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76f969e8 RG |
1 | //SPDX-License-Identifier: GPL-2.0 |
2 | #include <linux/cgroup.h> | |
3 | #include <linux/sched.h> | |
4 | #include <linux/sched/task.h> | |
5 | #include <linux/sched/signal.h> | |
6 | ||
7 | #include "cgroup-internal.h" | |
8 | ||
4c476d8c RG |
9 | #include <trace/events/cgroup.h> |
10 | ||
76f969e8 RG |
11 | /* |
12 | * Propagate the cgroup frozen state upwards by the cgroup tree. | |
13 | */ | |
14 | static void cgroup_propagate_frozen(struct cgroup *cgrp, bool frozen) | |
15 | { | |
16 | int desc = 1; | |
17 | ||
18 | /* | |
19 | * If the new state is frozen, some freezing ancestor cgroups may change | |
20 | * their state too, depending on if all their descendants are frozen. | |
21 | * | |
22 | * Otherwise, all ancestor cgroups are forced into the non-frozen state. | |
23 | */ | |
24 | while ((cgrp = cgroup_parent(cgrp))) { | |
25 | if (frozen) { | |
26 | cgrp->freezer.nr_frozen_descendants += desc; | |
27 | if (!test_bit(CGRP_FROZEN, &cgrp->flags) && | |
28 | test_bit(CGRP_FREEZE, &cgrp->flags) && | |
29 | cgrp->freezer.nr_frozen_descendants == | |
30 | cgrp->nr_descendants) { | |
31 | set_bit(CGRP_FROZEN, &cgrp->flags); | |
32 | cgroup_file_notify(&cgrp->events_file); | |
4c476d8c | 33 | TRACE_CGROUP_PATH(notify_frozen, cgrp, 1); |
76f969e8 RG |
34 | desc++; |
35 | } | |
36 | } else { | |
37 | cgrp->freezer.nr_frozen_descendants -= desc; | |
38 | if (test_bit(CGRP_FROZEN, &cgrp->flags)) { | |
39 | clear_bit(CGRP_FROZEN, &cgrp->flags); | |
40 | cgroup_file_notify(&cgrp->events_file); | |
4c476d8c | 41 | TRACE_CGROUP_PATH(notify_frozen, cgrp, 0); |
76f969e8 RG |
42 | desc++; |
43 | } | |
44 | } | |
45 | } | |
46 | } | |
47 | ||
48 | /* | |
49 | * Revisit the cgroup frozen state. | |
50 | * Checks if the cgroup is really frozen and perform all state transitions. | |
51 | */ | |
52 | void cgroup_update_frozen(struct cgroup *cgrp) | |
53 | { | |
54 | bool frozen; | |
55 | ||
56 | lockdep_assert_held(&css_set_lock); | |
57 | ||
58 | /* | |
59 | * If the cgroup has to be frozen (CGRP_FREEZE bit set), | |
60 | * and all tasks are frozen and/or stopped, let's consider | |
61 | * the cgroup frozen. Otherwise it's not frozen. | |
62 | */ | |
63 | frozen = test_bit(CGRP_FREEZE, &cgrp->flags) && | |
64 | cgrp->freezer.nr_frozen_tasks == __cgroup_task_count(cgrp); | |
65 | ||
66 | if (frozen) { | |
67 | /* Already there? */ | |
68 | if (test_bit(CGRP_FROZEN, &cgrp->flags)) | |
69 | return; | |
70 | ||
71 | set_bit(CGRP_FROZEN, &cgrp->flags); | |
72 | } else { | |
73 | /* Already there? */ | |
74 | if (!test_bit(CGRP_FROZEN, &cgrp->flags)) | |
75 | return; | |
76 | ||
77 | clear_bit(CGRP_FROZEN, &cgrp->flags); | |
78 | } | |
79 | cgroup_file_notify(&cgrp->events_file); | |
4c476d8c | 80 | TRACE_CGROUP_PATH(notify_frozen, cgrp, frozen); |
76f969e8 RG |
81 | |
82 | /* Update the state of ancestor cgroups. */ | |
83 | cgroup_propagate_frozen(cgrp, frozen); | |
84 | } | |
85 | ||
86 | /* | |
87 | * Increment cgroup's nr_frozen_tasks. | |
88 | */ | |
89 | static void cgroup_inc_frozen_cnt(struct cgroup *cgrp) | |
90 | { | |
91 | cgrp->freezer.nr_frozen_tasks++; | |
92 | } | |
93 | ||
94 | /* | |
95 | * Decrement cgroup's nr_frozen_tasks. | |
96 | */ | |
97 | static void cgroup_dec_frozen_cnt(struct cgroup *cgrp) | |
98 | { | |
99 | cgrp->freezer.nr_frozen_tasks--; | |
100 | WARN_ON_ONCE(cgrp->freezer.nr_frozen_tasks < 0); | |
101 | } | |
102 | ||
103 | /* | |
104 | * Enter frozen/stopped state, if not yet there. Update cgroup's counters, | |
105 | * and revisit the state of the cgroup, if necessary. | |
106 | */ | |
107 | void cgroup_enter_frozen(void) | |
108 | { | |
109 | struct cgroup *cgrp; | |
110 | ||
111 | if (current->frozen) | |
112 | return; | |
113 | ||
114 | spin_lock_irq(&css_set_lock); | |
115 | current->frozen = true; | |
116 | cgrp = task_dfl_cgroup(current); | |
117 | cgroup_inc_frozen_cnt(cgrp); | |
118 | cgroup_update_frozen(cgrp); | |
119 | spin_unlock_irq(&css_set_lock); | |
120 | } | |
121 | ||
122 | /* | |
123 | * Conditionally leave frozen/stopped state. Update cgroup's counters, | |
124 | * and revisit the state of the cgroup, if necessary. | |
125 | * | |
126 | * If always_leave is not set, and the cgroup is freezing, | |
127 | * we're racing with the cgroup freezing. In this case, we don't | |
128 | * drop the frozen counter to avoid a transient switch to | |
129 | * the unfrozen state. | |
130 | */ | |
131 | void cgroup_leave_frozen(bool always_leave) | |
132 | { | |
133 | struct cgroup *cgrp; | |
134 | ||
135 | spin_lock_irq(&css_set_lock); | |
136 | cgrp = task_dfl_cgroup(current); | |
137 | if (always_leave || !test_bit(CGRP_FREEZE, &cgrp->flags)) { | |
138 | cgroup_dec_frozen_cnt(cgrp); | |
139 | cgroup_update_frozen(cgrp); | |
140 | WARN_ON_ONCE(!current->frozen); | |
141 | current->frozen = false; | |
cb2c4cd8 RG |
142 | } else if (!(current->jobctl & JOBCTL_TRAP_FREEZE)) { |
143 | spin_lock(¤t->sighand->siglock); | |
144 | current->jobctl |= JOBCTL_TRAP_FREEZE; | |
145 | set_thread_flag(TIF_SIGPENDING); | |
146 | spin_unlock(¤t->sighand->siglock); | |
76f969e8 RG |
147 | } |
148 | spin_unlock_irq(&css_set_lock); | |
76f969e8 RG |
149 | } |
150 | ||
151 | /* | |
152 | * Freeze or unfreeze the task by setting or clearing the JOBCTL_TRAP_FREEZE | |
153 | * jobctl bit. | |
154 | */ | |
155 | static void cgroup_freeze_task(struct task_struct *task, bool freeze) | |
156 | { | |
157 | unsigned long flags; | |
158 | ||
159 | /* If the task is about to die, don't bother with freezing it. */ | |
160 | if (!lock_task_sighand(task, &flags)) | |
161 | return; | |
162 | ||
163 | if (freeze) { | |
164 | task->jobctl |= JOBCTL_TRAP_FREEZE; | |
165 | signal_wake_up(task, false); | |
166 | } else { | |
167 | task->jobctl &= ~JOBCTL_TRAP_FREEZE; | |
168 | wake_up_process(task); | |
169 | } | |
170 | ||
171 | unlock_task_sighand(task, &flags); | |
172 | } | |
173 | ||
174 | /* | |
175 | * Freeze or unfreeze all tasks in the given cgroup. | |
176 | */ | |
177 | static void cgroup_do_freeze(struct cgroup *cgrp, bool freeze) | |
178 | { | |
179 | struct css_task_iter it; | |
180 | struct task_struct *task; | |
181 | ||
182 | lockdep_assert_held(&cgroup_mutex); | |
183 | ||
184 | spin_lock_irq(&css_set_lock); | |
185 | if (freeze) | |
186 | set_bit(CGRP_FREEZE, &cgrp->flags); | |
187 | else | |
188 | clear_bit(CGRP_FREEZE, &cgrp->flags); | |
189 | spin_unlock_irq(&css_set_lock); | |
190 | ||
4c476d8c RG |
191 | if (freeze) |
192 | TRACE_CGROUP_PATH(freeze, cgrp); | |
193 | else | |
194 | TRACE_CGROUP_PATH(unfreeze, cgrp); | |
195 | ||
76f969e8 RG |
196 | css_task_iter_start(&cgrp->self, 0, &it); |
197 | while ((task = css_task_iter_next(&it))) { | |
198 | /* | |
199 | * Ignore kernel threads here. Freezing cgroups containing | |
200 | * kthreads isn't supported. | |
201 | */ | |
202 | if (task->flags & PF_KTHREAD) | |
203 | continue; | |
204 | cgroup_freeze_task(task, freeze); | |
205 | } | |
206 | css_task_iter_end(&it); | |
207 | ||
208 | /* | |
209 | * Cgroup state should be revisited here to cover empty leaf cgroups | |
210 | * and cgroups which descendants are already in the desired state. | |
211 | */ | |
212 | spin_lock_irq(&css_set_lock); | |
213 | if (cgrp->nr_descendants == cgrp->freezer.nr_frozen_descendants) | |
214 | cgroup_update_frozen(cgrp); | |
215 | spin_unlock_irq(&css_set_lock); | |
216 | } | |
217 | ||
218 | /* | |
219 | * Adjust the task state (freeze or unfreeze) and revisit the state of | |
220 | * source and destination cgroups. | |
221 | */ | |
222 | void cgroup_freezer_migrate_task(struct task_struct *task, | |
223 | struct cgroup *src, struct cgroup *dst) | |
224 | { | |
225 | lockdep_assert_held(&css_set_lock); | |
226 | ||
227 | /* | |
228 | * Kernel threads are not supposed to be frozen at all. | |
229 | */ | |
230 | if (task->flags & PF_KTHREAD) | |
231 | return; | |
232 | ||
742e8cd3 HW |
233 | /* |
234 | * It's not necessary to do changes if both of the src and dst cgroups | |
235 | * are not freezing and task is not frozen. | |
236 | */ | |
237 | if (!test_bit(CGRP_FREEZE, &src->flags) && | |
238 | !test_bit(CGRP_FREEZE, &dst->flags) && | |
239 | !task->frozen) | |
240 | return; | |
241 | ||
76f969e8 RG |
242 | /* |
243 | * Adjust counters of freezing and frozen tasks. | |
244 | * Note, that if the task is frozen, but the destination cgroup is not | |
245 | * frozen, we bump both counters to keep them balanced. | |
246 | */ | |
247 | if (task->frozen) { | |
248 | cgroup_inc_frozen_cnt(dst); | |
249 | cgroup_dec_frozen_cnt(src); | |
250 | } | |
251 | cgroup_update_frozen(dst); | |
252 | cgroup_update_frozen(src); | |
253 | ||
254 | /* | |
255 | * Force the task to the desired state. | |
256 | */ | |
257 | cgroup_freeze_task(task, test_bit(CGRP_FREEZE, &dst->flags)); | |
258 | } | |
259 | ||
76f969e8 RG |
260 | void cgroup_freeze(struct cgroup *cgrp, bool freeze) |
261 | { | |
262 | struct cgroup_subsys_state *css; | |
263 | struct cgroup *dsct; | |
264 | bool applied = false; | |
265 | ||
266 | lockdep_assert_held(&cgroup_mutex); | |
267 | ||
268 | /* | |
269 | * Nothing changed? Just exit. | |
270 | */ | |
271 | if (cgrp->freezer.freeze == freeze) | |
272 | return; | |
273 | ||
274 | cgrp->freezer.freeze = freeze; | |
275 | ||
276 | /* | |
277 | * Propagate changes downwards the cgroup tree. | |
278 | */ | |
279 | css_for_each_descendant_pre(css, &cgrp->self) { | |
280 | dsct = css->cgroup; | |
281 | ||
282 | if (cgroup_is_dead(dsct)) | |
283 | continue; | |
284 | ||
285 | if (freeze) { | |
286 | dsct->freezer.e_freeze++; | |
287 | /* | |
288 | * Already frozen because of ancestor's settings? | |
289 | */ | |
290 | if (dsct->freezer.e_freeze > 1) | |
291 | continue; | |
292 | } else { | |
293 | dsct->freezer.e_freeze--; | |
294 | /* | |
295 | * Still frozen because of ancestor's settings? | |
296 | */ | |
297 | if (dsct->freezer.e_freeze > 0) | |
298 | continue; | |
299 | ||
300 | WARN_ON_ONCE(dsct->freezer.e_freeze < 0); | |
301 | } | |
302 | ||
303 | /* | |
304 | * Do change actual state: freeze or unfreeze. | |
305 | */ | |
306 | cgroup_do_freeze(dsct, freeze); | |
307 | applied = true; | |
308 | } | |
309 | ||
310 | /* | |
311 | * Even if the actual state hasn't changed, let's notify a user. | |
312 | * The state can be enforced by an ancestor cgroup: the cgroup | |
313 | * can already be in the desired state or it can be locked in the | |
314 | * opposite state, so that the transition will never happen. | |
315 | * In both cases it's better to notify a user, that there is | |
316 | * nothing to wait for. | |
317 | */ | |
4c476d8c RG |
318 | if (!applied) { |
319 | TRACE_CGROUP_PATH(notify_frozen, cgrp, | |
320 | test_bit(CGRP_FROZEN, &cgrp->flags)); | |
76f969e8 | 321 | cgroup_file_notify(&cgrp->events_file); |
4c476d8c | 322 | } |
76f969e8 | 323 | } |