Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
1// SPDX-License-Identifier: GPL-2.0
2/* Copyright (C) 2025. Huawei Technologies Co., Ltd */
3#include <linux/bpf.h>
4#include <time.h>
5#include <bpf/bpf_tracing.h>
6#include <bpf/bpf_helpers.h>
7
8#define MAX_ENTRIES 8
9
10/* clang considers 'sum += 1' as usage but 'sum++' as non-usage. GCC
11 * is more consistent and considers both 'sum += 1' and 'sum++' as
12 * non-usage. This triggers warnings in the functions below.
13 *
14 * Starting with GCC 16 -Wunused-but-set-variable=2 can be used to
15 * mimic clang's behavior. */
16#if !defined(__clang__) && __GNUC__ > 15
17#pragma GCC diagnostic ignored "-Wunused-but-set-variable"
18#endif
19
20struct map_value {
21 struct bpf_timer timer;
22};
23
24struct {
25 __uint(type, BPF_MAP_TYPE_HASH);
26 __type(key, int);
27 __type(value, struct map_value);
28 __uint(max_entries, MAX_ENTRIES);
29} map SEC(".maps");
30
31static int timer_cb(void *map, void *key, struct map_value *value)
32{
33 volatile int sum = 0;
34 int i;
35
36 bpf_for(i, 0, 1024 * 1024) sum += i;
37
38 return 0;
39}
40
41static int start_cb(int key)
42{
43 struct map_value *value;
44
45 value = bpf_map_lookup_elem(&map, (void *)&key);
46 if (!value)
47 return 0;
48
49 bpf_timer_init(&value->timer, &map, CLOCK_MONOTONIC);
50 bpf_timer_set_callback(&value->timer, timer_cb);
51 /* Hope 100us will be enough to wake-up and run the overwrite thread */
52 bpf_timer_start(&value->timer, 100000, BPF_F_TIMER_CPU_PIN);
53
54 return 0;
55}
56
57static int overwrite_cb(int key)
58{
59 struct map_value zero = {};
60
61 /* Free the timer which may run on other CPU */
62 bpf_map_update_elem(&map, (void *)&key, &zero, BPF_ANY);
63
64 return 0;
65}
66
67SEC("syscall")
68int BPF_PROG(start_timer)
69{
70 bpf_loop(MAX_ENTRIES, start_cb, NULL, 0);
71 return 0;
72}
73
74SEC("syscall")
75int BPF_PROG(overwrite_timer)
76{
77 bpf_loop(MAX_ENTRIES, overwrite_cb, NULL, 0);
78 return 0;
79}
80
81char _license[] SEC("license") = "GPL";