linux/kernel/freezer.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * 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 */
DEFINE_STATIC_KEY_FALSE(freezer_active);
EXPORT_SYMBOL(…);

/*
 * indicate whether PM freezing is in effect, protected by
 * system_transition_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 freezer_active 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)
{ … }
EXPORT_SYMBOL(…);

bool frozen(struct task_struct *p)
{ … }

/* Refrigerator is place where frozen processes are stored :-). */
bool __refrigerator(bool check_kthr_stop)
{ … }
EXPORT_SYMBOL(…);

static void fake_signal_wake_up(struct task_struct *p)
{ … }

static int __set_task_frozen(struct task_struct *p, void *arg)
{ … }

static bool __freeze_task(struct task_struct *p)
{ … }

/**
 * 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)
{ … }

/*
 * Restore the saved_state before the task entered freezer. For typical task
 * in the __refrigerator(), saved_state == TASK_RUNNING so nothing happens
 * here. For tasks which were TASK_NORMAL | TASK_FREEZABLE, their initial state
 * is restored unless they got an expected wakeup (see ttwu_state_match()).
 * Returns 1 if the task state was restored.
 */
static int __restore_freezer_state(struct task_struct *p, void *arg)
{ … }

void __thaw_task(struct task_struct *p)
{ … }

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