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 <linux/mutex.h>
  16 #include <asm/semaphore.h>
  17
  18 /*
  19  * We dont want to execute off keventd since it might
  20  * hold a semaphore our callers hold too:
  21  */
  22 static struct workqueue_struct *helper_wq;
  23
  24 struct kthread_create_info
  25 {
  26         /* Information passed to kthread() from keventd. */
  27         int (*threadfn)(void *data);
  28         void *data;
  29         struct completion started;
  30
  31         /* Result passed back to kthread_create() from keventd. */
  32         struct task_struct *result;
  33         struct completion done;
  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 int kthread_should_stop(void)
  49 {
  50         return (kthread_stop_info.k == current);
  51 }
  52 EXPORT_SYMBOL(kthread_should_stop);
  53
  54 static void kthread_exit_files(void)
  55 {
  56         struct fs_struct *fs;
  57         struct task_struct *tsk = current;
  58
  59         exit_fs(tsk);           /* current->fs->count--; */
  60         fs = init_task.fs;
  61         tsk->fs = fs;
  62         atomic_inc(&fs->count);
  63         exit_files(tsk);
  64         current->files = init_task.files;
  65         atomic_inc(&tsk->files->count);
  66 }
  67
  68 static int kthread(void *_create)
  69 {
  70         struct kthread_create_info *create = _create;
  71         int (*threadfn)(void *data);
  72         void *data;
  73         sigset_t blocked;
  74         int ret = -EINTR;
  75
  76         kthread_exit_files();
  77
  78         /* Copy data: it's on keventd's stack */
  79         threadfn = create->threadfn;
  80         data = create->data;
  81
  82         /* Block and flush all signals (in case we're not from keventd). */
  83         sigfillset(&blocked);
  84         sigprocmask(SIG_BLOCK, &blocked, NULL);
  85         flush_signals(current);
  86
  87         /* By default we can run anywhere, unlike keventd. */
  88         set_cpus_allowed(current, CPU_MASK_ALL);
  89
  90         /* OK, tell user we're spawned, wait for stop or wakeup */
  91         __set_current_state(TASK_INTERRUPTIBLE);
  92         complete(&create->started);
  93         schedule();
  94
  95         if (!kthread_should_stop())
  96                 ret = threadfn(data);
  97
  98         /* It might have exited on its own, w/o kthread_stop.  Check. */
  99         if (kthread_should_stop()) {
 100                 kthread_stop_info.err = ret;
 101                 complete(&kthread_stop_info.done);
 102         }
 103         return 0;
 104 }
 105
 106 /* We are keventd: create a thread. */
 107 static void keventd_create_kthread(void *_create)
 108 {
 109         struct kthread_create_info *create = _create;
 110         int pid;
 111
 112         /* We want our own signal handler (we take no signals by default). */
 113         pid = kernel_thread(kthread, create, CLONE_FS | CLONE_FILES | SIGCHLD);
 114         if (pid < 0) {
 115                 create->result = ERR_PTR(pid);
 116         } else {
 117                 wait_for_completion(&create->started);
 118                 create->result = find_task_by_pid(pid);
 119         }
 120         complete(&create->done);
 121 }
 122
 123 struct task_struct *kthread_create(int (*threadfn)(void *data),
 124                                    void *data,
 125                                    const char namefmt[],
 126                                    ...)
 127 {
 128         struct kthread_create_info create;
 129         DECLARE_WORK(work, keventd_create_kthread, &create);
 130
 131         create.threadfn = threadfn;
 132         create.data = data;
 133         init_completion(&create.started);
 134         init_completion(&create.done);
 135
 136         /*
 137          * The workqueue needs to start up first:
 138          */
 139         if (!helper_wq)
 140                 work.func(work.data);
 141         else {
 142                 queue_work(helper_wq, &work);
 143                 wait_for_completion(&create.done);
 144         }
 145         if (!IS_ERR(create.result)) {
 146                 va_list args;
 147                 va_start(args, namefmt);
 148                 vsnprintf(create.result->comm, sizeof(create.result->comm),
 149                           namefmt, args);
 150                 va_end(args);
 151         }
 152
 153         return create.result;
 154 }
 155 EXPORT_SYMBOL(kthread_create);
 156
 157 void kthread_bind(struct task_struct *k, unsigned int cpu)
 158 {
 159         BUG_ON(k->state != TASK_INTERRUPTIBLE);
 160         /* Must have done schedule() in kthread() before we set_task_cpu */
 161         wait_task_inactive(k);
 162         set_task_cpu(k, cpu);
 163         k->cpus_allowed = cpumask_of_cpu(cpu);
 164 }
 165 EXPORT_SYMBOL(kthread_bind);
 166
 167 int kthread_stop(struct task_struct *k)
 168 {
 169         return kthread_stop_sem(k, NULL);
 170 }
 171 EXPORT_SYMBOL(kthread_stop);
 172
 173 int kthread_stop_sem(struct task_struct *k, struct semaphore *s)
 174 {
 175         int ret;
 176
 177         mutex_lock(&kthread_stop_lock);
 178
 179         /* It could exit after stop_info.k set, but before wake_up_process. */
 180         get_task_struct(k);
 181
 182         /* Must init completion *before* thread sees kthread_stop_info.k */
 183         init_completion(&kthread_stop_info.done);
 184         smp_wmb();
 185
 186         /* Now set kthread_should_stop() to true, and wake it up. */
 187         kthread_stop_info.k = k;
 188         if (s)
 189                 up(s);
 190         else
 191                 wake_up_process(k);
 192         put_task_struct(k);
 193
 194         /* Once it dies, reset stop ptr, gather result and we're done. */
 195         wait_for_completion(&kthread_stop_info.done);
 196         kthread_stop_info.k = NULL;
 197         ret = kthread_stop_info.err;
 198         mutex_unlock(&kthread_stop_lock);
 199
 200         return ret;
 201 }
 202 EXPORT_SYMBOL(kthread_stop_sem);
 203
 204 static __init int helper_init(void)
 205 {
 206         helper_wq = create_singlethread_workqueue("kthread");
 207         BUG_ON(!helper_wq);
 208
 209         return 0;
 210 }
 211 core_initcall(helper_init);
 212