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31#include <linux/kernel.h>
32#include <linux/threads.h>
33#include <linux/atomic.h>
34#include <linux/cgroup.h>
35#include <linux/slab.h>
36#include <linux/sched/task.h>
37
38#define PIDS_MAX (PID_MAX_LIMIT + 1ULL)
39#define PIDS_MAX_STR "max"
40
41struct pids_cgroup {
42 struct cgroup_subsys_state css;
43
44
45
46
47
48 atomic64_t counter;
49 atomic64_t limit;
50
51
52 struct cgroup_file events_file;
53
54
55 atomic64_t events_limit;
56};
57
58static struct pids_cgroup *css_pids(struct cgroup_subsys_state *css)
59{
60 return container_of(css, struct pids_cgroup, css);
61}
62
63static struct pids_cgroup *parent_pids(struct pids_cgroup *pids)
64{
65 return css_pids(pids->css.parent);
66}
67
68static struct cgroup_subsys_state *
69pids_css_alloc(struct cgroup_subsys_state *parent)
70{
71 struct pids_cgroup *pids;
72
73 pids = kzalloc(sizeof(struct pids_cgroup), GFP_KERNEL);
74 if (!pids)
75 return ERR_PTR(-ENOMEM);
76
77 atomic64_set(&pids->counter, 0);
78 atomic64_set(&pids->limit, PIDS_MAX);
79 atomic64_set(&pids->events_limit, 0);
80 return &pids->css;
81}
82
83static void pids_css_free(struct cgroup_subsys_state *css)
84{
85 kfree(css_pids(css));
86}
87
88
89
90
91
92
93
94
95
96static void pids_cancel(struct pids_cgroup *pids, int num)
97{
98
99
100
101
102 WARN_ON_ONCE(atomic64_add_negative(-num, &pids->counter));
103}
104
105
106
107
108
109
110static void pids_uncharge(struct pids_cgroup *pids, int num)
111{
112 struct pids_cgroup *p;
113
114 for (p = pids; parent_pids(p); p = parent_pids(p))
115 pids_cancel(p, num);
116}
117
118
119
120
121
122
123
124
125
126
127static void pids_charge(struct pids_cgroup *pids, int num)
128{
129 struct pids_cgroup *p;
130
131 for (p = pids; parent_pids(p); p = parent_pids(p))
132 atomic64_add(num, &p->counter);
133}
134
135
136
137
138
139
140
141
142
143
144static int pids_try_charge(struct pids_cgroup *pids, int num)
145{
146 struct pids_cgroup *p, *q;
147
148 for (p = pids; parent_pids(p); p = parent_pids(p)) {
149 int64_t new = atomic64_add_return(num, &p->counter);
150 int64_t limit = atomic64_read(&p->limit);
151
152
153
154
155
156
157 if (new > limit)
158 goto revert;
159 }
160
161 return 0;
162
163revert:
164 for (q = pids; q != p; q = parent_pids(q))
165 pids_cancel(q, num);
166 pids_cancel(p, num);
167
168 return -EAGAIN;
169}
170
171static int pids_can_attach(struct cgroup_taskset *tset)
172{
173 struct task_struct *task;
174 struct cgroup_subsys_state *dst_css;
175
176 cgroup_taskset_for_each(task, dst_css, tset) {
177 struct pids_cgroup *pids = css_pids(dst_css);
178 struct cgroup_subsys_state *old_css;
179 struct pids_cgroup *old_pids;
180
181
182
183
184
185
186 old_css = task_css(task, pids_cgrp_id);
187 old_pids = css_pids(old_css);
188
189 pids_charge(pids, 1);
190 pids_uncharge(old_pids, 1);
191 }
192
193 return 0;
194}
195
196static void pids_cancel_attach(struct cgroup_taskset *tset)
197{
198 struct task_struct *task;
199 struct cgroup_subsys_state *dst_css;
200
201 cgroup_taskset_for_each(task, dst_css, tset) {
202 struct pids_cgroup *pids = css_pids(dst_css);
203 struct cgroup_subsys_state *old_css;
204 struct pids_cgroup *old_pids;
205
206 old_css = task_css(task, pids_cgrp_id);
207 old_pids = css_pids(old_css);
208
209 pids_charge(old_pids, 1);
210 pids_uncharge(pids, 1);
211 }
212}
213
214
215
216
217
218static int pids_can_fork(struct task_struct *task, struct css_set *cset)
219{
220 struct cgroup_subsys_state *css;
221 struct pids_cgroup *pids;
222 int err;
223
224 if (cset)
225 css = cset->subsys[pids_cgrp_id];
226 else
227 css = task_css_check(current, pids_cgrp_id, true);
228 pids = css_pids(css);
229 err = pids_try_charge(pids, 1);
230 if (err) {
231
232 if (atomic64_inc_return(&pids->events_limit) == 1) {
233 pr_info("cgroup: fork rejected by pids controller in ");
234 pr_cont_cgroup_path(css->cgroup);
235 pr_cont("\n");
236 }
237 cgroup_file_notify(&pids->events_file);
238 }
239 return err;
240}
241
242static void pids_cancel_fork(struct task_struct *task, struct css_set *cset)
243{
244 struct cgroup_subsys_state *css;
245 struct pids_cgroup *pids;
246
247 if (cset)
248 css = cset->subsys[pids_cgrp_id];
249 else
250 css = task_css_check(current, pids_cgrp_id, true);
251 pids = css_pids(css);
252 pids_uncharge(pids, 1);
253}
254
255static void pids_release(struct task_struct *task)
256{
257 struct pids_cgroup *pids = css_pids(task_css(task, pids_cgrp_id));
258
259 pids_uncharge(pids, 1);
260}
261
262static ssize_t pids_max_write(struct kernfs_open_file *of, char *buf,
263 size_t nbytes, loff_t off)
264{
265 struct cgroup_subsys_state *css = of_css(of);
266 struct pids_cgroup *pids = css_pids(css);
267 int64_t limit;
268 int err;
269
270 buf = strstrip(buf);
271 if (!strcmp(buf, PIDS_MAX_STR)) {
272 limit = PIDS_MAX;
273 goto set_limit;
274 }
275
276 err = kstrtoll(buf, 0, &limit);
277 if (err)
278 return err;
279
280 if (limit < 0 || limit >= PIDS_MAX)
281 return -EINVAL;
282
283set_limit:
284
285
286
287
288 atomic64_set(&pids->limit, limit);
289 return nbytes;
290}
291
292static int pids_max_show(struct seq_file *sf, void *v)
293{
294 struct cgroup_subsys_state *css = seq_css(sf);
295 struct pids_cgroup *pids = css_pids(css);
296 int64_t limit = atomic64_read(&pids->limit);
297
298 if (limit >= PIDS_MAX)
299 seq_printf(sf, "%s\n", PIDS_MAX_STR);
300 else
301 seq_printf(sf, "%lld\n", limit);
302
303 return 0;
304}
305
306static s64 pids_current_read(struct cgroup_subsys_state *css,
307 struct cftype *cft)
308{
309 struct pids_cgroup *pids = css_pids(css);
310
311 return atomic64_read(&pids->counter);
312}
313
314static int pids_events_show(struct seq_file *sf, void *v)
315{
316 struct pids_cgroup *pids = css_pids(seq_css(sf));
317
318 seq_printf(sf, "max %lld\n", (s64)atomic64_read(&pids->events_limit));
319 return 0;
320}
321
322static struct cftype pids_files[] = {
323 {
324 .name = "max",
325 .write = pids_max_write,
326 .seq_show = pids_max_show,
327 .flags = CFTYPE_NOT_ON_ROOT,
328 },
329 {
330 .name = "current",
331 .read_s64 = pids_current_read,
332 .flags = CFTYPE_NOT_ON_ROOT,
333 },
334 {
335 .name = "events",
336 .seq_show = pids_events_show,
337 .file_offset = offsetof(struct pids_cgroup, events_file),
338 .flags = CFTYPE_NOT_ON_ROOT,
339 },
340 { }
341};
342
343struct cgroup_subsys pids_cgrp_subsys = {
344 .css_alloc = pids_css_alloc,
345 .css_free = pids_css_free,
346 .can_attach = pids_can_attach,
347 .cancel_attach = pids_cancel_attach,
348 .can_fork = pids_can_fork,
349 .cancel_fork = pids_cancel_fork,
350 .release = pids_release,
351 .legacy_cftypes = pids_files,
352 .dfl_cftypes = pids_files,
353 .threaded = true,
354};
355