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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>
/*
* 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 :-). */
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;
task_lock(current);
if (freezing(current)) {
frozen_process();
task_unlock(current);
} else {
task_unlock(current);
return was_frozen;
}
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);
/* prevent accounting of that task to load */
current->flags |= PF_FREEZING;
for (;;) {
set_current_state(TASK_UNINTERRUPTIBLE);
if (!frozen(current) ||
(check_kthr_stop && kthread_should_stop()))
break;
was_frozen = true;
schedule();
}
/* Remove the accounting blocker */
current->flags &= ~PF_FREEZING;
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)
{
/*
* 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);
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