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[linux-2.6.git] / kernel / kthread.c
1 /* Kernel thread helper functions.
2  *   Copyright (C) 2004 IBM Corporation, Rusty Russell.
3  *
4  * Creation is done via keventd, 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 <asm/semaphore.h>
16
17 /*
18  * We dont want to execute off keventd since it might
19  * hold a semaphore our callers hold too:
20  */
21 static struct workqueue_struct *helper_wq;
22
23 struct kthread_create_info
24 {
25         /* Information passed to kthread() from keventd. */
26         int (*threadfn)(void *data);
27         void *data;
28         struct completion started;
29
30         /* Result passed back to kthread_create() from keventd. */
31         struct task_struct *result;
32         struct completion done;
33 };
34
35 struct kthread_stop_info
36 {
37         struct task_struct *k;
38         int err;
39         struct completion done;
40 };
41
42 /* Thread stopping is done by setthing this var: lock serializes
43  * multiple kthread_stop calls. */
44 static DECLARE_MUTEX(kthread_stop_lock);
45 static struct kthread_stop_info kthread_stop_info;
46
47 int kthread_should_stop(void)
48 {
49         return (kthread_stop_info.k == current);
50 }
51 EXPORT_SYMBOL(kthread_should_stop);
52
53 static void kthread_exit_files(void)
54 {
55         struct fs_struct *fs;
56         struct task_struct *tsk = current;
57
58         exit_fs(tsk);           /* current->fs->count--; */
59         fs = init_task.fs;
60         tsk->fs = fs;
61         atomic_inc(&fs->count);
62         exit_files(tsk);
63         current->files = init_task.files;
64         atomic_inc(&tsk->files->count);
65 }
66
67 static int kthread(void *_create)
68 {
69         struct kthread_create_info *create = _create;
70         int (*threadfn)(void *data);
71         void *data;
72         sigset_t blocked;
73         int ret = -EINTR;
74
75         kthread_exit_files();
76
77         /* Copy data: it's on keventd's stack */
78         threadfn = create->threadfn;
79         data = create->data;
80
81         /* Block and flush all signals (in case we're not from keventd). */
82         sigfillset(&blocked);
83         sigprocmask(SIG_BLOCK, &blocked, NULL);
84         flush_signals(current);
85
86         /* By default we can run anywhere, unlike keventd. */
87         set_cpus_allowed(current, CPU_MASK_ALL);
88
89         /* OK, tell user we're spawned, wait for stop or wakeup */
90         __set_current_state(TASK_INTERRUPTIBLE);
91         complete(&create->started);
92         schedule();
93
94         if (!kthread_should_stop())
95                 ret = threadfn(data);
96
97         /* It might have exited on its own, w/o kthread_stop.  Check. */
98         if (kthread_should_stop()) {
99                 kthread_stop_info.err = ret;
100                 complete(&kthread_stop_info.done);
101         }
102         return 0;
103 }
104
105 /* We are keventd: create a thread. */
106 static void keventd_create_kthread(void *_create)
107 {
108         struct kthread_create_info *create = _create;
109         int pid;
110
111         /* We want our own signal handler (we take no signals by default). */
112         pid = kernel_thread(kthread, create, CLONE_FS | CLONE_FILES | SIGCHLD);
113         if (pid < 0) {
114                 create->result = ERR_PTR(pid);
115         } else {
116                 wait_for_completion(&create->started);
117                 create->result = find_task_by_pid(pid);
118         }
119         complete(&create->done);
120 }
121
122 struct task_struct *kthread_create(int (*threadfn)(void *data),
123                                    void *data,
124                                    const char namefmt[],
125                                    ...)
126 {
127         struct kthread_create_info create;
128         DECLARE_WORK(work, keventd_create_kthread, &create);
129
130         create.threadfn = threadfn;
131         create.data = data;
132         init_completion(&create.started);
133         init_completion(&create.done);
134
135         /*
136          * The workqueue needs to start up first:
137          */
138         if (!helper_wq)
139                 work.func(work.data);
140         else {
141                 queue_work(helper_wq, &work);
142                 wait_for_completion(&create.done);
143         }
144         if (!IS_ERR(create.result)) {
145                 va_list args;
146                 va_start(args, namefmt);
147                 vsnprintf(create.result->comm, sizeof(create.result->comm),
148                           namefmt, args);
149                 va_end(args);
150         }
151
152         return create.result;
153 }
154 EXPORT_SYMBOL(kthread_create);
155
156 void kthread_bind(struct task_struct *k, unsigned int cpu)
157 {
158         BUG_ON(k->state != TASK_INTERRUPTIBLE);
159         /* Must have done schedule() in kthread() before we set_task_cpu */
160         wait_task_inactive(k);
161         set_task_cpu(k, cpu);
162         k->cpus_allowed = cpumask_of_cpu(cpu);
163 }
164 EXPORT_SYMBOL(kthread_bind);
165
166 int kthread_stop(struct task_struct *k)
167 {
168         return kthread_stop_sem(k, NULL);
169 }
170 EXPORT_SYMBOL(kthread_stop);
171
172 int kthread_stop_sem(struct task_struct *k, struct semaphore *s)
173 {
174         int ret;
175
176         down(&kthread_stop_lock);
177
178         /* It could exit after stop_info.k set, but before wake_up_process. */
179         get_task_struct(k);
180
181         /* Must init completion *before* thread sees kthread_stop_info.k */
182         init_completion(&kthread_stop_info.done);
183         smp_wmb();
184
185         /* Now set kthread_should_stop() to true, and wake it up. */
186         kthread_stop_info.k = k;
187         if (s)
188                 up(s);
189         else
190                 wake_up_process(k);
191         put_task_struct(k);
192
193         /* Once it dies, reset stop ptr, gather result and we're done. */
194         wait_for_completion(&kthread_stop_info.done);
195         kthread_stop_info.k = NULL;
196         ret = kthread_stop_info.err;
197         up(&kthread_stop_lock);
198
199         return ret;
200 }
201 EXPORT_SYMBOL(kthread_stop_sem);
202
203 static __init int helper_init(void)
204 {
205         helper_wq = create_singlethread_workqueue("kthread");
206         BUG_ON(!helper_wq);
207
208         return 0;
209 }
210 core_initcall(helper_init);
211