// SPDX-License-Identifier: GPL-2.0 /* Copyright (c) 2021 Facebook */ #include "vmlinux.h" #include <bpf/bpf_helpers.h> #include <bpf/bpf_tracing.h> #ifndef EBUSY #define EBUSY 16 #endif char _license[] SEC("license") = "GPL"; int nr_del_errs = 0; int test_pid = 0; struct { __uint(type, BPF_MAP_TYPE_TASK_STORAGE); __uint(map_flags, BPF_F_NO_PREALLOC); __type(key, int); __type(value, long); } map_a SEC(".maps"); struct { __uint(type, BPF_MAP_TYPE_TASK_STORAGE); __uint(map_flags, BPF_F_NO_PREALLOC); __type(key, int); __type(value, long); } map_b SEC(".maps"); SEC("fentry/bpf_local_storage_lookup") int BPF_PROG(on_lookup) { struct task_struct *task = bpf_get_current_task_btf(); if (!test_pid || task->pid != test_pid) return 0; /* The bpf_task_storage_delete will call * bpf_local_storage_lookup. The prog->active will * stop the recursion. */ bpf_task_storage_delete(&map_a, task); bpf_task_storage_delete(&map_b, task); return 0; } SEC("fentry/bpf_local_storage_update") int BPF_PROG(on_update) { struct task_struct *task = bpf_get_current_task_btf(); long *ptr; if (!test_pid || task->pid != test_pid) return 0; ptr = bpf_task_storage_get(&map_a, task, 0, BPF_LOCAL_STORAGE_GET_F_CREATE); /* ptr will not be NULL when it is called from * the bpf_task_storage_get(&map_b,...F_CREATE) in * the BPF_PROG(on_enter) below. It is because * the value can be found in map_a and the kernel * does not need to acquire any spin_lock. */ if (ptr) { int err; *ptr += 1; err = bpf_task_storage_delete(&map_a, task); if (err == -EBUSY) nr_del_errs++; } /* This will still fail because map_b is empty and * this BPF_PROG(on_update) has failed to acquire * the percpu busy lock => meaning potential * deadlock is detected and it will fail to create * new storage. */ ptr = bpf_task_storage_get(&map_b, task, 0, BPF_LOCAL_STORAGE_GET_F_CREATE); if (ptr) *ptr += 1; return 0; } SEC("tp_btf/sys_enter") int BPF_PROG(on_enter, struct pt_regs *regs, long id) { struct task_struct *task; long *ptr; task = bpf_get_current_task_btf(); if (!test_pid || task->pid != test_pid) return 0; ptr = bpf_task_storage_get(&map_a, task, 0, BPF_LOCAL_STORAGE_GET_F_CREATE); if (ptr && !*ptr) *ptr = 200; ptr = bpf_task_storage_get(&map_b, task, 0, BPF_LOCAL_STORAGE_GET_F_CREATE); if (ptr && !*ptr) *ptr = 100; return 0; }