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![Ingo Molnar](/assets/img/avatar_default.png)
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234 lines
5.5 KiB
C
234 lines
5.5 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/*
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* kernel/freezer.c - Function to freeze a process
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*
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* Originally from kernel/power/process.c
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*/
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#include <linux/interrupt.h>
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#include <linux/suspend.h>
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#include <linux/export.h>
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#include <linux/syscalls.h>
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#include <linux/freezer.h>
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#include <linux/kthread.h>
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/* total number of freezing conditions in effect */
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DEFINE_STATIC_KEY_FALSE(freezer_active);
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EXPORT_SYMBOL(freezer_active);
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/*
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* indicate whether PM freezing is in effect, protected by
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* system_transition_mutex
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*/
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bool pm_freezing;
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bool pm_nosig_freezing;
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/* protects freezing and frozen transitions */
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static DEFINE_SPINLOCK(freezer_lock);
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/**
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* freezing_slow_path - slow path for testing whether a task needs to be frozen
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* @p: task to be tested
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*
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* This function is called by freezing() if freezer_active isn't zero
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* and tests whether @p needs to enter and stay in frozen state. Can be
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* called under any context. The freezers are responsible for ensuring the
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* target tasks see the updated state.
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*/
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bool freezing_slow_path(struct task_struct *p)
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{
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if (p->flags & (PF_NOFREEZE | PF_SUSPEND_TASK))
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return false;
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if (test_tsk_thread_flag(p, TIF_MEMDIE))
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return false;
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if (pm_nosig_freezing || cgroup_freezing(p))
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return true;
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if (pm_freezing && !(p->flags & PF_KTHREAD))
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return true;
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return false;
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}
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EXPORT_SYMBOL(freezing_slow_path);
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bool frozen(struct task_struct *p)
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{
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return READ_ONCE(p->__state) & TASK_FROZEN;
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}
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/* Refrigerator is place where frozen processes are stored :-). */
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bool __refrigerator(bool check_kthr_stop)
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{
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unsigned int state = get_current_state();
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bool was_frozen = false;
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pr_debug("%s entered refrigerator\n", current->comm);
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WARN_ON_ONCE(state && !(state & TASK_NORMAL));
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for (;;) {
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bool freeze;
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raw_spin_lock_irq(¤t->pi_lock);
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set_current_state(TASK_FROZEN);
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/* unstale saved_state so that __thaw_task() will wake us up */
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current->saved_state = TASK_RUNNING;
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raw_spin_unlock_irq(¤t->pi_lock);
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spin_lock_irq(&freezer_lock);
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freeze = freezing(current) && !(check_kthr_stop && kthread_should_stop());
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spin_unlock_irq(&freezer_lock);
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if (!freeze)
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break;
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was_frozen = true;
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schedule();
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}
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__set_current_state(TASK_RUNNING);
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pr_debug("%s left refrigerator\n", current->comm);
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return was_frozen;
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}
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EXPORT_SYMBOL(__refrigerator);
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static void fake_signal_wake_up(struct task_struct *p)
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{
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unsigned long flags;
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if (lock_task_sighand(p, &flags)) {
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signal_wake_up(p, 0);
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unlock_task_sighand(p, &flags);
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}
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}
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static int __set_task_frozen(struct task_struct *p, void *arg)
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{
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unsigned int state = READ_ONCE(p->__state);
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if (p->on_rq)
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return 0;
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if (p != current && task_curr(p))
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return 0;
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if (!(state & (TASK_FREEZABLE | __TASK_STOPPED | __TASK_TRACED)))
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return 0;
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/*
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* Only TASK_NORMAL can be augmented with TASK_FREEZABLE, since they
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* can suffer spurious wakeups.
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*/
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if (state & TASK_FREEZABLE)
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WARN_ON_ONCE(!(state & TASK_NORMAL));
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#ifdef CONFIG_LOCKDEP
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/*
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* It's dangerous to freeze with locks held; there be dragons there.
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*/
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if (!(state & __TASK_FREEZABLE_UNSAFE))
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WARN_ON_ONCE(debug_locks && p->lockdep_depth);
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#endif
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p->saved_state = p->__state;
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WRITE_ONCE(p->__state, TASK_FROZEN);
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return TASK_FROZEN;
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}
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static bool __freeze_task(struct task_struct *p)
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{
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/* TASK_FREEZABLE|TASK_STOPPED|TASK_TRACED -> TASK_FROZEN */
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return task_call_func(p, __set_task_frozen, NULL);
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}
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/**
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* freeze_task - send a freeze request to given task
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* @p: task to send the request to
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*
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* If @p is freezing, the freeze request is sent either by sending a fake
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* signal (if it's not a kernel thread) or waking it up (if it's a kernel
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* thread).
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*
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* RETURNS:
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* %false, if @p is not freezing or already frozen; %true, otherwise
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*/
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bool freeze_task(struct task_struct *p)
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{
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unsigned long flags;
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spin_lock_irqsave(&freezer_lock, flags);
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if (!freezing(p) || frozen(p) || __freeze_task(p)) {
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spin_unlock_irqrestore(&freezer_lock, flags);
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return false;
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}
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if (!(p->flags & PF_KTHREAD))
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fake_signal_wake_up(p);
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else
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wake_up_state(p, TASK_NORMAL);
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spin_unlock_irqrestore(&freezer_lock, flags);
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return true;
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}
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/*
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* Restore the saved_state before the task entered freezer. For typical task
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* in the __refrigerator(), saved_state == TASK_RUNNING so nothing happens
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* here. For tasks which were TASK_NORMAL | TASK_FREEZABLE, their initial state
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* is restored unless they got an expected wakeup (see ttwu_state_match()).
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* Returns 1 if the task state was restored.
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*/
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static int __restore_freezer_state(struct task_struct *p, void *arg)
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{
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unsigned int state = p->saved_state;
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if (state != TASK_RUNNING) {
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WRITE_ONCE(p->__state, state);
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p->saved_state = TASK_RUNNING;
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return 1;
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}
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return 0;
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}
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void __thaw_task(struct task_struct *p)
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{
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unsigned long flags;
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spin_lock_irqsave(&freezer_lock, flags);
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if (WARN_ON_ONCE(freezing(p)))
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goto unlock;
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if (!frozen(p) || task_call_func(p, __restore_freezer_state, NULL))
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goto unlock;
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wake_up_state(p, TASK_FROZEN);
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unlock:
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spin_unlock_irqrestore(&freezer_lock, flags);
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}
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/**
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* set_freezable - make %current freezable
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*
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* Mark %current freezable and enter refrigerator if necessary.
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*/
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bool set_freezable(void)
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{
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might_sleep();
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/*
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* Modify flags while holding freezer_lock. This ensures the
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* freezer notices that we aren't frozen yet or the freezing
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* condition is visible to try_to_freeze() below.
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*/
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spin_lock_irq(&freezer_lock);
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current->flags &= ~PF_NOFREEZE;
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spin_unlock_irq(&freezer_lock);
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return try_to_freeze();
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}
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EXPORT_SYMBOL(set_freezable);
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