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