linux/kernel/pid.c
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   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
  44struct 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
  58int pid_max = PID_MAX_DEFAULT;
  59
  60#define RESERVED_PIDS           300
  61
  62int pid_max_min = RESERVED_PIDS + 1;
  63int 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 */
  71struct 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};
  83EXPORT_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
  99static  __cacheline_aligned_in_smp DEFINE_SPINLOCK(pidmap_lock);
 100
 101void 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}
 115EXPORT_SYMBOL_GPL(put_pid);
 116
 117static 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
 123void 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
 159struct 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
 230out_unlock:
 231        spin_unlock_irq(&pidmap_lock);
 232        put_pid_ns(ns);
 233
 234out_free:
 235        spin_lock_irq(&pidmap_lock);
 236        while (++i <= ns->level) {
 237                upid = pid->numbers + i;
 238                idr_remove(&upid->ns->idr, upid->nr);
 239        }
 240
 241        /* On failure to allocate the first pid, reset the state */
 242        if (ns->pid_allocated == PIDNS_ADDING)
 243                idr_set_cursor(&ns->idr, 0);
 244
 245        spin_unlock_irq(&pidmap_lock);
 246
 247        kmem_cache_free(ns->pid_cachep, pid);
 248        return ERR_PTR(retval);
 249}
 250
 251void disable_pid_allocation(struct pid_namespace *ns)
 252{
 253        spin_lock_irq(&pidmap_lock);
 254        ns->pid_allocated &= ~PIDNS_ADDING;
 255        spin_unlock_irq(&pidmap_lock);
 256}
 257
 258struct pid *find_pid_ns(int nr, struct pid_namespace *ns)
 259{
 260        return idr_find(&ns->idr, nr);
 261}
 262EXPORT_SYMBOL_GPL(find_pid_ns);
 263
 264struct pid *find_vpid(int nr)
 265{
 266        return find_pid_ns(nr, task_active_pid_ns(current));
 267}
 268EXPORT_SYMBOL_GPL(find_vpid);
 269
 270static struct pid **task_pid_ptr(struct task_struct *task, enum pid_type type)
 271{
 272        return (type == PIDTYPE_PID) ?
 273                &task->thread_pid :
 274                &task->signal->pids[type];
 275}
 276
 277/*
 278 * attach_pid() must be called with the tasklist_lock write-held.
 279 */
 280void attach_pid(struct task_struct *task, enum pid_type type)
 281{
 282        struct pid *pid = *task_pid_ptr(task, type);
 283        hlist_add_head_rcu(&task->pid_links[type], &pid->tasks[type]);
 284}
 285
 286static void __change_pid(struct task_struct *task, enum pid_type type,
 287                        struct pid *new)
 288{
 289        struct pid **pid_ptr = task_pid_ptr(task, type);
 290        struct pid *pid;
 291        int tmp;
 292
 293        pid = *pid_ptr;
 294
 295        hlist_del_rcu(&task->pid_links[type]);
 296        *pid_ptr = new;
 297
 298        for (tmp = PIDTYPE_MAX; --tmp >= 0; )
 299                if (!hlist_empty(&pid->tasks[tmp]))
 300                        return;
 301
 302        free_pid(pid);
 303}
 304
 305void detach_pid(struct task_struct *task, enum pid_type type)
 306{
 307        __change_pid(task, type, NULL);
 308}
 309
 310void change_pid(struct task_struct *task, enum pid_type type,
 311                struct pid *pid)
 312{
 313        __change_pid(task, type, pid);
 314        attach_pid(task, type);
 315}
 316
 317/* transfer_pid is an optimization of attach_pid(new), detach_pid(old) */
 318void transfer_pid(struct task_struct *old, struct task_struct *new,
 319                           enum pid_type type)
 320{
 321        if (type == PIDTYPE_PID)
 322                new->thread_pid = old->thread_pid;
 323        hlist_replace_rcu(&old->pid_links[type], &new->pid_links[type]);
 324}
 325
 326struct task_struct *pid_task(struct pid *pid, enum pid_type type)
 327{
 328        struct task_struct *result = NULL;
 329        if (pid) {
 330                struct hlist_node *first;
 331                first = rcu_dereference_check(hlist_first_rcu(&pid->tasks[type]),
 332                                              lockdep_tasklist_lock_is_held());
 333                if (first)
 334                        result = hlist_entry(first, struct task_struct, pid_links[(type)]);
 335        }
 336        return result;
 337}
 338EXPORT_SYMBOL(pid_task);
 339
 340/*
 341 * Must be called under rcu_read_lock().
 342 */
 343struct task_struct *find_task_by_pid_ns(pid_t nr, struct pid_namespace *ns)
 344{
 345        RCU_LOCKDEP_WARN(!rcu_read_lock_held(),
 346                         "find_task_by_pid_ns() needs rcu_read_lock() protection");
 347        return pid_task(find_pid_ns(nr, ns), PIDTYPE_PID);
 348}
 349
 350struct task_struct *find_task_by_vpid(pid_t vnr)
 351{
 352        return find_task_by_pid_ns(vnr, task_active_pid_ns(current));
 353}
 354
 355struct task_struct *find_get_task_by_vpid(pid_t nr)
 356{
 357        struct task_struct *task;
 358
 359        rcu_read_lock();
 360        task = find_task_by_vpid(nr);
 361        if (task)
 362                get_task_struct(task);
 363        rcu_read_unlock();
 364
 365        return task;
 366}
 367
 368struct pid *get_task_pid(struct task_struct *task, enum pid_type type)
 369{
 370        struct pid *pid;
 371        rcu_read_lock();
 372        pid = get_pid(rcu_dereference(*task_pid_ptr(task, type)));
 373        rcu_read_unlock();
 374        return pid;
 375}
 376EXPORT_SYMBOL_GPL(get_task_pid);
 377
 378struct task_struct *get_pid_task(struct pid *pid, enum pid_type type)
 379{
 380        struct task_struct *result;
 381        rcu_read_lock();
 382        result = pid_task(pid, type);
 383        if (result)
 384                get_task_struct(result);
 385        rcu_read_unlock();
 386        return result;
 387}
 388EXPORT_SYMBOL_GPL(get_pid_task);
 389
 390struct pid *find_get_pid(pid_t nr)
 391{
 392        struct pid *pid;
 393
 394        rcu_read_lock();
 395        pid = get_pid(find_vpid(nr));
 396        rcu_read_unlock();
 397
 398        return pid;
 399}
 400EXPORT_SYMBOL_GPL(find_get_pid);
 401
 402pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns)
 403{
 404        struct upid *upid;
 405        pid_t nr = 0;
 406
 407        if (pid && ns->level <= pid->level) {
 408                upid = &pid->numbers[ns->level];
 409                if (upid->ns == ns)
 410                        nr = upid->nr;
 411        }
 412        return nr;
 413}
 414EXPORT_SYMBOL_GPL(pid_nr_ns);
 415
 416pid_t pid_vnr(struct pid *pid)
 417{
 418        return pid_nr_ns(pid, task_active_pid_ns(current));
 419}
 420EXPORT_SYMBOL_GPL(pid_vnr);
 421
 422pid_t __task_pid_nr_ns(struct task_struct *task, enum pid_type type,
 423                        struct pid_namespace *ns)
 424{
 425        pid_t nr = 0;
 426
 427        rcu_read_lock();
 428        if (!ns)
 429                ns = task_active_pid_ns(current);
 430        if (likely(pid_alive(task)))
 431                nr = pid_nr_ns(rcu_dereference(*task_pid_ptr(task, type)), ns);
 432        rcu_read_unlock();
 433
 434        return nr;
 435}
 436EXPORT_SYMBOL(__task_pid_nr_ns);
 437
 438struct pid_namespace *task_active_pid_ns(struct task_struct *tsk)
 439{
 440        return ns_of_pid(task_pid(tsk));
 441}
 442EXPORT_SYMBOL_GPL(task_active_pid_ns);
 443
 444/*
 445 * Used by proc to find the first pid that is greater than or equal to nr.
 446 *
 447 * If there is a pid at nr this function is exactly the same as find_pid_ns.
 448 */
 449struct pid *find_ge_pid(int nr, struct pid_namespace *ns)
 450{
 451        return idr_get_next(&ns->idr, &nr);
 452}
 453
 454void __init pid_idr_init(void)
 455{
 456        /* Verify no one has done anything silly: */
 457        BUILD_BUG_ON(PID_MAX_LIMIT >= PIDNS_ADDING);
 458
 459        /* bump default and minimum pid_max based on number of cpus */
 460        pid_max = min(pid_max_max, max_t(int, pid_max,
 461                                PIDS_PER_CPU_DEFAULT * num_possible_cpus()));
 462        pid_max_min = max_t(int, pid_max_min,
 463                                PIDS_PER_CPU_MIN * num_possible_cpus());
 464        pr_info("pid_max: default: %u minimum: %u\n", pid_max, pid_max_min);
 465
 466        idr_init(&init_pid_ns.idr);
 467
 468        init_pid_ns.pid_cachep = KMEM_CACHE(pid,
 469                        SLAB_HWCACHE_ALIGN | SLAB_PANIC | SLAB_ACCOUNT);
 470}
 471