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/* Kernel thread helper functions.
* Copyright (C) 2004 IBM Corporation, Rusty Russell.
*
* Creation is done via keventd, 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 <asm/semaphore.h>

/*
* We dont want to execute off keventd since it might
* hold a semaphore our callers hold too:
*/
static struct workqueue_struct *helper_wq;

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

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

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 DECLARE_MUTEX(kthread_stop_lock);
static struct kthread_stop_info kthread_stop_info;

int kthread_should_stop(void)
{
return (kthread_stop_info.k == current);
}
EXPORT_SYMBOL(kthread_should_stop);

static void kthread_exit_files(void)
{
struct fs_struct *fs;
struct task_struct *tsk = current;

exit_fs(tsk); /* current->fs->count--; */
fs = init_task.fs;
tsk->fs = fs;
atomic_inc(&fs->count);
  exit_files(tsk);
current->files = init_task.files;
atomic_inc(&tsk->files->count);
}

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

kthread_exit_files();

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

/* Block and flush all signals (in case we're not from keventd). */
sigfillset(&blocked);
sigprocmask(SIG_BLOCK, &blocked, NULL);
flush_signals(current);

/* By default we can run anywhere, unlike keventd. */
set_cpus_allowed(current, CPU_MASK_ALL);

/* OK, tell user we're spawned, wait for stop or wakeup */
__set_current_state(TASK_INTERRUPTIBLE);
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;
}

/* We are keventd: create a thread. */
static void keventd_create_kthread(void *_create)
{
struct kthread_create_info *create = _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);
create->result = find_task_by_pid(pid);
}
complete(&create->done);
}

struct task_struct *kthread_create(int (*threadfn)(void *data),
void *data,
const char namefmt[],
...)
{
struct kthread_create_info create;
DECLARE_WORK(work, keventd_create_kthread, &create);

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

/*
* The workqueue needs to start up first:
*/
if (!helper_wq)
work.func(work.data);
else {
queue_work(helper_wq, &work);
wait_for_completion(&create.done);
}
if (!IS_ERR(create.result)) {
va_list args;
va_start(args, namefmt);
vsnprintf(create.result->comm, sizeof(create.result->comm),
namefmt, args);
va_end(args);
}

return create.result;
}
EXPORT_SYMBOL(kthread_create);

void kthread_bind(struct task_struct *k, unsigned int cpu)
{
BUG_ON(k->state != TASK_INTERRUPTIBLE);
/* Must have done schedule() in kthread() before we set_task_cpu */
wait_task_inactive(k);
set_task_cpu(k, cpu);
k->cpus_allowed = cpumask_of_cpu(cpu);
}
EXPORT_SYMBOL(kthread_bind);

int kthread_stop(struct task_struct *k)
{
return kthread_stop_sem(k, NULL);
}
EXPORT_SYMBOL(kthread_stop);

int kthread_stop_sem(struct task_struct *k, struct semaphore *s)
{
int ret;

down(&kthread_stop_lock);

/* It could exit after stop_info.k set, but before wake_up_process. */
get_task_struct(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;
if (s)
up(s);
else
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;
up(&kthread_stop_lock);

return ret;
}
EXPORT_SYMBOL(kthread_stop_sem);

static __init int helper_init(void)
{
helper_wq = create_singlethread_workqueue("kthread");
BUG_ON(!helper_wq);

return 0;
}
core_initcall(helper_init);
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