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 | |