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 #define KTHREAD_NICE_LEVEL (-5)
  19
  20 static DEFINE_SPINLOCK(kthread_create_lock);
  21 static LIST_HEAD(kthread_create_list);
  22 struct task_struct *kthreadd_task;
  23
  24 struct kthread_create_info
  25 {
  26         /* Information passed to kthread() from kthreadd. */
  27         int (*threadfn)(void *data);
  28         void *data;
  29         struct completion started;
  30
  31         /* Result passed back to kthread_create() from kthreadd. */
  32         struct task_struct *result;
  33         struct completion done;
  34
  35         struct list_head list;
  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 int kthread(void *_create)
  64 {
  65         struct kthread_create_info *create = _create;
  66         int (*threadfn)(void *data);
  67         void *data;
  68         int ret = -EINTR;
  69
  70         /* Copy data: it's on kthread's stack */
  71         threadfn = create->threadfn;
  72         data = create->data;
  73
  74         /* OK, tell user we're spawned, wait for stop or wakeup */
  75         __set_current_state(TASK_UNINTERRUPTIBLE);
  76         complete(&create->started);
  77         schedule();
  78
  79         if (!kthread_should_stop())
  80                 ret = threadfn(data);
  81
  82         /* It might have exited on its own, w/o kthread_stop.  Check. */
  83         if (kthread_should_stop()) {
  84                 kthread_stop_info.err = ret;
  85                 complete(&kthread_stop_info.done);
  86         }
  87         return 0;
  88 }
  89
  90 static void create_kthread(struct kthread_create_info *create)
  91 {
  92         int pid;
  93
  94         /* We want our own signal handler (we take no signals by default). */
  95         pid = kernel_thread(kthread, create, CLONE_FS | CLONE_FILES | SIGCHLD);
  96         if (pid < 0) {
  97                 create->result = ERR_PTR(pid);
  98         } else {
  99                 struct sched_param param = { .sched_priority = 0 };
 100                 wait_for_completion(&create->started);
 101                 read_lock(&tasklist_lock);
 102                 create->result = find_task_by_pid(pid);
 103                 read_unlock(&tasklist_lock);
 104                 /*
 105                  * root may have changed our (kthreadd's) priority or CPU mask.
 106                  * The kernel thread should not inherit these properties.
 107                  */
 108                 sched_setscheduler(create->result, SCHED_NORMAL, &param);
 109                 set_user_nice(create->result, KTHREAD_NICE_LEVEL);
 110                 set_cpus_allowed(create->result, CPU_MASK_ALL);
 111         }
 112         complete(&create->done);
 113 }
 114
 115 /**
 116  * kthread_create - create a kthread.
 117  * @threadfn: the function to run until signal_pending(current).
 118  * @data: data ptr for @threadfn.
 119  * @namefmt: printf-style name for the thread.
 120  *
 121  * Description: This helper function creates and names a kernel
 122  * thread.  The thread will be stopped: use wake_up_process() to start
 123  * it.  See also kthread_run(), kthread_create_on_cpu().
 124  *
 125  * When woken, the thread will run @threadfn() with @data as its
 126  * argument. @threadfn() can either call do_exit() directly if it is a
 127  * standalone thread for which noone will call kthread_stop(), or
 128  * return when 'kthread_should_stop()' is true (which means
 129  * kthread_stop() has been called).  The return value should be zero
 130  * or a negative error number; it will be passed to kthread_stop().
 131  *
 132  * Returns a task_struct or ERR_PTR(-ENOMEM).
 133  */
 134 struct task_struct *kthread_create(int (*threadfn)(void *data),
 135                                    void *data,
 136                                    const char namefmt[],
 137                                    ...)
 138 {
 139         struct kthread_create_info create;
 140
 141         create.threadfn = threadfn;
 142         create.data = data;
 143         init_completion(&create.started);
 144         init_completion(&create.done);
 145
 146         spin_lock(&kthread_create_lock);
 147         list_add_tail(&create.list, &kthread_create_list);
 148         wake_up_process(kthreadd_task);
 149         spin_unlock(&kthread_create_lock);
 150
 151         wait_for_completion(&create.done);
 152
 153         if (!IS_ERR(create.result)) {
 154                 va_list args;
 155                 va_start(args, namefmt);
 156                 vsnprintf(create.result->comm, sizeof(create.result->comm),
 157                           namefmt, args);
 158                 va_end(args);
 159         }
 160         return create.result;
 161 }
 162 EXPORT_SYMBOL(kthread_create);
 163
 164 /**
 165  * kthread_bind - bind a just-created kthread to a cpu.
 166  * @k: thread created by kthread_create().
 167  * @cpu: cpu (might not be online, must be possible) for @k to run on.
 168  *
 169  * Description: This function is equivalent to set_cpus_allowed(),
 170  * except that @cpu doesn't need to be online, and the thread must be
 171  * stopped (i.e., just returned from kthread_create()).
 172  */
 173 void kthread_bind(struct task_struct *k, unsigned int cpu)
 174 {
 175         if (k->state != TASK_UNINTERRUPTIBLE) {
 176                 WARN_ON(1);
 177                 return;
 178         }
 179         /* Must have done schedule() in kthread() before we set_task_cpu */
 180         wait_task_inactive(k);
 181         set_task_cpu(k, cpu);
 182         k->cpus_allowed = cpumask_of_cpu(cpu);
 183 }
 184 EXPORT_SYMBOL(kthread_bind);
 185
 186 /**
 187  * kthread_stop - stop a thread created by kthread_create().
 188  * @k: thread created by kthread_create().
 189  *
 190  * Sets kthread_should_stop() for @k to return true, wakes it, and
 191  * waits for it to exit.  Your threadfn() must not call do_exit()
 192  * itself if you use this function!  This can also be called after
 193  * kthread_create() instead of calling wake_up_process(): the thread
 194  * will exit without calling threadfn().
 195  *
 196  * Returns the result of threadfn(), or %-EINTR if wake_up_process()
 197  * was never called.
 198  */
 199 int kthread_stop(struct task_struct *k)
 200 {
 201         int ret;
 202
 203         mutex_lock(&kthread_stop_lock);
 204
 205         /* It could exit after stop_info.k set, but before wake_up_process. */
 206         get_task_struct(k);
 207
 208         /* Must init completion *before* thread sees kthread_stop_info.k */
 209         init_completion(&kthread_stop_info.done);
 210         smp_wmb();
 211
 212         /* Now set kthread_should_stop() to true, and wake it up. */
 213         kthread_stop_info.k = k;
 214         wake_up_process(k);
 215         put_task_struct(k);
 216
 217         /* Once it dies, reset stop ptr, gather result and we're done. */
 218         wait_for_completion(&kthread_stop_info.done);
 219         kthread_stop_info.k = NULL;
 220         ret = kthread_stop_info.err;
 221         mutex_unlock(&kthread_stop_lock);
 222
 223         return ret;
 224 }
 225 EXPORT_SYMBOL(kthread_stop);
 226
 227 int kthreadd(void *unused)
 228 {
 229         struct task_struct *tsk = current;
 230
 231         /* Setup a clean context for our children to inherit. */
 232         set_task_comm(tsk, "kthreadd");
 233         ignore_signals(tsk);
 234         set_user_nice(tsk, KTHREAD_NICE_LEVEL);
 235         set_cpus_allowed(tsk, CPU_MASK_ALL);
 236
 237         current->flags |= PF_NOFREEZE;
 238
 239         for (;;) {
 240                 set_current_state(TASK_INTERRUPTIBLE);
 241                 if (list_empty(&kthread_create_list))
 242                         schedule();
 243                 __set_current_state(TASK_RUNNING);
 244
 245                 spin_lock(&kthread_create_lock);
 246                 while (!list_empty(&kthread_create_list)) {
 247                         struct kthread_create_info *create;
 248
 249                         create = list_entry(kthread_create_list.next,
 250                                             struct kthread_create_info, list);
 251                         list_del_init(&create->list);
 252                         spin_unlock(&kthread_create_lock);
 253
 254                         create_kthread(create);
 255
 256                         spin_lock(&kthread_create_lock);
 257                 }
 258                 spin_unlock(&kthread_create_lock);
 259         }
 260
 261         return 0;
 262 }