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_lookup")
BPF_PROG(on_lookup)31 int BPF_PROG(on_lookup)
32 {
33 struct task_struct *task = bpf_get_current_task_btf();
34
35 if (!test_pid || task->pid != test_pid)
36 return 0;
37
38 /* The bpf_task_storage_delete will call
39 * bpf_local_storage_lookup. The prog->active will
40 * stop the recursion.
41 */
42 bpf_task_storage_delete(&map_a, task);
43 bpf_task_storage_delete(&map_b, task);
44 return 0;
45 }
46
47 SEC("fentry/bpf_local_storage_update")
BPF_PROG(on_update)48 int BPF_PROG(on_update)
49 {
50 struct task_struct *task = bpf_get_current_task_btf();
51 long *ptr;
52
53 if (!test_pid || task->pid != test_pid)
54 return 0;
55
56 ptr = bpf_task_storage_get(&map_a, task, 0,
57 BPF_LOCAL_STORAGE_GET_F_CREATE);
58 /* ptr will not be NULL when it is called from
59 * the bpf_task_storage_get(&map_b,...F_CREATE) in
60 * the BPF_PROG(on_enter) below. It is because
61 * the value can be found in map_a and the kernel
62 * does not need to acquire any spin_lock.
63 */
64 if (ptr) {
65 int err;
66
67 *ptr += 1;
68 err = bpf_task_storage_delete(&map_a, task);
69 if (err == -EBUSY)
70 nr_del_errs++;
71 }
72
73 /* This will still fail because map_b is empty and
74 * this BPF_PROG(on_update) has failed to acquire
75 * the percpu busy lock => meaning potential
76 * deadlock is detected and it will fail to create
77 * new storage.
78 */
79 ptr = bpf_task_storage_get(&map_b, task, 0,
80 BPF_LOCAL_STORAGE_GET_F_CREATE);
81 if (ptr)
82 *ptr += 1;
83
84 return 0;
85 }
86
87 SEC("tp_btf/sys_enter")
BPF_PROG(on_enter,struct pt_regs * regs,long id)88 int BPF_PROG(on_enter, struct pt_regs *regs, long id)
89 {
90 struct task_struct *task;
91 long *ptr;
92
93 task = bpf_get_current_task_btf();
94 if (!test_pid || task->pid != test_pid)
95 return 0;
96
97 ptr = bpf_task_storage_get(&map_a, task, 0,
98 BPF_LOCAL_STORAGE_GET_F_CREATE);
99 if (ptr && !*ptr)
100 *ptr = 200;
101
102 ptr = bpf_task_storage_get(&map_b, task, 0,
103 BPF_LOCAL_STORAGE_GET_F_CREATE);
104 if (ptr && !*ptr)
105 *ptr = 100;
106 return 0;
107 }
108