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