2 * Generic pidhash and scalable, time-bounded PID allocator
4 * (C) 2002-2003 William Irwin, IBM
5 * (C) 2004 William Irwin, Oracle
6 * (C) 2002-2004 Ingo Molnar, Red Hat
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.
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.
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).
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
30 #include <linux/module.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>
40 #define pid_hashfn(nr, ns) \
41 hash_long((unsigned long)nr + (unsigned long)ns, pidhash_shift)
42 static struct hlist_head *pid_hash;
43 static int pidhash_shift;
44 struct pid init_struct_pid = INIT_STRUCT_PID;
46 int pid_max = PID_MAX_DEFAULT;
48 #define RESERVED_PIDS 300
50 int pid_max_min = RESERVED_PIDS + 1;
51 int pid_max_max = PID_MAX_LIMIT;
53 #define BITS_PER_PAGE (PAGE_SIZE*8)
54 #define BITS_PER_PAGE_MASK (BITS_PER_PAGE-1)
56 static inline int mk_pid(struct pid_namespace *pid_ns,
57 struct pidmap *map, int off)
59 return (map - pid_ns->pidmap)*BITS_PER_PAGE + off;
62 #define find_next_offset(map, off) \
63 find_next_zero_bit((map)->page, BITS_PER_PAGE, off)
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.
71 struct pid_namespace init_pid_ns = {
73 .refcount = ATOMIC_INIT(2),
76 [ 0 ... PIDMAP_ENTRIES-1] = { ATOMIC_INIT(BITS_PER_PAGE), NULL }
80 .child_reaper = &init_task,
82 EXPORT_SYMBOL_GPL(init_pid_ns);
84 int is_container_init(struct task_struct *tsk)
91 if (pid != NULL && pid->numbers[pid->level].nr == 1)
97 EXPORT_SYMBOL(is_container_init);
100 * Note: disable interrupts while the pidmap_lock is held as an
101 * interrupt might come in and do read_lock(&tasklist_lock).
103 * If we don't disable interrupts there is a nasty deadlock between
104 * detach_pid()->free_pid() and another cpu that does
105 * spin_lock(&pidmap_lock) followed by an interrupt routine that does
106 * read_lock(&tasklist_lock);
108 * After we clean up the tasklist_lock and know there are no
109 * irq handlers that take it we can leave the interrupts enabled.
110 * For now it is easier to be safe than to prove it can't happen.
113 static __cacheline_aligned_in_smp DEFINE_SPINLOCK(pidmap_lock);
115 static void free_pidmap(struct upid *upid)
118 struct pidmap *map = upid->ns->pidmap + nr / BITS_PER_PAGE;
119 int offset = nr & BITS_PER_PAGE_MASK;
121 clear_bit(offset, map->page);
122 atomic_inc(&map->nr_free);
125 static int alloc_pidmap(struct pid_namespace *pid_ns)
127 int i, offset, max_scan, pid, last = pid_ns->last_pid;
133 offset = pid & BITS_PER_PAGE_MASK;
134 map = &pid_ns->pidmap[pid/BITS_PER_PAGE];
135 max_scan = (pid_max + BITS_PER_PAGE - 1)/BITS_PER_PAGE - !offset;
136 for (i = 0; i <= max_scan; ++i) {
137 if (unlikely(!map->page)) {
138 void *page = kzalloc(PAGE_SIZE, GFP_KERNEL);
140 * Free the page if someone raced with us
143 spin_lock_irq(&pidmap_lock);
148 spin_unlock_irq(&pidmap_lock);
149 if (unlikely(!map->page))
152 if (likely(atomic_read(&map->nr_free))) {
154 if (!test_and_set_bit(offset, map->page)) {
155 atomic_dec(&map->nr_free);
156 pid_ns->last_pid = pid;
159 offset = find_next_offset(map, offset);
160 pid = mk_pid(pid_ns, map, offset);
162 * find_next_offset() found a bit, the pid from it
163 * is in-bounds, and if we fell back to the last
164 * bitmap block and the final block was the same
165 * as the starting point, pid is before last_pid.
167 } while (offset < BITS_PER_PAGE && pid < pid_max &&
168 (i != max_scan || pid < last ||
169 !((last+1) & BITS_PER_PAGE_MASK)));
171 if (map < &pid_ns->pidmap[(pid_max-1)/BITS_PER_PAGE]) {
175 map = &pid_ns->pidmap[0];
176 offset = RESERVED_PIDS;
177 if (unlikely(last == offset))
180 pid = mk_pid(pid_ns, map, offset);
185 int next_pidmap(struct pid_namespace *pid_ns, int last)
188 struct pidmap *map, *end;
190 offset = (last + 1) & BITS_PER_PAGE_MASK;
191 map = &pid_ns->pidmap[(last + 1)/BITS_PER_PAGE];
192 end = &pid_ns->pidmap[PIDMAP_ENTRIES];
193 for (; map < end; map++, offset = 0) {
194 if (unlikely(!map->page))
196 offset = find_next_bit((map)->page, BITS_PER_PAGE, offset);
197 if (offset < BITS_PER_PAGE)
198 return mk_pid(pid_ns, map, offset);
203 void put_pid(struct pid *pid)
205 struct pid_namespace *ns;
210 ns = pid->numbers[pid->level].ns;
211 if ((atomic_read(&pid->count) == 1) ||
212 atomic_dec_and_test(&pid->count)) {
213 kmem_cache_free(ns->pid_cachep, pid);
217 EXPORT_SYMBOL_GPL(put_pid);
219 static void delayed_put_pid(struct rcu_head *rhp)
221 struct pid *pid = container_of(rhp, struct pid, rcu);
225 void free_pid(struct pid *pid)
227 /* We can be called with write_lock_irq(&tasklist_lock) held */
231 spin_lock_irqsave(&pidmap_lock, flags);
232 for (i = 0; i <= pid->level; i++)
233 hlist_del_rcu(&pid->numbers[i].pid_chain);
234 spin_unlock_irqrestore(&pidmap_lock, flags);
236 for (i = 0; i <= pid->level; i++)
237 free_pidmap(pid->numbers + i);
239 call_rcu(&pid->rcu, delayed_put_pid);
242 struct pid *alloc_pid(struct pid_namespace *ns)
247 struct pid_namespace *tmp;
250 pid = kmem_cache_alloc(ns->pid_cachep, GFP_KERNEL);
255 for (i = ns->level; i >= 0; i--) {
256 nr = alloc_pidmap(tmp);
260 pid->numbers[i].nr = nr;
261 pid->numbers[i].ns = tmp;
266 pid->level = ns->level;
267 atomic_set(&pid->count, 1);
268 for (type = 0; type < PIDTYPE_MAX; ++type)
269 INIT_HLIST_HEAD(&pid->tasks[type]);
271 spin_lock_irq(&pidmap_lock);
272 for (i = ns->level; i >= 0; i--) {
273 upid = &pid->numbers[i];
274 hlist_add_head_rcu(&upid->pid_chain,
275 &pid_hash[pid_hashfn(upid->nr, upid->ns)]);
277 spin_unlock_irq(&pidmap_lock);
283 while (++i <= ns->level)
284 free_pidmap(pid->numbers + i);
286 kmem_cache_free(ns->pid_cachep, pid);
291 struct pid *find_pid_ns(int nr, struct pid_namespace *ns)
293 struct hlist_node *elem;
296 hlist_for_each_entry_rcu(pnr, elem,
297 &pid_hash[pid_hashfn(nr, ns)], pid_chain)
298 if (pnr->nr == nr && pnr->ns == ns)
299 return container_of(pnr, struct pid,
304 EXPORT_SYMBOL_GPL(find_pid_ns);
306 struct pid *find_vpid(int nr)
308 return find_pid_ns(nr, current->nsproxy->pid_ns);
310 EXPORT_SYMBOL_GPL(find_vpid);
312 struct pid *find_pid(int nr)
314 return find_pid_ns(nr, &init_pid_ns);
316 EXPORT_SYMBOL_GPL(find_pid);
319 * attach_pid() must be called with the tasklist_lock write-held.
321 void attach_pid(struct task_struct *task, enum pid_type type,
324 struct pid_link *link;
326 link = &task->pids[type];
328 hlist_add_head_rcu(&link->node, &pid->tasks[type]);
331 static void __change_pid(struct task_struct *task, enum pid_type type,
334 struct pid_link *link;
338 link = &task->pids[type];
341 hlist_del_rcu(&link->node);
344 for (tmp = PIDTYPE_MAX; --tmp >= 0; )
345 if (!hlist_empty(&pid->tasks[tmp]))
351 void detach_pid(struct task_struct *task, enum pid_type type)
353 __change_pid(task, type, NULL);
356 void change_pid(struct task_struct *task, enum pid_type type,
359 __change_pid(task, type, pid);
360 attach_pid(task, type, pid);
363 /* transfer_pid is an optimization of attach_pid(new), detach_pid(old) */
364 void transfer_pid(struct task_struct *old, struct task_struct *new,
367 new->pids[type].pid = old->pids[type].pid;
368 hlist_replace_rcu(&old->pids[type].node, &new->pids[type].node);
371 struct task_struct *pid_task(struct pid *pid, enum pid_type type)
373 struct task_struct *result = NULL;
375 struct hlist_node *first;
376 first = rcu_dereference(pid->tasks[type].first);
378 result = hlist_entry(first, struct task_struct, pids[(type)].node);
382 EXPORT_SYMBOL(pid_task);
385 * Must be called under rcu_read_lock() or with tasklist_lock read-held.
387 struct task_struct *find_task_by_pid_type_ns(int type, int nr,
388 struct pid_namespace *ns)
390 return pid_task(find_pid_ns(nr, ns), type);
393 EXPORT_SYMBOL(find_task_by_pid_type_ns);
395 struct task_struct *find_task_by_vpid(pid_t vnr)
397 return find_task_by_pid_type_ns(PIDTYPE_PID, vnr,
398 current->nsproxy->pid_ns);
400 EXPORT_SYMBOL(find_task_by_vpid);
402 struct task_struct *find_task_by_pid_ns(pid_t nr, struct pid_namespace *ns)
404 return find_task_by_pid_type_ns(PIDTYPE_PID, nr, ns);
406 EXPORT_SYMBOL(find_task_by_pid_ns);
408 struct pid *get_task_pid(struct task_struct *task, enum pid_type type)
412 pid = get_pid(task->pids[type].pid);
417 struct task_struct *get_pid_task(struct pid *pid, enum pid_type type)
419 struct task_struct *result;
421 result = pid_task(pid, type);
423 get_task_struct(result);
428 struct pid *find_get_pid(pid_t nr)
433 pid = get_pid(find_vpid(nr));
439 pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns)
444 if (pid && ns->level <= pid->level) {
445 upid = &pid->numbers[ns->level];
452 pid_t pid_vnr(struct pid *pid)
454 return pid_nr_ns(pid, current->nsproxy->pid_ns);
456 EXPORT_SYMBOL_GPL(pid_vnr);
458 pid_t task_pid_nr_ns(struct task_struct *tsk, struct pid_namespace *ns)
460 return pid_nr_ns(task_pid(tsk), ns);
462 EXPORT_SYMBOL(task_pid_nr_ns);
464 pid_t task_tgid_nr_ns(struct task_struct *tsk, struct pid_namespace *ns)
466 return pid_nr_ns(task_tgid(tsk), ns);
468 EXPORT_SYMBOL(task_tgid_nr_ns);
470 pid_t task_pgrp_nr_ns(struct task_struct *tsk, struct pid_namespace *ns)
472 return pid_nr_ns(task_pgrp(tsk), ns);
474 EXPORT_SYMBOL(task_pgrp_nr_ns);
476 pid_t task_session_nr_ns(struct task_struct *tsk, struct pid_namespace *ns)
478 return pid_nr_ns(task_session(tsk), ns);
480 EXPORT_SYMBOL(task_session_nr_ns);
483 * Used by proc to find the first pid that is greater then or equal to nr.
485 * If there is a pid at nr this function is exactly the same as find_pid.
487 struct pid *find_ge_pid(int nr, struct pid_namespace *ns)
492 pid = find_pid_ns(nr, ns);
495 nr = next_pidmap(ns, nr);
500 EXPORT_SYMBOL_GPL(find_get_pid);
503 * The pid hash table is scaled according to the amount of memory in the
504 * machine. From a minimum of 16 slots up to 4096 slots at one gigabyte or
507 void __init pidhash_init(void)
510 unsigned long megabytes = nr_kernel_pages >> (20 - PAGE_SHIFT);
512 pidhash_shift = max(4, fls(megabytes * 4));
513 pidhash_shift = min(12, pidhash_shift);
514 pidhash_size = 1 << pidhash_shift;
516 printk("PID hash table entries: %d (order: %d, %Zd bytes)\n",
517 pidhash_size, pidhash_shift,
518 pidhash_size * sizeof(struct hlist_head));
520 pid_hash = alloc_bootmem(pidhash_size * sizeof(*(pid_hash)));
522 panic("Could not alloc pidhash!\n");
523 for (i = 0; i < pidhash_size; i++)
524 INIT_HLIST_HEAD(&pid_hash[i]);
527 void __init pidmap_init(void)
529 init_pid_ns.pidmap[0].page = kzalloc(PAGE_SIZE, GFP_KERNEL);
530 /* Reserve PID 0. We never call free_pidmap(0) */
531 set_bit(0, init_pid_ns.pidmap[0].page);
532 atomic_dec(&init_pid_ns.pidmap[0].nr_free);
534 init_pid_ns.pid_cachep = KMEM_CACHE(pid,
535 SLAB_HWCACHE_ALIGN | SLAB_PANIC);