1 // SPDX-License-Identifier: GPL-2.0-only
3 * kernel/freezer.c - Function to freeze a process
5 * Originally from kernel/power/process.c
8 #include <linux/interrupt.h>
9 #include <linux/suspend.h>
10 #include <linux/export.h>
11 #include <linux/syscalls.h>
12 #include <linux/freezer.h>
13 #include <linux/kthread.h>
15 /* total number of freezing conditions in effect */
16 DEFINE_STATIC_KEY_FALSE(freezer_active);
17 EXPORT_SYMBOL(freezer_active);
20 * indicate whether PM freezing is in effect, protected by
21 * system_transition_mutex
24 bool pm_nosig_freezing;
26 /* protects freezing and frozen transitions */
27 static DEFINE_SPINLOCK(freezer_lock);
30 * freezing_slow_path - slow path for testing whether a task needs to be frozen
31 * @p: task to be tested
33 * This function is called by freezing() if freezer_active isn't zero
34 * and tests whether @p needs to enter and stay in frozen state. Can be
35 * called under any context. The freezers are responsible for ensuring the
36 * target tasks see the updated state.
38 bool freezing_slow_path(struct task_struct *p)
40 if (p->flags & (PF_NOFREEZE | PF_SUSPEND_TASK))
43 if (test_tsk_thread_flag(p, TIF_MEMDIE))
46 if (pm_nosig_freezing || cgroup_freezing(p))
49 if (pm_freezing && !(p->flags & PF_KTHREAD))
54 EXPORT_SYMBOL(freezing_slow_path);
56 bool frozen(struct task_struct *p)
58 return READ_ONCE(p->__state) & TASK_FROZEN;
61 /* Refrigerator is place where frozen processes are stored :-). */
62 bool __refrigerator(bool check_kthr_stop)
64 unsigned int state = get_current_state();
65 bool was_frozen = false;
67 pr_debug("%s entered refrigerator\n", current->comm);
69 WARN_ON_ONCE(state && !(state & TASK_NORMAL));
74 raw_spin_lock_irq(¤t->pi_lock);
75 set_current_state(TASK_FROZEN);
76 /* unstale saved_state so that __thaw_task() will wake us up */
77 current->saved_state = TASK_RUNNING;
78 raw_spin_unlock_irq(¤t->pi_lock);
80 spin_lock_irq(&freezer_lock);
81 freeze = freezing(current) && !(check_kthr_stop && kthread_should_stop());
82 spin_unlock_irq(&freezer_lock);
90 __set_current_state(TASK_RUNNING);
92 pr_debug("%s left refrigerator\n", current->comm);
96 EXPORT_SYMBOL(__refrigerator);
98 static void fake_signal_wake_up(struct task_struct *p)
102 if (lock_task_sighand(p, &flags)) {
103 signal_wake_up(p, 0);
104 unlock_task_sighand(p, &flags);
108 static int __set_task_frozen(struct task_struct *p, void *arg)
110 unsigned int state = READ_ONCE(p->__state);
115 if (p != current && task_curr(p))
118 if (!(state & (TASK_FREEZABLE | __TASK_STOPPED | __TASK_TRACED)))
122 * Only TASK_NORMAL can be augmented with TASK_FREEZABLE, since they
123 * can suffer spurious wakeups.
125 if (state & TASK_FREEZABLE)
126 WARN_ON_ONCE(!(state & TASK_NORMAL));
128 #ifdef CONFIG_LOCKDEP
130 * It's dangerous to freeze with locks held; there be dragons there.
132 if (!(state & __TASK_FREEZABLE_UNSAFE))
133 WARN_ON_ONCE(debug_locks && p->lockdep_depth);
136 p->saved_state = p->__state;
137 WRITE_ONCE(p->__state, TASK_FROZEN);
141 static bool __freeze_task(struct task_struct *p)
143 /* TASK_FREEZABLE|TASK_STOPPED|TASK_TRACED -> TASK_FROZEN */
144 return task_call_func(p, __set_task_frozen, NULL);
148 * freeze_task - send a freeze request to given task
149 * @p: task to send the request to
151 * If @p is freezing, the freeze request is sent either by sending a fake
152 * signal (if it's not a kernel thread) or waking it up (if it's a kernel
156 * %false, if @p is not freezing or already frozen; %true, otherwise
158 bool freeze_task(struct task_struct *p)
162 spin_lock_irqsave(&freezer_lock, flags);
163 if (!freezing(p) || frozen(p) || __freeze_task(p)) {
164 spin_unlock_irqrestore(&freezer_lock, flags);
168 if (!(p->flags & PF_KTHREAD))
169 fake_signal_wake_up(p);
171 wake_up_state(p, TASK_NORMAL);
173 spin_unlock_irqrestore(&freezer_lock, flags);
178 * Restore the saved_state before the task entered freezer. For typical task
179 * in the __refrigerator(), saved_state == TASK_RUNNING so nothing happens
180 * here. For tasks which were TASK_NORMAL | TASK_FREEZABLE, their initial state
181 * is restored unless they got an expected wakeup (see ttwu_state_match()).
182 * Returns 1 if the task state was restored.
184 static int __restore_freezer_state(struct task_struct *p, void *arg)
186 unsigned int state = p->saved_state;
188 if (state != TASK_RUNNING) {
189 WRITE_ONCE(p->__state, state);
196 void __thaw_task(struct task_struct *p)
200 spin_lock_irqsave(&freezer_lock, flags);
201 if (WARN_ON_ONCE(freezing(p)))
204 if (task_call_func(p, __restore_freezer_state, NULL))
207 wake_up_state(p, TASK_FROZEN);
209 spin_unlock_irqrestore(&freezer_lock, flags);
213 * set_freezable - make %current freezable
215 * Mark %current freezable and enter refrigerator if necessary.
217 bool set_freezable(void)
222 * Modify flags while holding freezer_lock. This ensures the
223 * freezer notices that we aren't frozen yet or the freezing
224 * condition is visible to try_to_freeze() below.
226 spin_lock_irq(&freezer_lock);
227 current->flags &= ~PF_NOFREEZE;
228 spin_unlock_irq(&freezer_lock);
230 return try_to_freeze();
232 EXPORT_SYMBOL(set_freezable);