tjh.dev
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) 2026 Meta Platforms, Inc. and affiliates. */
3#include <vmlinux.h>
4#include <bpf/bpf_helpers.h>
5#include <bpf/bpf_tracing.h>
6
7#define CLOCK_MONOTONIC 1
8
9char _license[] SEC("license") = "GPL";
10
11struct elem {
12 struct bpf_timer timer;
13};
14
15struct {
16 __uint(type, BPF_MAP_TYPE_ARRAY);
17 __uint(max_entries, 1);
18 __type(key, int);
19 __type(value, struct elem);
20} timer_map SEC(".maps");
21
22volatile int in_timer_start;
23volatile int tp_called;
24
25static int timer_cb(void *map, int *key, struct elem *value)
26{
27 return 0;
28}
29
30SEC("tp_btf/hrtimer_cancel")
31int BPF_PROG(tp_hrtimer_cancel, struct hrtimer *hrtimer)
32{
33 struct bpf_timer *timer;
34 int key = 0;
35
36 if (!in_timer_start)
37 return 0;
38
39 tp_called = 1;
40 timer = bpf_map_lookup_elem(&timer_map, &key);
41
42 /*
43 * Call bpf_timer_start() from the tracepoint within hrtimer logic
44 * on the same timer to make sure it doesn't deadlock.
45 */
46 bpf_timer_start(timer, 1000000000, 0);
47 return 0;
48}
49
50SEC("syscall")
51int start_timer(void *ctx)
52{
53 struct bpf_timer *timer;
54 int key = 0;
55
56 timer = bpf_map_lookup_elem(&timer_map, &key);
57 /* claude may complain here that there is no NULL check. Ignoring it. */
58 bpf_timer_init(timer, &timer_map, CLOCK_MONOTONIC);
59 bpf_timer_set_callback(timer, timer_cb);
60
61 /*
62 * call hrtimer_start() twice, so that 2nd call does
63 * remove_hrtimer() and trace_hrtimer_cancel() tracepoint.
64 */
65 in_timer_start = 1;
66 bpf_timer_start(timer, 1000000000, 0);
67 bpf_timer_start(timer, 1000000000, 0);
68 in_timer_start = 0;
69 return 0;
70}