xref: /openbmc/linux/kernel/kthread.c (revision e868d61272caa648214046a096e5a6bfc068dc8c)
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 static DEFINE_SPINLOCK(kthread_create_lock);
19 static LIST_HEAD(kthread_create_list);
20 struct task_struct *kthreadd_task;
21 
22 struct kthread_create_info
23 {
24 	/* Information passed to kthread() from kthreadd. */
25 	int (*threadfn)(void *data);
26 	void *data;
27 	struct completion started;
28 
29 	/* Result passed back to kthread_create() from kthreadd. */
30 	struct task_struct *result;
31 	struct completion done;
32 
33 	struct list_head list;
34 };
35 
36 struct kthread_stop_info
37 {
38 	struct task_struct *k;
39 	int err;
40 	struct completion done;
41 };
42 
43 /* Thread stopping is done by setthing this var: lock serializes
44  * multiple kthread_stop calls. */
45 static DEFINE_MUTEX(kthread_stop_lock);
46 static struct kthread_stop_info kthread_stop_info;
47 
48 /**
49  * kthread_should_stop - should this kthread return now?
50  *
51  * When someone calls kthread_stop() on your kthread, it will be woken
52  * and this will return true.  You should then return, and your return
53  * value will be passed through to kthread_stop().
54  */
55 int kthread_should_stop(void)
56 {
57 	return (kthread_stop_info.k == current);
58 }
59 EXPORT_SYMBOL(kthread_should_stop);
60 
61 static int kthread(void *_create)
62 {
63 	struct kthread_create_info *create = _create;
64 	int (*threadfn)(void *data);
65 	void *data;
66 	int ret = -EINTR;
67 
68 	/* Copy data: it's on kthread's stack */
69 	threadfn = create->threadfn;
70 	data = create->data;
71 
72 	/* OK, tell user we're spawned, wait for stop or wakeup */
73 	__set_current_state(TASK_INTERRUPTIBLE);
74 	complete(&create->started);
75 	schedule();
76 
77 	if (!kthread_should_stop())
78 		ret = threadfn(data);
79 
80 	/* It might have exited on its own, w/o kthread_stop.  Check. */
81 	if (kthread_should_stop()) {
82 		kthread_stop_info.err = ret;
83 		complete(&kthread_stop_info.done);
84 	}
85 	return 0;
86 }
87 
88 static void create_kthread(struct kthread_create_info *create)
89 {
90 	int pid;
91 
92 	/* We want our own signal handler (we take no signals by default). */
93 	pid = kernel_thread(kthread, create, CLONE_FS | CLONE_FILES | SIGCHLD);
94 	if (pid < 0) {
95 		create->result = ERR_PTR(pid);
96 	} else {
97 		wait_for_completion(&create->started);
98 		read_lock(&tasklist_lock);
99 		create->result = find_task_by_pid(pid);
100 		read_unlock(&tasklist_lock);
101 	}
102 	complete(&create->done);
103 }
104 
105 /**
106  * kthread_create - create a kthread.
107  * @threadfn: the function to run until signal_pending(current).
108  * @data: data ptr for @threadfn.
109  * @namefmt: printf-style name for the thread.
110  *
111  * Description: This helper function creates and names a kernel
112  * thread.  The thread will be stopped: use wake_up_process() to start
113  * it.  See also kthread_run(), kthread_create_on_cpu().
114  *
115  * When woken, the thread will run @threadfn() with @data as its
116  * argument. @threadfn() can either call do_exit() directly if it is a
117  * standalone thread for which noone will call kthread_stop(), or
118  * return when 'kthread_should_stop()' is true (which means
119  * kthread_stop() has been called).  The return value should be zero
120  * or a negative error number; it will be passed to kthread_stop().
121  *
122  * Returns a task_struct or ERR_PTR(-ENOMEM).
123  */
124 struct task_struct *kthread_create(int (*threadfn)(void *data),
125 				   void *data,
126 				   const char namefmt[],
127 				   ...)
128 {
129 	struct kthread_create_info create;
130 
131 	create.threadfn = threadfn;
132 	create.data = data;
133 	init_completion(&create.started);
134 	init_completion(&create.done);
135 
136 	spin_lock(&kthread_create_lock);
137 	list_add_tail(&create.list, &kthread_create_list);
138 	wake_up_process(kthreadd_task);
139 	spin_unlock(&kthread_create_lock);
140 
141 	wait_for_completion(&create.done);
142 
143 	if (!IS_ERR(create.result)) {
144 		va_list args;
145 		va_start(args, namefmt);
146 		vsnprintf(create.result->comm, sizeof(create.result->comm),
147 			  namefmt, args);
148 		va_end(args);
149 	}
150 	return create.result;
151 }
152 EXPORT_SYMBOL(kthread_create);
153 
154 /**
155  * kthread_bind - bind a just-created kthread to a cpu.
156  * @k: thread created by kthread_create().
157  * @cpu: cpu (might not be online, must be possible) for @k to run on.
158  *
159  * Description: This function is equivalent to set_cpus_allowed(),
160  * except that @cpu doesn't need to be online, and the thread must be
161  * stopped (i.e., just returned from kthread_create()).
162  */
163 void kthread_bind(struct task_struct *k, unsigned int cpu)
164 {
165 	BUG_ON(k->state != TASK_INTERRUPTIBLE);
166 	/* Must have done schedule() in kthread() before we set_task_cpu */
167 	wait_task_inactive(k);
168 	set_task_cpu(k, cpu);
169 	k->cpus_allowed = cpumask_of_cpu(cpu);
170 }
171 EXPORT_SYMBOL(kthread_bind);
172 
173 /**
174  * kthread_stop - stop a thread created by kthread_create().
175  * @k: thread created by kthread_create().
176  *
177  * Sets kthread_should_stop() for @k to return true, wakes it, and
178  * waits for it to exit.  Your threadfn() must not call do_exit()
179  * itself if you use this function!  This can also be called after
180  * kthread_create() instead of calling wake_up_process(): the thread
181  * will exit without calling threadfn().
182  *
183  * Returns the result of threadfn(), or %-EINTR if wake_up_process()
184  * was never called.
185  */
186 int kthread_stop(struct task_struct *k)
187 {
188 	int ret;
189 
190 	mutex_lock(&kthread_stop_lock);
191 
192 	/* It could exit after stop_info.k set, but before wake_up_process. */
193 	get_task_struct(k);
194 
195 	/* Must init completion *before* thread sees kthread_stop_info.k */
196 	init_completion(&kthread_stop_info.done);
197 	smp_wmb();
198 
199 	/* Now set kthread_should_stop() to true, and wake it up. */
200 	kthread_stop_info.k = k;
201 	wake_up_process(k);
202 	put_task_struct(k);
203 
204 	/* Once it dies, reset stop ptr, gather result and we're done. */
205 	wait_for_completion(&kthread_stop_info.done);
206 	kthread_stop_info.k = NULL;
207 	ret = kthread_stop_info.err;
208 	mutex_unlock(&kthread_stop_lock);
209 
210 	return ret;
211 }
212 EXPORT_SYMBOL(kthread_stop);
213 
214 
215 static __init void kthreadd_setup(void)
216 {
217 	struct task_struct *tsk = current;
218 
219 	set_task_comm(tsk, "kthreadd");
220 
221 	ignore_signals(tsk);
222 
223 	set_user_nice(tsk, -5);
224 	set_cpus_allowed(tsk, CPU_MASK_ALL);
225 }
226 
227 int kthreadd(void *unused)
228 {
229 	/* Setup a clean context for our children to inherit. */
230 	kthreadd_setup();
231 
232 	current->flags |= PF_NOFREEZE;
233 
234 	for (;;) {
235 		set_current_state(TASK_INTERRUPTIBLE);
236 		if (list_empty(&kthread_create_list))
237 			schedule();
238 		__set_current_state(TASK_RUNNING);
239 
240 		spin_lock(&kthread_create_lock);
241 		while (!list_empty(&kthread_create_list)) {
242 			struct kthread_create_info *create;
243 
244 			create = list_entry(kthread_create_list.next,
245 					    struct kthread_create_info, list);
246 			list_del_init(&create->list);
247 			spin_unlock(&kthread_create_lock);
248 
249 			create_kthread(create);
250 
251 			spin_lock(&kthread_create_lock);
252 		}
253 		spin_unlock(&kthread_create_lock);
254 	}
255 
256 	return 0;
257 }
258