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// 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;
}
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