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/* Kernel thread helper functions.
* Copyright (C) 2004 IBM Corporation, Rusty Russell.
*
* Creation is done via kthreadd, so that we get a clean environment
* even if we're invoked from userspace (think modprobe, hotplug cpu,
* etc.).
*/
#include <linux/sched.h>
#include <linux/kthread.h>
#include <linux/completion.h>
#include <linux/err.h>
#include <linux/cpuset.h>
#include <linux/unistd.h>
#include <linux/file.h>
#include <linux/module.h>
#include <linux/mutex.h>
#include <linux/slab.h>
#include <linux/freezer.h>
#include <trace/events/sched.h>

static DEFINE_SPINLOCK(kthread_create_lock);
static LIST_HEAD(kthread_create_list);
struct task_struct *kthreadd_task;

struct kthread_create_info
{
/* Information passed to kthread() from kthreadd. */
int (*threadfn)(void *data);
void *data;
int node;

/* Result passed back to kthread_create() from kthreadd. */
struct task_struct *result;
struct completion done;

struct list_head list;
};

struct kthread {
int should_stop;
void *data;
struct completion exited;
};

#define to_kthread(tsk) \
container_of((tsk)->vfork_done, struct kthread, exited)

/**
* kthread_should_stop - should this kthread return now?
*
* When someone calls kthread_stop() on your kthread, it will be woken
* and this will return true. You should then return, and your return
* value will be passed through to kthread_stop().
*/
int kthread_should_stop(void)
{
return to_kthread(current)->should_stop;
}
EXPORT_SYMBOL(kthread_should_stop);

/**
* kthread_data - return data value specified on kthread creation
* @task: kthread task in question
*
* Return the data value specified when kthread @task was created.
* The caller is responsible for ensuring the validity of @task when
* calling this function.
*/
void *kthread_data(struct task_struct *task)
{
return to_kthread(task)->data;
}

static int kthread(void *_create)
{
/* Copy data: it's on kthread's stack */
struct kthread_create_info *create = _create;
int (*threadfn)(void *data) = create->threadfn;
void *data = create->data;
struct kthread self;
int ret;

self.should_stop = 0;
self.data = data;
init_completion(&self.exited);
current->vfork_done = &self.exited;

/* OK, tell user we're spawned, wait for stop or wakeup */
__set_current_state(TASK_UNINTERRUPTIBLE);
create->result = current;
complete(&create->done);
schedule();

ret = -EINTR;
if (!self.should_stop)
ret = threadfn(data);

/* we can't just return, we must preserve "self" on stack */
do_exit(ret);
}

/* called from do_fork() to get node information for about to be created task */
int tsk_fork_get_node(struct task_struct *tsk)
{
#ifdef CONFIG_NUMA
if (tsk == kthreadd_task)
return tsk->pref_node_fork;
#endif
return numa_node_id();
}

static void create_kthread(struct kthread_create_info *create)
{
int pid;

#ifdef CONFIG_NUMA
current->pref_node_fork = create->node;
#endif
/* We want our own signal handler (we take no signals by default). */
pid = kernel_thread(kthread, create, CLONE_FS | CLONE_FILES | SIGCHLD);
if (pid < 0) {
create->result = ERR_PTR(pid);
complete(&create->done);
}
}

/**
* kthread_create_on_node - create a kthread.
* @threadfn: the function to run until signal_pending(current).
* @data: data ptr for @threadfn.
* @node: memory node number.
* @namefmt: printf-style name for the thread.
*
* Description: This helper function creates and names a kernel
* thread. The thread will be stopped: use wake_up_process() to start
* it. See also kthread_run().
*
* If thread is going to be bound on a particular cpu, give its node
* in @node, to get NUMA affinity for kthread stack, or else give -1.
* When woken, the thread will run @threadfn() with @data as its
* argument. @threadfn() can either call do_exit() directly if it is a
* standalone thread for which no one will call kthread_stop(), or
* return when 'kthread_should_stop()' is true (which means
* kthread_stop() has been called). The return value should be zero
* or a negative error number; it will be passed to kthread_stop().
*
* Returns a task_struct or ERR_PTR(-ENOMEM).
*/
struct task_struct *kthread_create_on_node(int (*threadfn)(void *data),
void *data,
int node,
const char namefmt[],
...)
{
struct kthread_create_info create;

create.threadfn = threadfn;
create.data = data;
create.node = node;
init_completion(&create.done);

spin_lock(&kthread_create_lock);
list_add_tail(&create.list, &kthread_create_list);
spin_unlock(&kthread_create_lock);

wake_up_process(kthreadd_task);
wait_for_completion(&create.done);

if (!IS_ERR(create.result)) {
static const struct sched_param param = { .sched_priority = 0 };
va_list args;

va_start(args, namefmt);
vsnprintf(create.result->comm, sizeof(create.result->comm),
namefmt, args);
va_end(args);
/*
* root may have changed our (kthreadd's) priority or CPU mask.
* The kernel thread should not inherit these properties.
*/
sched_setscheduler_nocheck(create.result, SCHED_NORMAL, &param);
set_cpus_allowed_ptr(create.result, cpu_all_mask);
}
return create.result;
}
EXPORT_SYMBOL(kthread_create_on_node);

/**
* kthread_bind - bind a just-created kthread to a cpu.
* @p: thread created by kthread_create().
* @cpu: cpu (might not be online, must be possible) for @k to run on.
*
* Description: This function is equivalent to set_cpus_allowed(),
* except that @cpu doesn't need to be online, and the thread must be
* stopped (i.e., just returned from kthread_create()).
*/
void kthread_bind(struct task_struct *p, unsigned int cpu)
{
/* Must have done schedule() in kthread() before we set_task_cpu */
if (!wait_task_inactive(p, TASK_UNINTERRUPTIBLE)) {
WARN_ON(1);
return;
}

/* It's safe because the task is inactive. */
do_set_cpus_allowed(p, cpumask_of(cpu));
p->flags |= PF_THREAD_BOUND;
}
EXPORT_SYMBOL(kthread_bind);

/**
* kthread_stop - stop a thread created by kthread_create().
* @k: thread created by kthread_create().
*
* Sets kthread_should_stop() for @k to return true, wakes it, and
* waits for it to exit. This can also be called after kthread_create()
* instead of calling wake_up_process(): the thread will exit without
* calling threadfn().
*
* If threadfn() may call do_exit() itself, the caller must ensure
* task_struct can't go away.
*
* Returns the result of threadfn(), or %-EINTR if wake_up_process()
* was never called.
*/
int kthread_stop(struct task_struct *k)
{
struct kthread *kthread;
int ret;

trace_sched_kthread_stop(k);
get_task_struct(k);

kthread = to_kthread(k);
barrier(); /* it might have exited */
if (k->vfork_done != NULL) {
kthread->should_stop = 1;
wake_up_process(k);
wait_for_completion(&kthread->exited);
}
ret = k->exit_code;

put_task_struct(k);
trace_sched_kthread_stop_ret(ret);

return ret;
}
EXPORT_SYMBOL(kthread_stop);

int kthreadd(void *unused)
{
struct task_struct *tsk = current;

/* Setup a clean context for our children to inherit. */
set_task_comm(tsk, "kthreadd");
ignore_signals(tsk);
set_cpus_allowed_ptr(tsk, cpu_all_mask);
set_mems_allowed(node_states[N_HIGH_MEMORY]);

current->flags |= PF_NOFREEZE | PF_FREEZER_NOSIG;

for (;;) {
set_current_state(TASK_INTERRUPTIBLE);
if (list_empty(&kthread_create_list))
schedule();
__set_current_state(TASK_RUNNING);

spin_lock(&kthread_create_lock);
while (!list_empty(&kthread_create_list)) {
struct kthread_create_info *create;

create = list_entry(kthread_create_list.next,
struct kthread_create_info, list);
list_del_init(&create->list);
spin_unlock(&kthread_create_lock);

create_kthread(create);

spin_lock(&kthread_create_lock);
}
spin_unlock(&kthread_create_lock);
}

return 0;
}

void __init_kthread_worker(struct kthread_worker *worker,
const char *name,
struct lock_class_key *key)
{
spin_lock_init(&worker->lock);
lockdep_set_class_and_name(&worker->lock, key, name);
INIT_LIST_HEAD(&worker->work_list);
worker->task = NULL;
}
EXPORT_SYMBOL_GPL(__init_kthread_worker);

/**
* kthread_worker_fn - kthread function to process kthread_worker
* @worker_ptr: pointer to initialized kthread_worker
*
* This function can be used as @threadfn to kthread_create() or
* kthread_run() with @worker_ptr argument pointing to an initialized
* kthread_worker. The started kthread will process work_list until
* the it is stopped with kthread_stop(). A kthread can also call
* this function directly after extra initialization.
*
* Different kthreads can be used for the same kthread_worker as long
* as there's only one kthread attached to it at any given time. A
* kthread_worker without an attached kthread simply collects queued
* kthread_works.
*/
int kthread_worker_fn(void *worker_ptr)
{
struct kthread_worker *worker = worker_ptr;
struct kthread_work *work;

WARN_ON(worker->task);
worker->task = current;
repeat:
set_current_state(TASK_INTERRUPTIBLE); /* mb paired w/ kthread_stop */

if (kthread_should_stop()) {
__set_current_state(TASK_RUNNING);
spin_lock_irq(&worker->lock);
worker->task = NULL;
spin_unlock_irq(&worker->lock);
return 0;
}

work = NULL;
spin_lock_irq(&worker->lock);
if (!list_empty(&worker->work_list)) {
work = list_first_entry(&worker->work_list,
struct kthread_work, node);
list_del_init(&work->node);
}
spin_unlock_irq(&worker->lock);

if (work) {
__set_current_state(TASK_RUNNING);
work->func(work);
smp_wmb(); /* wmb worker-b0 paired with flush-b1 */
work->done_seq = work->queue_seq;
smp_mb(); /* mb worker-b1 paired with flush-b0 */
if (atomic_read(&work->flushing))
wake_up_all(&work->done);
} else if (!freezing(current))
schedule();

try_to_freeze();
goto repeat;
}
EXPORT_SYMBOL_GPL(kthread_worker_fn);

/**
* queue_kthread_work - queue a kthread_work
* @worker: target kthread_worker
* @work: kthread_work to queue
*
* Queue @work to work processor @task for async execution. @task
* must have been created with kthread_worker_create(). Returns %true
* if @work was successfully queued, %false if it was already pending.
*/
bool queue_kthread_work(struct kthread_worker *worker,
struct kthread_work *work)
{
bool ret = false;
unsigned long flags;

spin_lock_irqsave(&worker->lock, flags);
if (list_empty(&work->node)) {
list_add_tail(&work->node, &worker->work_list);
work->queue_seq++;
if (likely(worker->task))
wake_up_process(worker->task);
ret = true;
}
spin_unlock_irqrestore(&worker->lock, flags);
return ret;
}
EXPORT_SYMBOL_GPL(queue_kthread_work);

/**
* flush_kthread_work - flush a kthread_work
* @work: work to flush
*
* If @work is queued or executing, wait for it to finish execution.
*/
void flush_kthread_work(struct kthread_work *work)
{
int seq = work->queue_seq;

atomic_inc(&work->flushing);

/*
* mb flush-b0 paired with worker-b1, to make sure either
* worker sees the above increment or we see done_seq update.
*/
smp_mb__after_atomic_inc();

/* A - B <= 0 tests whether B is in front of A regardless of overflow */
wait_event(work->done, seq - work->done_seq <= 0);
atomic_dec(&work->flushing);

/*
* rmb flush-b1 paired with worker-b0, to make sure our caller
* sees every change made by work->func().
*/
smp_mb__after_atomic_dec();
}
EXPORT_SYMBOL_GPL(flush_kthread_work);

struct kthread_flush_work {
struct kthread_work work;
struct completion done;
};

static void kthread_flush_work_fn(struct kthread_work *work)
{
struct kthread_flush_work *fwork =
container_of(work, struct kthread_flush_work, work);
complete(&fwork->done);
}

/**
* flush_kthread_worker - flush all current works on a kthread_worker
* @worker: worker to flush
*
* Wait until all currently executing or pending works on @worker are
* finished.
*/
void flush_kthread_worker(struct kthread_worker *worker)
{
struct kthread_flush_work fwork = {
KTHREAD_WORK_INIT(fwork.work, kthread_flush_work_fn),
COMPLETION_INITIALIZER_ONSTACK(fwork.done),
};

queue_kthread_work(worker, &fwork.work);
wait_for_completion(&fwork.done);
}
EXPORT_SYMBOL_GPL(flush_kthread_worker);
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