kernel/pid.c

   1 /*
   2  * Generic pidhash and scalable, time-bounded PID allocator
   3  *
   4  * (C) 2002-2003 Nadia Yvette Chambers, IBM
   5  * (C) 2004 Nadia Yvette Chambers, Oracle
   6  * (C) 2002-2004 Ingo Molnar, Red Hat
   7  *
   8  * pid-structures are backing objects for tasks sharing a given ID to chain
   9  * against. There is very little to them aside from hashing them and
  10  * parking tasks using given ID's on a list.
  11  *
  12  * The hash is always changed with the tasklist_lock write-acquired,
  13  * and the hash is only accessed with the tasklist_lock at least
  14  * read-acquired, so there's no additional SMP locking needed here.
  15  *
  16  * We have a list of bitmap pages, which bitmaps represent the PID space.
  17  * Allocating and freeing PIDs is completely lockless. The worst-case
  18  * allocation scenario when all but one out of 1 million PIDs possible are
  19  * allocated already: the scanning of 32 list entries and at most PAGE_SIZE
  20  * bytes. The typical fastpath is a single successful setbit. Freeing is O(1).
  21  *
  22  * Pid namespaces:
  23  *    (C) 2007 Pavel Emelyanov <xemul@openvz.org>, OpenVZ, SWsoft Inc.
  24  *    (C) 2007 Sukadev Bhattiprolu <sukadev@us.ibm.com>, IBM
  25  *     Many thanks to Oleg Nesterov for comments and help
  26  *
  27  */
  28
  29 #include <linux/mm.h>
  30 #include <linux/export.h>
  31 #include <linux/slab.h>
  32 #include <linux/init.h>
  33 #include <linux/rculist.h>
  34 #include <linux/bootmem.h>
  35 #include <linux/hash.h>
  36 #include <linux/pid_namespace.h>
  37 #include <linux/init_task.h>
  38 #include <linux/syscalls.h>
  39 #include <linux/proc_ns.h>
  40 #include <linux/proc_fs.h>
  41 #include <linux/sched/task.h>
  42 #include <linux/idr.h>
  43
  44 struct pid init_struct_pid = INIT_STRUCT_PID;
  45
  46 int pid_max = PID_MAX_DEFAULT;
  47
  48 #define RESERVED_PIDS           300
  49
  50 int pid_max_min = RESERVED_PIDS + 1;
  51 int pid_max_max = PID_MAX_LIMIT;
  52
  53 /*
  54  * PID-map pages start out as NULL, they get allocated upon
  55  * first use and are never deallocated. This way a low pid_max
  56  * value does not cause lots of bitmaps to be allocated, but
  57  * the scheme scales to up to 4 million PIDs, runtime.
  58  */
  59 struct pid_namespace init_pid_ns = {
  60         .kref = KREF_INIT(2),
  61         .idr = IDR_INIT,
  62         .pid_allocated = PIDNS_ADDING,
  63         .level = 0,
  64         .child_reaper = &init_task,
  65         .user_ns = &init_user_ns,
  66         .ns.inum = PROC_PID_INIT_INO,
  67 #ifdef CONFIG_PID_NS
  68         .ns.ops = &pidns_operations,
  69 #endif
  70 };
  71 EXPORT_SYMBOL_GPL(init_pid_ns);
  72
  73 /*
  74  * Note: disable interrupts while the pidmap_lock is held as an
  75  * interrupt might come in and do read_lock(&tasklist_lock).
  76  *
  77  * If we don't disable interrupts there is a nasty deadlock between
  78  * detach_pid()->free_pid() and another cpu that does
  79  * spin_lock(&pidmap_lock) followed by an interrupt routine that does
  80  * read_lock(&tasklist_lock);
  81  *
  82  * After we clean up the tasklist_lock and know there are no
  83  * irq handlers that take it we can leave the interrupts enabled.
  84  * For now it is easier to be safe than to prove it can't happen.
  85  */
  86
  87 static  __cacheline_aligned_in_smp DEFINE_SPINLOCK(pidmap_lock);
  88
  89 void put_pid(struct pid *pid)
  90 {
  91         struct pid_namespace *ns;
  92
  93         if (!pid)
  94                 return;
  95
  96         ns = pid->numbers[pid->level].ns;
  97         if ((atomic_read(&pid->count) == 1) ||
  98              atomic_dec_and_test(&pid->count)) {
  99                 kmem_cache_free(ns->pid_cachep, pid);
 100                 put_pid_ns(ns);
 101         }
 102 }
 103 EXPORT_SYMBOL_GPL(put_pid);
 104
 105 static void delayed_put_pid(struct rcu_head *rhp)
 106 {
 107         struct pid *pid = container_of(rhp, struct pid, rcu);
 108         put_pid(pid);
 109 }
 110
 111 void free_pid(struct pid *pid)
 112 {
 113         /* We can be called with write_lock_irq(&tasklist_lock) held */
 114         int i;
 115         unsigned long flags;
 116
 117         spin_lock_irqsave(&pidmap_lock, flags);
 118         for (i = 0; i <= pid->level; i++) {
 119                 struct upid *upid = pid->numbers + i;
 120                 struct pid_namespace *ns = upid->ns;
 121                 switch (--ns->pid_allocated) {
 122                 case 2:
 123                 case 1:
 124                         /* When all that is left in the pid namespace
 125                          * is the reaper wake up the reaper.  The reaper
 126                          * may be sleeping in zap_pid_ns_processes().
 127                          */
 128                         wake_up_process(ns->child_reaper);
 129                         break;
 130                 case PIDNS_ADDING:
 131                         /* Handle a fork failure of the first process */
 132                         WARN_ON(ns->child_reaper);
 133                         ns->pid_allocated = 0;
 134                         /* fall through */
 135                 case 0:
 136                         schedule_work(&ns->proc_work);
 137                         break;
 138                 }
 139
 140                 idr_remove(&ns->idr, upid->nr);
 141         }
 142         spin_unlock_irqrestore(&pidmap_lock, flags);
 143
 144         call_rcu(&pid->rcu, delayed_put_pid);
 145 }
 146
 147 struct pid *alloc_pid(struct pid_namespace *ns)
 148 {
 149         struct pid *pid;
 150         enum pid_type type;
 151         int i, nr;
 152         struct pid_namespace *tmp;
 153         struct upid *upid;
 154         int retval = -ENOMEM;
 155
 156         pid = kmem_cache_alloc(ns->pid_cachep, GFP_KERNEL);
 157         if (!pid)
 158                 return ERR_PTR(retval);
 159
 160         tmp = ns;
 161         pid->level = ns->level;
 162
 163         for (i = ns->level; i >= 0; i--) {
 164                 int pid_min = 1;
 165
 166                 idr_preload(GFP_KERNEL);
 167                 spin_lock_irq(&pidmap_lock);
 168
 169                 /*
 170                  * init really needs pid 1, but after reaching the maximum
 171                  * wrap back to RESERVED_PIDS
 172                  */
 173                 if (idr_get_cursor(&tmp->idr) > RESERVED_PIDS)
 174                         pid_min = RESERVED_PIDS;
 175
 176                 /*
 177                  * Store a null pointer so find_pid_ns does not find
 178                  * a partially initialized PID (see below).
 179                  */
 180                 nr = idr_alloc_cyclic(&tmp->idr, NULL, pid_min,
 181                                       pid_max, GFP_ATOMIC);
 182                 spin_unlock_irq(&pidmap_lock);
 183                 idr_preload_end();
 184
 185                 if (nr < 0) {
 186                         retval = nr;
 187                         goto out_free;
 188                 }
 189
 190                 pid->numbers[i].nr = nr;
 191                 pid->numbers[i].ns = tmp;
 192                 tmp = tmp->parent;
 193         }
 194
 195         if (unlikely(is_child_reaper(pid))) {
 196                 if (pid_ns_prepare_proc(ns)) {
 197                         disable_pid_allocation(ns);
 198                         goto out_free;
 199                 }
 200         }
 201
 202         get_pid_ns(ns);
 203         atomic_set(&pid->count, 1);
 204         for (type = 0; type < PIDTYPE_MAX; ++type)
 205                 INIT_HLIST_HEAD(&pid->tasks[type]);
 206
 207         upid = pid->numbers + ns->level;
 208         spin_lock_irq(&pidmap_lock);
 209         if (!(ns->pid_allocated & PIDNS_ADDING))
 210                 goto out_unlock;
 211         for ( ; upid >= pid->numbers; --upid) {
 212                 /* Make the PID visible to find_pid_ns. */
 213                 idr_replace(&upid->ns->idr, pid, upid->nr);
 214                 upid->ns->pid_allocated++;
 215         }
 216         spin_unlock_irq(&pidmap_lock);
 217
 218         return pid;
 219
 220 out_unlock:
 221         spin_unlock_irq(&pidmap_lock);
 222         put_pid_ns(ns);
 223
 224 out_free:
 225         spin_lock_irq(&pidmap_lock);
 226         while (++i <= ns->level)
 227                 idr_remove(&ns->idr, (pid->numbers + i)->nr);
 228
 229         spin_unlock_irq(&pidmap_lock);
 230
 231         kmem_cache_free(ns->pid_cachep, pid);
 232         return ERR_PTR(retval);
 233 }
 234
 235 void disable_pid_allocation(struct pid_namespace *ns)
 236 {
 237         spin_lock_irq(&pidmap_lock);
 238         ns->pid_allocated &= ~PIDNS_ADDING;
 239         spin_unlock_irq(&pidmap_lock);
 240 }
 241
 242 struct pid *find_pid_ns(int nr, struct pid_namespace *ns)
 243 {
 244         return idr_find(&ns->idr, nr);
 245 }
 246 EXPORT_SYMBOL_GPL(find_pid_ns);
 247
 248 struct pid *find_vpid(int nr)
 249 {
 250         return find_pid_ns(nr, task_active_pid_ns(current));
 251 }
 252 EXPORT_SYMBOL_GPL(find_vpid);
 253
 254 /*
 255  * attach_pid() must be called with the tasklist_lock write-held.
 256  */
 257 void attach_pid(struct task_struct *task, enum pid_type type)
 258 {
 259         struct pid_link *link = &task->pids[type];
 260         hlist_add_head_rcu(&link->node, &link->pid->tasks[type]);
 261 }
 262
 263 static void __change_pid(struct task_struct *task, enum pid_type type,
 264                         struct pid *new)
 265 {
 266         struct pid_link *link;
 267         struct pid *pid;
 268         int tmp;
 269
 270         link = &task->pids[type];
 271         pid = link->pid;
 272
 273         hlist_del_rcu(&link->node);
 274         link->pid = new;
 275
 276         for (tmp = PIDTYPE_MAX; --tmp >= 0; )
 277                 if (!hlist_empty(&pid->tasks[tmp]))
 278                         return;
 279
 280         free_pid(pid);
 281 }
 282
 283 void detach_pid(struct task_struct *task, enum pid_type type)
 284 {
 285         __change_pid(task, type, NULL);
 286 }
 287
 288 void change_pid(struct task_struct *task, enum pid_type type,
 289                 struct pid *pid)
 290 {
 291         __change_pid(task, type, pid);
 292         attach_pid(task, type);
 293 }
 294
 295 /* transfer_pid is an optimization of attach_pid(new), detach_pid(old) */
 296 void transfer_pid(struct task_struct *old, struct task_struct *new,
 297                            enum pid_type type)
 298 {
 299         new->pids[type].pid = old->pids[type].pid;
 300         hlist_replace_rcu(&old->pids[type].node, &new->pids[type].node);
 301 }
 302
 303 struct task_struct *pid_task(struct pid *pid, enum pid_type type)
 304 {
 305         struct task_struct *result = NULL;
 306         if (pid) {
 307                 struct hlist_node *first;
 308                 first = rcu_dereference_check(hlist_first_rcu(&pid->tasks[type]),
 309                                               lockdep_tasklist_lock_is_held());
 310                 if (first)
 311                         result = hlist_entry(first, struct task_struct, pids[(type)].node);
 312         }
 313         return result;
 314 }
 315 EXPORT_SYMBOL(pid_task);
 316
 317 /*
 318  * Must be called under rcu_read_lock().
 319  */
 320 struct task_struct *find_task_by_pid_ns(pid_t nr, struct pid_namespace *ns)
 321 {
 322         RCU_LOCKDEP_WARN(!rcu_read_lock_held(),
 323                          "find_task_by_pid_ns() needs rcu_read_lock() protection");
 324         return pid_task(find_pid_ns(nr, ns), PIDTYPE_PID);
 325 }
 326
 327 struct task_struct *find_task_by_vpid(pid_t vnr)
 328 {
 329         return find_task_by_pid_ns(vnr, task_active_pid_ns(current));
 330 }
 331
 332 struct pid *get_task_pid(struct task_struct *task, enum pid_type type)
 333 {
 334         struct pid *pid;
 335         rcu_read_lock();
 336         if (type != PIDTYPE_PID)
 337                 task = task->group_leader;
 338         pid = get_pid(rcu_dereference(task->pids[type].pid));
 339         rcu_read_unlock();
 340         return pid;
 341 }
 342 EXPORT_SYMBOL_GPL(get_task_pid);
 343
 344 struct task_struct *get_pid_task(struct pid *pid, enum pid_type type)
 345 {
 346         struct task_struct *result;
 347         rcu_read_lock();
 348         result = pid_task(pid, type);
 349         if (result)
 350                 get_task_struct(result);
 351         rcu_read_unlock();
 352         return result;
 353 }
 354 EXPORT_SYMBOL_GPL(get_pid_task);
 355
 356 struct pid *find_get_pid(pid_t nr)
 357 {
 358         struct pid *pid;
 359
 360         rcu_read_lock();
 361         pid = get_pid(find_vpid(nr));
 362         rcu_read_unlock();
 363
 364         return pid;
 365 }
 366 EXPORT_SYMBOL_GPL(find_get_pid);
 367
 368 pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns)
 369 {
 370         struct upid *upid;
 371         pid_t nr = 0;
 372
 373         if (pid && ns->level <= pid->level) {
 374                 upid = &pid->numbers[ns->level];
 375                 if (upid->ns == ns)
 376                         nr = upid->nr;
 377         }
 378         return nr;
 379 }
 380 EXPORT_SYMBOL_GPL(pid_nr_ns);
 381
 382 pid_t pid_vnr(struct pid *pid)
 383 {
 384         return pid_nr_ns(pid, task_active_pid_ns(current));
 385 }
 386 EXPORT_SYMBOL_GPL(pid_vnr);
 387
 388 pid_t __task_pid_nr_ns(struct task_struct *task, enum pid_type type,
 389                         struct pid_namespace *ns)
 390 {
 391         pid_t nr = 0;
 392
 393         rcu_read_lock();
 394         if (!ns)
 395                 ns = task_active_pid_ns(current);
 396         if (likely(pid_alive(task))) {
 397                 if (type != PIDTYPE_PID) {
 398                         if (type == __PIDTYPE_TGID)
 399                                 type = PIDTYPE_PID;
 400
 401                         task = task->group_leader;
 402                 }
 403                 nr = pid_nr_ns(rcu_dereference(task->pids[type].pid), ns);
 404         }
 405         rcu_read_unlock();
 406
 407         return nr;
 408 }
 409 EXPORT_SYMBOL(__task_pid_nr_ns);
 410
 411 struct pid_namespace *task_active_pid_ns(struct task_struct *tsk)
 412 {
 413         return ns_of_pid(task_pid(tsk));
 414 }
 415 EXPORT_SYMBOL_GPL(task_active_pid_ns);
 416
 417 /*
 418  * Used by proc to find the first pid that is greater than or equal to nr.
 419  *
 420  * If there is a pid at nr this function is exactly the same as find_pid_ns.
 421  */
 422 struct pid *find_ge_pid(int nr, struct pid_namespace *ns)
 423 {
 424         return idr_get_next(&ns->idr, &nr);
 425 }
 426
 427 void __init pid_idr_init(void)
 428 {
 429         /* Verify no one has done anything silly: */
 430         BUILD_BUG_ON(PID_MAX_LIMIT >= PIDNS_ADDING);
 431
 432         /* bump default and minimum pid_max based on number of cpus */
 433         pid_max = min(pid_max_max, max_t(int, pid_max,
 434                                 PIDS_PER_CPU_DEFAULT * num_possible_cpus()));
 435         pid_max_min = max_t(int, pid_max_min,
 436                                 PIDS_PER_CPU_MIN * num_possible_cpus());
 437         pr_info("pid_max: default: %u minimum: %u\n", pid_max, pid_max_min);
 438
 439         idr_init(&init_pid_ns.idr);
 440
 441         init_pid_ns.pid_cachep = KMEM_CACHE(pid,
 442                         SLAB_HWCACHE_ALIGN | SLAB_PANIC | SLAB_ACCOUNT);
 443 }