freezer.c

  1// SPDX-License-Identifier: GPL-2.0-only
  2/*
  3 * kernel/freezer.c - Function to freeze a process
  4 *
  5 * Originally from kernel/power/process.c
  6 */
  7
  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/oom.h>
 14#include <linux/kthread.h>
 15
 16/* total number of freezing conditions in effect */
 17DEFINE_STATIC_KEY_FALSE(freezer_active);
 18EXPORT_SYMBOL(freezer_active);
 19
 20/*
 21 * indicate whether PM freezing is in effect, protected by
 22 * system_transition_mutex
 23 */
 24bool pm_freezing;
 25bool pm_nosig_freezing;
 26
 27/* protects freezing and frozen transitions */
 28static DEFINE_SPINLOCK(freezer_lock);
 29
 30/**
 31 * freezing_slow_path - slow path for testing whether a task needs to be frozen
 32 * @p: task to be tested
 33 *
 34 * This function is called by freezing() if freezer_active isn't zero
 35 * and tests whether @p needs to enter and stay in frozen state.  Can be
 36 * called under any context.  The freezers are responsible for ensuring the
 37 * target tasks see the updated state.
 38 */
 39bool freezing_slow_path(struct task_struct *p)
 40{
 41	if (p->flags & (PF_NOFREEZE | PF_SUSPEND_TASK))
 42		return false;
 43
 44	if (tsk_is_oom_victim(p))
 45		return false;
 46
 47	if (pm_nosig_freezing || cgroup1_freezing(p))
 48		return true;
 49
 50	if (pm_freezing && !(p->flags & PF_KTHREAD))
 51		return true;
 52
 53	return false;
 54}
 55EXPORT_SYMBOL(freezing_slow_path);
 56
 57bool frozen(struct task_struct *p)
 58{
 59	return READ_ONCE(p->__state) & TASK_FROZEN;
 60}
 61
 62/* Refrigerator is place where frozen processes are stored :-). */
 63bool __refrigerator(bool check_kthr_stop)
 64{
 65	unsigned int state = get_current_state();
 66	bool was_frozen = false;
 67
 68	pr_debug("%s entered refrigerator\n", current->comm);
 69
 70	WARN_ON_ONCE(state && !(state & TASK_NORMAL));
 71
 72	for (;;) {
 73		bool freeze;
 74
 75		raw_spin_lock_irq(&current->pi_lock);
 76		WRITE_ONCE(current->__state, TASK_FROZEN);
 77		/* unstale saved_state so that __thaw_task() will wake us up */
 78		current->saved_state = TASK_RUNNING;
 79		raw_spin_unlock_irq(&current->pi_lock);
 80
 81		spin_lock_irq(&freezer_lock);
 82		freeze = freezing(current) && !(check_kthr_stop && kthread_should_stop());
 83		spin_unlock_irq(&freezer_lock);
 84
 85		if (!freeze)
 86			break;
 87
 88		was_frozen = true;
 89		schedule();
 90	}
 91	__set_current_state(TASK_RUNNING);
 92
 93	pr_debug("%s left refrigerator\n", current->comm);
 94
 95	return was_frozen;
 96}
 97EXPORT_SYMBOL(__refrigerator);
 98
 99static void fake_signal_wake_up(struct task_struct *p)
100{
101	unsigned long flags;
102
103	if (lock_task_sighand(p, &flags)) {
104		signal_wake_up(p, 0);
105		unlock_task_sighand(p, &flags);
106	}
107}
108
109static int __set_task_frozen(struct task_struct *p, void *arg)
110{
111	unsigned int state = READ_ONCE(p->__state);
112
113	/*
114	 * Allow freezing the sched_delayed tasks; they will not execute until
115	 * ttwu() fixes them up, so it is safe to swap their state now, instead
116	 * of waiting for them to get fully dequeued.
117	 */
118	if (task_is_runnable(p))
119		return 0;
120
121	if (p != current && task_curr(p))
122		return 0;
123
124	if (!(state & (TASK_FREEZABLE | __TASK_STOPPED | __TASK_TRACED)))
125		return 0;
126
127	/*
128	 * Only TASK_NORMAL can be augmented with TASK_FREEZABLE, since they
129	 * can suffer spurious wakeups.
130	 */
131	if (state & TASK_FREEZABLE)
132		WARN_ON_ONCE(!(state & TASK_NORMAL));
133
134#ifdef CONFIG_LOCKDEP
135	/*
136	 * It's dangerous to freeze with locks held; there be dragons there.
137	 */
138	if (!(state & __TASK_FREEZABLE_UNSAFE))
139		WARN_ON_ONCE(debug_locks && p->lockdep_depth);
140#endif
141
142	p->saved_state = p->__state;
143	WRITE_ONCE(p->__state, TASK_FROZEN);
144	return TASK_FROZEN;
145}
146
147static bool __freeze_task(struct task_struct *p)
148{
149	/* TASK_FREEZABLE|TASK_STOPPED|TASK_TRACED -> TASK_FROZEN */
150	return task_call_func(p, __set_task_frozen, NULL);
151}
152
153/**
154 * freeze_task - send a freeze request to given task
155 * @p: task to send the request to
156 *
157 * If @p is freezing, the freeze request is sent either by sending a fake
158 * signal (if it's not a kernel thread) or waking it up (if it's a kernel
159 * thread).
160 *
161 * RETURNS:
162 * %false, if @p is not freezing or already frozen; %true, otherwise
163 */
164bool freeze_task(struct task_struct *p)
165{
166	unsigned long flags;
167
168	spin_lock_irqsave(&freezer_lock, flags);
169	if (!freezing(p) || frozen(p) || __freeze_task(p)) {
170		spin_unlock_irqrestore(&freezer_lock, flags);
171		return false;
172	}
173
174	if (!(p->flags & PF_KTHREAD))
175		fake_signal_wake_up(p);
176	else
177		wake_up_state(p, TASK_NORMAL);
178
179	spin_unlock_irqrestore(&freezer_lock, flags);
180	return true;
181}
182
183/*
184 * Restore the saved_state before the task entered freezer. For typical task
185 * in the __refrigerator(), saved_state == TASK_RUNNING so nothing happens
186 * here. For tasks which were TASK_NORMAL | TASK_FREEZABLE, their initial state
187 * is restored unless they got an expected wakeup (see ttwu_state_match()).
188 * Returns 1 if the task state was restored.
189 */
190static int __restore_freezer_state(struct task_struct *p, void *arg)
191{
192	unsigned int state = p->saved_state;
193
194	if (state != TASK_RUNNING) {
195		WRITE_ONCE(p->__state, state);
196		p->saved_state = TASK_RUNNING;
197		return 1;
198	}
199
200	return 0;
201}
202
203void __thaw_task(struct task_struct *p)
204{
205	guard(spinlock_irqsave)(&freezer_lock);
206	if (frozen(p) && !task_call_func(p, __restore_freezer_state, NULL))
207		wake_up_state(p, TASK_FROZEN);
208}
209
210/*
211 * thaw_process - Thaw a frozen process
212 * @p: the process to be thawed
213 *
214 * Iterate over all threads of @p and call __thaw_task() on each.
215 */
216void thaw_process(struct task_struct *p)
217{
218	struct task_struct *t;
219
220	rcu_read_lock();
221	for_each_thread(p, t) {
222		__thaw_task(t);
223	}
224	rcu_read_unlock();
225}
226
227/**
228 * set_freezable - make %current freezable
229 *
230 * Mark %current freezable and enter refrigerator if necessary.
231 */
232bool set_freezable(void)
233{
234	might_sleep();
235
236	/*
237	 * Modify flags while holding freezer_lock.  This ensures the
238	 * freezer notices that we aren't frozen yet or the freezing
239	 * condition is visible to try_to_freeze() below.
240	 */
241	spin_lock_irq(&freezer_lock);
242	current->flags &= ~PF_NOFREEZE;
243	spin_unlock_irq(&freezer_lock);
244
245	return try_to_freeze();
246}
247EXPORT_SYMBOL(set_freezable);