_value *value;
+
+	value = bpf_map_lookup_elem(&array, from);
+	if (!value)
+		return 1;
+
+	new = bpf_obj_new(typeof(*new));
+	if (!new) {
+		nomem_err = true;
+		return 1;
+	}
+
+	old = bpf_kptr_xchg(&value->data, new);
+	if (old)
+		bpf_obj_drop(old);
+
+	(*from)++;
+	return 0;
+}
+
+static void del_then_add_array(int from)
+{
+	int i;
+
+	i = from;
+	bpf_loop(512, del_array, &i, 0);
+
+	i = from;
+	bpf_loop(512, add_array, &i, 0);
+}
+
+SEC("fentry/bpf_fentry_test1")
+int BPF_PROG2(test0, int, a)
+{
+	del_then_add_array(0);
+	return 0;
+}
+
+SEC("fentry/bpf_fentry_test2")
+int BPF_PROG2(test1, int, a, u64, b)
+{
+	del_then_add_array(512);
+	return 0;
+}
+
+SEC("fentry/bpf_fentry_test3")
+int BPF_PROG2(test2, char, a, int, b, u64, c)
+{
+	del_then_add_array(1024);
+	return 0;
+}
+
+SEC("fentry/bpf_fentry_test4")
+int BPF_PROG2(test3, void *, a, char, b, int, c, u64, d)
+{
+	del_then_add_array(1536);
+	return 0;
+}