f85671c6ef
In commit 22df776a9a ("tasks: Extract rcu_users out of union"), the
'refcount_t rcu_users' field was extracted out of a union with the
'struct rcu_head rcu' field. This allows us to safely perform a
refcount_inc_not_zero() on task->rcu_users when acquiring a reference on
a task struct. A prior patch leveraged this by making struct task_struct
an RCU-protected object in the verifier, and by bpf_task_acquire() to
use the task->rcu_users field for synchronization.
Now that we can use RCU to protect tasks, we no longer need
bpf_task_kptr_get(), or bpf_task_acquire_not_zero(). bpf_task_kptr_get()
is truly completely unnecessary, as we can just use RCU to get the
object. bpf_task_acquire_not_zero() is now equivalent to
bpf_task_acquire().
In addition to these changes, this patch also updates the associated
selftests to no longer use these kfuncs.
Signed-off-by: David Vernet <void@manifault.com>
Link: https://lore.kernel.org/r/20230331195733.699708-3-void@manifault.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
76 lines
1.7 KiB
C
76 lines
1.7 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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/* Copyright (c) 2022 Meta Platforms, Inc. and affiliates. */
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#ifndef _TASK_KFUNC_COMMON_H
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#define _TASK_KFUNC_COMMON_H
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#include <errno.h>
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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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struct __tasks_kfunc_map_value {
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struct task_struct __kptr * task;
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};
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struct hash_map {
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__uint(type, BPF_MAP_TYPE_HASH);
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__type(key, int);
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__type(value, struct __tasks_kfunc_map_value);
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__uint(max_entries, 1);
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} __tasks_kfunc_map SEC(".maps");
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struct task_struct *bpf_task_acquire(struct task_struct *p) __ksym;
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void bpf_task_release(struct task_struct *p) __ksym;
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struct task_struct *bpf_task_from_pid(s32 pid) __ksym;
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void bpf_rcu_read_lock(void) __ksym;
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void bpf_rcu_read_unlock(void) __ksym;
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static inline struct __tasks_kfunc_map_value *tasks_kfunc_map_value_lookup(struct task_struct *p)
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{
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s32 pid;
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long status;
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status = bpf_probe_read_kernel(&pid, sizeof(pid), &p->pid);
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if (status)
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return NULL;
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return bpf_map_lookup_elem(&__tasks_kfunc_map, &pid);
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}
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static inline int tasks_kfunc_map_insert(struct task_struct *p)
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{
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struct __tasks_kfunc_map_value local, *v;
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long status;
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struct task_struct *acquired, *old;
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s32 pid;
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status = bpf_probe_read_kernel(&pid, sizeof(pid), &p->pid);
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if (status)
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return status;
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local.task = NULL;
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status = bpf_map_update_elem(&__tasks_kfunc_map, &pid, &local, BPF_NOEXIST);
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if (status)
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return status;
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v = bpf_map_lookup_elem(&__tasks_kfunc_map, &pid);
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if (!v) {
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bpf_map_delete_elem(&__tasks_kfunc_map, &pid);
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return -ENOENT;
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}
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acquired = bpf_task_acquire(p);
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if (!acquired)
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return -ENOENT;
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old = bpf_kptr_xchg(&v->task, acquired);
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if (old) {
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bpf_task_release(old);
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return -EEXIST;
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}
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return 0;
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}
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#endif /* _TASK_KFUNC_COMMON_H */
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