/* * 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> /* * freezing is complete, mark current process as frozen */static inline void frozen_process(void){	if (!unlikely(current->flags & PF_NOFREEZE)) {		current->flags |= PF_FROZEN;		smp_wmb();	}	clear_freeze_flag(current);} /* Refrigerator is place where frozen processes are stored :-). */void refrigerator(void){	/* Hmm, should we be allowed to suspend when there are realtime	   processes around? */	long save; 	task_lock(current);	if (freezing(current)) {		frozen_process();		task_unlock(current);	} else {		task_unlock(current);		return;	}	save = current->state;	pr_debug("%s entered refrigerator\n", current->comm); 	spin_lock_irq(&current->sighand->siglock);	recalc_sigpending(); /* We sent fake signal, clean it up */	spin_unlock_irq(&current->sighand->siglock); 	/* prevent accounting of that task to load */	current->flags |= PF_FREEZING; 	for (;;) {		set_current_state(TASK_UNINTERRUPTIBLE);		if (!frozen(current))			break;		schedule();	} 	/* Remove the accounting blocker */	current->flags &= ~PF_FREEZING; 	pr_debug("%s left refrigerator\n", current->comm);	__set_current_state(save);}EXPORT_SYMBOL(refrigerator); static void fake_signal_wake_up(struct task_struct *p){	unsigned long flags; 	spin_lock_irqsave(&p->sighand->siglock, flags);	signal_wake_up(p, 0);	spin_unlock_irqrestore(&p->sighand->siglock, flags);} /** *	freeze_task - send a freeze request to given task *	@p: task to send the request to *	@sig_only: if set, the request will only be sent if the task has the *		PF_FREEZER_NOSIG flag unset *	Return value: 'false', if @sig_only is set and the task has *		PF_FREEZER_NOSIG set or the task is frozen, 'true', otherwise * *	The freeze request is sent by setting the tasks's TIF_FREEZE flag and *	either sending a fake signal to it or waking it up, depending on whether *	or not it has PF_FREEZER_NOSIG set.  If @sig_only is set and the task *	has PF_FREEZER_NOSIG set (ie. it is a typical kernel thread), its *	TIF_FREEZE flag will not be set. */bool freeze_task(struct task_struct *p, bool sig_only){	/*	 * We first check if the task is freezing and next if it has already	 * been frozen to avoid the race with frozen_process() which first marks	 * the task as frozen and next clears its TIF_FREEZE.	 */	if (!freezing(p)) {		smp_rmb();		if (frozen(p))			return false; 		if (!sig_only || should_send_signal(p))			set_freeze_flag(p);		else			return false;	} 	if (should_send_signal(p)) {		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 if (sig_only) {		return false;	} else {		wake_up_state(p, TASK_INTERRUPTIBLE);	} 	return true;} void cancel_freezing(struct task_struct *p){	unsigned long flags; 	if (freezing(p)) {		pr_debug("  clean up: %s\n", p->comm);		clear_freeze_flag(p);		spin_lock_irqsave(&p->sighand->siglock, flags);		recalc_sigpending_and_wake(p);		spin_unlock_irqrestore(&p->sighand->siglock, flags);	}} static int __thaw_process(struct task_struct *p){	if (frozen(p)) {		p->flags &= ~PF_FROZEN;		return 1;	}	clear_freeze_flag(p);	return 0;} /* * Wake up a frozen process * * task_lock() is needed to prevent the race with refrigerator() which may * occur if the freezing of tasks fails.  Namely, without the lock, if the * freezing of tasks failed, thaw_tasks() might have run before a task in * refrigerator() could call frozen_process(), in which case the task would be * frozen and no one would thaw it. */int thaw_process(struct task_struct *p){	task_lock(p);	if (__thaw_process(p) == 1) {		task_unlock(p);		wake_up_process(p);		return 1;	}	task_unlock(p);	return 0;}EXPORT_SYMBOL(thaw_process);