// 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/oom.h>
#include <linux/kthread.h>

/* total number of freezing conditions in effect */
DEFINE_STATIC_KEY_FALSE(freezer_active);
EXPORT_SYMBOL(freezer_active);

/*
 * 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)
{
        if (p->flags & (PF_NOFREEZE | PF_SUSPEND_TASK))
                return false;

        if (tsk_is_oom_victim(p))
                return false;

        if (pm_nosig_freezing || cgroup1_freezing(p))
                return true;

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

        return false;
}
EXPORT_SYMBOL(freezing_slow_path);

bool frozen(struct task_struct *p)
{
        return READ_ONCE(p->__state) & TASK_FROZEN;
}

/* Refrigerator is place where frozen processes are stored :-). */
bool __refrigerator(bool check_kthr_stop)
{
        unsigned int state = get_current_state();
        bool was_frozen = false;

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

        WARN_ON_ONCE(state && !(state & TASK_NORMAL));

        for (;;) {
                bool freeze;

                raw_spin_lock_irq(&current->pi_lock);
                WRITE_ONCE(current->__state, TASK_FROZEN);
                /* unstale saved_state so that __thaw_task() will wake us up */
                current->saved_state = TASK_RUNNING;
                raw_spin_unlock_irq(&current->pi_lock);

                spin_lock_irq(&freezer_lock);
                freeze = freezing(current) && !(check_kthr_stop && kthread_should_stop());
                spin_unlock_irq(&freezer_lock);

                if (!freeze)
                        break;

                was_frozen = true;
                schedule();
        }
        __set_current_state(TASK_RUNNING);

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

        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);
        }
}

static int __set_task_frozen(struct task_struct *p, void *arg)
{
        unsigned int state = READ_ONCE(p->__state);

        /*
         * Allow freezing the sched_delayed tasks; they will not execute until
         * ttwu() fixes them up, so it is safe to swap their state now, instead
         * of waiting for them to get fully dequeued.
         */
        if (task_is_runnable(p))
                return 0;

        if (p != current && task_curr(p))
                return 0;

        if (!(state & (TASK_FREEZABLE | __TASK_STOPPED | __TASK_TRACED)))
                return 0;

        /*
         * Only TASK_NORMAL can be augmented with TASK_FREEZABLE, since they
         * can suffer spurious wakeups.
         */
        if (state & TASK_FREEZABLE)
                WARN_ON_ONCE(!(state & TASK_NORMAL));

#ifdef CONFIG_LOCKDEP
        /*
         * It's dangerous to freeze with locks held; there be dragons there.
         */
        if (!(state & __TASK_FREEZABLE_UNSAFE))
                WARN_ON_ONCE(debug_locks && p->lockdep_depth);
#endif

        p->saved_state = p->__state;
        WRITE_ONCE(p->__state, TASK_FROZEN);
        return TASK_FROZEN;
}

static bool __freeze_task(struct task_struct *p)
{
        /* TASK_FREEZABLE|TASK_STOPPED|TASK_TRACED -> TASK_FROZEN */
        return task_call_func(p, __set_task_frozen, NULL);
}

/**
 * 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) || __freeze_task(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_NORMAL);

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

/*
 * 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)
{
        unsigned int state = p->saved_state;

        if (state != TASK_RUNNING) {
                WRITE_ONCE(p->__state, state);
                p->saved_state = TASK_RUNNING;
                return 1;
        }

        return 0;
}

void __thaw_task(struct task_struct *p)
{
        guard(spinlock_irqsave)(&freezer_lock);
        if (frozen(p) && !task_call_func(p, __restore_freezer_state, NULL))
                wake_up_state(p, TASK_FROZEN);
}

/*
 * thaw_process - Thaw a frozen process
 * @p: the process to be thawed
 *
 * Iterate over all threads of @p and call __thaw_task() on each.
 */
void thaw_process(struct task_struct *p)
{
        struct task_struct *t;

        rcu_read_lock();
        for_each_thread(p, t) {
                __thaw_task(t);
        }
        rcu_read_unlock();
}

/**
 * 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);