xref: /openbmc/linux/kernel/power/process.c (revision 236bdb88)
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  */
26 unsigned int __read_mostly freeze_timeout_msecs = 20 * MSEC_PER_SEC;
27 
28 static 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_all_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  */
121 int 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  */
165 int 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 
179 void 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 
217 void 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