1 // SPDX-License-Identifier: GPL-2.0
2 /* Copyright (c) 2021 Facebook */
3
4 #include "vmlinux.h"
5 #include <bpf/bpf_helpers.h>
6 #include <bpf/bpf_tracing.h>
7
8 #ifndef EBUSY
9 #define EBUSY 16
10 #endif
11
12 char _license[] SEC("license") = "GPL";
13 int nr_del_errs = 0;
14 int test_pid = 0;
15
16 struct {
17 __uint(type, BPF_MAP_TYPE_TASK_STORAGE);
18 __uint(map_flags, BPF_F_NO_PREALLOC);
19 __type(key, int);
20 __type(value, long);
21 } map_a SEC(".maps");
22
23 struct {
24 __uint(type, BPF_MAP_TYPE_TASK_STORAGE);
25 __uint(map_flags, BPF_F_NO_PREALLOC);
26 __type(key, int);
27 __type(value, long);
28 } map_b SEC(".maps");
29
30 SEC("fentry/bpf_local_storage_update")
31 int BPF_PROG(on_update)
32 {
33 struct task_struct *task = bpf_get_current_task_btf();
34 long *ptr;
35
36 if (!test_pid || task->pid != test_pid)
37 return 0;
38
39 ptr = bpf_task_storage_get(&map_a, task, 0,
40 BPF_LOCAL_STORAGE_GET_F_CREATE);
41 /* ptr will not be NULL when it is called from
42 * the bpf_task_storage_get(&map_b,...F_CREATE) in
43 * the BPF_PROG(on_enter) below. It is because
44 * the value can be found in map_a and the kernel
45 * does not need to acquire any spin_lock.
46 */
47 if (ptr) {
48 int err;
49
50 *ptr += 1;
51 err = bpf_task_storage_delete(&map_a, task);
52 if (err == -EBUSY)
53 nr_del_errs++;
54 }
55
56 /* This will still fail because map_b is empty and
57 * this BPF_PROG(on_update) has failed to acquire
58 * the percpu busy lock => meaning potential
59 * deadlock is detected and it will fail to create
60 * new storage.
61 */
62 ptr = bpf_task_storage_get(&map_b, task, 0,
63 BPF_LOCAL_STORAGE_GET_F_CREATE);
64 if (ptr)
65 *ptr += 1;
66
67 return 0;
68 }
69
70 SEC("tp_btf/sys_enter")
71 int BPF_PROG(on_enter, struct pt_regs *regs, long id)
72 {
73 struct task_struct *task;
74 long *ptr;
75
76 task = bpf_get_current_task_btf();
77 if (!test_pid || task->pid != test_pid)
78 return 0;
79
80 ptr = bpf_task_storage_get(&map_a, task, 0,
81 BPF_LOCAL_STORAGE_GET_F_CREATE);
82 if (ptr && !*ptr)
83 *ptr = 200;
84
85 ptr = bpf_task_storage_get(&map_b, task, 0,
86 BPF_LOCAL_STORAGE_GET_F_CREATE);
87 if (ptr && !*ptr)
88 *ptr = 100;
89 return 0;
90 }
91
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