freezer.c 7.5 KB
Newer Older
Roman Gushchin's avatar
Roman Gushchin committed
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
//SPDX-License-Identifier: GPL-2.0
#include <linux/cgroup.h>
#include <linux/sched.h>
#include <linux/sched/task.h>
#include <linux/sched/signal.h>

#include "cgroup-internal.h"

/*
 * Propagate the cgroup frozen state upwards by the cgroup tree.
 */
static void cgroup_propagate_frozen(struct cgroup *cgrp, bool frozen)
{
	int desc = 1;

	/*
	 * If the new state is frozen, some freezing ancestor cgroups may change
	 * their state too, depending on if all their descendants are frozen.
	 *
	 * Otherwise, all ancestor cgroups are forced into the non-frozen state.
	 */
	while ((cgrp = cgroup_parent(cgrp))) {
		if (frozen) {
			cgrp->freezer.nr_frozen_descendants += desc;
			if (!test_bit(CGRP_FROZEN, &cgrp->flags) &&
			    test_bit(CGRP_FREEZE, &cgrp->flags) &&
			    cgrp->freezer.nr_frozen_descendants ==
			    cgrp->nr_descendants) {
				set_bit(CGRP_FROZEN, &cgrp->flags);
				cgroup_file_notify(&cgrp->events_file);
				desc++;
			}
		} else {
			cgrp->freezer.nr_frozen_descendants -= desc;
			if (test_bit(CGRP_FROZEN, &cgrp->flags)) {
				clear_bit(CGRP_FROZEN, &cgrp->flags);
				cgroup_file_notify(&cgrp->events_file);
				desc++;
			}
		}
	}
}

/*
 * Revisit the cgroup frozen state.
 * Checks if the cgroup is really frozen and perform all state transitions.
 */
void cgroup_update_frozen(struct cgroup *cgrp)
{
	bool frozen;

	lockdep_assert_held(&css_set_lock);

	/*
	 * If the cgroup has to be frozen (CGRP_FREEZE bit set),
	 * and all tasks are frozen and/or stopped, let's consider
	 * the cgroup frozen. Otherwise it's not frozen.
	 */
	frozen = test_bit(CGRP_FREEZE, &cgrp->flags) &&
		cgrp->freezer.nr_frozen_tasks == __cgroup_task_count(cgrp);

	if (frozen) {
		/* Already there? */
		if (test_bit(CGRP_FROZEN, &cgrp->flags))
			return;

		set_bit(CGRP_FROZEN, &cgrp->flags);
	} else {
		/* Already there? */
		if (!test_bit(CGRP_FROZEN, &cgrp->flags))
			return;

		clear_bit(CGRP_FROZEN, &cgrp->flags);
	}
	cgroup_file_notify(&cgrp->events_file);

	/* Update the state of ancestor cgroups. */
	cgroup_propagate_frozen(cgrp, frozen);
}

/*
 * Increment cgroup's nr_frozen_tasks.
 */
static void cgroup_inc_frozen_cnt(struct cgroup *cgrp)
{
	cgrp->freezer.nr_frozen_tasks++;
}

/*
 * Decrement cgroup's nr_frozen_tasks.
 */
static void cgroup_dec_frozen_cnt(struct cgroup *cgrp)
{
	cgrp->freezer.nr_frozen_tasks--;
	WARN_ON_ONCE(cgrp->freezer.nr_frozen_tasks < 0);
}

/*
 * Enter frozen/stopped state, if not yet there. Update cgroup's counters,
 * and revisit the state of the cgroup, if necessary.
 */
void cgroup_enter_frozen(void)
{
	struct cgroup *cgrp;

	if (current->frozen)
		return;

	spin_lock_irq(&css_set_lock);
	current->frozen = true;
	cgrp = task_dfl_cgroup(current);
	cgroup_inc_frozen_cnt(cgrp);
	cgroup_update_frozen(cgrp);
	spin_unlock_irq(&css_set_lock);
}

/*
 * Conditionally leave frozen/stopped state. Update cgroup's counters,
 * and revisit the state of the cgroup, if necessary.
 *
 * If always_leave is not set, and the cgroup is freezing,
 * we're racing with the cgroup freezing. In this case, we don't
 * drop the frozen counter to avoid a transient switch to
 * the unfrozen state.
 */
void cgroup_leave_frozen(bool always_leave)
{
	struct cgroup *cgrp;

	spin_lock_irq(&css_set_lock);
	cgrp = task_dfl_cgroup(current);
	if (always_leave || !test_bit(CGRP_FREEZE, &cgrp->flags)) {
		cgroup_dec_frozen_cnt(cgrp);
		cgroup_update_frozen(cgrp);
		WARN_ON_ONCE(!current->frozen);
		current->frozen = false;
	}
	spin_unlock_irq(&css_set_lock);

	if (unlikely(current->frozen)) {
		/*
		 * If the task remained in the frozen state,
		 * make sure it won't reach userspace without
		 * entering the signal handling loop.
		 */
		spin_lock_irq(&current->sighand->siglock);
		recalc_sigpending();
		spin_unlock_irq(&current->sighand->siglock);
	}
}

/*
 * Freeze or unfreeze the task by setting or clearing the JOBCTL_TRAP_FREEZE
 * jobctl bit.
 */
static void cgroup_freeze_task(struct task_struct *task, bool freeze)
{
	unsigned long flags;

	/* If the task is about to die, don't bother with freezing it. */
	if (!lock_task_sighand(task, &flags))
		return;

	if (freeze) {
		task->jobctl |= JOBCTL_TRAP_FREEZE;
		signal_wake_up(task, false);
	} else {
		task->jobctl &= ~JOBCTL_TRAP_FREEZE;
		wake_up_process(task);
	}

	unlock_task_sighand(task, &flags);
}

/*
 * Freeze or unfreeze all tasks in the given cgroup.
 */
static void cgroup_do_freeze(struct cgroup *cgrp, bool freeze)
{
	struct css_task_iter it;
	struct task_struct *task;

	lockdep_assert_held(&cgroup_mutex);

	spin_lock_irq(&css_set_lock);
	if (freeze)
		set_bit(CGRP_FREEZE, &cgrp->flags);
	else
		clear_bit(CGRP_FREEZE, &cgrp->flags);
	spin_unlock_irq(&css_set_lock);

	css_task_iter_start(&cgrp->self, 0, &it);
	while ((task = css_task_iter_next(&it))) {
		/*
		 * Ignore kernel threads here. Freezing cgroups containing
		 * kthreads isn't supported.
		 */
		if (task->flags & PF_KTHREAD)
			continue;
		cgroup_freeze_task(task, freeze);
	}
	css_task_iter_end(&it);

	/*
	 * Cgroup state should be revisited here to cover empty leaf cgroups
	 * and cgroups which descendants are already in the desired state.
	 */
	spin_lock_irq(&css_set_lock);
	if (cgrp->nr_descendants == cgrp->freezer.nr_frozen_descendants)
		cgroup_update_frozen(cgrp);
	spin_unlock_irq(&css_set_lock);
}

/*
 * Adjust the task state (freeze or unfreeze) and revisit the state of
 * source and destination cgroups.
 */
void cgroup_freezer_migrate_task(struct task_struct *task,
				 struct cgroup *src, struct cgroup *dst)
{
	lockdep_assert_held(&css_set_lock);

	/*
	 * Kernel threads are not supposed to be frozen at all.
	 */
	if (task->flags & PF_KTHREAD)
		return;

	/*
	 * Adjust counters of freezing and frozen tasks.
	 * Note, that if the task is frozen, but the destination cgroup is not
	 * frozen, we bump both counters to keep them balanced.
	 */
	if (task->frozen) {
		cgroup_inc_frozen_cnt(dst);
		cgroup_dec_frozen_cnt(src);
	}
	cgroup_update_frozen(dst);
	cgroup_update_frozen(src);

	/*
	 * Force the task to the desired state.
	 */
	cgroup_freeze_task(task, test_bit(CGRP_FREEZE, &dst->flags));
}

void cgroup_freezer_frozen_exit(struct task_struct *task)
{
	struct cgroup *cgrp = task_dfl_cgroup(task);

	lockdep_assert_held(&css_set_lock);

	cgroup_dec_frozen_cnt(cgrp);
	cgroup_update_frozen(cgrp);
}

void cgroup_freeze(struct cgroup *cgrp, bool freeze)
{
	struct cgroup_subsys_state *css;
	struct cgroup *dsct;
	bool applied = false;

	lockdep_assert_held(&cgroup_mutex);

	/*
	 * Nothing changed? Just exit.
	 */
	if (cgrp->freezer.freeze == freeze)
		return;

	cgrp->freezer.freeze = freeze;

	/*
	 * Propagate changes downwards the cgroup tree.
	 */
	css_for_each_descendant_pre(css, &cgrp->self) {
		dsct = css->cgroup;

		if (cgroup_is_dead(dsct))
			continue;

		if (freeze) {
			dsct->freezer.e_freeze++;
			/*
			 * Already frozen because of ancestor's settings?
			 */
			if (dsct->freezer.e_freeze > 1)
				continue;
		} else {
			dsct->freezer.e_freeze--;
			/*
			 * Still frozen because of ancestor's settings?
			 */
			if (dsct->freezer.e_freeze > 0)
				continue;

			WARN_ON_ONCE(dsct->freezer.e_freeze < 0);
		}

		/*
		 * Do change actual state: freeze or unfreeze.
		 */
		cgroup_do_freeze(dsct, freeze);
		applied = true;
	}

	/*
	 * Even if the actual state hasn't changed, let's notify a user.
	 * The state can be enforced by an ancestor cgroup: the cgroup
	 * can already be in the desired state or it can be locked in the
	 * opposite state, so that the transition will never happen.
	 * In both cases it's better to notify a user, that there is
	 * nothing to wait for.
	 */
	if (!applied)
		cgroup_file_notify(&cgrp->events_file);
}