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// 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(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 (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;
}
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(¤t->pi_lock);
set_current_state(TASK_FROZEN);
/* unstale saved_state so that __thaw_task() will wake us up */
current->saved_state = TASK_RUNNING;
raw_spin_unlock_irq(¤t->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);
if (p->on_rq)
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);
return 1;
}
return 0;
}
void __thaw_task(struct task_struct *p)
{
unsigned long flags;
spin_lock_irqsave(&freezer_lock, flags);
if (WARN_ON_ONCE(freezing(p)))
goto unlock;
if (task_call_func(p, __restore_freezer_state, NULL))
goto unlock;
wake_up_state(p, TASK_FROZEN);
unlock:
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);
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