kernel/sched/autogroup.c

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