selftests/bpf: Add update_elem failure test for task storage uptr

This patch test the following failures in syscall update_elem
1. The first update_elem(BPF_F_LOCK) should be EOPNOTSUPP. syscall.c takes
care of unpinning the uptr.
2. The second update_elem(BPF_EXIST) fails. syscall.c takes care of
unpinning the uptr.
3. The forth update_elem(BPF_NOEXIST) fails. bpf_local_storage_update
takes care of unpinning the uptr.

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

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

···
 #include "task_storage_nodeadlock.skel.h"
 #include "uptr_test_common.h"
 #include "task_ls_uptr.skel.h"
+#include "uptr_update_failure.skel.h"
 
 static void test_sys_enter_exit(void)
 {
···
 	munmap(mem, page_size * 2);
 }
 
+static void test_uptr_update_failure(void)
+{
+	struct value_lock_type value = {};
+	struct uptr_update_failure *skel;
+	int err, task_fd, map_fd;
+
+	task_fd = sys_pidfd_open(getpid(), 0);
+	if (!ASSERT_OK_FD(task_fd, "task_fd"))
+		return;
+
+	skel = uptr_update_failure__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "skel_open_and_load"))
+		goto out;
+
+	map_fd = bpf_map__fd(skel->maps.datamap);
+
+	value.udata = &udata;
+	err = bpf_map_update_elem(map_fd, &task_fd, &value, BPF_F_LOCK);
+	if (!ASSERT_ERR(err, "update_elem(udata, BPF_F_LOCK)"))
+		goto out;
+	ASSERT_EQ(errno, EOPNOTSUPP, "errno");
+
+	err = bpf_map_update_elem(map_fd, &task_fd, &value, BPF_EXIST);
+	if (!ASSERT_ERR(err, "update_elem(udata, BPF_EXIST)"))
+		goto out;
+	ASSERT_EQ(errno, ENOENT, "errno");
+
+	err = bpf_map_update_elem(map_fd, &task_fd, &value, BPF_NOEXIST);
+	if (!ASSERT_OK(err, "update_elem(udata, BPF_NOEXIST)"))
+		goto out;
+
+	value.udata = &udata2;
+	err = bpf_map_update_elem(map_fd, &task_fd, &value, BPF_NOEXIST);
+	if (!ASSERT_ERR(err, "update_elem(udata2, BPF_NOEXIST)"))
+		goto out;
+	ASSERT_EQ(errno, EEXIST, "errno");
+
+out:
+	uptr_update_failure__destroy(skel);
+	close(task_fd);
+}
+
 void test_task_local_storage(void)
 {
 	if (test__start_subtest("sys_enter_exit"))
···
 		test_uptr_basic();
 	if (test__start_subtest("uptr_across_pages"))
 		test_uptr_across_pages();
+	if (test__start_subtest("uptr_update_failure"))
+		test_uptr_update_failure();
 }

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

···
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2024 Meta Platforms, Inc. and affiliates. */
+
+#include <vmlinux.h>
+#include <bpf/bpf_helpers.h>
+#include "uptr_test_common.h"
+
+struct {
+	__uint(type, BPF_MAP_TYPE_TASK_STORAGE);
+	__uint(map_flags, BPF_F_NO_PREALLOC);
+	__type(key, int);
+	__type(value, struct value_lock_type);
+} datamap SEC(".maps");
+
+/* load test only. not used */
+SEC("syscall")
+int not_used(void *ctx)
+{
+	struct value_lock_type *ptr;
+	struct task_struct *task;
+	struct user_data *udata;
+
+	task = bpf_get_current_task_btf();
+	ptr = bpf_task_storage_get(&datamap, task, 0, 0);
+	if (!ptr)
+		return 0;
+
+	bpf_spin_lock(&ptr->lock);
+
+	udata = ptr->udata;
+	if (!udata) {
+		bpf_spin_unlock(&ptr->lock);
+		return 0;
+	}
+	udata->result = MAGIC_VALUE + udata->a + udata->b;
+
+	bpf_spin_unlock(&ptr->lock);
+
+	return 0;
+}
+
+char _license[] SEC("license") = "GPL";

tools/testing/selftests/bpf/uptr_test_common.h

···
 	struct nested_udata nested;
 };
 
+struct value_lock_type {
+	struct user_data __uptr *udata;
+	struct bpf_spin_lock lock;
+};
+
 #endif