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