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") 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") 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") 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