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/cpuset.h>
  13 #include <linux/unistd.h>
  14 #include <linux/file.h>
  15 #include <linux/module.h>
  16 #include <linux/mutex.h>
  17 #include <linux/slab.h>
  18 #include <linux/freezer.h>
  19 #include <trace/events/sched.h>
  20
  21 static DEFINE_SPINLOCK(kthread_create_lock);
  22 static LIST_HEAD(kthread_create_list);
  23 struct task_struct *kthreadd_task;
  24
  25 struct kthread_create_info
  26 {
  27         /* Information passed to kthread() from kthreadd. */
  28         int (*threadfn)(void *data);
  29         void *data;
  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 {
  39         int should_stop;
  40         struct completion exited;
  41 };
  42
  43 #define to_kthread(tsk) \
  44         container_of((tsk)->vfork_done, struct kthread, exited)
  45
  46 /**
  47  * kthread_should_stop - should this kthread return now?
  48  *
  49  * When someone calls kthread_stop() on your kthread, it will be woken
  50  * and this will return true.  You should then return, and your return
  51  * value will be passed through to kthread_stop().
  52  */
  53 int kthread_should_stop(void)
  54 {
  55         return to_kthread(current)->should_stop;
  56 }
  57 EXPORT_SYMBOL(kthread_should_stop);
  58
  59 static int kthread(void *_create)
  60 {
  61         /* Copy data: it's on kthread's stack */
  62         struct kthread_create_info *create = _create;
  63         int (*threadfn)(void *data) = create->threadfn;
  64         void *data = create->data;
  65         struct kthread self;
  66         int ret;
  67
  68         self.should_stop = 0;
  69         init_completion(&self.exited);
  70         current->vfork_done = &self.exited;
  71
  72         /* OK, tell user we're spawned, wait for stop or wakeup */
  73         __set_current_state(TASK_UNINTERRUPTIBLE);
  74         create->result = current;
  75         complete(&create->done);
  76         schedule();
  77
  78         ret = -EINTR;
  79         if (!self.should_stop)
  80                 ret = threadfn(data);
  81
  82         /* we can't just return, we must preserve "self" on stack */
  83         do_exit(ret);
  84 }
  85
  86 static void create_kthread(struct kthread_create_info *create)
  87 {
  88         int pid;
  89
  90         /* We want our own signal handler (we take no signals by default). */
  91         pid = kernel_thread(kthread, create, CLONE_FS | CLONE_FILES | SIGCHLD);
  92         if (pid < 0) {
  93                 create->result = ERR_PTR(pid);
  94                 complete(&create->done);
  95         }
  96 }
  97
  98 /**
  99  * kthread_create - create a kthread.
 100  * @threadfn: the function to run until signal_pending(current).
 101  * @data: data ptr for @threadfn.
 102  * @namefmt: printf-style name for the thread.
 103  *
 104  * Description: This helper function creates and names a kernel
 105  * thread.  The thread will be stopped: use wake_up_process() to start
 106  * it.  See also kthread_run().
 107  *
 108  * When woken, the thread will run @threadfn() with @data as its
 109  * argument. @threadfn() can either call do_exit() directly if it is a
 110  * standalone thread for which noone will call kthread_stop(), or
 111  * return when 'kthread_should_stop()' is true (which means
 112  * kthread_stop() has been called).  The return value should be zero
 113  * or a negative error number; it will be passed to kthread_stop().
 114  *
 115  * Returns a task_struct or ERR_PTR(-ENOMEM).
 116  */
 117 struct task_struct *kthread_create(int (*threadfn)(void *data),
 118                                    void *data,
 119                                    const char namefmt[],
 120                                    ...)
 121 {
 122         struct kthread_create_info create;
 123
 124         create.threadfn = threadfn;
 125         create.data = data;
 126         init_completion(&create.done);
 127
 128         spin_lock(&kthread_create_lock);
 129         list_add_tail(&create.list, &kthread_create_list);
 130         spin_unlock(&kthread_create_lock);
 131
 132         wake_up_process(kthreadd_task);
 133         wait_for_completion(&create.done);
 134
 135         if (!IS_ERR(create.result)) {
 136                 struct sched_param param = { .sched_priority = 0 };
 137                 va_list args;
 138
 139                 va_start(args, namefmt);
 140                 vsnprintf(create.result->comm, sizeof(create.result->comm),
 141                           namefmt, args);
 142                 va_end(args);
 143                 /*
 144                  * root may have changed our (kthreadd's) priority or CPU mask.
 145                  * The kernel thread should not inherit these properties.
 146                  */
 147                 sched_setscheduler_nocheck(create.result, SCHED_NORMAL, &param);
 148                 set_cpus_allowed_ptr(create.result, cpu_all_mask);
 149         }
 150         return create.result;
 151 }
 152 EXPORT_SYMBOL(kthread_create);
 153
 154 /**
 155  * kthread_bind - bind a just-created kthread to a cpu.
 156  * @p: thread created by kthread_create().
 157  * @cpu: cpu (might not be online, must be possible) for @k to run on.
 158  *
 159  * Description: This function is equivalent to set_cpus_allowed(),
 160  * except that @cpu doesn't need to be online, and the thread must be
 161  * stopped (i.e., just returned from kthread_create()).
 162  */
 163 void kthread_bind(struct task_struct *p, unsigned int cpu)
 164 {
 165         /* Must have done schedule() in kthread() before we set_task_cpu */
 166         if (!wait_task_inactive(p, TASK_UNINTERRUPTIBLE)) {
 167                 WARN_ON(1);
 168                 return;
 169         }
 170
 171         p->cpus_allowed = cpumask_of_cpu(cpu);
 172         p->rt.nr_cpus_allowed = 1;
 173         p->flags |= PF_THREAD_BOUND;
 174 }
 175 EXPORT_SYMBOL(kthread_bind);
 176
 177 /**
 178  * kthread_stop - stop a thread created by kthread_create().
 179  * @k: thread created by kthread_create().
 180  *
 181  * Sets kthread_should_stop() for @k to return true, wakes it, and
 182  * waits for it to exit. This can also be called after kthread_create()
 183  * instead of calling wake_up_process(): the thread will exit without
 184  * calling threadfn().
 185  *
 186  * If threadfn() may call do_exit() itself, the caller must ensure
 187  * task_struct can't go away.
 188  *
 189  * Returns the result of threadfn(), or %-EINTR if wake_up_process()
 190  * was never called.
 191  */
 192 int kthread_stop(struct task_struct *k)
 193 {
 194         struct kthread *kthread;
 195         int ret;
 196
 197         trace_sched_kthread_stop(k);
 198         get_task_struct(k);
 199
 200         kthread = to_kthread(k);
 201         barrier(); /* it might have exited */
 202         if (k->vfork_done != NULL) {
 203                 kthread->should_stop = 1;
 204                 wake_up_process(k);
 205                 wait_for_completion(&kthread->exited);
 206         }
 207         ret = k->exit_code;
 208
 209         put_task_struct(k);
 210         trace_sched_kthread_stop_ret(ret);
 211
 212         return ret;
 213 }
 214 EXPORT_SYMBOL(kthread_stop);
 215
 216 int kthreadd(void *unused)
 217 {
 218         struct task_struct *tsk = current;
 219
 220         /* Setup a clean context for our children to inherit. */
 221         set_task_comm(tsk, "kthreadd");
 222         ignore_signals(tsk);
 223         set_cpus_allowed_ptr(tsk, cpu_all_mask);
 224         set_mems_allowed(node_states[N_HIGH_MEMORY]);
 225
 226         current->flags |= PF_NOFREEZE | PF_FREEZER_NOSIG;
 227
 228         for (;;) {
 229                 set_current_state(TASK_INTERRUPTIBLE);
 230                 if (list_empty(&kthread_create_list))
 231                         schedule();
 232                 __set_current_state(TASK_RUNNING);
 233
 234                 spin_lock(&kthread_create_lock);
 235                 while (!list_empty(&kthread_create_list)) {
 236                         struct kthread_create_info *create;
 237
 238                         create = list_entry(kthread_create_list.next,
 239                                             struct kthread_create_info, list);
 240                         list_del_init(&create->list);
 241                         spin_unlock(&kthread_create_lock);
 242
 243                         create_kthread(create);
 244
 245                         spin_lock(&kthread_create_lock);
 246                 }
 247                 spin_unlock(&kthread_create_lock);
 248         }
 249
 250         return 0;
 251 }
 252
 253 /**
 254  * kthread_worker_fn - kthread function to process kthread_worker
 255  * @worker_ptr: pointer to initialized kthread_worker
 256  *
 257  * This function can be used as @threadfn to kthread_create() or
 258  * kthread_run() with @worker_ptr argument pointing to an initialized
 259  * kthread_worker.  The started kthread will process work_list until
 260  * the it is stopped with kthread_stop().  A kthread can also call
 261  * this function directly after extra initialization.
 262  *
 263  * Different kthreads can be used for the same kthread_worker as long
 264  * as there's only one kthread attached to it at any given time.  A
 265  * kthread_worker without an attached kthread simply collects queued
 266  * kthread_works.
 267  */
 268 int kthread_worker_fn(void *worker_ptr)
 269 {
 270         struct kthread_worker *worker = worker_ptr;
 271         struct kthread_work *work;
 272
 273         WARN_ON(worker->task);
 274         worker->task = current;
 275 repeat:
 276         set_current_state(TASK_INTERRUPTIBLE);  /* mb paired w/ kthread_stop */
 277
 278         if (kthread_should_stop()) {
 279                 __set_current_state(TASK_RUNNING);
 280                 spin_lock_irq(&worker->lock);
 281                 worker->task = NULL;
 282                 spin_unlock_irq(&worker->lock);
 283                 return 0;
 284         }
 285
 286         work = NULL;
 287         spin_lock_irq(&worker->lock);
 288         if (!list_empty(&worker->work_list)) {
 289                 work = list_first_entry(&worker->work_list,
 290                                         struct kthread_work, node);
 291                 list_del_init(&work->node);
 292         }
 293         spin_unlock_irq(&worker->lock);
 294
 295         if (work) {
 296                 __set_current_state(TASK_RUNNING);
 297                 work->func(work);
 298                 smp_wmb();      /* wmb worker-b0 paired with flush-b1 */
 299                 work->done_seq = work->queue_seq;
 300                 smp_mb();       /* mb worker-b1 paired with flush-b0 */
 301                 if (atomic_read(&work->flushing))
 302                         wake_up_all(&work->done);
 303         } else if (!freezing(current))
 304                 schedule();
 305
 306         try_to_freeze();
 307         goto repeat;
 308 }
 309 EXPORT_SYMBOL_GPL(kthread_worker_fn);
 310
 311 /**
 312  * queue_kthread_work - queue a kthread_work
 313  * @worker: target kthread_worker
 314  * @work: kthread_work to queue
 315  *
 316  * Queue @work to work processor @task for async execution.  @task
 317  * must have been created with kthread_worker_create().  Returns %true
 318  * if @work was successfully queued, %false if it was already pending.
 319  */
 320 bool queue_kthread_work(struct kthread_worker *worker,
 321                         struct kthread_work *work)
 322 {
 323         bool ret = false;
 324         unsigned long flags;
 325
 326         spin_lock_irqsave(&worker->lock, flags);
 327         if (list_empty(&work->node)) {
 328                 list_add_tail(&work->node, &worker->work_list);
 329                 work->queue_seq++;
 330                 if (likely(worker->task))
 331                         wake_up_process(worker->task);
 332                 ret = true;
 333         }
 334         spin_unlock_irqrestore(&worker->lock, flags);
 335         return ret;
 336 }
 337 EXPORT_SYMBOL_GPL(queue_kthread_work);
 338
 339 /**
 340  * flush_kthread_work - flush a kthread_work
 341  * @work: work to flush
 342  *
 343  * If @work is queued or executing, wait for it to finish execution.
 344  */
 345 void flush_kthread_work(struct kthread_work *work)
 346 {
 347         int seq = work->queue_seq;
 348
 349         atomic_inc(&work->flushing);
 350
 351         /*
 352          * mb flush-b0 paired with worker-b1, to make sure either
 353          * worker sees the above increment or we see done_seq update.
 354          */
 355         smp_mb__after_atomic_inc();
 356
 357         /* A - B <= 0 tests whether B is in front of A regardless of overflow */
 358         wait_event(work->done, seq - work->done_seq <= 0);
 359         atomic_dec(&work->flushing);
 360
 361         /*
 362          * rmb flush-b1 paired with worker-b0, to make sure our caller
 363          * sees every change made by work->func().
 364          */
 365         smp_mb__after_atomic_dec();
 366 }
 367 EXPORT_SYMBOL_GPL(flush_kthread_work);
 368
 369 struct kthread_flush_work {
 370         struct kthread_work     work;
 371         struct completion       done;
 372 };
 373
 374 static void kthread_flush_work_fn(struct kthread_work *work)
 375 {
 376         struct kthread_flush_work *fwork =
 377                 container_of(work, struct kthread_flush_work, work);
 378         complete(&fwork->done);
 379 }
 380
 381 /**
 382  * flush_kthread_worker - flush all current works on a kthread_worker
 383  * @worker: worker to flush
 384  *
 385  * Wait until all currently executing or pending works on @worker are
 386  * finished.
 387  */
 388 void flush_kthread_worker(struct kthread_worker *worker)
 389 {
 390         struct kthread_flush_work fwork = {
 391                 KTHREAD_WORK_INIT(fwork.work, kthread_flush_work_fn),
 392                 COMPLETION_INITIALIZER_ONSTACK(fwork.done),
 393         };
 394
 395         queue_kthread_work(worker, &fwork.work);
 396         wait_for_completion(&fwork.done);
 397 }
 398 EXPORT_SYMBOL_GPL(flush_kthread_worker);