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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/unistd.h>
#include <linux/file.h>
#include <linux/module.h>
#include <linux/mutex.h>
#include <trace/sched.h>

#define KTHREAD_NICE_LEVEL (-5)

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

DEFINE_TRACE(sched_kthread_stop);
DEFINE_TRACE(sched_kthread_stop_ret);

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

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

struct list_head list;
};

struct kthread_stop_info
{
struct task_struct *k;
int err;
struct completion done;
};

/* Thread stopping is done by setthing this var: lock serializes
* multiple kthread_stop calls. */
static DEFINE_MUTEX(kthread_stop_lock);
static struct kthread_stop_info kthread_stop_info;

/**
* 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 (kthread_stop_info.k == current);
}
EXPORT_SYMBOL(kthread_should_stop);

static int kthread(void *_create)
{
struct kthread_create_info *create = _create;
int (*threadfn)(void *data);
void *data;
int ret = -EINTR;

/* Copy data: it's on kthread's stack */
threadfn = create->threadfn;
data = create->data;

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

if (!kthread_should_stop())
ret = threadfn(data);

/* It might have exited on its own, w/o kthread_stop. Check. */
if (kthread_should_stop()) {
kthread_stop_info.err = ret;
complete(&kthread_stop_info.done);
}
return 0;
}

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

/* 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);
else
wait_for_completion(&create->started);
complete(&create->done);
}

/**
* kthread_create - create a kthread.
* @threadfn: the function to run until signal_pending(current).
* @data: data ptr for @threadfn.
* @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(), kthread_create_on_cpu().
*
* 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 noone 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(int (*threadfn)(void *data),
void *data,
const char namefmt[],
...)
{
struct kthread_create_info create;

create.threadfn = threadfn;
create.data = data;
init_completion(&create.started);
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)) {
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_user_nice(create.result, KTHREAD_NICE_LEVEL);
set_cpus_allowed_ptr(create.result, cpu_all_mask);
}
return create.result;
}
EXPORT_SYMBOL(kthread_create);

/**
* kthread_bind - bind a just-created kthread to a cpu.
* @k: 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 *k, unsigned int cpu)
{
/* Must have done schedule() in kthread() before we set_task_cpu */
if (!wait_task_inactive(k, TASK_UNINTERRUPTIBLE)) {
WARN_ON(1);
return;
}
set_task_cpu(k, cpu);
k->cpus_allowed = cpumask_of_cpu(cpu);
k->rt.nr_cpus_allowed = 1;
k->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. Your threadfn() must not call do_exit()
* itself if you use this function! This can also be called after
* kthread_create() instead of calling wake_up_process(): the thread
* will exit without calling threadfn().
*
* Returns the result of threadfn(), or %-EINTR if wake_up_process()
* was never called.
*/
int kthread_stop(struct task_struct *k)
{
int ret;

mutex_lock(&kthread_stop_lock);

/* It could exit after stop_info.k set, but before wake_up_process. */
get_task_struct(k);

trace_sched_kthread_stop(k);

/* Must init completion *before* thread sees kthread_stop_info.k */
init_completion(&kthread_stop_info.done);
smp_wmb();

/* Now set kthread_should_stop() to true, and wake it up. */
kthread_stop_info.k = k;
wake_up_process(k);
put_task_struct(k);

/* Once it dies, reset stop ptr, gather result and we're done. */
wait_for_completion(&kthread_stop_info.done);
kthread_stop_info.k = NULL;
ret = kthread_stop_info.err;
mutex_unlock(&kthread_stop_lock);

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_user_nice(tsk, KTHREAD_NICE_LEVEL);
set_cpus_allowed_ptr(tsk, cpu_all_mask);

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;
}
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