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Linux/kernel/sched/autogroup.c

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

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