kernel/kthread.c

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