1 // SPDX-License-Identifier: GPL-2.0
2
3 /*
4 * Auto-group scheduling implementation:
5 */
6
7 unsigned int __read_mostly sysctl_sched_autogroup_enabled = 1;
8 static struct autogroup autogroup_default;
9 static atomic_t autogroup_seq_nr;
10
11 #ifdef CONFIG_SYSCTL
12 static struct ctl_table sched_autogroup_sysctls[] = {
13 {
14 .procname = "sched_autogroup_enabled",
15 .data = &sysctl_sched_autogroup_enabled,
16 .maxlen = sizeof(unsigned int),
17 .mode = 0644,
18 .proc_handler = proc_dointvec_minmax,
19 .extra1 = SYSCTL_ZERO,
20 .extra2 = SYSCTL_ONE,
21 },
22 };
23
24 static void __init sched_autogroup_sysctl_init(void)
25 {
26 register_sysctl_init("kernel", sched_autogroup_sysctls);
27 }
28 #else
29 #define sched_autogroup_sysctl_init() do { } while (0)
30 #endif
31
32 void __init autogroup_init(struct task_struct *init_task)
33 {
34 autogroup_default.tg = &root_task_group;
35 kref_init(&autogroup_default.kref);
36 init_rwsem(&autogroup_default.lock);
37 init_task->signal->autogroup = &autogroup_default;
38 sched_autogroup_sysctl_init();
39 }
40
41 void autogroup_free(struct task_group *tg)
42 {
43 kfree(tg->autogroup);
44 }
45
46 static inline void autogroup_destroy(struct kref *kref)
47 {
48 struct autogroup *ag = container_of(kref, struct autogroup, kref);
49
50 #ifdef CONFIG_RT_GROUP_SCHED
51 /* We've redirected RT tasks to the root task group... */
52 ag->tg->rt_se = NULL;
53 ag->tg->rt_rq = NULL;
54 #endif
55 sched_release_group(ag->tg);
56 sched_destroy_group(ag->tg);
57 }
58
59 static inline void autogroup_kref_put(struct autogroup *ag)
60 {
61 kref_put(&ag->kref, autogroup_destroy);
62 }
63
64 static inline struct autogroup *autogroup_kref_get(struct autogroup *ag)
65 {
66 kref_get(&ag->kref);
67 return ag;
68 }
69
70 static inline struct autogroup *autogroup_task_get(struct task_struct *p)
71 {
72 struct autogroup *ag;
73 unsigned long flags;
74
75 if (!lock_task_sighand(p, &flags))
76 return autogroup_kref_get(&autogroup_default);
77
78 ag = autogroup_kref_get(p->signal->autogroup);
79 unlock_task_sighand(p, &flags);
80
81 return ag;
82 }
83
84 static inline struct autogroup *autogroup_create(void)
85 {
86 struct autogroup *ag = kzalloc(sizeof(*ag), GFP_KERNEL);
87 struct task_group *tg;
88
89 if (!ag)
90 goto out_fail;
91
92 tg = sched_create_group(&root_task_group);
93 if (IS_ERR(tg))
94 goto out_free;
95
96 kref_init(&ag->kref);
97 init_rwsem(&ag->lock);
98 ag->id = atomic_inc_return(&autogroup_seq_nr);
99 ag->tg = tg;
100 #ifdef CONFIG_RT_GROUP_SCHED
101 /*
102 * Autogroup RT tasks are redirected to the root task group
103 * so we don't have to move tasks around upon policy change,
104 * or flail around trying to allocate bandwidth on the fly.
105 * A bandwidth exception in __sched_setscheduler() allows
106 * the policy change to proceed.
107 */
108 free_rt_sched_group(tg);
109 tg->rt_se = root_task_group.rt_se;
110 tg->rt_rq = root_task_group.rt_rq;
111 #endif
112 tg->autogroup = ag;
113
114 sched_online_group(tg, &root_task_group);
115 return ag;
116
117 out_free:
118 kfree(ag);
119 out_fail:
120 if (printk_ratelimit()) {
121 printk(KERN_WARNING "autogroup_create: %s failure.\n",
122 ag ? "sched_create_group()" : "kzalloc()");
123 }
124
125 return autogroup_kref_get(&autogroup_default);
126 }
127
128 bool task_wants_autogroup(struct task_struct *p, struct task_group *tg)
129 {
130 if (tg != &root_task_group)
131 return false;
132 /*
133 * If we race with autogroup_move_group() the caller can use the old
134 * value of signal->autogroup but in this case sched_move_task() will
135 * be called again before autogroup_kref_put().
136 *
137 * However, there is no way sched_autogroup_exit_task() could tell us
138 * to avoid autogroup->tg, so we abuse PF_EXITING flag for this case.
139 */
140 if (p->flags & PF_EXITING)
141 return false;
142
143 return true;
144 }
145
146 void sched_autogroup_exit_task(struct task_struct *p)
147 {
148 /*
149 * We are going to call exit_notify() and autogroup_move_group() can't
150 * see this thread after that: we can no longer use signal->autogroup.
151 * See the PF_EXITING check in task_wants_autogroup().
152 */
153 sched_move_task(p);
154 }
155
156 static void
157 autogroup_move_group(struct task_struct *p, struct autogroup *ag)
158 {
159 struct autogroup *prev;
160 struct task_struct *t;
161 unsigned long flags;
162
163 if (WARN_ON_ONCE(!lock_task_sighand(p, &flags)))
164 return;
165
166 prev = p->signal->autogroup;
167 if (prev == ag) {
168 unlock_task_sighand(p, &flags);
169 return;
170 }
171
172 p->signal->autogroup = autogroup_kref_get(ag);
173 /*
174 * We can't avoid sched_move_task() after we changed signal->autogroup,
175 * this process can already run with task_group() == prev->tg or we can
176 * race with cgroup code which can read autogroup = prev under rq->lock.
177 * In the latter case for_each_thread() can not miss a migrating thread,
178 * cpu_cgroup_attach() must not be possible after cgroup_exit() and it
179 * can't be removed from thread list, we hold ->siglock.
180 *
181 * If an exiting thread was already removed from thread list we rely on
182 * sched_autogroup_exit_task().
183 */
184 for_each_thread(p, t)
185 sched_move_task(t);
186
187 unlock_task_sighand(p, &flags);
188 autogroup_kref_put(prev);
189 }
190
191 /* Allocates GFP_KERNEL, cannot be called under any spinlock: */
192 void sched_autogroup_create_attach(struct task_struct *p)
193 {
194 struct autogroup *ag = autogroup_create();
195
196 autogroup_move_group(p, ag);
197
198 /* Drop extra reference added by autogroup_create(): */
199 autogroup_kref_put(ag);
200 }
201 EXPORT_SYMBOL(sched_autogroup_create_attach);
202
203 /* Cannot be called under siglock. Currently has no users: */
204 void sched_autogroup_detach(struct task_struct *p)
205 {
206 autogroup_move_group(p, &autogroup_default);
207 }
208 EXPORT_SYMBOL(sched_autogroup_detach);
209
210 void sched_autogroup_fork(struct signal_struct *sig)
211 {
212 sig->autogroup = autogroup_task_get(current);
213 }
214
215 void sched_autogroup_exit(struct signal_struct *sig)
216 {
217 autogroup_kref_put(sig->autogroup);
218 }
219
220 static int __init setup_autogroup(char *str)
221 {
222 sysctl_sched_autogroup_enabled = 0;
223
224 return 1;
225 }
226 __setup("noautogroup", setup_autogroup);
227
228 #ifdef CONFIG_PROC_FS
229
230 int proc_sched_autogroup_set_nice(struct task_struct *p, int nice)
231 {
232 static unsigned long next = INITIAL_JIFFIES;
233 struct autogroup *ag;
234 unsigned long shares;
235 int err, idx;
236
237 if (nice < MIN_NICE || nice > MAX_NICE)
238 return -EINVAL;
239
240 err = security_task_setnice(current, nice);
241 if (err)
242 return err;
243
244 if (nice < 0 && !can_nice(current, nice))
245 return -EPERM;
246
247 /* This is a heavy operation, taking global locks.. */
248 if (!capable(CAP_SYS_ADMIN) && time_before(jiffies, next))
249 return -EAGAIN;
250
251 next = HZ / 10 + jiffies;
252 ag = autogroup_task_get(p);
253
254 idx = array_index_nospec(nice + 20, 40);
255 shares = scale_load(sched_prio_to_weight[idx]);
256
257 down_write(&ag->lock);
258 err = sched_group_set_shares(ag->tg, shares);
259 if (!err)
260 ag->nice = nice;
261 up_write(&ag->lock);
262
263 autogroup_kref_put(ag);
264
265 return err;
266 }
267
268 void proc_sched_autogroup_show_task(struct task_struct *p, struct seq_file *m)
269 {
270 struct autogroup *ag = autogroup_task_get(p);
271
272 if (!task_group_is_autogroup(ag->tg))
273 goto out;
274
275 down_read(&ag->lock);
276 seq_printf(m, "/autogroup-%ld nice %d\n", ag->id, ag->nice);
277 up_read(&ag->lock);
278
279 out:
280 autogroup_kref_put(ag);
281 }
282 #endif /* CONFIG_PROC_FS */
283
284 int autogroup_path(struct task_group *tg, char *buf, int buflen)
285 {
286 if (!task_group_is_autogroup(tg))
287 return 0;
288
289 return snprintf(buf, buflen, "%s-%ld", "/autogroup", tg->autogroup->id);
290 }
291
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