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/memblock.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 = {
  45         .count          = ATOMIC_INIT(1),
  46         .tasks          = {
  47                 { .first = NULL },
  48                 { .first = NULL },
  49                 { .first = NULL },
  50         },
  51         .level          = 0,
  52         .numbers        = { {
  53                 .nr             = 0,
  54                 .ns             = &init_pid_ns,
  55         }, }
  56 };
  57
  58 int pid_max = PID_MAX_DEFAULT;
  59
  60 #define RESERVED_PIDS           300
  61
  62 int pid_max_min = RESERVED_PIDS + 1;
  63 int pid_max_max = PID_MAX_LIMIT;
  64
  65 /*
  66  * PID-map pages start out as NULL, they get allocated upon
  67  * first use and are never deallocated. This way a low pid_max
  68  * value does not cause lots of bitmaps to be allocated, but
  69  * the scheme scales to up to 4 million PIDs, runtime.
  70  */
  71 struct pid_namespace init_pid_ns = {
  72         .kref = KREF_INIT(2),
  73         .idr = IDR_INIT(init_pid_ns.idr),
  74         .pid_allocated = PIDNS_ADDING,
  75         .level = 0,
  76         .child_reaper = &init_task,
  77         .user_ns = &init_user_ns,
  78         .ns.inum = PROC_PID_INIT_INO,
  79 #ifdef CONFIG_PID_NS
  80         .ns.ops = &pidns_operations,
  81 #endif
  82 };
  83 EXPORT_SYMBOL_GPL(init_pid_ns);
  84
  85 /*
  86  * Note: disable interrupts while the pidmap_lock is held as an
  87  * interrupt might come in and do read_lock(&tasklist_lock).
  88  *
  89  * If we don't disable interrupts there is a nasty deadlock between
  90  * detach_pid()->free_pid() and another cpu that does
  91  * spin_lock(&pidmap_lock) followed by an interrupt routine that does
  92  * read_lock(&tasklist_lock);
  93  *
  94  * After we clean up the tasklist_lock and know there are no
  95  * irq handlers that take it we can leave the interrupts enabled.
  96  * For now it is easier to be safe than to prove it can't happen.
  97  */
  98
  99 static  __cacheline_aligned_in_smp DEFINE_SPINLOCK(pidmap_lock);
 100
 101 void put_pid(struct pid *pid)
 102 {
 103         struct pid_namespace *ns;
 104
 105         if (!pid)
 106                 return;
 107
 108         ns = pid->numbers[pid->level].ns;
 109         if ((atomic_read(&pid->count) == 1) ||
 110              atomic_dec_and_test(&pid->count)) {
 111                 kmem_cache_free(ns->pid_cachep, pid);
 112                 put_pid_ns(ns);
 113         }
 114 }
 115 EXPORT_SYMBOL_GPL(put_pid);
 116
 117 static void delayed_put_pid(struct rcu_head *rhp)
 118 {
 119         struct pid *pid = container_of(rhp, struct pid, rcu);
 120         put_pid(pid);
 121 }
 122
 123 void free_pid(struct pid *pid)
 124 {
 125         /* We can be called with write_lock_irq(&tasklist_lock) held */
 126         int i;
 127         unsigned long flags;
 128
 129         spin_lock_irqsave(&pidmap_lock, flags);
 130         for (i = 0; i <= pid->level; i++) {
 131                 struct upid *upid = pid->numbers + i;
 132                 struct pid_namespace *ns = upid->ns;
 133                 switch (--ns->pid_allocated) {
 134                 case 2:
 135                 case 1:
 136                         /* When all that is left in the pid namespace
 137                          * is the reaper wake up the reaper.  The reaper
 138                          * may be sleeping in zap_pid_ns_processes().
 139                          */
 140                         wake_up_process(ns->child_reaper);
 141                         break;
 142                 case PIDNS_ADDING:
 143                         /* Handle a fork failure of the first process */
 144                         WARN_ON(ns->child_reaper);
 145                         ns->pid_allocated = 0;
 146                         /* fall through */
 147                 case 0:
 148                         schedule_work(&ns->proc_work);
 149                         break;
 150                 }
 151
 152                 idr_remove(&ns->idr, upid->nr);
 153         }
 154         spin_unlock_irqrestore(&pidmap_lock, flags);
 155
 156         call_rcu(&pid->rcu, delayed_put_pid);
 157 }
 158
 159 struct pid *alloc_pid(struct pid_namespace *ns)
 160 {
 161         struct pid *pid;
 162         enum pid_type type;
 163         int i, nr;
 164         struct pid_namespace *tmp;
 165         struct upid *upid;
 166         int retval = -ENOMEM;
 167
 168         pid = kmem_cache_alloc(ns->pid_cachep, GFP_KERNEL);
 169         if (!pid)
 170                 return ERR_PTR(retval);
 171
 172         tmp = ns;
 173         pid->level = ns->level;
 174
 175         for (i = ns->level; i >= 0; i--) {
 176                 int pid_min = 1;
 177
 178                 idr_preload(GFP_KERNEL);
 179                 spin_lock_irq(&pidmap_lock);
 180
 181                 /*
 182                  * init really needs pid 1, but after reaching the maximum
 183                  * wrap back to RESERVED_PIDS
 184                  */
 185                 if (idr_get_cursor(&tmp->idr) > RESERVED_PIDS)
 186                         pid_min = RESERVED_PIDS;
 187
 188                 /*
 189                  * Store a null pointer so find_pid_ns does not find
 190                  * a partially initialized PID (see below).
 191                  */
 192                 nr = idr_alloc_cyclic(&tmp->idr, NULL, pid_min,
 193                                       pid_max, GFP_ATOMIC);
 194                 spin_unlock_irq(&pidmap_lock);
 195                 idr_preload_end();
 196
 197                 if (nr < 0) {
 198                         retval = (nr == -ENOSPC) ? -EAGAIN : nr;
 199                         goto out_free;
 200                 }
 201
 202                 pid->numbers[i].nr = nr;
 203                 pid->numbers[i].ns = tmp;
 204                 tmp = tmp->parent;
 205         }
 206
 207         if (unlikely(is_child_reaper(pid))) {
 208                 if (pid_ns_prepare_proc(ns))
 209                         goto out_free;
 210         }
 211
 212         get_pid_ns(ns);
 213         atomic_set(&pid->count, 1);
 214         for (type = 0; type < PIDTYPE_MAX; ++type)
 215                 INIT_HLIST_HEAD(&pid->tasks[type]);
 216
 217         upid = pid->numbers + ns->level;
 218         spin_lock_irq(&pidmap_lock);
 219         if (!(ns->pid_allocated & PIDNS_ADDING))
 220                 goto out_unlock;
 221         for ( ; upid >= pid->numbers; --upid) {
 222                 /* Make the PID visible to find_pid_ns. */
 223                 idr_replace(&upid->ns->idr, pid, upid->nr);
 224                 upid->ns->pid_allocated++;
 225         }
 226         spin_unlock_irq(&pidmap_lock);
 227
 228         return pid;
 229
 230 out_unlock:
 231         spin_unlock_irq(&pidmap_lock);
 232         put_pid_ns(ns);
 233
 234 out_free:
 235         spin_lock_irq(&pidmap_lock);
 236         while (++i <= ns->level)
 237                 idr_remove(&ns->idr, (pid->numbers + i)->nr);
 238
 239         /* On failure to allocate the first pid, reset the state */
 240         if (ns->pid_allocated == PIDNS_ADDING)
 241                 idr_set_cursor(&ns->idr, 0);
 242
 243         spin_unlock_irq(&pidmap_lock);
 244
 245         kmem_cache_free(ns->pid_cachep, pid);
 246         return ERR_PTR(retval);
 247 }
 248
 249 void disable_pid_allocation(struct pid_namespace *ns)
 250 {
 251         spin_lock_irq(&pidmap_lock);
 252         ns->pid_allocated &= ~PIDNS_ADDING;
 253         spin_unlock_irq(&pidmap_lock);
 254 }
 255
 256 struct pid *find_pid_ns(int nr, struct pid_namespace *ns)
 257 {
 258         return idr_find(&ns->idr, nr);
 259 }
 260 EXPORT_SYMBOL_GPL(find_pid_ns);
 261
 262 struct pid *find_vpid(int nr)
 263 {
 264         return find_pid_ns(nr, task_active_pid_ns(current));
 265 }
 266 EXPORT_SYMBOL_GPL(find_vpid);
 267
 268 static struct pid **task_pid_ptr(struct task_struct *task, enum pid_type type)
 269 {
 270         return (type == PIDTYPE_PID) ?
 271                 &task->thread_pid :
 272                 &task->signal->pids[type];
 273 }
 274
 275 /*
 276  * attach_pid() must be called with the tasklist_lock write-held.
 277  */
 278 void attach_pid(struct task_struct *task, enum pid_type type)
 279 {
 280         struct pid *pid = *task_pid_ptr(task, type);
 281         hlist_add_head_rcu(&task->pid_links[type], &pid->tasks[type]);
 282 }
 283
 284 static void __change_pid(struct task_struct *task, enum pid_type type,
 285                         struct pid *new)
 286 {
 287         struct pid **pid_ptr = task_pid_ptr(task, type);
 288         struct pid *pid;
 289         int tmp;
 290
 291         pid = *pid_ptr;
 292
 293         hlist_del_rcu(&task->pid_links[type]);
 294         *pid_ptr = new;
 295
 296         for (tmp = PIDTYPE_MAX; --tmp >= 0; )
 297                 if (!hlist_empty(&pid->tasks[tmp]))
 298                         return;
 299
 300         free_pid(pid);
 301 }
 302
 303 void detach_pid(struct task_struct *task, enum pid_type type)
 304 {
 305         __change_pid(task, type, NULL);
 306 }
 307
 308 void change_pid(struct task_struct *task, enum pid_type type,
 309                 struct pid *pid)
 310 {
 311         __change_pid(task, type, pid);
 312         attach_pid(task, type);
 313 }
 314
 315 /* transfer_pid is an optimization of attach_pid(new), detach_pid(old) */
 316 void transfer_pid(struct task_struct *old, struct task_struct *new,
 317                            enum pid_type type)
 318 {
 319         if (type == PIDTYPE_PID)
 320                 new->thread_pid = old->thread_pid;
 321         hlist_replace_rcu(&old->pid_links[type], &new->pid_links[type]);
 322 }
 323
 324 struct task_struct *pid_task(struct pid *pid, enum pid_type type)
 325 {
 326         struct task_struct *result = NULL;
 327         if (pid) {
 328                 struct hlist_node *first;
 329                 first = rcu_dereference_check(hlist_first_rcu(&pid->tasks[type]),
 330                                               lockdep_tasklist_lock_is_held());
 331                 if (first)
 332                         result = hlist_entry(first, struct task_struct, pid_links[(type)]);
 333         }
 334         return result;
 335 }
 336 EXPORT_SYMBOL(pid_task);
 337
 338 /*
 339  * Must be called under rcu_read_lock().
 340  */
 341 struct task_struct *find_task_by_pid_ns(pid_t nr, struct pid_namespace *ns)
 342 {
 343         RCU_LOCKDEP_WARN(!rcu_read_lock_held(),
 344                          "find_task_by_pid_ns() needs rcu_read_lock() protection");
 345         return pid_task(find_pid_ns(nr, ns), PIDTYPE_PID);
 346 }
 347
 348 struct task_struct *find_task_by_vpid(pid_t vnr)
 349 {
 350         return find_task_by_pid_ns(vnr, task_active_pid_ns(current));
 351 }
 352
 353 struct task_struct *find_get_task_by_vpid(pid_t nr)
 354 {
 355         struct task_struct *task;
 356
 357         rcu_read_lock();
 358         task = find_task_by_vpid(nr);
 359         if (task)
 360                 get_task_struct(task);
 361         rcu_read_unlock();
 362
 363         return task;
 364 }
 365
 366 struct pid *get_task_pid(struct task_struct *task, enum pid_type type)
 367 {
 368         struct pid *pid;
 369         rcu_read_lock();
 370         pid = get_pid(rcu_dereference(*task_pid_ptr(task, type)));
 371         rcu_read_unlock();
 372         return pid;
 373 }
 374 EXPORT_SYMBOL_GPL(get_task_pid);
 375
 376 struct task_struct *get_pid_task(struct pid *pid, enum pid_type type)
 377 {
 378         struct task_struct *result;
 379         rcu_read_lock();
 380         result = pid_task(pid, type);
 381         if (result)
 382                 get_task_struct(result);
 383         rcu_read_unlock();
 384         return result;
 385 }
 386 EXPORT_SYMBOL_GPL(get_pid_task);
 387
 388 struct pid *find_get_pid(pid_t nr)
 389 {
 390         struct pid *pid;
 391
 392         rcu_read_lock();
 393         pid = get_pid(find_vpid(nr));
 394         rcu_read_unlock();
 395
 396         return pid;
 397 }
 398 EXPORT_SYMBOL_GPL(find_get_pid);
 399
 400 pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns)
 401 {
 402         struct upid *upid;
 403         pid_t nr = 0;
 404
 405         if (pid && ns->level <= pid->level) {
 406                 upid = &pid->numbers[ns->level];
 407                 if (upid->ns == ns)
 408                         nr = upid->nr;
 409         }
 410         return nr;
 411 }
 412 EXPORT_SYMBOL_GPL(pid_nr_ns);
 413
 414 pid_t pid_vnr(struct pid *pid)
 415 {
 416         return pid_nr_ns(pid, task_active_pid_ns(current));
 417 }
 418 EXPORT_SYMBOL_GPL(pid_vnr);
 419
 420 pid_t __task_pid_nr_ns(struct task_struct *task, enum pid_type type,
 421                         struct pid_namespace *ns)
 422 {
 423         pid_t nr = 0;
 424
 425         rcu_read_lock();
 426         if (!ns)
 427                 ns = task_active_pid_ns(current);
 428         if (likely(pid_alive(task)))
 429                 nr = pid_nr_ns(rcu_dereference(*task_pid_ptr(task, type)), ns);
 430         rcu_read_unlock();
 431
 432         return nr;
 433 }
 434 EXPORT_SYMBOL(__task_pid_nr_ns);
 435
 436 struct pid_namespace *task_active_pid_ns(struct task_struct *tsk)
 437 {
 438         return ns_of_pid(task_pid(tsk));
 439 }
 440 EXPORT_SYMBOL_GPL(task_active_pid_ns);
 441
 442 /*
 443  * Used by proc to find the first pid that is greater than or equal to nr.
 444  *
 445  * If there is a pid at nr this function is exactly the same as find_pid_ns.
 446  */
 447 struct pid *find_ge_pid(int nr, struct pid_namespace *ns)
 448 {
 449         return idr_get_next(&ns->idr, &nr);
 450 }
 451
 452 void __init pid_idr_init(void)
 453 {
 454         /* Verify no one has done anything silly: */
 455         BUILD_BUG_ON(PID_MAX_LIMIT >= PIDNS_ADDING);
 456
 457         /* bump default and minimum pid_max based on number of cpus */
 458         pid_max = min(pid_max_max, max_t(int, pid_max,
 459                                 PIDS_PER_CPU_DEFAULT * num_possible_cpus()));
 460         pid_max_min = max_t(int, pid_max_min,
 461                                 PIDS_PER_CPU_MIN * num_possible_cpus());
 462         pr_info("pid_max: default: %u minimum: %u\n", pid_max, pid_max_min);
 463
 464         idr_init(&init_pid_ns.idr);
 465
 466         init_pid_ns.pid_cachep = KMEM_CACHE(pid,
 467                         SLAB_HWCACHE_ALIGN | SLAB_PANIC | SLAB_ACCOUNT);
 468 }