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/*
* kernel/freezer.c - Function to freeze a process
*
* Originally from kernel/power/process.c
*/

#include <linux/interrupt.h>
#include <linux/suspend.h>
#include <linux/export.h>
#include <linux/syscalls.h>
#include <linux/freezer.h>
#include <linux/kthread.h>

/* total number of freezing conditions in effect */
atomic_t system_freezing_cnt = ATOMIC_INIT(0);
EXPORT_SYMBOL(system_freezing_cnt);

/* indicate whether PM freezing is in effect, protected by pm_mutex */
bool pm_freezing;
bool pm_nosig_freezing;

/* protects freezing and frozen transitions */
static DEFINE_SPINLOCK(freezer_lock);

/**
* freezing_slow_path - slow path for testing whether a task needs to be frozen
* @p: task to be tested
*
* This function is called by freezing() if system_freezing_cnt isn't zero
* and tests whether @p needs to enter and stay in frozen state. Can be
* called under any context. The freezers are responsible for ensuring the
* target tasks see the updated state.
*/
bool freezing_slow_path(struct task_struct *p)
{
if (p->flags & PF_NOFREEZE)
return false;

if (pm_nosig_freezing || cgroup_freezing(p))
return true;

if (pm_freezing && !(p->flags & PF_KTHREAD))
return true;

return false;
}
EXPORT_SYMBOL(freezing_slow_path);

/* Refrigerator is place where frozen processes are stored :-). */
bool __refrigerator(bool check_kthr_stop)
{
/* Hmm, should we be allowed to suspend when there are realtime
processes around? */
bool was_frozen = false;
long save = current->state;

pr_debug("%s entered refrigerator\n", current->comm);

for (;;) {
set_current_state(TASK_UNINTERRUPTIBLE);

spin_lock_irq(&freezer_lock);
current->flags |= PF_FROZEN;
if (!freezing(current) ||
(check_kthr_stop && kthread_should_stop()))
current->flags &= ~PF_FROZEN;
spin_unlock_irq(&freezer_lock);

if (!(current->flags & PF_FROZEN))
break;
was_frozen = true;
schedule();
}

pr_debug("%s left refrigerator\n", current->comm);

/*
* Restore saved task state before returning. The mb'd version
* needs to be used; otherwise, it might silently break
* synchronization which depends on ordered task state change.
*/
set_current_state(save);

return was_frozen;
}
EXPORT_SYMBOL(__refrigerator);

static void fake_signal_wake_up(struct task_struct *p)
{
unsigned long flags;

if (lock_task_sighand(p, &flags)) {
signal_wake_up(p, 0);
unlock_task_sighand(p, &flags);
}
}

/**
* freeze_task - send a freeze request to given task
* @p: task to send the request to
*
* If @p is freezing, the freeze request is sent either by sending a fake
* signal (if it's not a kernel thread) or waking it up (if it's a kernel
* thread).
*
* RETURNS:
* %false, if @p is not freezing or already frozen; %true, otherwise
*/
bool freeze_task(struct task_struct *p)
{
unsigned long flags;

spin_lock_irqsave(&freezer_lock, flags);
if (!freezing(p) || frozen(p)) {
spin_unlock_irqrestore(&freezer_lock, flags);
return false;
}

if (!(p->flags & PF_KTHREAD)) {
fake_signal_wake_up(p);
/*
* fake_signal_wake_up() goes through p's scheduler
* lock and guarantees that TASK_STOPPED/TRACED ->
* TASK_RUNNING transition can't race with task state
* testing in try_to_freeze_tasks().
*/
} else {
wake_up_state(p, TASK_INTERRUPTIBLE);
}

spin_unlock_irqrestore(&freezer_lock, flags);
return true;
}

void __thaw_task(struct task_struct *p)
{
unsigned long flags;

/*
* Clear freezing and kick @p if FROZEN. Clearing is guaranteed to
* be visible to @p as waking up implies wmb. Waking up inside
* freezer_lock also prevents wakeups from leaking outside
* refrigerator.
*/
spin_lock_irqsave(&freezer_lock, flags);
if (frozen(p))
wake_up_process(p);
spin_unlock_irqrestore(&freezer_lock, flags);
}

/**
* set_freezable - make %current freezable
*
* Mark %current freezable and enter refrigerator if necessary.
*/
bool set_freezable(void)
{
might_sleep();

/*
* Modify flags while holding freezer_lock. This ensures the
* freezer notices that we aren't frozen yet or the freezing
* condition is visible to try_to_freeze() below.
*/
spin_lock_irq(&freezer_lock);
current->flags &= ~PF_NOFREEZE;
spin_unlock_irq(&freezer_lock);

return try_to_freeze();
}
EXPORT_SYMBOL(set_freezable);
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