1// SPDX-License-Identifier: GPL-2.0-only
   2/* Kernel thread helper functions.
   3 *   Copyright (C) 2004 IBM Corporation, Rusty Russell.
   4 *   Copyright (C) 2009 Red Hat, Inc.
   5 *
   6 * Creation is done via kthreadd, so that we get a clean environment
   7 * even if we're invoked from userspace (think modprobe, hotplug cpu,
   8 * etc.).
   9 */
  10#include <uapi/linux/sched/types.h>
  11#include <linux/mm.h>
  12#include <linux/mmu_context.h>
  13#include <linux/sched.h>
  14#include <linux/sched/mm.h>
  15#include <linux/sched/task.h>
  16#include <linux/kthread.h>
  17#include <linux/completion.h>
  18#include <linux/err.h>
  19#include <linux/cgroup.h>
  20#include <linux/cpuset.h>
  21#include <linux/unistd.h>
  22#include <linux/file.h>
  23#include <linux/export.h>
  24#include <linux/mutex.h>
  25#include <linux/slab.h>
  26#include <linux/freezer.h>
  27#include <linux/ptrace.h>
  28#include <linux/uaccess.h>
  29#include <linux/numa.h>
  30#include <linux/sched/isolation.h>
  31#include <trace/events/sched.h>
  32
  33
  34static DEFINE_SPINLOCK(kthread_create_lock);
  35static LIST_HEAD(kthread_create_list);
  36struct task_struct *kthreadd_task;
  37
  38struct kthread_create_info
  39{
  40	/* Information passed to kthread() from kthreadd. */
  41	int (*threadfn)(void *data);
  42	void *data;
  43	int node;
  44
  45	/* Result passed back to kthread_create() from kthreadd. */
  46	struct task_struct *result;
  47	struct completion *done;
  48
  49	struct list_head list;
  50};
  51
  52struct kthread {
  53	unsigned long flags;
  54	unsigned int cpu;
  55	int result;
  56	int (*threadfn)(void *);
  57	void *data;
 
  58	struct completion parked;
  59	struct completion exited;
  60#ifdef CONFIG_BLK_CGROUP
  61	struct cgroup_subsys_state *blkcg_css;
  62#endif
  63	/* To store the full name if task comm is truncated. */
  64	char *full_name;
  65};
  66
  67enum KTHREAD_BITS {
  68	KTHREAD_IS_PER_CPU = 0,
  69	KTHREAD_SHOULD_STOP,
  70	KTHREAD_SHOULD_PARK,
  71};
  72
  73static inline struct kthread *to_kthread(struct task_struct *k)
  74{
  75	WARN_ON(!(k->flags & PF_KTHREAD));
  76	return k->worker_private;
  77}
  78
  79/*
  80 * Variant of to_kthread() that doesn't assume @p is a kthread.
  81 *
  82 * Per construction; when:
  83 *
  84 *   (p->flags & PF_KTHREAD) && p->worker_private
  85 *
  86 * the task is both a kthread and struct kthread is persistent. However
  87 * PF_KTHREAD on it's own is not, kernel_thread() can exec() (See umh.c and
  88 * begin_new_exec()).
  89 */
  90static inline struct kthread *__to_kthread(struct task_struct *p)
  91{
  92	void *kthread = p->worker_private;
  93	if (kthread && !(p->flags & PF_KTHREAD))
  94		kthread = NULL;
  95	return kthread;
  96}
  97
  98void get_kthread_comm(char *buf, size_t buf_size, struct task_struct *tsk)
  99{
 100	struct kthread *kthread = to_kthread(tsk);
 101
 102	if (!kthread || !kthread->full_name) {
 103		__get_task_comm(buf, buf_size, tsk);
 104		return;
 105	}
 106
 107	strscpy_pad(buf, kthread->full_name, buf_size);
 108}
 109
 110bool set_kthread_struct(struct task_struct *p)
 111{
 112	struct kthread *kthread;
 113
 114	if (WARN_ON_ONCE(to_kthread(p)))
 115		return false;
 116
 117	kthread = kzalloc(sizeof(*kthread), GFP_KERNEL);
 118	if (!kthread)
 119		return false;
 120
 121	init_completion(&kthread->exited);
 122	init_completion(&kthread->parked);
 123	p->vfork_done = &kthread->exited;
 124
 125	p->worker_private = kthread;
 126	return true;
 127}
 128
 129void free_kthread_struct(struct task_struct *k)
 130{
 131	struct kthread *kthread;
 132
 133	/*
 134	 * Can be NULL if kmalloc() in set_kthread_struct() failed.
 
 135	 */
 136	kthread = to_kthread(k);
 137	if (!kthread)
 138		return;
 139
 140#ifdef CONFIG_BLK_CGROUP
 141	WARN_ON_ONCE(kthread->blkcg_css);
 142#endif
 143	k->worker_private = NULL;
 144	kfree(kthread->full_name);
 145	kfree(kthread);
 146}
 147
 148/**
 149 * kthread_should_stop - should this kthread return now?
 150 *
 151 * When someone calls kthread_stop() on your kthread, it will be woken
 152 * and this will return true.  You should then return, and your return
 153 * value will be passed through to kthread_stop().
 154 */
 155bool kthread_should_stop(void)
 156{
 157	return test_bit(KTHREAD_SHOULD_STOP, &to_kthread(current)->flags);
 158}
 159EXPORT_SYMBOL(kthread_should_stop);
 160
 161bool __kthread_should_park(struct task_struct *k)
 162{
 163	return test_bit(KTHREAD_SHOULD_PARK, &to_kthread(k)->flags);
 164}
 165EXPORT_SYMBOL_GPL(__kthread_should_park);
 166
 167/**
 168 * kthread_should_park - should this kthread park now?
 169 *
 170 * When someone calls kthread_park() on your kthread, it will be woken
 171 * and this will return true.  You should then do the necessary
 172 * cleanup and call kthread_parkme()
 173 *
 174 * Similar to kthread_should_stop(), but this keeps the thread alive
 175 * and in a park position. kthread_unpark() "restarts" the thread and
 176 * calls the thread function again.
 177 */
 178bool kthread_should_park(void)
 179{
 180	return __kthread_should_park(current);
 181}
 182EXPORT_SYMBOL_GPL(kthread_should_park);
 183
 184/**
 185 * kthread_freezable_should_stop - should this freezable kthread return now?
 186 * @was_frozen: optional out parameter, indicates whether %current was frozen
 187 *
 188 * kthread_should_stop() for freezable kthreads, which will enter
 189 * refrigerator if necessary.  This function is safe from kthread_stop() /
 190 * freezer deadlock and freezable kthreads should use this function instead
 191 * of calling try_to_freeze() directly.
 192 */
 193bool kthread_freezable_should_stop(bool *was_frozen)
 194{
 195	bool frozen = false;
 196
 197	might_sleep();
 198
 199	if (unlikely(freezing(current)))
 200		frozen = __refrigerator(true);
 201
 202	if (was_frozen)
 203		*was_frozen = frozen;
 204
 205	return kthread_should_stop();
 206}
 207EXPORT_SYMBOL_GPL(kthread_freezable_should_stop);
 208
 209/**
 210 * kthread_func - return the function specified on kthread creation
 211 * @task: kthread task in question
 212 *
 213 * Returns NULL if the task is not a kthread.
 214 */
 215void *kthread_func(struct task_struct *task)
 216{
 217	struct kthread *kthread = __to_kthread(task);
 218	if (kthread)
 219		return kthread->threadfn;
 220	return NULL;
 221}
 222EXPORT_SYMBOL_GPL(kthread_func);
 223
 224/**
 225 * kthread_data - return data value specified on kthread creation
 226 * @task: kthread task in question
 227 *
 228 * Return the data value specified when kthread @task was created.
 229 * The caller is responsible for ensuring the validity of @task when
 230 * calling this function.
 231 */
 232void *kthread_data(struct task_struct *task)
 233{
 234	return to_kthread(task)->data;
 235}
 236EXPORT_SYMBOL_GPL(kthread_data);
 237
 238/**
 239 * kthread_probe_data - speculative version of kthread_data()
 240 * @task: possible kthread task in question
 241 *
 242 * @task could be a kthread task.  Return the data value specified when it
 243 * was created if accessible.  If @task isn't a kthread task or its data is
 244 * inaccessible for any reason, %NULL is returned.  This function requires
 245 * that @task itself is safe to dereference.
 246 */
 247void *kthread_probe_data(struct task_struct *task)
 248{
 249	struct kthread *kthread = __to_kthread(task);
 250	void *data = NULL;
 251
 252	if (kthread)
 253		copy_from_kernel_nofault(&data, &kthread->data, sizeof(data));
 254	return data;
 255}
 256
 257static void __kthread_parkme(struct kthread *self)
 258{
 259	for (;;) {
 260		/*
 261		 * TASK_PARKED is a special state; we must serialize against
 262		 * possible pending wakeups to avoid store-store collisions on
 263		 * task->state.
 264		 *
 265		 * Such a collision might possibly result in the task state
 266		 * changin from TASK_PARKED and us failing the
 267		 * wait_task_inactive() in kthread_park().
 268		 */
 269		set_special_state(TASK_PARKED);
 270		if (!test_bit(KTHREAD_SHOULD_PARK, &self->flags))
 271			break;
 272
 273		/*
 274		 * Thread is going to call schedule(), do not preempt it,
 275		 * or the caller of kthread_park() may spend more time in
 276		 * wait_task_inactive().
 277		 */
 278		preempt_disable();
 279		complete(&self->parked);
 280		schedule_preempt_disabled();
 281		preempt_enable();
 282	}
 283	__set_current_state(TASK_RUNNING);
 284}
 285
 286void kthread_parkme(void)
 287{
 288	__kthread_parkme(to_kthread(current));
 289}
 290EXPORT_SYMBOL_GPL(kthread_parkme);
 291
 292/**
 293 * kthread_exit - Cause the current kthread return @result to kthread_stop().
 294 * @result: The integer value to return to kthread_stop().
 295 *
 296 * While kthread_exit can be called directly, it exists so that
 297 * functions which do some additional work in non-modular code such as
 298 * module_put_and_kthread_exit can be implemented.
 299 *
 300 * Does not return.
 301 */
 302void __noreturn kthread_exit(long result)
 303{
 304	struct kthread *kthread = to_kthread(current);
 305	kthread->result = result;
 306	do_exit(0);
 307}
 308
 309/**
 310 * kthread_complete_and_exit - Exit the current kthread.
 311 * @comp: Completion to complete
 312 * @code: The integer value to return to kthread_stop().
 313 *
 314 * If present complete @comp and the reuturn code to kthread_stop().
 315 *
 316 * A kernel thread whose module may be removed after the completion of
 317 * @comp can use this function exit safely.
 318 *
 319 * Does not return.
 320 */
 321void __noreturn kthread_complete_and_exit(struct completion *comp, long code)
 322{
 323	if (comp)
 324		complete(comp);
 325
 326	kthread_exit(code);
 327}
 328EXPORT_SYMBOL(kthread_complete_and_exit);
 329
 330static int kthread(void *_create)
 331{
 332	static const struct sched_param param = { .sched_priority = 0 };
 333	/* Copy data: it's on kthread's stack */
 334	struct kthread_create_info *create = _create;
 335	int (*threadfn)(void *data) = create->threadfn;
 336	void *data = create->data;
 337	struct completion *done;
 338	struct kthread *self;
 339	int ret;
 340
 
 341	self = to_kthread(current);
 342
 343	/* Release the structure when caller killed by a fatal signal. */
 344	done = xchg(&create->done, NULL);
 345	if (!done) {
 346		kfree(create);
 347		kthread_exit(-EINTR);
 
 
 
 
 
 
 348	}
 349
 350	self->threadfn = threadfn;
 351	self->data = data;
 352
 353	/*
 354	 * The new thread inherited kthreadd's priority and CPU mask. Reset
 355	 * back to default in case they have been changed.
 356	 */
 357	sched_setscheduler_nocheck(current, SCHED_NORMAL, &param);
 358	set_cpus_allowed_ptr(current, housekeeping_cpumask(HK_TYPE_KTHREAD));
 359
 360	/* OK, tell user we're spawned, wait for stop or wakeup */
 361	__set_current_state(TASK_UNINTERRUPTIBLE);
 362	create->result = current;
 363	/*
 364	 * Thread is going to call schedule(), do not preempt it,
 365	 * or the creator may spend more time in wait_task_inactive().
 366	 */
 367	preempt_disable();
 368	complete(done);
 369	schedule_preempt_disabled();
 370	preempt_enable();
 371
 372	ret = -EINTR;
 373	if (!test_bit(KTHREAD_SHOULD_STOP, &self->flags)) {
 374		cgroup_kthread_ready();
 375		__kthread_parkme(self);
 376		ret = threadfn(data);
 377	}
 378	kthread_exit(ret);
 379}
 380
 381/* called from kernel_clone() to get node information for about to be created task */
 382int tsk_fork_get_node(struct task_struct *tsk)
 383{
 384#ifdef CONFIG_NUMA
 385	if (tsk == kthreadd_task)
 386		return tsk->pref_node_fork;
 387#endif
 388	return NUMA_NO_NODE;
 389}
 390
 391static void create_kthread(struct kthread_create_info *create)
 392{
 393	int pid;
 394
 395#ifdef CONFIG_NUMA
 396	current->pref_node_fork = create->node;
 397#endif
 398	/* We want our own signal handler (we take no signals by default). */
 399	pid = kernel_thread(kthread, create, CLONE_FS | CLONE_FILES | SIGCHLD);
 400	if (pid < 0) {
 401		/* Release the structure when caller killed by a fatal signal. */
 402		struct completion *done = xchg(&create->done, NULL);
 403
 404		if (!done) {
 405			kfree(create);
 406			return;
 407		}
 408		create->result = ERR_PTR(pid);
 409		complete(done);
 410	}
 411}
 412
 413static __printf(4, 0)
 414struct task_struct *__kthread_create_on_node(int (*threadfn)(void *data),
 415						    void *data, int node,
 416						    const char namefmt[],
 417						    va_list args)
 418{
 419	DECLARE_COMPLETION_ONSTACK(done);
 420	struct task_struct *task;
 421	struct kthread_create_info *create = kmalloc(sizeof(*create),
 422						     GFP_KERNEL);
 423
 424	if (!create)
 425		return ERR_PTR(-ENOMEM);
 426	create->threadfn = threadfn;
 427	create->data = data;
 428	create->node = node;
 429	create->done = &done;
 430
 431	spin_lock(&kthread_create_lock);
 432	list_add_tail(&create->list, &kthread_create_list);
 433	spin_unlock(&kthread_create_lock);
 434
 435	wake_up_process(kthreadd_task);
 436	/*
 437	 * Wait for completion in killable state, for I might be chosen by
 438	 * the OOM killer while kthreadd is trying to allocate memory for
 439	 * new kernel thread.
 440	 */
 441	if (unlikely(wait_for_completion_killable(&done))) {
 442		/*
 443		 * If I was killed by a fatal signal before kthreadd (or new
 444		 * kernel thread) calls complete(), leave the cleanup of this
 445		 * structure to that thread.
 446		 */
 447		if (xchg(&create->done, NULL))
 448			return ERR_PTR(-EINTR);
 449		/*
 450		 * kthreadd (or new kernel thread) will call complete()
 451		 * shortly.
 452		 */
 453		wait_for_completion(&done);
 454	}
 455	task = create->result;
 456	if (!IS_ERR(task)) {
 
 457		char name[TASK_COMM_LEN];
 458		va_list aq;
 459		int len;
 460
 461		/*
 462		 * task is already visible to other tasks, so updating
 463		 * COMM must be protected.
 464		 */
 465		va_copy(aq, args);
 466		len = vsnprintf(name, sizeof(name), namefmt, aq);
 467		va_end(aq);
 468		if (len >= TASK_COMM_LEN) {
 469			struct kthread *kthread = to_kthread(task);
 470
 471			/* leave it truncated when out of memory. */
 472			kthread->full_name = kvasprintf(GFP_KERNEL, namefmt, args);
 473		}
 474		set_task_comm(task, name);
 
 
 
 
 
 
 
 475	}
 476	kfree(create);
 477	return task;
 478}
 479
 480/**
 481 * kthread_create_on_node - create a kthread.
 482 * @threadfn: the function to run until signal_pending(current).
 483 * @data: data ptr for @threadfn.
 484 * @node: task and thread structures for the thread are allocated on this node
 485 * @namefmt: printf-style name for the thread.
 486 *
 487 * Description: This helper function creates and names a kernel
 488 * thread.  The thread will be stopped: use wake_up_process() to start
 489 * it.  See also kthread_run().  The new thread has SCHED_NORMAL policy and
 490 * is affine to all CPUs.
 491 *
 492 * If thread is going to be bound on a particular cpu, give its node
 493 * in @node, to get NUMA affinity for kthread stack, or else give NUMA_NO_NODE.
 494 * When woken, the thread will run @threadfn() with @data as its
 495 * argument. @threadfn() can either return directly if it is a
 496 * standalone thread for which no one will call kthread_stop(), or
 497 * return when 'kthread_should_stop()' is true (which means
 498 * kthread_stop() has been called).  The return value should be zero
 499 * or a negative error number; it will be passed to kthread_stop().
 500 *
 501 * Returns a task_struct or ERR_PTR(-ENOMEM) or ERR_PTR(-EINTR).
 502 */
 503struct task_struct *kthread_create_on_node(int (*threadfn)(void *data),
 504					   void *data, int node,
 505					   const char namefmt[],
 506					   ...)
 507{
 508	struct task_struct *task;
 509	va_list args;
 510
 511	va_start(args, namefmt);
 512	task = __kthread_create_on_node(threadfn, data, node, namefmt, args);
 513	va_end(args);
 514
 515	return task;
 516}
 517EXPORT_SYMBOL(kthread_create_on_node);
 518
 519static void __kthread_bind_mask(struct task_struct *p, const struct cpumask *mask, unsigned int state)
 520{
 521	unsigned long flags;
 522
 523	if (!wait_task_inactive(p, state)) {
 524		WARN_ON(1);
 525		return;
 526	}
 527
 528	/* It's safe because the task is inactive. */
 529	raw_spin_lock_irqsave(&p->pi_lock, flags);
 530	do_set_cpus_allowed(p, mask);
 531	p->flags |= PF_NO_SETAFFINITY;
 532	raw_spin_unlock_irqrestore(&p->pi_lock, flags);
 533}
 534
 535static void __kthread_bind(struct task_struct *p, unsigned int cpu, unsigned int state)
 536{
 537	__kthread_bind_mask(p, cpumask_of(cpu), state);
 538}
 539
 540void kthread_bind_mask(struct task_struct *p, const struct cpumask *mask)
 541{
 542	__kthread_bind_mask(p, mask, TASK_UNINTERRUPTIBLE);
 543}
 544
 545/**
 546 * kthread_bind - bind a just-created kthread to a cpu.
 547 * @p: thread created by kthread_create().
 548 * @cpu: cpu (might not be online, must be possible) for @k to run on.
 549 *
 550 * Description: This function is equivalent to set_cpus_allowed(),
 551 * except that @cpu doesn't need to be online, and the thread must be
 552 * stopped (i.e., just returned from kthread_create()).
 553 */
 554void kthread_bind(struct task_struct *p, unsigned int cpu)
 555{
 556	__kthread_bind(p, cpu, TASK_UNINTERRUPTIBLE);
 557}
 558EXPORT_SYMBOL(kthread_bind);
 559
 560/**
 561 * kthread_create_on_cpu - Create a cpu bound kthread
 562 * @threadfn: the function to run until signal_pending(current).
 563 * @data: data ptr for @threadfn.
 564 * @cpu: The cpu on which the thread should be bound,
 565 * @namefmt: printf-style name for the thread. Format is restricted
 566 *	     to "name.*%u". Code fills in cpu number.
 567 *
 568 * Description: This helper function creates and names a kernel thread
 569 */
 570struct task_struct *kthread_create_on_cpu(int (*threadfn)(void *data),
 571					  void *data, unsigned int cpu,
 572					  const char *namefmt)
 573{
 574	struct task_struct *p;
 575
 576	p = kthread_create_on_node(threadfn, data, cpu_to_node(cpu), namefmt,
 577				   cpu);
 578	if (IS_ERR(p))
 579		return p;
 580	kthread_bind(p, cpu);
 581	/* CPU hotplug need to bind once again when unparking the thread. */
 582	to_kthread(p)->cpu = cpu;
 583	return p;
 584}
 585EXPORT_SYMBOL(kthread_create_on_cpu);
 586
 587void kthread_set_per_cpu(struct task_struct *k, int cpu)
 588{
 589	struct kthread *kthread = to_kthread(k);
 590	if (!kthread)
 591		return;
 592
 593	WARN_ON_ONCE(!(k->flags & PF_NO_SETAFFINITY));
 594
 595	if (cpu < 0) {
 596		clear_bit(KTHREAD_IS_PER_CPU, &kthread->flags);
 597		return;
 598	}
 599
 600	kthread->cpu = cpu;
 601	set_bit(KTHREAD_IS_PER_CPU, &kthread->flags);
 602}
 603
 604bool kthread_is_per_cpu(struct task_struct *p)
 605{
 606	struct kthread *kthread = __to_kthread(p);
 607	if (!kthread)
 608		return false;
 609
 610	return test_bit(KTHREAD_IS_PER_CPU, &kthread->flags);
 611}
 612
 613/**
 614 * kthread_unpark - unpark a thread created by kthread_create().
 615 * @k:		thread created by kthread_create().
 616 *
 617 * Sets kthread_should_park() for @k to return false, wakes it, and
 618 * waits for it to return. If the thread is marked percpu then its
 619 * bound to the cpu again.
 620 */
 621void kthread_unpark(struct task_struct *k)
 622{
 623	struct kthread *kthread = to_kthread(k);
 624
 625	/*
 626	 * Newly created kthread was parked when the CPU was offline.
 627	 * The binding was lost and we need to set it again.
 628	 */
 629	if (test_bit(KTHREAD_IS_PER_CPU, &kthread->flags))
 630		__kthread_bind(k, kthread->cpu, TASK_PARKED);
 631
 632	clear_bit(KTHREAD_SHOULD_PARK, &kthread->flags);
 633	/*
 634	 * __kthread_parkme() will either see !SHOULD_PARK or get the wakeup.
 635	 */
 636	wake_up_state(k, TASK_PARKED);
 637}
 638EXPORT_SYMBOL_GPL(kthread_unpark);
 639
 640/**
 641 * kthread_park - park a thread created by kthread_create().
 642 * @k: thread created by kthread_create().
 643 *
 644 * Sets kthread_should_park() for @k to return true, wakes it, and
 645 * waits for it to return. This can also be called after kthread_create()
 646 * instead of calling wake_up_process(): the thread will park without
 647 * calling threadfn().
 648 *
 649 * Returns 0 if the thread is parked, -ENOSYS if the thread exited.
 650 * If called by the kthread itself just the park bit is set.
 651 */
 652int kthread_park(struct task_struct *k)
 653{
 654	struct kthread *kthread = to_kthread(k);
 655
 656	if (WARN_ON(k->flags & PF_EXITING))
 657		return -ENOSYS;
 658
 659	if (WARN_ON_ONCE(test_bit(KTHREAD_SHOULD_PARK, &kthread->flags)))
 660		return -EBUSY;
 661
 662	set_bit(KTHREAD_SHOULD_PARK, &kthread->flags);
 663	if (k != current) {
 664		wake_up_process(k);
 665		/*
 666		 * Wait for __kthread_parkme() to complete(), this means we
 667		 * _will_ have TASK_PARKED and are about to call schedule().
 668		 */
 669		wait_for_completion(&kthread->parked);
 670		/*
 671		 * Now wait for that schedule() to complete and the task to
 672		 * get scheduled out.
 673		 */
 674		WARN_ON_ONCE(!wait_task_inactive(k, TASK_PARKED));
 675	}
 676
 677	return 0;
 678}
 679EXPORT_SYMBOL_GPL(kthread_park);
 680
 681/**
 682 * kthread_stop - stop a thread created by kthread_create().
 683 * @k: thread created by kthread_create().
 684 *
 685 * Sets kthread_should_stop() for @k to return true, wakes it, and
 686 * waits for it to exit. This can also be called after kthread_create()
 687 * instead of calling wake_up_process(): the thread will exit without
 688 * calling threadfn().
 689 *
 690 * If threadfn() may call kthread_exit() itself, the caller must ensure
 691 * task_struct can't go away.
 692 *
 693 * Returns the result of threadfn(), or %-EINTR if wake_up_process()
 694 * was never called.
 695 */
 696int kthread_stop(struct task_struct *k)
 697{
 698	struct kthread *kthread;
 699	int ret;
 700
 701	trace_sched_kthread_stop(k);
 702
 703	get_task_struct(k);
 704	kthread = to_kthread(k);
 705	set_bit(KTHREAD_SHOULD_STOP, &kthread->flags);
 706	kthread_unpark(k);
 707	set_tsk_thread_flag(k, TIF_NOTIFY_SIGNAL);
 708	wake_up_process(k);
 709	wait_for_completion(&kthread->exited);
 710	ret = kthread->result;
 711	put_task_struct(k);
 712
 713	trace_sched_kthread_stop_ret(ret);
 714	return ret;
 715}
 716EXPORT_SYMBOL(kthread_stop);
 717
 718int kthreadd(void *unused)
 719{
 720	struct task_struct *tsk = current;
 721
 722	/* Setup a clean context for our children to inherit. */
 723	set_task_comm(tsk, "kthreadd");
 724	ignore_signals(tsk);
 725	set_cpus_allowed_ptr(tsk, housekeeping_cpumask(HK_TYPE_KTHREAD));
 726	set_mems_allowed(node_states[N_MEMORY]);
 727
 728	current->flags |= PF_NOFREEZE;
 729	cgroup_init_kthreadd();
 730
 731	for (;;) {
 732		set_current_state(TASK_INTERRUPTIBLE);
 733		if (list_empty(&kthread_create_list))
 734			schedule();
 735		__set_current_state(TASK_RUNNING);
 736
 737		spin_lock(&kthread_create_lock);
 738		while (!list_empty(&kthread_create_list)) {
 739			struct kthread_create_info *create;
 740
 741			create = list_entry(kthread_create_list.next,
 742					    struct kthread_create_info, list);
 743			list_del_init(&create->list);
 744			spin_unlock(&kthread_create_lock);
 745
 746			create_kthread(create);
 747
 748			spin_lock(&kthread_create_lock);
 749		}
 750		spin_unlock(&kthread_create_lock);
 751	}
 752
 753	return 0;
 754}
 755
 756void __kthread_init_worker(struct kthread_worker *worker,
 757				const char *name,
 758				struct lock_class_key *key)
 759{
 760	memset(worker, 0, sizeof(struct kthread_worker));
 761	raw_spin_lock_init(&worker->lock);
 762	lockdep_set_class_and_name(&worker->lock, key, name);
 763	INIT_LIST_HEAD(&worker->work_list);
 764	INIT_LIST_HEAD(&worker->delayed_work_list);
 765}
 766EXPORT_SYMBOL_GPL(__kthread_init_worker);
 767
 768/**
 769 * kthread_worker_fn - kthread function to process kthread_worker
 770 * @worker_ptr: pointer to initialized kthread_worker
 771 *
 772 * This function implements the main cycle of kthread worker. It processes
 773 * work_list until it is stopped with kthread_stop(). It sleeps when the queue
 774 * is empty.
 775 *
 776 * The works are not allowed to keep any locks, disable preemption or interrupts
 777 * when they finish. There is defined a safe point for freezing when one work
 778 * finishes and before a new one is started.
 779 *
 780 * Also the works must not be handled by more than one worker at the same time,
 781 * see also kthread_queue_work().
 782 */
 783int kthread_worker_fn(void *worker_ptr)
 784{
 785	struct kthread_worker *worker = worker_ptr;
 786	struct kthread_work *work;
 787
 788	/*
 789	 * FIXME: Update the check and remove the assignment when all kthread
 790	 * worker users are created using kthread_create_worker*() functions.
 791	 */
 792	WARN_ON(worker->task && worker->task != current);
 793	worker->task = current;
 794
 795	if (worker->flags & KTW_FREEZABLE)
 796		set_freezable();
 797
 798repeat:
 799	set_current_state(TASK_INTERRUPTIBLE);	/* mb paired w/ kthread_stop */
 800
 801	if (kthread_should_stop()) {
 802		__set_current_state(TASK_RUNNING);
 803		raw_spin_lock_irq(&worker->lock);
 804		worker->task = NULL;
 805		raw_spin_unlock_irq(&worker->lock);
 806		return 0;
 807	}
 808
 809	work = NULL;
 810	raw_spin_lock_irq(&worker->lock);
 811	if (!list_empty(&worker->work_list)) {
 812		work = list_first_entry(&worker->work_list,
 813					struct kthread_work, node);
 814		list_del_init(&work->node);
 815	}
 816	worker->current_work = work;
 817	raw_spin_unlock_irq(&worker->lock);
 818
 819	if (work) {
 820		kthread_work_func_t func = work->func;
 821		__set_current_state(TASK_RUNNING);
 822		trace_sched_kthread_work_execute_start(work);
 823		work->func(work);
 824		/*
 825		 * Avoid dereferencing work after this point.  The trace
 826		 * event only cares about the address.
 827		 */
 828		trace_sched_kthread_work_execute_end(work, func);
 829	} else if (!freezing(current))
 830		schedule();
 831
 832	try_to_freeze();
 833	cond_resched();
 834	goto repeat;
 835}
 836EXPORT_SYMBOL_GPL(kthread_worker_fn);
 837
 838static __printf(3, 0) struct kthread_worker *
 839__kthread_create_worker(int cpu, unsigned int flags,
 840			const char namefmt[], va_list args)
 841{
 842	struct kthread_worker *worker;
 843	struct task_struct *task;
 844	int node = NUMA_NO_NODE;
 845
 846	worker = kzalloc(sizeof(*worker), GFP_KERNEL);
 847	if (!worker)
 848		return ERR_PTR(-ENOMEM);
 849
 850	kthread_init_worker(worker);
 851
 852	if (cpu >= 0)
 853		node = cpu_to_node(cpu);
 854
 855	task = __kthread_create_on_node(kthread_worker_fn, worker,
 856						node, namefmt, args);
 857	if (IS_ERR(task))
 858		goto fail_task;
 859
 860	if (cpu >= 0)
 861		kthread_bind(task, cpu);
 862
 863	worker->flags = flags;
 864	worker->task = task;
 865	wake_up_process(task);
 866	return worker;
 867
 868fail_task:
 869	kfree(worker);
 870	return ERR_CAST(task);
 871}
 872
 873/**
 874 * kthread_create_worker - create a kthread worker
 875 * @flags: flags modifying the default behavior of the worker
 876 * @namefmt: printf-style name for the kthread worker (task).
 877 *
 878 * Returns a pointer to the allocated worker on success, ERR_PTR(-ENOMEM)
 879 * when the needed structures could not get allocated, and ERR_PTR(-EINTR)
 880 * when the caller was killed by a fatal signal.
 881 */
 882struct kthread_worker *
 883kthread_create_worker(unsigned int flags, const char namefmt[], ...)
 884{
 885	struct kthread_worker *worker;
 886	va_list args;
 887
 888	va_start(args, namefmt);
 889	worker = __kthread_create_worker(-1, flags, namefmt, args);
 890	va_end(args);
 891
 892	return worker;
 893}
 894EXPORT_SYMBOL(kthread_create_worker);
 895
 896/**
 897 * kthread_create_worker_on_cpu - create a kthread worker and bind it
 898 *	to a given CPU and the associated NUMA node.
 899 * @cpu: CPU number
 900 * @flags: flags modifying the default behavior of the worker
 901 * @namefmt: printf-style name for the kthread worker (task).
 902 *
 903 * Use a valid CPU number if you want to bind the kthread worker
 904 * to the given CPU and the associated NUMA node.
 905 *
 906 * A good practice is to add the cpu number also into the worker name.
 907 * For example, use kthread_create_worker_on_cpu(cpu, "helper/%d", cpu).
 908 *
 909 * CPU hotplug:
 910 * The kthread worker API is simple and generic. It just provides a way
 911 * to create, use, and destroy workers.
 912 *
 913 * It is up to the API user how to handle CPU hotplug. They have to decide
 914 * how to handle pending work items, prevent queuing new ones, and
 915 * restore the functionality when the CPU goes off and on. There are a
 916 * few catches:
 917 *
 918 *    - CPU affinity gets lost when it is scheduled on an offline CPU.
 919 *
 920 *    - The worker might not exist when the CPU was off when the user
 921 *      created the workers.
 922 *
 923 * Good practice is to implement two CPU hotplug callbacks and to
 924 * destroy/create the worker when the CPU goes down/up.
 925 *
 926 * Return:
 927 * The pointer to the allocated worker on success, ERR_PTR(-ENOMEM)
 928 * when the needed structures could not get allocated, and ERR_PTR(-EINTR)
 929 * when the caller was killed by a fatal signal.
 930 */
 931struct kthread_worker *
 932kthread_create_worker_on_cpu(int cpu, unsigned int flags,
 933			     const char namefmt[], ...)
 934{
 935	struct kthread_worker *worker;
 936	va_list args;
 937
 938	va_start(args, namefmt);
 939	worker = __kthread_create_worker(cpu, flags, namefmt, args);
 940	va_end(args);
 941
 942	return worker;
 943}
 944EXPORT_SYMBOL(kthread_create_worker_on_cpu);
 945
 946/*
 947 * Returns true when the work could not be queued at the moment.
 948 * It happens when it is already pending in a worker list
 949 * or when it is being cancelled.
 950 */
 951static inline bool queuing_blocked(struct kthread_worker *worker,
 952				   struct kthread_work *work)
 953{
 954	lockdep_assert_held(&worker->lock);
 955
 956	return !list_empty(&work->node) || work->canceling;
 957}
 958
 959static void kthread_insert_work_sanity_check(struct kthread_worker *worker,
 960					     struct kthread_work *work)
 961{
 962	lockdep_assert_held(&worker->lock);
 963	WARN_ON_ONCE(!list_empty(&work->node));
 964	/* Do not use a work with >1 worker, see kthread_queue_work() */
 965	WARN_ON_ONCE(work->worker && work->worker != worker);
 966}
 967
 968/* insert @work before @pos in @worker */
 969static void kthread_insert_work(struct kthread_worker *worker,
 970				struct kthread_work *work,
 971				struct list_head *pos)
 972{
 973	kthread_insert_work_sanity_check(worker, work);
 974
 975	trace_sched_kthread_work_queue_work(worker, work);
 976
 977	list_add_tail(&work->node, pos);
 978	work->worker = worker;
 979	if (!worker->current_work && likely(worker->task))
 980		wake_up_process(worker->task);
 981}
 982
 983/**
 984 * kthread_queue_work - queue a kthread_work
 985 * @worker: target kthread_worker
 986 * @work: kthread_work to queue
 987 *
 988 * Queue @work to work processor @task for async execution.  @task
 989 * must have been created with kthread_worker_create().  Returns %true
 990 * if @work was successfully queued, %false if it was already pending.
 991 *
 992 * Reinitialize the work if it needs to be used by another worker.
 993 * For example, when the worker was stopped and started again.
 994 */
 995bool kthread_queue_work(struct kthread_worker *worker,
 996			struct kthread_work *work)
 997{
 998	bool ret = false;
 999	unsigned long flags;
1000
1001	raw_spin_lock_irqsave(&worker->lock, flags);
1002	if (!queuing_blocked(worker, work)) {
1003		kthread_insert_work(worker, work, &worker->work_list);
1004		ret = true;
1005	}
1006	raw_spin_unlock_irqrestore(&worker->lock, flags);
1007	return ret;
1008}
1009EXPORT_SYMBOL_GPL(kthread_queue_work);
1010
1011/**
1012 * kthread_delayed_work_timer_fn - callback that queues the associated kthread
1013 *	delayed work when the timer expires.
1014 * @t: pointer to the expired timer
1015 *
1016 * The format of the function is defined by struct timer_list.
1017 * It should have been called from irqsafe timer with irq already off.
1018 */
1019void kthread_delayed_work_timer_fn(struct timer_list *t)
1020{
1021	struct kthread_delayed_work *dwork = from_timer(dwork, t, timer);
1022	struct kthread_work *work = &dwork->work;
1023	struct kthread_worker *worker = work->worker;
1024	unsigned long flags;
1025
1026	/*
1027	 * This might happen when a pending work is reinitialized.
1028	 * It means that it is used a wrong way.
1029	 */
1030	if (WARN_ON_ONCE(!worker))
1031		return;
1032
1033	raw_spin_lock_irqsave(&worker->lock, flags);
1034	/* Work must not be used with >1 worker, see kthread_queue_work(). */
1035	WARN_ON_ONCE(work->worker != worker);
1036
1037	/* Move the work from worker->delayed_work_list. */
1038	WARN_ON_ONCE(list_empty(&work->node));
1039	list_del_init(&work->node);
1040	if (!work->canceling)
1041		kthread_insert_work(worker, work, &worker->work_list);
1042
1043	raw_spin_unlock_irqrestore(&worker->lock, flags);
1044}
1045EXPORT_SYMBOL(kthread_delayed_work_timer_fn);
1046
1047static void __kthread_queue_delayed_work(struct kthread_worker *worker,
1048					 struct kthread_delayed_work *dwork,
1049					 unsigned long delay)
1050{
1051	struct timer_list *timer = &dwork->timer;
1052	struct kthread_work *work = &dwork->work;
1053
1054	WARN_ON_ONCE(timer->function != kthread_delayed_work_timer_fn);
 
1055
1056	/*
1057	 * If @delay is 0, queue @dwork->work immediately.  This is for
1058	 * both optimization and correctness.  The earliest @timer can
1059	 * expire is on the closest next tick and delayed_work users depend
1060	 * on that there's no such delay when @delay is 0.
1061	 */
1062	if (!delay) {
1063		kthread_insert_work(worker, work, &worker->work_list);
1064		return;
1065	}
1066
1067	/* Be paranoid and try to detect possible races already now. */
1068	kthread_insert_work_sanity_check(worker, work);
1069
1070	list_add(&work->node, &worker->delayed_work_list);
1071	work->worker = worker;
1072	timer->expires = jiffies + delay;
1073	add_timer(timer);
1074}
1075
1076/**
1077 * kthread_queue_delayed_work - queue the associated kthread work
1078 *	after a delay.
1079 * @worker: target kthread_worker
1080 * @dwork: kthread_delayed_work to queue
1081 * @delay: number of jiffies to wait before queuing
1082 *
1083 * If the work has not been pending it starts a timer that will queue
1084 * the work after the given @delay. If @delay is zero, it queues the
1085 * work immediately.
1086 *
1087 * Return: %false if the @work has already been pending. It means that
1088 * either the timer was running or the work was queued. It returns %true
1089 * otherwise.
1090 */
1091bool kthread_queue_delayed_work(struct kthread_worker *worker,
1092				struct kthread_delayed_work *dwork,
1093				unsigned long delay)
1094{
1095	struct kthread_work *work = &dwork->work;
1096	unsigned long flags;
1097	bool ret = false;
1098
1099	raw_spin_lock_irqsave(&worker->lock, flags);
1100
1101	if (!queuing_blocked(worker, work)) {
1102		__kthread_queue_delayed_work(worker, dwork, delay);
1103		ret = true;
1104	}
1105
1106	raw_spin_unlock_irqrestore(&worker->lock, flags);
1107	return ret;
1108}
1109EXPORT_SYMBOL_GPL(kthread_queue_delayed_work);
1110
1111struct kthread_flush_work {
1112	struct kthread_work	work;
1113	struct completion	done;
1114};
1115
1116static void kthread_flush_work_fn(struct kthread_work *work)
1117{
1118	struct kthread_flush_work *fwork =
1119		container_of(work, struct kthread_flush_work, work);
1120	complete(&fwork->done);
1121}
1122
1123/**
1124 * kthread_flush_work - flush a kthread_work
1125 * @work: work to flush
1126 *
1127 * If @work is queued or executing, wait for it to finish execution.
1128 */
1129void kthread_flush_work(struct kthread_work *work)
1130{
1131	struct kthread_flush_work fwork = {
1132		KTHREAD_WORK_INIT(fwork.work, kthread_flush_work_fn),
1133		COMPLETION_INITIALIZER_ONSTACK(fwork.done),
1134	};
1135	struct kthread_worker *worker;
1136	bool noop = false;
1137
1138	worker = work->worker;
1139	if (!worker)
1140		return;
1141
1142	raw_spin_lock_irq(&worker->lock);
1143	/* Work must not be used with >1 worker, see kthread_queue_work(). */
1144	WARN_ON_ONCE(work->worker != worker);
1145
1146	if (!list_empty(&work->node))
1147		kthread_insert_work(worker, &fwork.work, work->node.next);
1148	else if (worker->current_work == work)
1149		kthread_insert_work(worker, &fwork.work,
1150				    worker->work_list.next);
1151	else
1152		noop = true;
1153
1154	raw_spin_unlock_irq(&worker->lock);
1155
1156	if (!noop)
1157		wait_for_completion(&fwork.done);
1158}
1159EXPORT_SYMBOL_GPL(kthread_flush_work);
1160
1161/*
1162 * Make sure that the timer is neither set nor running and could
1163 * not manipulate the work list_head any longer.
1164 *
1165 * The function is called under worker->lock. The lock is temporary
1166 * released but the timer can't be set again in the meantime.
1167 */
1168static void kthread_cancel_delayed_work_timer(struct kthread_work *work,
1169					      unsigned long *flags)
1170{
1171	struct kthread_delayed_work *dwork =
1172		container_of(work, struct kthread_delayed_work, work);
1173	struct kthread_worker *worker = work->worker;
1174
1175	/*
1176	 * del_timer_sync() must be called to make sure that the timer
1177	 * callback is not running. The lock must be temporary released
1178	 * to avoid a deadlock with the callback. In the meantime,
1179	 * any queuing is blocked by setting the canceling counter.
1180	 */
1181	work->canceling++;
1182	raw_spin_unlock_irqrestore(&worker->lock, *flags);
1183	del_timer_sync(&dwork->timer);
1184	raw_spin_lock_irqsave(&worker->lock, *flags);
1185	work->canceling--;
1186}
1187
1188/*
1189 * This function removes the work from the worker queue.
1190 *
1191 * It is called under worker->lock. The caller must make sure that
1192 * the timer used by delayed work is not running, e.g. by calling
1193 * kthread_cancel_delayed_work_timer().
1194 *
1195 * The work might still be in use when this function finishes. See the
1196 * current_work proceed by the worker.
1197 *
1198 * Return: %true if @work was pending and successfully canceled,
1199 *	%false if @work was not pending
1200 */
1201static bool __kthread_cancel_work(struct kthread_work *work)
1202{
1203	/*
1204	 * Try to remove the work from a worker list. It might either
1205	 * be from worker->work_list or from worker->delayed_work_list.
1206	 */
1207	if (!list_empty(&work->node)) {
1208		list_del_init(&work->node);
1209		return true;
1210	}
1211
1212	return false;
1213}
1214
1215/**
1216 * kthread_mod_delayed_work - modify delay of or queue a kthread delayed work
1217 * @worker: kthread worker to use
1218 * @dwork: kthread delayed work to queue
1219 * @delay: number of jiffies to wait before queuing
1220 *
1221 * If @dwork is idle, equivalent to kthread_queue_delayed_work(). Otherwise,
1222 * modify @dwork's timer so that it expires after @delay. If @delay is zero,
1223 * @work is guaranteed to be queued immediately.
1224 *
1225 * Return: %false if @dwork was idle and queued, %true otherwise.
1226 *
1227 * A special case is when the work is being canceled in parallel.
1228 * It might be caused either by the real kthread_cancel_delayed_work_sync()
1229 * or yet another kthread_mod_delayed_work() call. We let the other command
1230 * win and return %true here. The return value can be used for reference
1231 * counting and the number of queued works stays the same. Anyway, the caller
1232 * is supposed to synchronize these operations a reasonable way.
1233 *
1234 * This function is safe to call from any context including IRQ handler.
1235 * See __kthread_cancel_work() and kthread_delayed_work_timer_fn()
1236 * for details.
1237 */
1238bool kthread_mod_delayed_work(struct kthread_worker *worker,
1239			      struct kthread_delayed_work *dwork,
1240			      unsigned long delay)
1241{
1242	struct kthread_work *work = &dwork->work;
1243	unsigned long flags;
1244	int ret;
1245
1246	raw_spin_lock_irqsave(&worker->lock, flags);
1247
1248	/* Do not bother with canceling when never queued. */
1249	if (!work->worker) {
1250		ret = false;
1251		goto fast_queue;
1252	}
1253
1254	/* Work must not be used with >1 worker, see kthread_queue_work() */
1255	WARN_ON_ONCE(work->worker != worker);
1256
1257	/*
1258	 * Temporary cancel the work but do not fight with another command
1259	 * that is canceling the work as well.
1260	 *
1261	 * It is a bit tricky because of possible races with another
1262	 * mod_delayed_work() and cancel_delayed_work() callers.
1263	 *
1264	 * The timer must be canceled first because worker->lock is released
1265	 * when doing so. But the work can be removed from the queue (list)
1266	 * only when it can be queued again so that the return value can
1267	 * be used for reference counting.
1268	 */
1269	kthread_cancel_delayed_work_timer(work, &flags);
1270	if (work->canceling) {
1271		/* The number of works in the queue does not change. */
1272		ret = true;
1273		goto out;
1274	}
1275	ret = __kthread_cancel_work(work);
1276
1277fast_queue:
1278	__kthread_queue_delayed_work(worker, dwork, delay);
1279out:
1280	raw_spin_unlock_irqrestore(&worker->lock, flags);
1281	return ret;
1282}
1283EXPORT_SYMBOL_GPL(kthread_mod_delayed_work);
1284
1285static bool __kthread_cancel_work_sync(struct kthread_work *work, bool is_dwork)
1286{
1287	struct kthread_worker *worker = work->worker;
1288	unsigned long flags;
1289	int ret = false;
1290
1291	if (!worker)
1292		goto out;
1293
1294	raw_spin_lock_irqsave(&worker->lock, flags);
1295	/* Work must not be used with >1 worker, see kthread_queue_work(). */
1296	WARN_ON_ONCE(work->worker != worker);
1297
1298	if (is_dwork)
1299		kthread_cancel_delayed_work_timer(work, &flags);
1300
1301	ret = __kthread_cancel_work(work);
1302
1303	if (worker->current_work != work)
1304		goto out_fast;
1305
1306	/*
1307	 * The work is in progress and we need to wait with the lock released.
1308	 * In the meantime, block any queuing by setting the canceling counter.
1309	 */
1310	work->canceling++;
1311	raw_spin_unlock_irqrestore(&worker->lock, flags);
1312	kthread_flush_work(work);
1313	raw_spin_lock_irqsave(&worker->lock, flags);
1314	work->canceling--;
1315
1316out_fast:
1317	raw_spin_unlock_irqrestore(&worker->lock, flags);
1318out:
1319	return ret;
1320}
1321
1322/**
1323 * kthread_cancel_work_sync - cancel a kthread work and wait for it to finish
1324 * @work: the kthread work to cancel
1325 *
1326 * Cancel @work and wait for its execution to finish.  This function
1327 * can be used even if the work re-queues itself. On return from this
1328 * function, @work is guaranteed to be not pending or executing on any CPU.
1329 *
1330 * kthread_cancel_work_sync(&delayed_work->work) must not be used for
1331 * delayed_work's. Use kthread_cancel_delayed_work_sync() instead.
1332 *
1333 * The caller must ensure that the worker on which @work was last
1334 * queued can't be destroyed before this function returns.
1335 *
1336 * Return: %true if @work was pending, %false otherwise.
1337 */
1338bool kthread_cancel_work_sync(struct kthread_work *work)
1339{
1340	return __kthread_cancel_work_sync(work, false);
1341}
1342EXPORT_SYMBOL_GPL(kthread_cancel_work_sync);
1343
1344/**
1345 * kthread_cancel_delayed_work_sync - cancel a kthread delayed work and
1346 *	wait for it to finish.
1347 * @dwork: the kthread delayed work to cancel
1348 *
1349 * This is kthread_cancel_work_sync() for delayed works.
1350 *
1351 * Return: %true if @dwork was pending, %false otherwise.
1352 */
1353bool kthread_cancel_delayed_work_sync(struct kthread_delayed_work *dwork)
1354{
1355	return __kthread_cancel_work_sync(&dwork->work, true);
1356}
1357EXPORT_SYMBOL_GPL(kthread_cancel_delayed_work_sync);
1358
1359/**
1360 * kthread_flush_worker - flush all current works on a kthread_worker
1361 * @worker: worker to flush
1362 *
1363 * Wait until all currently executing or pending works on @worker are
1364 * finished.
1365 */
1366void kthread_flush_worker(struct kthread_worker *worker)
1367{
1368	struct kthread_flush_work fwork = {
1369		KTHREAD_WORK_INIT(fwork.work, kthread_flush_work_fn),
1370		COMPLETION_INITIALIZER_ONSTACK(fwork.done),
1371	};
1372
1373	kthread_queue_work(worker, &fwork.work);
1374	wait_for_completion(&fwork.done);
1375}
1376EXPORT_SYMBOL_GPL(kthread_flush_worker);
1377
1378/**
1379 * kthread_destroy_worker - destroy a kthread worker
1380 * @worker: worker to be destroyed
1381 *
1382 * Flush and destroy @worker.  The simple flush is enough because the kthread
1383 * worker API is used only in trivial scenarios.  There are no multi-step state
1384 * machines needed.
1385 */
1386void kthread_destroy_worker(struct kthread_worker *worker)
1387{
1388	struct task_struct *task;
1389
1390	task = worker->task;
1391	if (WARN_ON(!task))
1392		return;
1393
1394	kthread_flush_worker(worker);
1395	kthread_stop(task);
1396	WARN_ON(!list_empty(&worker->work_list));
1397	kfree(worker);
1398}
1399EXPORT_SYMBOL(kthread_destroy_worker);
1400
1401/**
1402 * kthread_use_mm - make the calling kthread operate on an address space
1403 * @mm: address space to operate on
1404 */
1405void kthread_use_mm(struct mm_struct *mm)
1406{
1407	struct mm_struct *active_mm;
1408	struct task_struct *tsk = current;
1409
1410	WARN_ON_ONCE(!(tsk->flags & PF_KTHREAD));
1411	WARN_ON_ONCE(tsk->mm);
1412
1413	task_lock(tsk);
1414	/* Hold off tlb flush IPIs while switching mm's */
1415	local_irq_disable();
1416	active_mm = tsk->active_mm;
1417	if (active_mm != mm) {
1418		mmgrab(mm);
1419		tsk->active_mm = mm;
1420	}
1421	tsk->mm = mm;
1422	membarrier_update_current_mm(mm);
1423	switch_mm_irqs_off(active_mm, mm, tsk);
1424	local_irq_enable();
1425	task_unlock(tsk);
1426#ifdef finish_arch_post_lock_switch
1427	finish_arch_post_lock_switch();
1428#endif
1429
1430	/*
1431	 * When a kthread starts operating on an address space, the loop
1432	 * in membarrier_{private,global}_expedited() may not observe
1433	 * that tsk->mm, and not issue an IPI. Membarrier requires a
1434	 * memory barrier after storing to tsk->mm, before accessing
1435	 * user-space memory. A full memory barrier for membarrier
1436	 * {PRIVATE,GLOBAL}_EXPEDITED is implicitly provided by
1437	 * mmdrop(), or explicitly with smp_mb().
1438	 */
1439	if (active_mm != mm)
1440		mmdrop(active_mm);
1441	else
1442		smp_mb();
 
 
1443}
1444EXPORT_SYMBOL_GPL(kthread_use_mm);
1445
1446/**
1447 * kthread_unuse_mm - reverse the effect of kthread_use_mm()
1448 * @mm: address space to operate on
1449 */
1450void kthread_unuse_mm(struct mm_struct *mm)
1451{
1452	struct task_struct *tsk = current;
1453
1454	WARN_ON_ONCE(!(tsk->flags & PF_KTHREAD));
1455	WARN_ON_ONCE(!tsk->mm);
1456
 
 
1457	task_lock(tsk);
1458	/*
1459	 * When a kthread stops operating on an address space, the loop
1460	 * in membarrier_{private,global}_expedited() may not observe
1461	 * that tsk->mm, and not issue an IPI. Membarrier requires a
1462	 * memory barrier after accessing user-space memory, before
1463	 * clearing tsk->mm.
1464	 */
1465	smp_mb__after_spinlock();
1466	sync_mm_rss(mm);
1467	local_irq_disable();
1468	tsk->mm = NULL;
1469	membarrier_update_current_mm(NULL);
1470	/* active_mm is still 'mm' */
1471	enter_lazy_tlb(mm, tsk);
1472	local_irq_enable();
1473	task_unlock(tsk);
1474}
1475EXPORT_SYMBOL_GPL(kthread_unuse_mm);
1476
1477#ifdef CONFIG_BLK_CGROUP
1478/**
1479 * kthread_associate_blkcg - associate blkcg to current kthread
1480 * @css: the cgroup info
1481 *
1482 * Current thread must be a kthread. The thread is running jobs on behalf of
1483 * other threads. In some cases, we expect the jobs attach cgroup info of
1484 * original threads instead of that of current thread. This function stores
1485 * original thread's cgroup info in current kthread context for later
1486 * retrieval.
1487 */
1488void kthread_associate_blkcg(struct cgroup_subsys_state *css)
1489{
1490	struct kthread *kthread;
1491
1492	if (!(current->flags & PF_KTHREAD))
1493		return;
1494	kthread = to_kthread(current);
1495	if (!kthread)
1496		return;
1497
1498	if (kthread->blkcg_css) {
1499		css_put(kthread->blkcg_css);
1500		kthread->blkcg_css = NULL;
1501	}
1502	if (css) {
1503		css_get(css);
1504		kthread->blkcg_css = css;
1505	}
1506}
1507EXPORT_SYMBOL(kthread_associate_blkcg);
1508
1509/**
1510 * kthread_blkcg - get associated blkcg css of current kthread
1511 *
1512 * Current thread must be a kthread.
1513 */
1514struct cgroup_subsys_state *kthread_blkcg(void)
1515{
1516	struct kthread *kthread;
1517
1518	if (current->flags & PF_KTHREAD) {
1519		kthread = to_kthread(current);
1520		if (kthread)
1521			return kthread->blkcg_css;
1522	}
1523	return NULL;
1524}
 
1525#endif