xref: /openbmc/linux/kernel/kthread.c (revision f42b3800)
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 
17 #define KTHREAD_NICE_LEVEL (-5)
18 
19 static DEFINE_SPINLOCK(kthread_create_lock);
20 static LIST_HEAD(kthread_create_list);
21 struct task_struct *kthreadd_task;
22 
23 struct kthread_create_info
24 {
25 	/* Information passed to kthread() from kthreadd. */
26 	int (*threadfn)(void *data);
27 	void *data;
28 	struct completion started;
29 
30 	/* Result passed back to kthread_create() from kthreadd. */
31 	struct task_struct *result;
32 	struct completion done;
33 
34 	struct list_head list;
35 };
36 
37 struct kthread_stop_info
38 {
39 	struct task_struct *k;
40 	int err;
41 	struct completion done;
42 };
43 
44 /* Thread stopping is done by setthing this var: lock serializes
45  * multiple kthread_stop calls. */
46 static DEFINE_MUTEX(kthread_stop_lock);
47 static struct kthread_stop_info kthread_stop_info;
48 
49 /**
50  * kthread_should_stop - should this kthread return now?
51  *
52  * When someone calls kthread_stop() on your kthread, it will be woken
53  * and this will return true.  You should then return, and your return
54  * value will be passed through to kthread_stop().
55  */
56 int kthread_should_stop(void)
57 {
58 	return (kthread_stop_info.k == current);
59 }
60 EXPORT_SYMBOL(kthread_should_stop);
61 
62 static int kthread(void *_create)
63 {
64 	struct kthread_create_info *create = _create;
65 	int (*threadfn)(void *data);
66 	void *data;
67 	int ret = -EINTR;
68 
69 	/* Copy data: it's on kthread's stack */
70 	threadfn = create->threadfn;
71 	data = create->data;
72 
73 	/* OK, tell user we're spawned, wait for stop or wakeup */
74 	__set_current_state(TASK_UNINTERRUPTIBLE);
75 	complete(&create->started);
76 	schedule();
77 
78 	if (!kthread_should_stop())
79 		ret = threadfn(data);
80 
81 	/* It might have exited on its own, w/o kthread_stop.  Check. */
82 	if (kthread_should_stop()) {
83 		kthread_stop_info.err = ret;
84 		complete(&kthread_stop_info.done);
85 	}
86 	return 0;
87 }
88 
89 static void create_kthread(struct kthread_create_info *create)
90 {
91 	int pid;
92 
93 	/* We want our own signal handler (we take no signals by default). */
94 	pid = kernel_thread(kthread, create, CLONE_FS | CLONE_FILES | SIGCHLD);
95 	if (pid < 0) {
96 		create->result = ERR_PTR(pid);
97 	} else {
98 		struct sched_param param = { .sched_priority = 0 };
99 		wait_for_completion(&create->started);
100 		read_lock(&tasklist_lock);
101 		create->result = find_task_by_pid(pid);
102 		read_unlock(&tasklist_lock);
103 		/*
104 		 * root may have changed our (kthreadd's) priority or CPU mask.
105 		 * The kernel thread should not inherit these properties.
106 		 */
107 		sched_setscheduler(create->result, SCHED_NORMAL, &param);
108 		set_user_nice(create->result, KTHREAD_NICE_LEVEL);
109 		set_cpus_allowed(create->result, CPU_MASK_ALL);
110 	}
111 	complete(&create->done);
112 }
113 
114 /**
115  * kthread_create - create a kthread.
116  * @threadfn: the function to run until signal_pending(current).
117  * @data: data ptr for @threadfn.
118  * @namefmt: printf-style name for the thread.
119  *
120  * Description: This helper function creates and names a kernel
121  * thread.  The thread will be stopped: use wake_up_process() to start
122  * it.  See also kthread_run(), kthread_create_on_cpu().
123  *
124  * When woken, the thread will run @threadfn() with @data as its
125  * argument. @threadfn() can either call do_exit() directly if it is a
126  * standalone thread for which noone will call kthread_stop(), or
127  * return when 'kthread_should_stop()' is true (which means
128  * kthread_stop() has been called).  The return value should be zero
129  * or a negative error number; it will be passed to kthread_stop().
130  *
131  * Returns a task_struct or ERR_PTR(-ENOMEM).
132  */
133 struct task_struct *kthread_create(int (*threadfn)(void *data),
134 				   void *data,
135 				   const char namefmt[],
136 				   ...)
137 {
138 	struct kthread_create_info create;
139 
140 	create.threadfn = threadfn;
141 	create.data = data;
142 	init_completion(&create.started);
143 	init_completion(&create.done);
144 
145 	spin_lock(&kthread_create_lock);
146 	list_add_tail(&create.list, &kthread_create_list);
147 	wake_up_process(kthreadd_task);
148 	spin_unlock(&kthread_create_lock);
149 
150 	wait_for_completion(&create.done);
151 
152 	if (!IS_ERR(create.result)) {
153 		va_list args;
154 		va_start(args, namefmt);
155 		vsnprintf(create.result->comm, sizeof(create.result->comm),
156 			  namefmt, args);
157 		va_end(args);
158 	}
159 	return create.result;
160 }
161 EXPORT_SYMBOL(kthread_create);
162 
163 /**
164  * kthread_bind - bind a just-created kthread to a cpu.
165  * @k: thread created by kthread_create().
166  * @cpu: cpu (might not be online, must be possible) for @k to run on.
167  *
168  * Description: This function is equivalent to set_cpus_allowed(),
169  * except that @cpu doesn't need to be online, and the thread must be
170  * stopped (i.e., just returned from kthread_create()).
171  */
172 void kthread_bind(struct task_struct *k, unsigned int cpu)
173 {
174 	if (k->state != TASK_UNINTERRUPTIBLE) {
175 		WARN_ON(1);
176 		return;
177 	}
178 	/* Must have done schedule() in kthread() before we set_task_cpu */
179 	wait_task_inactive(k);
180 	set_task_cpu(k, cpu);
181 	k->cpus_allowed = cpumask_of_cpu(cpu);
182 }
183 EXPORT_SYMBOL(kthread_bind);
184 
185 /**
186  * kthread_stop - stop a thread created by kthread_create().
187  * @k: thread created by kthread_create().
188  *
189  * Sets kthread_should_stop() for @k to return true, wakes it, and
190  * waits for it to exit.  Your threadfn() must not call do_exit()
191  * itself if you use this function!  This can also be called after
192  * kthread_create() instead of calling wake_up_process(): the thread
193  * will exit without calling threadfn().
194  *
195  * Returns the result of threadfn(), or %-EINTR if wake_up_process()
196  * was never called.
197  */
198 int kthread_stop(struct task_struct *k)
199 {
200 	int ret;
201 
202 	mutex_lock(&kthread_stop_lock);
203 
204 	/* It could exit after stop_info.k set, but before wake_up_process. */
205 	get_task_struct(k);
206 
207 	/* Must init completion *before* thread sees kthread_stop_info.k */
208 	init_completion(&kthread_stop_info.done);
209 	smp_wmb();
210 
211 	/* Now set kthread_should_stop() to true, and wake it up. */
212 	kthread_stop_info.k = k;
213 	wake_up_process(k);
214 	put_task_struct(k);
215 
216 	/* Once it dies, reset stop ptr, gather result and we're done. */
217 	wait_for_completion(&kthread_stop_info.done);
218 	kthread_stop_info.k = NULL;
219 	ret = kthread_stop_info.err;
220 	mutex_unlock(&kthread_stop_lock);
221 
222 	return ret;
223 }
224 EXPORT_SYMBOL(kthread_stop);
225 
226 int kthreadd(void *unused)
227 {
228 	struct task_struct *tsk = current;
229 
230 	/* Setup a clean context for our children to inherit. */
231 	set_task_comm(tsk, "kthreadd");
232 	ignore_signals(tsk);
233 	set_user_nice(tsk, KTHREAD_NICE_LEVEL);
234 	set_cpus_allowed(tsk, CPU_MASK_ALL);
235 
236 	current->flags |= PF_NOFREEZE;
237 
238 	for (;;) {
239 		set_current_state(TASK_INTERRUPTIBLE);
240 		if (list_empty(&kthread_create_list))
241 			schedule();
242 		__set_current_state(TASK_RUNNING);
243 
244 		spin_lock(&kthread_create_lock);
245 		while (!list_empty(&kthread_create_list)) {
246 			struct kthread_create_info *create;
247 
248 			create = list_entry(kthread_create_list.next,
249 					    struct kthread_create_info, list);
250 			list_del_init(&create->list);
251 			spin_unlock(&kthread_create_lock);
252 
253 			create_kthread(create);
254 
255 			spin_lock(&kthread_create_lock);
256 		}
257 		spin_unlock(&kthread_create_lock);
258 	}
259 
260 	return 0;
261 }
262