1 /* Kernel thread helper functions.
2 * Copyright (C) 2004 IBM Corporation, Rusty Russell.
3 *
4 * Creation is done via kthreadd, so that we get a clean environment
5 * even if we're invoked from userspace (think modprobe, hotplug cpu,
6 * etc.).
7 */
8 #include <linux/sched.h>
9 #include <linux/kthread.h>
10 #include <linux/completion.h>
11 #include <linux/err.h>
12 #include <linux/unistd.h>
13 #include <linux/file.h>
14 #include <linux/module.h>
15 #include <linux/mutex.h>
16 #include <asm/semaphore.h>
17
18 #define KTHREAD_NICE_LEVEL (-5)
19
20 static DEFINE_SPINLOCK(kthread_create_lock);
21 static LIST_HEAD(kthread_create_list);
22 struct task_struct *kthreadd_task;
23
24 struct kthread_create_info
25 {
26 /* Information passed to kthread() from kthreadd. */
27 int (*threadfn)(void *data);
28 void *data;
29 struct completion started;
30
31 /* Result passed back to kthread_create() from kthreadd. */
32 struct task_struct *result;
33 struct completion done;
34
35 struct list_head list;
36 };
37
38 struct kthread_stop_info
39 {
40 struct task_struct *k;
41 int err;
42 struct completion done;
43 };
44
45 /* Thread stopping is done by setthing this var: lock serializes
46 * multiple kthread_stop calls. */
47 static DEFINE_MUTEX(kthread_stop_lock);
48 static struct kthread_stop_info kthread_stop_info;
49
50 /**
51 * kthread_should_stop - should this kthread return now?
52 *
53 * When someone calls kthread_stop() on your kthread, it will be woken
54 * and this will return true. You should then return, and your return
55 * value will be passed through to kthread_stop().
56 */
57 int kthread_should_stop(void)
58 {
59 return (kthread_stop_info.k == current);
60 }
61 EXPORT_SYMBOL(kthread_should_stop);
62
63 static int kthread(void *_create)
64 {
65 struct kthread_create_info *create = _create;
66 int (*threadfn)(void *data);
67 void *data;
68 int ret = -EINTR;
69
70 /* Copy data: it's on kthread's stack */
71 threadfn = create->threadfn;
72 data = create->data;
73
74 /* OK, tell user we're spawned, wait for stop or wakeup */
75 __set_current_state(TASK_UNINTERRUPTIBLE);
76 complete(&create->started);
77 schedule();
78
79 if (!kthread_should_stop())
80 ret = threadfn(data);
81
82 /* It might have exited on its own, w/o kthread_stop. Check. */
83 if (kthread_should_stop()) {
84 kthread_stop_info.err = ret;
85 complete(&kthread_stop_info.done);
86 }
87 return 0;
88 }
89
90 static void create_kthread(struct kthread_create_info *create)
91 {
92 int pid;
93
94 /* We want our own signal handler (we take no signals by default). */
95 pid = kernel_thread(kthread, create, CLONE_FS | CLONE_FILES | SIGCHLD);
96 if (pid < 0) {
97 create->result = ERR_PTR(pid);
98 } else {
99 struct sched_param param = { .sched_priority = 0 };
100 wait_for_completion(&create->started);
101 read_lock(&tasklist_lock);
102 create->result = find_task_by_pid(pid);
103 read_unlock(&tasklist_lock);
104 /*
105 * root may have changed our (kthreadd's) priority or CPU mask.
106 * The kernel thread should not inherit these properties.
107 */
108 sched_setscheduler(create->result, SCHED_NORMAL, ¶m);
109 set_user_nice(create->result, KTHREAD_NICE_LEVEL);
110 set_cpus_allowed(create->result, CPU_MASK_ALL);
111 }
112 complete(&create->done);
113 }
114
115 /**
116 * kthread_create - create a kthread.
117 * @threadfn: the function to run until signal_pending(current).
118 * @data: data ptr for @threadfn.
119 * @namefmt: printf-style name for the thread.
120 *
121 * Description: This helper function creates and names a kernel
122 * thread. The thread will be stopped: use wake_up_process() to start
123 * it. See also kthread_run(), kthread_create_on_cpu().
124 *
125 * When woken, the thread will run @threadfn() with @data as its
126 * argument. @threadfn() can either call do_exit() directly if it is a
127 * standalone thread for which noone will call kthread_stop(), or
128 * return when 'kthread_should_stop()' is true (which means
129 * kthread_stop() has been called). The return value should be zero
130 * or a negative error number; it will be passed to kthread_stop().
131 *
132 * Returns a task_struct or ERR_PTR(-ENOMEM).
133 */
134 struct task_struct *kthread_create(int (*threadfn)(void *data),
135 void *data,
136 const char namefmt[],
137 ...)
138 {
139 struct kthread_create_info create;
140
141 create.threadfn = threadfn;
142 create.data = data;
143 init_completion(&create.started);
144 init_completion(&create.done);
145
146 spin_lock(&kthread_create_lock);
147 list_add_tail(&create.list, &kthread_create_list);
148 wake_up_process(kthreadd_task);
149 spin_unlock(&kthread_create_lock);
150
151 wait_for_completion(&create.done);
152
153 if (!IS_ERR(create.result)) {
154 va_list args;
155 va_start(args, namefmt);
156 vsnprintf(create.result->comm, sizeof(create.result->comm),
157 namefmt, args);
158 va_end(args);
159 }
160 return create.result;
161 }
162 EXPORT_SYMBOL(kthread_create);
163
164 /**
165 * kthread_bind - bind a just-created kthread to a cpu.
166 * @k: thread created by kthread_create().
167 * @cpu: cpu (might not be online, must be possible) for @k to run on.
168 *
169 * Description: This function is equivalent to set_cpus_allowed(),
170 * except that @cpu doesn't need to be online, and the thread must be
171 * stopped (i.e., just returned from kthread_create()).
172 */
173 void kthread_bind(struct task_struct *k, unsigned int cpu)
174 {
175 if (k->state != TASK_UNINTERRUPTIBLE) {
176 WARN_ON(1);
177 return;
178 }
179 /* Must have done schedule() in kthread() before we set_task_cpu */
180 wait_task_inactive(k);
181 set_task_cpu(k, cpu);
182 k->cpus_allowed = cpumask_of_cpu(cpu);
183 }
184 EXPORT_SYMBOL(kthread_bind);
185
186 /**
187 * kthread_stop - stop a thread created by kthread_create().
188 * @k: thread created by kthread_create().
189 *
190 * Sets kthread_should_stop() for @k to return true, wakes it, and
191 * waits for it to exit. Your threadfn() must not call do_exit()
192 * itself if you use this function! This can also be called after
193 * kthread_create() instead of calling wake_up_process(): the thread
194 * will exit without calling threadfn().
195 *
196 * Returns the result of threadfn(), or %-EINTR if wake_up_process()
197 * was never called.
198 */
199 int kthread_stop(struct task_struct *k)
200 {
201 int ret;
202
203 mutex_lock(&kthread_stop_lock);
204
205 /* It could exit after stop_info.k set, but before wake_up_process. */
206 get_task_struct(k);
207
208 /* Must init completion *before* thread sees kthread_stop_info.k */
209 init_completion(&kthread_stop_info.done);
210 smp_wmb();
211
212 /* Now set kthread_should_stop() to true, and wake it up. */
213 kthread_stop_info.k = k;
214 wake_up_process(k);
215 put_task_struct(k);
216
217 /* Once it dies, reset stop ptr, gather result and we're done. */
218 wait_for_completion(&kthread_stop_info.done);
219 kthread_stop_info.k = NULL;
220 ret = kthread_stop_info.err;
221 mutex_unlock(&kthread_stop_lock);
222
223 return ret;
224 }
225 EXPORT_SYMBOL(kthread_stop);
226
227 int kthreadd(void *unused)
228 {
229 struct task_struct *tsk = current;
230
231 /* Setup a clean context for our children to inherit. */
232 set_task_comm(tsk, "kthreadd");
233 ignore_signals(tsk);
234 set_user_nice(tsk, KTHREAD_NICE_LEVEL);
235 set_cpus_allowed(tsk, CPU_MASK_ALL);
236
237 current->flags |= PF_NOFREEZE;
238
239 for (;;) {
240 set_current_state(TASK_INTERRUPTIBLE);
241 if (list_empty(&kthread_create_list))
242 schedule();
243 __set_current_state(TASK_RUNNING);
244
245 spin_lock(&kthread_create_lock);
246 while (!list_empty(&kthread_create_list)) {
247 struct kthread_create_info *create;
248
249 create = list_entry(kthread_create_list.next,
250 struct kthread_create_info, list);
251 list_del_init(&create->list);
252 spin_unlock(&kthread_create_lock);
253
254 create_kthread(create);
255
256 spin_lock(&kthread_create_lock);
257 }
258 spin_unlock(&kthread_create_lock);
259 }
260
261 return 0;
262 }
263
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