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
11 enum vhost_task_flags {
12 VHOST_TASK_FLAGS_STOP,
13 VHOST_TASK_FLAGS_KILLED,
14 };
15
16 struct 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
27 static 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))
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(VHOST_TASK_FLAGS_KILLED, &vtsk->flags);
62 vtsk->handle_sigkill(vtsk->data);
63 }
64 mutex_unlock(&vtsk->exit_mutex);
65 complete(&vtsk->exited);
66
67 do_exit(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 */
76 void vhost_task_wake(struct vhost_task *vtsk)
77 {
78 wake_up_process(vtsk->task);
79 }
80 EXPORT_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 */
89 void 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(VHOST_TASK_FLAGS_STOP, &vtsk->flags);
94 vhost_task_wake(vtsk);
95 }
96 mutex_unlock(&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 kfree(vtsk);
104 }
105 EXPORT_SYMBOL_GPL(vhost_task_stop);
106
107 /**
108 * vhost_task_create - create a copy of a task to be used by the kernel
109 * @fn: vhost worker function
110 * @handle_sigkill: vhost function to handle when we are killed
111 * @arg: data to be passed to fn and handled_kill
112 * @name: the thread's name
113 *
114 * This returns a specialized task for use by the vhost layer or NULL on
115 * failure. The returned task is inactive, and the caller must fire it up
116 * through vhost_task_start().
117 */
118 struct vhost_task *vhost_task_create(bool (*fn)(void *),
119 void (*handle_sigkill)(void *), void *arg,
120 const char *name)
121 {
122 struct kernel_clone_args args = {
123 .flags = CLONE_FS | CLONE_UNTRACED | CLONE_VM |
124 CLONE_THREAD | CLONE_SIGHAND,
125 .exit_signal = 0,
126 .fn = vhost_task_fn,
127 .name = name,
128 .user_worker = 1,
129 .no_files = 1,
130 };
131 struct vhost_task *vtsk;
132 struct task_struct *tsk;
133
134 vtsk = kzalloc(sizeof(*vtsk), GFP_KERNEL);
135 if (!vtsk)
136 return NULL;
137 init_completion(&vtsk->exited);
138 mutex_init(&vtsk->exit_mutex);
139 vtsk->data = arg;
140 vtsk->fn = fn;
141 vtsk->handle_sigkill = handle_sigkill;
142
143 args.fn_arg = vtsk;
144
145 tsk = copy_process(NULL, 0, NUMA_NO_NODE, &args);
146 if (IS_ERR(tsk)) {
147 kfree(vtsk);
148 return NULL;
149 }
150
151 vtsk->task = tsk;
152 return vtsk;
153 }
154 EXPORT_SYMBOL_GPL(vhost_task_create);
155
156 /**
157 * vhost_task_start - start a vhost_task created with vhost_task_create
158 * @vtsk: vhost_task to wake up
159 */
160 void vhost_task_start(struct vhost_task *vtsk)
161 {
162 wake_up_new_task(vtsk->task);
163 }
164 EXPORT_SYMBOL_GPL(vhost_task_start);
165
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