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