kernel/sched/autogroup.c

   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 int autogroup_path(struct task_group *tg, char *buf, int buflen)
 263 {
 264         if (!task_group_is_autogroup(tg))
 265                 return 0;
 266
 267         return snprintf(buf, buflen, "%s-%ld", "/autogroup", tg->autogroup->id);
 268 }