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_ns(pid, &init_pid_ns);
 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_ptr(create->result, CPU_MASK_ALL_PTR);
 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         spin_unlock(&kthread_create_lock);
 148
 149         wake_up_process(kthreadd_task);
 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, 0);
 180         set_task_cpu(k, cpu);
 181         k->cpus_allowed = cpumask_of_cpu(cpu);
 182         k->rt.nr_cpus_allowed = 1;
 183         k->flags |= PF_THREAD_BOUND;
 184 }
 185 EXPORT_SYMBOL(kthread_bind);
 186
 187 /**
 188  * kthread_stop - stop a thread created by kthread_create().
 189  * @k: thread created by kthread_create().
 190  *
 191  * Sets kthread_should_stop() for @k to return true, wakes it, and
 192  * waits for it to exit.  Your threadfn() must not call do_exit()
 193  * itself if you use this function!  This can also be called after
 194  * kthread_create() instead of calling wake_up_process(): the thread
 195  * will exit without calling threadfn().
 196  *
 197  * Returns the result of threadfn(), or %-EINTR if wake_up_process()
 198  * was never called.
 199  */
 200 int kthread_stop(struct task_struct *k)
 201 {
 202         int ret;
 203
 204         mutex_lock(&kthread_stop_lock);
 205
 206         /* It could exit after stop_info.k set, but before wake_up_process. */
 207         get_task_struct(k);
 208
 209         /* Must init completion *before* thread sees kthread_stop_info.k */
 210         init_completion(&kthread_stop_info.done);
 211         smp_wmb();
 212
 213         /* Now set kthread_should_stop() to true, and wake it up. */
 214         kthread_stop_info.k = k;
 215         wake_up_process(k);
 216         put_task_struct(k);
 217
 218         /* Once it dies, reset stop ptr, gather result and we're done. */
 219         wait_for_completion(&kthread_stop_info.done);
 220         kthread_stop_info.k = NULL;
 221         ret = kthread_stop_info.err;
 222         mutex_unlock(&kthread_stop_lock);
 223
 224         return ret;
 225 }
 226 EXPORT_SYMBOL(kthread_stop);
 227
 228 int kthreadd(void *unused)
 229 {
 230         struct task_struct *tsk = current;
 231
 232         /* Setup a clean context for our children to inherit. */
 233         set_task_comm(tsk, "kthreadd");
 234         ignore_signals(tsk);
 235         set_user_nice(tsk, KTHREAD_NICE_LEVEL);
 236         set_cpus_allowed_ptr(tsk, CPU_MASK_ALL_PTR);
 237
 238         current->flags |= PF_NOFREEZE | PF_FREEZER_NOSIG;
 239
 240         for (;;) {
 241                 set_current_state(TASK_INTERRUPTIBLE);
 242                 if (list_empty(&kthread_create_list))
 243                         schedule();
 244                 __set_current_state(TASK_RUNNING);
 245
 246                 spin_lock(&kthread_create_lock);
 247                 while (!list_empty(&kthread_create_list)) {
 248                         struct kthread_create_info *create;
 249
 250                         create = list_entry(kthread_create_list.next,
 251                                             struct kthread_create_info, list);
 252                         list_del_init(&create->list);
 253                         spin_unlock(&kthread_create_lock);
 254
 255                         create_kthread(create);
 256
 257                         spin_lock(&kthread_create_lock);
 258                 }
 259                 spin_unlock(&kthread_create_lock);
 260         }
 261
 262         return 0;
 263 }