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 <trace/sched.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 DEFINE_TRACE(sched_kthread_stop);
  25 DEFINE_TRACE(sched_kthread_stop_ret);
  26
  27 struct kthread_create_info
  28 {
  29         /* Information passed to kthread() from kthreadd. */
  30         int (*threadfn)(void *data);
  31         void *data;
  32         struct completion started;
  33
  34         /* Result passed back to kthread_create() from kthreadd. */
  35         struct task_struct *result;
  36         struct completion done;
  37
  38         struct list_head list;
  39 };
  40
  41 struct kthread_stop_info
  42 {
  43         struct task_struct *k;
  44         int err;
  45         struct completion done;
  46 };
  47
  48 /* Thread stopping is done by setthing this var: lock serializes
  49  * multiple kthread_stop calls. */
  50 static DEFINE_MUTEX(kthread_stop_lock);
  51 static struct kthread_stop_info kthread_stop_info;
  52
  53 /**
  54  * kthread_should_stop - should this kthread return now?
  55  *
  56  * When someone calls kthread_stop() on your kthread, it will be woken
  57  * and this will return true.  You should then return, and your return
  58  * value will be passed through to kthread_stop().
  59  */
  60 int kthread_should_stop(void)
  61 {
  62         return (kthread_stop_info.k == current);
  63 }
  64 EXPORT_SYMBOL(kthread_should_stop);
  65
  66 static int kthread(void *_create)
  67 {
  68         struct kthread_create_info *create = _create;
  69         int (*threadfn)(void *data);
  70         void *data;
  71         int ret = -EINTR;
  72
  73         /* Copy data: it's on kthread's stack */
  74         threadfn = create->threadfn;
  75         data = create->data;
  76
  77         /* OK, tell user we're spawned, wait for stop or wakeup */
  78         __set_current_state(TASK_UNINTERRUPTIBLE);
  79         create->result = current;
  80         complete(&create->started);
  81         schedule();
  82
  83         if (!kthread_should_stop())
  84                 ret = threadfn(data);
  85
  86         /* It might have exited on its own, w/o kthread_stop.  Check. */
  87         if (kthread_should_stop()) {
  88                 kthread_stop_info.err = ret;
  89                 complete(&kthread_stop_info.done);
  90         }
  91         return 0;
  92 }
  93
  94 static void create_kthread(struct kthread_create_info *create)
  95 {
  96         int pid;
  97
  98         /* We want our own signal handler (we take no signals by default). */
  99         pid = kernel_thread(kthread, create, CLONE_FS | CLONE_FILES | SIGCHLD);
 100         if (pid < 0)
 101                 create->result = ERR_PTR(pid);
 102         else
 103                 wait_for_completion(&create->started);
 104         complete(&create->done);
 105 }
 106
 107 /**
 108  * kthread_create - create a kthread.
 109  * @threadfn: the function to run until signal_pending(current).
 110  * @data: data ptr for @threadfn.
 111  * @namefmt: printf-style name for the thread.
 112  *
 113  * Description: This helper function creates and names a kernel
 114  * thread.  The thread will be stopped: use wake_up_process() to start
 115  * it.  See also kthread_run(), kthread_create_on_cpu().
 116  *
 117  * When woken, the thread will run @threadfn() with @data as its
 118  * argument. @threadfn() can either call do_exit() directly if it is a
 119  * standalone thread for which noone will call kthread_stop(), or
 120  * return when 'kthread_should_stop()' is true (which means
 121  * kthread_stop() has been called).  The return value should be zero
 122  * or a negative error number; it will be passed to kthread_stop().
 123  *
 124  * Returns a task_struct or ERR_PTR(-ENOMEM).
 125  */
 126 struct task_struct *kthread_create(int (*threadfn)(void *data),
 127                                    void *data,
 128                                    const char namefmt[],
 129                                    ...)
 130 {
 131         struct kthread_create_info create;
 132
 133         create.threadfn = threadfn;
 134         create.data = data;
 135         init_completion(&create.started);
 136         init_completion(&create.done);
 137
 138         spin_lock(&kthread_create_lock);
 139         list_add_tail(&create.list, &kthread_create_list);
 140         spin_unlock(&kthread_create_lock);
 141
 142         wake_up_process(kthreadd_task);
 143         wait_for_completion(&create.done);
 144
 145         if (!IS_ERR(create.result)) {
 146                 struct sched_param param = { .sched_priority = 0 };
 147                 va_list args;
 148
 149                 va_start(args, namefmt);
 150                 vsnprintf(create.result->comm, sizeof(create.result->comm),
 151                           namefmt, args);
 152                 va_end(args);
 153                 /*
 154                  * root may have changed our (kthreadd's) priority or CPU mask.
 155                  * The kernel thread should not inherit these properties.
 156                  */
 157                 sched_setscheduler_nocheck(create.result, SCHED_NORMAL, &param);
 158                 set_user_nice(create.result, KTHREAD_NICE_LEVEL);
 159                 set_cpus_allowed_ptr(create.result, cpu_all_mask);
 160         }
 161         return create.result;
 162 }
 163 EXPORT_SYMBOL(kthread_create);
 164
 165 /**
 166  * kthread_bind - bind a just-created kthread to a cpu.
 167  * @k: thread created by kthread_create().
 168  * @cpu: cpu (might not be online, must be possible) for @k to run on.
 169  *
 170  * Description: This function is equivalent to set_cpus_allowed(),
 171  * except that @cpu doesn't need to be online, and the thread must be
 172  * stopped (i.e., just returned from kthread_create()).
 173  */
 174 void kthread_bind(struct task_struct *k, unsigned int cpu)
 175 {
 176         /* Must have done schedule() in kthread() before we set_task_cpu */
 177         if (!wait_task_inactive(k, TASK_UNINTERRUPTIBLE)) {
 178                 WARN_ON(1);
 179                 return;
 180         }
 181         set_task_cpu(k, cpu);
 182         k->cpus_allowed = cpumask_of_cpu(cpu);
 183         k->rt.nr_cpus_allowed = 1;
 184         k->flags |= PF_THREAD_BOUND;
 185 }
 186 EXPORT_SYMBOL(kthread_bind);
 187
 188 /**
 189  * kthread_stop - stop a thread created by kthread_create().
 190  * @k: thread created by kthread_create().
 191  *
 192  * Sets kthread_should_stop() for @k to return true, wakes it, and
 193  * waits for it to exit.  Your threadfn() must not call do_exit()
 194  * itself if you use this function!  This can also be called after
 195  * kthread_create() instead of calling wake_up_process(): the thread
 196  * will exit without calling threadfn().
 197  *
 198  * Returns the result of threadfn(), or %-EINTR if wake_up_process()
 199  * was never called.
 200  */
 201 int kthread_stop(struct task_struct *k)
 202 {
 203         int ret;
 204
 205         mutex_lock(&kthread_stop_lock);
 206
 207         /* It could exit after stop_info.k set, but before wake_up_process. */
 208         get_task_struct(k);
 209
 210         trace_sched_kthread_stop(k);
 211
 212         /* Must init completion *before* thread sees kthread_stop_info.k */
 213         init_completion(&kthread_stop_info.done);
 214         smp_wmb();
 215
 216         /* Now set kthread_should_stop() to true, and wake it up. */
 217         kthread_stop_info.k = k;
 218         wake_up_process(k);
 219         put_task_struct(k);
 220
 221         /* Once it dies, reset stop ptr, gather result and we're done. */
 222         wait_for_completion(&kthread_stop_info.done);
 223         kthread_stop_info.k = NULL;
 224         ret = kthread_stop_info.err;
 225         mutex_unlock(&kthread_stop_lock);
 226
 227         trace_sched_kthread_stop_ret(ret);
 228
 229         return ret;
 230 }
 231 EXPORT_SYMBOL(kthread_stop);
 232
 233 int kthreadd(void *unused)
 234 {
 235         struct task_struct *tsk = current;
 236
 237         /* Setup a clean context for our children to inherit. */
 238         set_task_comm(tsk, "kthreadd");
 239         ignore_signals(tsk);
 240         set_user_nice(tsk, KTHREAD_NICE_LEVEL);
 241         set_cpus_allowed_ptr(tsk, cpu_all_mask);
 242
 243         current->flags |= PF_NOFREEZE | PF_FREEZER_NOSIG;
 244
 245         for (;;) {
 246                 set_current_state(TASK_INTERRUPTIBLE);
 247                 if (list_empty(&kthread_create_list))
 248                         schedule();
 249                 __set_current_state(TASK_RUNNING);
 250
 251                 spin_lock(&kthread_create_lock);
 252                 while (!list_empty(&kthread_create_list)) {
 253                         struct kthread_create_info *create;
 254
 255                         create = list_entry(kthread_create_list.next,
 256                                             struct kthread_create_info, list);
 257                         list_del_init(&create->list);
 258                         spin_unlock(&kthread_create_lock);
 259
 260                         create_kthread(create);
 261
 262                         spin_lock(&kthread_create_lock);
 263                 }
 264                 spin_unlock(&kthread_create_lock);
 265         }
 266
 267         return 0;
 268 }