/* * 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);