kernel/sched/autogroup.c

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