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/*
* 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_FREEZER_NOSIG))
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;
/*
* No point in checking freezing() again - the caller already did.
* Proceed to enter FROZEN.
*/
spin_lock_irq(&freezer_lock);
repeat:
current->flags |= PF_FROZEN;
spin_unlock_irq(&freezer_lock);
save = current->state;
pr_debug("%s entered refrigerator\n", current->comm);
spin_lock_irq(¤t->sighand->siglock);
recalc_sigpending(); /* We sent fake signal, clean it up */
spin_unlock_irq(¤t->sighand->siglock);
for (;;) {
set_current_state(TASK_UNINTERRUPTIBLE);
if (!freezing(current) ||
(check_kthr_stop && kthread_should_stop()))
break;
was_frozen = true;
schedule();
}
/* leave FROZEN */
spin_lock_irq(&freezer_lock);
if (freezing(current))
goto repeat;
current->flags &= ~PF_FROZEN;
spin_unlock_irq(&freezer_lock);
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;
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)
{
unsigned long flags;
spin_lock_irqsave(&freezer_lock, flags);
if (!freezing(p) || frozen(p)) {
spin_unlock_irqrestore(&freezer_lock, flags);
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 {
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.
*
* If !FROZEN, @p hasn't reached refrigerator, recalc sigpending to
* avoid leaving dangling TIF_SIGPENDING behind.
*/
spin_lock_irqsave(&freezer_lock, flags);
if (frozen(p)) {
wake_up_process(p);
} else {
spin_lock(&p->sighand->siglock);
recalc_sigpending_and_wake(p);
spin_unlock(&p->sighand->siglock);
}
spin_unlock_irqrestore(&freezer_lock, flags);
}
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