Release 4.15 kernel/freezer.c

/*
 * 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;

/*
 * Temporary export for the deadlock workaround in ata_scsi_hotplug().
 * Remove once the hack becomes unnecessary.
 */

EXPORT_SYMBOL_GPL(pm_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 | PF_SUSPEND_TASK))
		return false;

	if (test_tsk_thread_flag(p, TIF_MEMDIE))
		return false;

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

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

	return false;
}
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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;
}
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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);
	}
}

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/**
 * 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;

	/*
         * This check can race with freezer_do_not_count, but worst case that
         * will result in an extra wakeup being sent to the task.  It does not
         * race with freezer_count(), the barriers in freezer_count() and
         * freezer_should_skip() ensure that either freezer_count() sees
         * freezing == true in try_to_freeze() and freezes, or
         * freezer_should_skip() sees !PF_FREEZE_SKIP and freezes the task
         * normally.
         */
	if (freezer_should_skip(p))
		return false;

	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);
	else
		wake_up_state(p, TASK_INTERRUPTIBLE);

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

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

	spin_lock_irqsave(&freezer_lock, flags);
	if (frozen(p))
		wake_up_process(p);
	spin_unlock_irqrestore(&freezer_lock, flags);
}

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/**
 * 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();
}
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EXPORT_SYMBOL(set_freezable);
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Directory: kernel

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