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_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 }