tools/testing/selftests/bpf/progs/task_ls_recursion.c

   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 }