1// SPDX-License-Identifier: GPL-2.0
2/*
3 * drivers/power/process.c - Functions for starting/stopping processes on
4 *                           suspend transitions.
5 *
6 * Originally from swsusp.
7 */
8
9#include <linux/interrupt.h>
10#include <linux/oom.h>
11#include <linux/suspend.h>
12#include <linux/module.h>
13#include <linux/sched/debug.h>
14#include <linux/sched/task.h>
15#include <linux/syscalls.h>
16#include <linux/freezer.h>
17#include <linux/delay.h>
18#include <linux/workqueue.h>
19#include <linux/kmod.h>
20#include <trace/events/power.h>
21#include <linux/cpuset.h>
22
23/*
24 * Timeout for stopping processes
25 */
26unsigned int __read_mostly freeze_timeout_msecs = 20 * MSEC_PER_SEC;
27
28static int try_to_freeze_tasks(bool user_only)
29{
30	const char *what = user_only ? "user space processes" :
31					"remaining freezable tasks";
32	struct task_struct *g, *p;
33	unsigned long end_time;
34	unsigned int todo;
35	bool wq_busy = false;
36	ktime_t start, end, elapsed;
37	unsigned int elapsed_msecs;
38	bool wakeup = false;
39	int sleep_usecs = USEC_PER_MSEC;
40
41	pr_info("Freezing %s\n", what);
42
43	start = ktime_get_boottime();
44
45	end_time = jiffies + msecs_to_jiffies(freeze_timeout_msecs);
46
47	if (!user_only)
48		freeze_workqueues_begin();
49
50	while (true) {
51		todo = 0;
52		read_lock(&tasklist_lock);
53		for_each_process_thread(g, p) {
54			if (p == current || !freeze_task(p))
55				continue;
56
57			todo++;
58		}
59		read_unlock(&tasklist_lock);
60
61		if (!user_only) {
62			wq_busy = freeze_workqueues_busy();
63			todo += wq_busy;
64		}
65
66		if (!todo || time_after(jiffies, end_time))
67			break;
68
69		if (pm_wakeup_pending()) {
70			wakeup = true;
71			break;
72		}
73
74		/*
75		 * We need to retry, but first give the freezing tasks some
76		 * time to enter the refrigerator.  Start with an initial
77		 * 1 ms sleep followed by exponential backoff until 8 ms.
78		 */
79		usleep_range(sleep_usecs / 2, sleep_usecs);
80		if (sleep_usecs < 8 * USEC_PER_MSEC)
81			sleep_usecs *= 2;
82	}
83
84	end = ktime_get_boottime();
85	elapsed = ktime_sub(end, start);
86	elapsed_msecs = ktime_to_ms(elapsed);
87
88	if (todo) {
89		pr_err("Freezing %s %s after %d.%03d seconds "
90		       "(%d tasks refusing to freeze, wq_busy=%d):\n", what,
91		       wakeup ? "aborted" : "failed",
92		       elapsed_msecs / 1000, elapsed_msecs % 1000,
93		       todo - wq_busy, wq_busy);
94
95		if (wq_busy)
96			show_freezable_workqueues();
97
98		if (!wakeup || pm_debug_messages_on) {
99			read_lock(&tasklist_lock);
100			for_each_process_thread(g, p) {
101				if (p != current && freezing(p) && !frozen(p))
102					sched_show_task(p);
103			}
104			read_unlock(&tasklist_lock);
105		}
106	} else {
107		pr_info("Freezing %s completed (elapsed %d.%03d seconds)\n",
108			what, elapsed_msecs / 1000, elapsed_msecs % 1000);
109	}
110
111	return todo ? -EBUSY : 0;
112}
113
114/**
115 * freeze_processes - Signal user space processes to enter the refrigerator.
116 * The current thread will not be frozen.  The same process that calls
117 * freeze_processes must later call thaw_processes.
118 *
119 * On success, returns 0.  On failure, -errno and system is fully thawed.
120 */
121int freeze_processes(void)
122{
123	int error;
124
125	error = __usermodehelper_disable(UMH_FREEZING);
126	if (error)
127		return error;
128
129	/* Make sure this task doesn't get frozen */
130	current->flags |= PF_SUSPEND_TASK;
131
132	if (!pm_freezing)
133		static_branch_inc(&freezer_active);
134
135	pm_wakeup_clear(0);
136	pm_freezing = true;
137	error = try_to_freeze_tasks(true);
138	if (!error)
139		__usermodehelper_set_disable_depth(UMH_DISABLED);
140
141	BUG_ON(in_atomic());
142
143	/*
144	 * Now that the whole userspace is frozen we need to disable
145	 * the OOM killer to disallow any further interference with
146	 * killable tasks. There is no guarantee oom victims will
147	 * ever reach a point they go away we have to wait with a timeout.
148	 */
149	if (!error && !oom_killer_disable(msecs_to_jiffies(freeze_timeout_msecs)))
150		error = -EBUSY;
151
152	if (error)
153		thaw_processes();
154	return error;
155}
156
157/**
158 * freeze_kernel_threads - Make freezable kernel threads go to the refrigerator.
159 *
160 * On success, returns 0.  On failure, -errno and only the kernel threads are
161 * thawed, so as to give a chance to the caller to do additional cleanups
162 * (if any) before thawing the userspace tasks. So, it is the responsibility
163 * of the caller to thaw the userspace tasks, when the time is right.
164 */
165int freeze_kernel_threads(void)
166{
167	int error;
168
169	pm_nosig_freezing = true;
170	error = try_to_freeze_tasks(false);
171
172	BUG_ON(in_atomic());
173
174	if (error)
175		thaw_kernel_threads();
176	return error;
177}
178
179void thaw_processes(void)
180{
181	struct task_struct *g, *p;
182	struct task_struct *curr = current;
183
184	trace_suspend_resume(TPS("thaw_processes"), 0, true);
185	if (pm_freezing)
186		static_branch_dec(&freezer_active);
187	pm_freezing = false;
188	pm_nosig_freezing = false;
189
190	oom_killer_enable();
191
192	pr_info("Restarting tasks ... ");
193
194	__usermodehelper_set_disable_depth(UMH_FREEZING);
195	thaw_workqueues();
196
197	cpuset_wait_for_hotplug();
198
199	read_lock(&tasklist_lock);
200	for_each_process_thread(g, p) {
201		/* No other threads should have PF_SUSPEND_TASK set */
202		WARN_ON((p != curr) && (p->flags & PF_SUSPEND_TASK));
203		__thaw_task(p);
204	}
205	read_unlock(&tasklist_lock);
206
207	WARN_ON(!(curr->flags & PF_SUSPEND_TASK));
208	curr->flags &= ~PF_SUSPEND_TASK;
209
210	usermodehelper_enable();
211
212	schedule();
213	pr_cont("done.\n");
214	trace_suspend_resume(TPS("thaw_processes"), 0, false);
215}
216
217void thaw_kernel_threads(void)
218{
219	struct task_struct *g, *p;
220
221	pm_nosig_freezing = false;
222	pr_info("Restarting kernel threads ... ");
223
224	thaw_workqueues();
225
226	read_lock(&tasklist_lock);
227	for_each_process_thread(g, p) {
228		if (p->flags & PF_KTHREAD)
229			__thaw_task(p);
230	}
231	read_unlock(&tasklist_lock);
232
233	schedule();
234	pr_cont("done.\n");
235}
236