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         complete(&create->started);
  80         schedule();
  81
  82         if (!kthread_should_stop())
  83                 ret = threadfn(data);
  84
  85         /* It might have exited on its own, w/o kthread_stop.  Check. */
  86         if (kthread_should_stop()) {
  87                 kthread_stop_info.err = ret;
  88                 complete(&kthread_stop_info.done);
  89         }
  90         return 0;
  91 }
  92
  93 static void create_kthread(struct kthread_create_info *create)
  94 {
  95         int pid;
  96
  97         /* We want our own signal handler (we take no signals by default). */
  98         pid = kernel_thread(kthread, create, CLONE_FS | CLONE_FILES | SIGCHLD);
  99         if (pid < 0) {
 100                 create->result = ERR_PTR(pid);
 101         } else {
 102                 struct sched_param param = { .sched_priority = 0 };
 103                 wait_for_completion(&create->started);
 104                 read_lock(&tasklist_lock);
 105                 create->result = find_task_by_pid_ns(pid, &init_pid_ns);
 106                 read_unlock(&tasklist_lock);
 107                 /*
 108                  * root may have changed our (kthreadd's) priority or CPU mask.
 109                  * The kernel thread should not inherit these properties.
 110                  */
 111                 sched_setscheduler(create->result, SCHED_NORMAL, &param);
 112                 set_user_nice(create->result, KTHREAD_NICE_LEVEL);
 113                 set_cpus_allowed_ptr(create->result, CPU_MASK_ALL_PTR);
 114         }
 115         complete(&create->done);
 116 }
 117
 118 /**
 119  * kthread_create - create a kthread.
 120  * @threadfn: the function to run until signal_pending(current).
 121  * @data: data ptr for @threadfn.
 122  * @namefmt: printf-style name for the thread.
 123  *
 124  * Description: This helper function creates and names a kernel
 125  * thread.  The thread will be stopped: use wake_up_process() to start
 126  * it.  See also kthread_run(), kthread_create_on_cpu().
 127  *
 128  * When woken, the thread will run @threadfn() with @data as its
 129  * argument. @threadfn() can either call do_exit() directly if it is a
 130  * standalone thread for which noone will call kthread_stop(), or
 131  * return when 'kthread_should_stop()' is true (which means
 132  * kthread_stop() has been called).  The return value should be zero
 133  * or a negative error number; it will be passed to kthread_stop().
 134  *
 135  * Returns a task_struct or ERR_PTR(-ENOMEM).
 136  */
 137 struct task_struct *kthread_create(int (*threadfn)(void *data),
 138                                    void *data,
 139                                    const char namefmt[],
 140                                    ...)
 141 {
 142         struct kthread_create_info create;
 143
 144         create.threadfn = threadfn;
 145         create.data = data;
 146         init_completion(&create.started);
 147         init_completion(&create.done);
 148
 149         spin_lock(&kthread_create_lock);
 150         list_add_tail(&create.list, &kthread_create_list);
 151         spin_unlock(&kthread_create_lock);
 152
 153         wake_up_process(kthreadd_task);
 154         wait_for_completion(&create.done);
 155
 156         if (!IS_ERR(create.result)) {
 157                 va_list args;
 158                 va_start(args, namefmt);
 159                 vsnprintf(create.result->comm, sizeof(create.result->comm),
 160                           namefmt, args);
 161                 va_end(args);
 162         }
 163         return create.result;
 164 }
 165 EXPORT_SYMBOL(kthread_create);
 166
 167 /**
 168  * kthread_bind - bind a just-created kthread to a cpu.
 169  * @k: thread created by kthread_create().
 170  * @cpu: cpu (might not be online, must be possible) for @k to run on.
 171  *
 172  * Description: This function is equivalent to set_cpus_allowed(),
 173  * except that @cpu doesn't need to be online, and the thread must be
 174  * stopped (i.e., just returned from kthread_create()).
 175  */
 176 void kthread_bind(struct task_struct *k, unsigned int cpu)
 177 {
 178         /* Must have done schedule() in kthread() before we set_task_cpu */
 179         if (!wait_task_inactive(k, TASK_UNINTERRUPTIBLE)) {
 180                 WARN_ON(1);
 181                 return;
 182         }
 183         set_task_cpu(k, cpu);
 184         k->cpus_allowed = cpumask_of_cpu(cpu);
 185         k->rt.nr_cpus_allowed = 1;
 186         k->flags |= PF_THREAD_BOUND;
 187 }
 188 EXPORT_SYMBOL(kthread_bind);
 189
 190 /**
 191  * kthread_stop - stop a thread created by kthread_create().
 192  * @k: thread created by kthread_create().
 193  *
 194  * Sets kthread_should_stop() for @k to return true, wakes it, and
 195  * waits for it to exit.  Your threadfn() must not call do_exit()
 196  * itself if you use this function!  This can also be called after
 197  * kthread_create() instead of calling wake_up_process(): the thread
 198  * will exit without calling threadfn().
 199  *
 200  * Returns the result of threadfn(), or %-EINTR if wake_up_process()
 201  * was never called.
 202  */
 203 int kthread_stop(struct task_struct *k)
 204 {
 205         int ret;
 206
 207         mutex_lock(&kthread_stop_lock);
 208
 209         /* It could exit after stop_info.k set, but before wake_up_process. */
 210         get_task_struct(k);
 211
 212         trace_sched_kthread_stop(k);
 213
 214         /* Must init completion *before* thread sees kthread_stop_info.k */
 215         init_completion(&kthread_stop_info.done);
 216         smp_wmb();
 217
 218         /* Now set kthread_should_stop() to true, and wake it up. */
 219         kthread_stop_info.k = k;
 220         wake_up_process(k);
 221         put_task_struct(k);
 222
 223         /* Once it dies, reset stop ptr, gather result and we're done. */
 224         wait_for_completion(&kthread_stop_info.done);
 225         kthread_stop_info.k = NULL;
 226         ret = kthread_stop_info.err;
 227         mutex_unlock(&kthread_stop_lock);
 228
 229         trace_sched_kthread_stop_ret(ret);
 230
 231         return ret;
 232 }
 233 EXPORT_SYMBOL(kthread_stop);
 234
 235 int kthreadd(void *unused)
 236 {
 237         struct task_struct *tsk = current;
 238
 239         /* Setup a clean context for our children to inherit. */
 240         set_task_comm(tsk, "kthreadd");
 241         ignore_signals(tsk);
 242         set_user_nice(tsk, KTHREAD_NICE_LEVEL);
 243         set_cpus_allowed_ptr(tsk, CPU_MASK_ALL_PTR);
 244
 245         current->flags |= PF_NOFREEZE | PF_FREEZER_NOSIG;
 246
 247         for (;;) {
 248                 set_current_state(TASK_INTERRUPTIBLE);
 249                 if (list_empty(&kthread_create_list))
 250                         schedule();
 251                 __set_current_state(TASK_RUNNING);
 252
 253                 spin_lock(&kthread_create_lock);
 254                 while (!list_empty(&kthread_create_list)) {
 255                         struct kthread_create_info *create;
 256
 257                         create = list_entry(kthread_create_list.next,
 258                                             struct kthread_create_info, list);
 259                         list_del_init(&create->list);
 260                         spin_unlock(&kthread_create_lock);
 261
 262                         create_kthread(create);
 263
 264                         spin_lock(&kthread_create_lock);
 265                 }
 266                 spin_unlock(&kthread_create_lock);
 267         }
 268
 269         return 0;
 270 }