1// SPDX-License-Identifier: GPL-2.0
2
3/*
4 * Auto-group scheduling implementation:
5 */
6
7unsigned int __read_mostly sysctl_sched_autogroup_enabled = 1;
8static struct autogroup autogroup_default;
9static atomic_t autogroup_seq_nr;
10
11#ifdef CONFIG_SYSCTL
12static 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
24static 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
32void __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
41void autogroup_free(struct task_group *tg)
42{
43	kfree(tg->autogroup);
44}
45
46static 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
59static inline void autogroup_kref_put(struct autogroup *ag)
60{
61	kref_put(&ag->kref, autogroup_destroy);
62}
63
64static inline struct autogroup *autogroup_kref_get(struct autogroup *ag)
65{
66	kref_get(&ag->kref);
67	return ag;
68}
69
70static 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
84static 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
117out_free:
118	kfree(ag);
119out_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
128bool 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
146void 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
156static void
157autogroup_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: */
192void 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}
201EXPORT_SYMBOL(sched_autogroup_create_attach);
202
203/* Cannot be called under siglock. Currently has no users: */
204void sched_autogroup_detach(struct task_struct *p)
205{
206	autogroup_move_group(p, &autogroup_default);
207}
208EXPORT_SYMBOL(sched_autogroup_detach);
209
210void sched_autogroup_fork(struct signal_struct *sig)
211{
212	sig->autogroup = autogroup_task_get(current);
213}
214
215void sched_autogroup_exit(struct signal_struct *sig)
216{
217	autogroup_kref_put(sig->autogroup);
218}
219
220static 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
230int 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
268void 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
279out:
280	autogroup_kref_put(ag);
281}
282#endif /* CONFIG_PROC_FS */
283
284int 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