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
  17 #define KTHREAD_NICE_LEVEL (-5)
  18
  19 static DEFINE_SPINLOCK(kthread_create_lock);
  20 static LIST_HEAD(kthread_create_list);
  21 struct task_struct *kthreadd_task;
  22
  23 struct kthread_create_info
  24 {
  25         /* Information passed to kthread() from kthreadd. */
  26         int (*threadfn)(void *data);
  27         void *data;
  28         struct completion started;
  29
  30         /* Result passed back to kthread_create() from kthreadd. */
  31         struct task_struct *result;
  32         struct completion done;
  33
  34         struct list_head list;
  35 };
  36
  37 struct kthread_stop_info
  38 {
  39         struct task_struct *k;
  40         int err;
  41         struct completion done;
  42 };
  43
  44 /* Thread stopping is done by setthing this var: lock serializes
  45  * multiple kthread_stop calls. */
  46 static DEFINE_MUTEX(kthread_stop_lock);
  47 static struct kthread_stop_info kthread_stop_info;
  48
  49 /**
  50  * kthread_should_stop - should this kthread return now?
  51  *
  52  * When someone calls kthread_stop() on your kthread, it will be woken
  53  * and this will return true.  You should then return, and your return
  54  * value will be passed through to kthread_stop().
  55  */
  56 int kthread_should_stop(void)
  57 {
  58         return (kthread_stop_info.k == current);
  59 }
  60 EXPORT_SYMBOL(kthread_should_stop);
  61
  62 static int kthread(void *_create)
  63 {
  64         struct kthread_create_info *create = _create;
  65         int (*threadfn)(void *data);
  66         void *data;
  67         int ret = -EINTR;
  68
  69         /* Copy data: it's on kthread's stack */
  70         threadfn = create->threadfn;
  71         data = create->data;
  72
  73         /* OK, tell user we're spawned, wait for stop or wakeup */
  74         __set_current_state(TASK_UNINTERRUPTIBLE);
  75         complete(&create->started);
  76         schedule();
  77
  78         if (!kthread_should_stop())
  79                 ret = threadfn(data);
  80
  81         /* It might have exited on its own, w/o kthread_stop.  Check. */
  82         if (kthread_should_stop()) {
  83                 kthread_stop_info.err = ret;
  84                 complete(&kthread_stop_info.done);
  85         }
  86         return 0;
  87 }
  88
  89 static void create_kthread(struct kthread_create_info *create)
  90 {
  91         int pid;
  92
  93         /* We want our own signal handler (we take no signals by default). */
  94         pid = kernel_thread(kthread, create, CLONE_FS | CLONE_FILES | SIGCHLD);
  95         if (pid < 0) {
  96                 create->result = ERR_PTR(pid);
  97         } else {
  98                 struct sched_param param = { .sched_priority = 0 };
  99                 wait_for_completion(&create->started);
 100                 read_lock(&tasklist_lock);
 101                 create->result = find_task_by_pid(pid);
 102                 read_unlock(&tasklist_lock);
 103                 /*
 104                  * root may have changed our (kthreadd's) priority or CPU mask.
 105                  * The kernel thread should not inherit these properties.
 106                  */
 107                 sched_setscheduler(create->result, SCHED_NORMAL, &param);
 108                 set_user_nice(create->result, KTHREAD_NICE_LEVEL);
 109                 set_cpus_allowed(create->result, CPU_MASK_ALL);
 110         }
 111         complete(&create->done);
 112 }
 113
 114 /**
 115  * kthread_create - create a kthread.
 116  * @threadfn: the function to run until signal_pending(current).
 117  * @data: data ptr for @threadfn.
 118  * @namefmt: printf-style name for the thread.
 119  *
 120  * Description: This helper function creates and names a kernel
 121  * thread.  The thread will be stopped: use wake_up_process() to start
 122  * it.  See also kthread_run(), kthread_create_on_cpu().
 123  *
 124  * When woken, the thread will run @threadfn() with @data as its
 125  * argument. @threadfn() can either call do_exit() directly if it is a
 126  * standalone thread for which noone will call kthread_stop(), or
 127  * return when 'kthread_should_stop()' is true (which means
 128  * kthread_stop() has been called).  The return value should be zero
 129  * or a negative error number; it will be passed to kthread_stop().
 130  *
 131  * Returns a task_struct or ERR_PTR(-ENOMEM).
 132  */
 133 struct task_struct *kthread_create(int (*threadfn)(void *data),
 134                                    void *data,
 135                                    const char namefmt[],
 136                                    ...)
 137 {
 138         struct kthread_create_info create;
 139
 140         create.threadfn = threadfn;
 141         create.data = data;
 142         init_completion(&create.started);
 143         init_completion(&create.done);
 144
 145         spin_lock(&kthread_create_lock);
 146         list_add_tail(&create.list, &kthread_create_list);
 147         wake_up_process(kthreadd_task);
 148         spin_unlock(&kthread_create_lock);
 149
 150         wait_for_completion(&create.done);
 151
 152         if (!IS_ERR(create.result)) {
 153                 va_list args;
 154                 va_start(args, namefmt);
 155                 vsnprintf(create.result->comm, sizeof(create.result->comm),
 156                           namefmt, args);
 157                 va_end(args);
 158         }
 159         return create.result;
 160 }
 161 EXPORT_SYMBOL(kthread_create);
 162
 163 /**
 164  * kthread_bind - bind a just-created kthread to a cpu.
 165  * @k: thread created by kthread_create().
 166  * @cpu: cpu (might not be online, must be possible) for @k to run on.
 167  *
 168  * Description: This function is equivalent to set_cpus_allowed(),
 169  * except that @cpu doesn't need to be online, and the thread must be
 170  * stopped (i.e., just returned from kthread_create()).
 171  */
 172 void kthread_bind(struct task_struct *k, unsigned int cpu)
 173 {
 174         if (k->state != TASK_UNINTERRUPTIBLE) {
 175                 WARN_ON(1);
 176                 return;
 177         }
 178         /* Must have done schedule() in kthread() before we set_task_cpu */
 179         wait_task_inactive(k);
 180         set_task_cpu(k, cpu);
 181         k->cpus_allowed = cpumask_of_cpu(cpu);
 182         k->rt.nr_cpus_allowed = 1;
 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 }