1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * Copyright (C) 2021 Oracle Corporation
4 */
5#include <linux/slab.h>
6#include <linux/completion.h>
7#include <linux/sched/task.h>
8#include <linux/sched/vhost_task.h>
9#include <linux/sched/signal.h>
10
11enum vhost_task_flags {
12 VHOST_TASK_FLAGS_STOP,
13 VHOST_TASK_FLAGS_KILLED,
14};
15
16struct vhost_task {
17 bool (*fn)(void *data);
18 void (*handle_sigkill)(void *data);
19 void *data;
20 struct completion exited;
21 unsigned long flags;
22 struct task_struct *task;
23 /* serialize SIGKILL and vhost_task_stop calls */
24 struct mutex exit_mutex;
25};
26
27static int vhost_task_fn(void *data)
28{
29 struct vhost_task *vtsk = data;
30
31 for (;;) {
32 bool did_work;
33
34 if (signal_pending(current)) {
35 struct ksignal ksig;
36
37 if (get_signal(ksig: &ksig))
38 break;
39 }
40
41 /* mb paired w/ vhost_task_stop */
42 set_current_state(TASK_INTERRUPTIBLE);
43
44 if (test_bit(VHOST_TASK_FLAGS_STOP, &vtsk->flags)) {
45 __set_current_state(TASK_RUNNING);
46 break;
47 }
48
49 did_work = vtsk->fn(vtsk->data);
50 if (!did_work)
51 schedule();
52 }
53
54 mutex_lock(&vtsk->exit_mutex);
55 /*
56 * If a vhost_task_stop and SIGKILL race, we can ignore the SIGKILL.
57 * When the vhost layer has called vhost_task_stop it's already stopped
58 * new work and flushed.
59 */
60 if (!test_bit(VHOST_TASK_FLAGS_STOP, &vtsk->flags)) {
61 set_bit(nr: VHOST_TASK_FLAGS_KILLED, addr: &vtsk->flags);
62 vtsk->handle_sigkill(vtsk->data);
63 }
64 mutex_unlock(lock: &vtsk->exit_mutex);
65 complete(&vtsk->exited);
66
67 do_exit(error_code: 0);
68}
69
70/**
71 * vhost_task_wake - wakeup the vhost_task
72 * @vtsk: vhost_task to wake
73 *
74 * wake up the vhost_task worker thread
75 */
76void vhost_task_wake(struct vhost_task *vtsk)
77{
78 wake_up_process(tsk: vtsk->task);
79}
80EXPORT_SYMBOL_GPL(vhost_task_wake);
81
82/**
83 * vhost_task_stop - stop a vhost_task
84 * @vtsk: vhost_task to stop
85 *
86 * vhost_task_fn ensures the worker thread exits after
87 * VHOST_TASK_FLAGS_STOP becomes true.
88 */
89void vhost_task_stop(struct vhost_task *vtsk)
90{
91 mutex_lock(&vtsk->exit_mutex);
92 if (!test_bit(VHOST_TASK_FLAGS_KILLED, &vtsk->flags)) {
93 set_bit(nr: VHOST_TASK_FLAGS_STOP, addr: &vtsk->flags);
94 vhost_task_wake(vtsk);
95 }
96 mutex_unlock(lock: &vtsk->exit_mutex);
97
98 /*
99 * Make sure vhost_task_fn is no longer accessing the vhost_task before
100 * freeing it below.
101 */
102 wait_for_completion(&vtsk->exited);
103 put_task_struct(t: vtsk->task);
104 kfree(objp: vtsk);
105}
106EXPORT_SYMBOL_GPL(vhost_task_stop);
107
108/**
109 * vhost_task_create - create a copy of a task to be used by the kernel
110 * @fn: vhost worker function
111 * @handle_sigkill: vhost function to handle when we are killed
112 * @arg: data to be passed to fn and handled_kill
113 * @name: the thread's name
114 *
115 * This returns a specialized task for use by the vhost layer or ERR_PTR() on
116 * failure. The returned task is inactive, and the caller must fire it up
117 * through vhost_task_start().
118 */
119struct vhost_task *vhost_task_create(bool (*fn)(void *),
120 void (*handle_sigkill)(void *), void *arg,
121 const char *name)
122{
123 struct kernel_clone_args args = {
124 .flags = CLONE_FS | CLONE_UNTRACED | CLONE_VM |
125 CLONE_THREAD | CLONE_SIGHAND,
126 .exit_signal = 0,
127 .fn = vhost_task_fn,
128 .name = name,
129 .user_worker = 1,
130 .no_files = 1,
131 };
132 struct vhost_task *vtsk;
133 struct task_struct *tsk;
134
135 vtsk = kzalloc(sizeof(*vtsk), GFP_KERNEL);
136 if (!vtsk)
137 return ERR_PTR(error: -ENOMEM);
138 init_completion(x: &vtsk->exited);
139 mutex_init(&vtsk->exit_mutex);
140 vtsk->data = arg;
141 vtsk->fn = fn;
142 vtsk->handle_sigkill = handle_sigkill;
143
144 args.fn_arg = vtsk;
145
146 tsk = copy_process(NULL, trace: 0, NUMA_NO_NODE, args: &args);
147 if (IS_ERR(ptr: tsk)) {
148 kfree(objp: vtsk);
149 return ERR_CAST(ptr: tsk);
150 }
151
152 vtsk->task = get_task_struct(t: tsk);
153 return vtsk;
154}
155EXPORT_SYMBOL_GPL(vhost_task_create);
156
157/**
158 * vhost_task_start - start a vhost_task created with vhost_task_create
159 * @vtsk: vhost_task to wake up
160 */
161void vhost_task_start(struct vhost_task *vtsk)
162{
163 wake_up_new_task(tsk: vtsk->task);
164}
165EXPORT_SYMBOL_GPL(vhost_task_start);
166

source code of linux/kernel/vhost_task.c