kernel/sched/autogroup.c

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