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