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         int node;
  31
  32         /* Result passed back to kthread_create() from kthreadd. */
  33         struct task_struct *result;
  34         struct completion done;
  35
  36         struct list_head list;
  37 };
  38
  39 struct kthread {
  40         int should_stop;
  41         void *data;
  42         struct completion exited;
  43 };
  44
  45 #define to_kthread(tsk) \
  46         container_of((tsk)->vfork_done, struct kthread, exited)
  47
  48 /**
  49  * kthread_should_stop - should this kthread return now?
  50  *
  51  * When someone calls kthread_stop() on your kthread, it will be woken
  52  * and this will return true.  You should then return, and your return
  53  * value will be passed through to kthread_stop().
  54  */
  55 int kthread_should_stop(void)
  56 {
  57         return to_kthread(current)->should_stop;
  58 }
  59 EXPORT_SYMBOL(kthread_should_stop);
  60
  61 /**
  62  * kthread_data - return data value specified on kthread creation
  63  * @task: kthread task in question
  64  *
  65  * Return the data value specified when kthread @task was created.
  66  * The caller is responsible for ensuring the validity of @task when
  67  * calling this function.
  68  */
  69 void *kthread_data(struct task_struct *task)
  70 {
  71         return to_kthread(task)->data;
  72 }
  73
  74 static int kthread(void *_create)
  75 {
  76         /* Copy data: it's on kthread's stack */
  77         struct kthread_create_info *create = _create;
  78         int (*threadfn)(void *data) = create->threadfn;
  79         void *data = create->data;
  80         struct kthread self;
  81         int ret;
  82
  83         self.should_stop = 0;
  84         self.data = data;
  85         init_completion(&self.exited);
  86         current->vfork_done = &self.exited;
  87
  88         /* OK, tell user we're spawned, wait for stop or wakeup */
  89         __set_current_state(TASK_UNINTERRUPTIBLE);
  90         create->result = current;
  91         complete(&create->done);
  92         schedule();
  93
  94         ret = -EINTR;
  95         if (!self.should_stop)
  96                 ret = threadfn(data);
  97
  98         /* we can't just return, we must preserve "self" on stack */
  99         do_exit(ret);
 100 }
 101
 102 /* called from do_fork() to get node information for about to be created task */
 103 int tsk_fork_get_node(struct task_struct *tsk)
 104 {
 105 #ifdef CONFIG_NUMA
 106         if (tsk == kthreadd_task)
 107                 return tsk->pref_node_fork;
 108 #endif
 109         return numa_node_id();
 110 }
 111
 112 static void create_kthread(struct kthread_create_info *create)
 113 {
 114         int pid;
 115
 116 #ifdef CONFIG_NUMA
 117         current->pref_node_fork = create->node;
 118 #endif
 119         /* We want our own signal handler (we take no signals by default). */
 120         pid = kernel_thread(kthread, create, CLONE_FS | CLONE_FILES | SIGCHLD);
 121         if (pid < 0) {
 122                 create->result = ERR_PTR(pid);
 123                 complete(&create->done);
 124         }
 125 }
 126
 127 /**
 128  * kthread_create_on_node - create a kthread.
 129  * @threadfn: the function to run until signal_pending(current).
 130  * @data: data ptr for @threadfn.
 131  * @node: memory node number.
 132  * @namefmt: printf-style name for the thread.
 133  *
 134  * Description: This helper function creates and names a kernel
 135  * thread.  The thread will be stopped: use wake_up_process() to start
 136  * it.  See also kthread_run().
 137  *
 138  * If thread is going to be bound on a particular cpu, give its node
 139  * in @node, to get NUMA affinity for kthread stack, or else give -1.
 140  * When woken, the thread will run @threadfn() with @data as its
 141  * argument. @threadfn() can either call do_exit() directly if it is a
 142  * standalone thread for which no one will call kthread_stop(), or
 143  * return when 'kthread_should_stop()' is true (which means
 144  * kthread_stop() has been called).  The return value should be zero
 145  * or a negative error number; it will be passed to kthread_stop().
 146  *
 147  * Returns a task_struct or ERR_PTR(-ENOMEM).
 148  */
 149 struct task_struct *kthread_create_on_node(int (*threadfn)(void *data),
 150                                            void *data,
 151                                            int node,
 152                                            const char namefmt[],
 153                                            ...)
 154 {
 155         struct kthread_create_info create;
 156
 157         create.threadfn = threadfn;
 158         create.data = data;
 159         create.node = node;
 160         init_completion(&create.done);
 161
 162         spin_lock(&kthread_create_lock);
 163         list_add_tail(&create.list, &kthread_create_list);
 164         spin_unlock(&kthread_create_lock);
 165
 166         wake_up_process(kthreadd_task);
 167         wait_for_completion(&create.done);
 168
 169         if (!IS_ERR(create.result)) {
 170                 static const struct sched_param param = { .sched_priority = 0 };
 171                 va_list args;
 172
 173                 va_start(args, namefmt);
 174                 vsnprintf(create.result->comm, sizeof(create.result->comm),
 175                           namefmt, args);
 176                 va_end(args);
 177                 /*
 178                  * root may have changed our (kthreadd's) priority or CPU mask.
 179                  * The kernel thread should not inherit these properties.
 180                  */
 181                 sched_setscheduler_nocheck(create.result, SCHED_NORMAL, &param);
 182                 set_cpus_allowed_ptr(create.result, cpu_all_mask);
 183         }
 184         return create.result;
 185 }
 186 EXPORT_SYMBOL(kthread_create_on_node);
 187
 188 /**
 189  * kthread_bind - bind a just-created kthread to a cpu.
 190  * @p: thread created by kthread_create().
 191  * @cpu: cpu (might not be online, must be possible) for @k to run on.
 192  *
 193  * Description: This function is equivalent to set_cpus_allowed(),
 194  * except that @cpu doesn't need to be online, and the thread must be
 195  * stopped (i.e., just returned from kthread_create()).
 196  */
 197 void kthread_bind(struct task_struct *p, unsigned int cpu)
 198 {
 199         /* Must have done schedule() in kthread() before we set_task_cpu */
 200         if (!wait_task_inactive(p, TASK_UNINTERRUPTIBLE)) {
 201                 WARN_ON(1);
 202                 return;
 203         }
 204
 205         /* It's safe because the task is inactive. */
 206         do_set_cpus_allowed(p, cpumask_of(cpu));
 207         p->flags |= PF_THREAD_BOUND;
 208 }
 209 EXPORT_SYMBOL(kthread_bind);
 210
 211 /**
 212  * kthread_stop - stop a thread created by kthread_create().
 213  * @k: thread created by kthread_create().
 214  *
 215  * Sets kthread_should_stop() for @k to return true, wakes it, and
 216  * waits for it to exit. This can also be called after kthread_create()
 217  * instead of calling wake_up_process(): the thread will exit without
 218  * calling threadfn().
 219  *
 220  * If threadfn() may call do_exit() itself, the caller must ensure
 221  * task_struct can't go away.
 222  *
 223  * Returns the result of threadfn(), or %-EINTR if wake_up_process()
 224  * was never called.
 225  */
 226 int kthread_stop(struct task_struct *k)
 227 {
 228         struct kthread *kthread;
 229         int ret;
 230
 231         trace_sched_kthread_stop(k);
 232         get_task_struct(k);
 233
 234         kthread = to_kthread(k);
 235         barrier(); /* it might have exited */
 236         if (k->vfork_done != NULL) {
 237                 kthread->should_stop = 1;
 238                 wake_up_process(k);
 239                 wait_for_completion(&kthread->exited);
 240         }
 241         ret = k->exit_code;
 242
 243         put_task_struct(k);
 244         trace_sched_kthread_stop_ret(ret);
 245
 246         return ret;
 247 }
 248 EXPORT_SYMBOL(kthread_stop);
 249
 250 int kthreadd(void *unused)
 251 {
 252         struct task_struct *tsk = current;
 253
 254         /* Setup a clean context for our children to inherit. */
 255         set_task_comm(tsk, "kthreadd");
 256         ignore_signals(tsk);
 257         set_cpus_allowed_ptr(tsk, cpu_all_mask);
 258         set_mems_allowed(node_states[N_HIGH_MEMORY]);
 259
 260         current->flags |= PF_NOFREEZE | PF_FREEZER_NOSIG;
 261
 262         for (;;) {
 263                 set_current_state(TASK_INTERRUPTIBLE);
 264                 if (list_empty(&kthread_create_list))
 265                         schedule();
 266                 __set_current_state(TASK_RUNNING);
 267
 268                 spin_lock(&kthread_create_lock);
 269                 while (!list_empty(&kthread_create_list)) {
 270                         struct kthread_create_info *create;
 271
 272                         create = list_entry(kthread_create_list.next,
 273                                             struct kthread_create_info, list);
 274                         list_del_init(&create->list);
 275                         spin_unlock(&kthread_create_lock);
 276
 277                         create_kthread(create);
 278
 279                         spin_lock(&kthread_create_lock);
 280                 }
 281                 spin_unlock(&kthread_create_lock);
 282         }
 283
 284         return 0;
 285 }
 286
 287 void __init_kthread_worker(struct kthread_worker *worker,
 288                                 const char *name,
 289                                 struct lock_class_key *key)
 290 {
 291         spin_lock_init(&worker->lock);
 292         lockdep_set_class_and_name(&worker->lock, key, name);
 293         INIT_LIST_HEAD(&worker->work_list);
 294         worker->task = NULL;
 295 }
 296 EXPORT_SYMBOL_GPL(__init_kthread_worker);
 297
 298 /**
 299  * kthread_worker_fn - kthread function to process kthread_worker
 300  * @worker_ptr: pointer to initialized kthread_worker
 301  *
 302  * This function can be used as @threadfn to kthread_create() or
 303  * kthread_run() with @worker_ptr argument pointing to an initialized
 304  * kthread_worker.  The started kthread will process work_list until
 305  * the it is stopped with kthread_stop().  A kthread can also call
 306  * this function directly after extra initialization.
 307  *
 308  * Different kthreads can be used for the same kthread_worker as long
 309  * as there's only one kthread attached to it at any given time.  A
 310  * kthread_worker without an attached kthread simply collects queued
 311  * kthread_works.
 312  */
 313 int kthread_worker_fn(void *worker_ptr)
 314 {
 315         struct kthread_worker *worker = worker_ptr;
 316         struct kthread_work *work;
 317
 318         WARN_ON(worker->task);
 319         worker->task = current;
 320 repeat:
 321         set_current_state(TASK_INTERRUPTIBLE);  /* mb paired w/ kthread_stop */
 322
 323         if (kthread_should_stop()) {
 324                 __set_current_state(TASK_RUNNING);
 325                 spin_lock_irq(&worker->lock);
 326                 worker->task = NULL;
 327                 spin_unlock_irq(&worker->lock);
 328                 return 0;
 329         }
 330
 331         work = NULL;
 332         spin_lock_irq(&worker->lock);
 333         if (!list_empty(&worker->work_list)) {
 334                 work = list_first_entry(&worker->work_list,
 335                                         struct kthread_work, node);
 336                 list_del_init(&work->node);
 337         }
 338         spin_unlock_irq(&worker->lock);
 339
 340         if (work) {
 341                 __set_current_state(TASK_RUNNING);
 342                 work->func(work);
 343                 smp_wmb();      /* wmb worker-b0 paired with flush-b1 */
 344                 work->done_seq = work->queue_seq;
 345                 smp_mb();       /* mb worker-b1 paired with flush-b0 */
 346                 if (atomic_read(&work->flushing))
 347                         wake_up_all(&work->done);
 348         } else if (!freezing(current))
 349                 schedule();
 350
 351         try_to_freeze();
 352         goto repeat;
 353 }
 354 EXPORT_SYMBOL_GPL(kthread_worker_fn);
 355
 356 /**
 357  * queue_kthread_work - queue a kthread_work
 358  * @worker: target kthread_worker
 359  * @work: kthread_work to queue
 360  *
 361  * Queue @work to work processor @task for async execution.  @task
 362  * must have been created with kthread_worker_create().  Returns %true
 363  * if @work was successfully queued, %false if it was already pending.
 364  */
 365 bool queue_kthread_work(struct kthread_worker *worker,
 366                         struct kthread_work *work)
 367 {
 368         bool ret = false;
 369         unsigned long flags;
 370
 371         spin_lock_irqsave(&worker->lock, flags);
 372         if (list_empty(&work->node)) {
 373                 list_add_tail(&work->node, &worker->work_list);
 374                 work->queue_seq++;
 375                 if (likely(worker->task))
 376                         wake_up_process(worker->task);
 377                 ret = true;
 378         }
 379         spin_unlock_irqrestore(&worker->lock, flags);
 380         return ret;
 381 }
 382 EXPORT_SYMBOL_GPL(queue_kthread_work);
 383
 384 /**
 385  * flush_kthread_work - flush a kthread_work
 386  * @work: work to flush
 387  *
 388  * If @work is queued or executing, wait for it to finish execution.
 389  */
 390 void flush_kthread_work(struct kthread_work *work)
 391 {
 392         int seq = work->queue_seq;
 393
 394         atomic_inc(&work->flushing);
 395
 396         /*
 397          * mb flush-b0 paired with worker-b1, to make sure either
 398          * worker sees the above increment or we see done_seq update.
 399          */
 400         smp_mb__after_atomic_inc();
 401
 402         /* A - B <= 0 tests whether B is in front of A regardless of overflow */
 403         wait_event(work->done, seq - work->done_seq <= 0);
 404         atomic_dec(&work->flushing);
 405
 406         /*
 407          * rmb flush-b1 paired with worker-b0, to make sure our caller
 408          * sees every change made by work->func().
 409          */
 410         smp_mb__after_atomic_dec();
 411 }
 412 EXPORT_SYMBOL_GPL(flush_kthread_work);
 413
 414 struct kthread_flush_work {
 415         struct kthread_work     work;
 416         struct completion       done;
 417 };
 418
 419 static void kthread_flush_work_fn(struct kthread_work *work)
 420 {
 421         struct kthread_flush_work *fwork =
 422                 container_of(work, struct kthread_flush_work, work);
 423         complete(&fwork->done);
 424 }
 425
 426 /**
 427  * flush_kthread_worker - flush all current works on a kthread_worker
 428  * @worker: worker to flush
 429  *
 430  * Wait until all currently executing or pending works on @worker are
 431  * finished.
 432  */
 433 void flush_kthread_worker(struct kthread_worker *worker)
 434 {
 435         struct kthread_flush_work fwork = {
 436                 KTHREAD_WORK_INIT(fwork.work, kthread_flush_work_fn),
 437                 COMPLETION_INITIALIZER_ONSTACK(fwork.done),
 438         };
 439
 440         queue_kthread_work(worker, &fwork.work);
 441         wait_for_completion(&fwork.done);
 442 }
 443 EXPORT_SYMBOL_GPL(flush_kthread_worker);