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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/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
42#define pid_hashfn(nr, ns) \
43 hash_long((unsigned long)nr + (unsigned long)ns, pidhash_shift)
44static struct hlist_head *pid_hash;
45static unsigned int pidhash_shift = 4;
46struct pid init_struct_pid = INIT_STRUCT_PID;
47
48int pid_max = PID_MAX_DEFAULT;
49
50#define RESERVED_PIDS 300
51
52int pid_max_min = RESERVED_PIDS + 1;
53int pid_max_max = PID_MAX_LIMIT;
54
55static inline int mk_pid(struct pid_namespace *pid_ns,
56 struct pidmap *map, int off)
57{
58 return (map - pid_ns->pidmap)*BITS_PER_PAGE + off;
59}
60
61#define find_next_offset(map, off) \
62 find_next_zero_bit((map)->page, BITS_PER_PAGE, off)
63
64/*
65 * PID-map pages start out as NULL, they get allocated upon
66 * first use and are never deallocated. This way a low pid_max
67 * value does not cause lots of bitmaps to be allocated, but
68 * the scheme scales to up to 4 million PIDs, runtime.
69 */
70struct pid_namespace init_pid_ns = {
71 .kref = {
72 .refcount = ATOMIC_INIT(2),
73 },
74 .pidmap = {
75 [ 0 ... PIDMAP_ENTRIES-1] = { ATOMIC_INIT(BITS_PER_PAGE), NULL }
76 },
77 .last_pid = 0,
78 .nr_hashed = PIDNS_HASH_ADDING,
79 .level = 0,
80 .child_reaper = &init_task,
81 .user_ns = &init_user_ns,
82 .proc_inum = PROC_PID_INIT_INO,
83};
84EXPORT_SYMBOL_GPL(init_pid_ns);
85
86/*
87 * Note: disable interrupts while the pidmap_lock is held as an
88 * interrupt might come in and do read_lock(&tasklist_lock).
89 *
90 * If we don't disable interrupts there is a nasty deadlock between
91 * detach_pid()->free_pid() and another cpu that does
92 * spin_lock(&pidmap_lock) followed by an interrupt routine that does
93 * read_lock(&tasklist_lock);
94 *
95 * After we clean up the tasklist_lock and know there are no
96 * irq handlers that take it we can leave the interrupts enabled.
97 * For now it is easier to be safe than to prove it can't happen.
98 */
99
100static __cacheline_aligned_in_smp DEFINE_SPINLOCK(pidmap_lock);
101
102static void free_pidmap(struct upid *upid)
103{
104 int nr = upid->nr;
105 struct pidmap *map = upid->ns->pidmap + nr / BITS_PER_PAGE;
106 int offset = nr & BITS_PER_PAGE_MASK;
107
108 clear_bit(offset, map->page);
109 atomic_inc(&map->nr_free);
110}
111
112/*
113 * If we started walking pids at 'base', is 'a' seen before 'b'?
114 */
115static int pid_before(int base, int a, int b)
116{
117 /*
118 * This is the same as saying
119 *
120 * (a - base + MAXUINT) % MAXUINT < (b - base + MAXUINT) % MAXUINT
121 * and that mapping orders 'a' and 'b' with respect to 'base'.
122 */
123 return (unsigned)(a - base) < (unsigned)(b - base);
124}
125
126/*
127 * We might be racing with someone else trying to set pid_ns->last_pid
128 * at the pid allocation time (there's also a sysctl for this, but racing
129 * with this one is OK, see comment in kernel/pid_namespace.c about it).
130 * We want the winner to have the "later" value, because if the
131 * "earlier" value prevails, then a pid may get reused immediately.
132 *
133 * Since pids rollover, it is not sufficient to just pick the bigger
134 * value. We have to consider where we started counting from.
135 *
136 * 'base' is the value of pid_ns->last_pid that we observed when
137 * we started looking for a pid.
138 *
139 * 'pid' is the pid that we eventually found.
140 */
141static void set_last_pid(struct pid_namespace *pid_ns, int base, int pid)
142{
143 int prev;
144 int last_write = base;
145 do {
146 prev = last_write;
147 last_write = cmpxchg(&pid_ns->last_pid, prev, pid);
148 } while ((prev != last_write) && (pid_before(base, last_write, pid)));
149}
150
151static int alloc_pidmap(struct pid_namespace *pid_ns)
152{
153 int i, offset, max_scan, pid, last = pid_ns->last_pid;
154 struct pidmap *map;
155
156 pid = last + 1;
157 if (pid >= pid_max)
158 pid = RESERVED_PIDS;
159 offset = pid & BITS_PER_PAGE_MASK;
160 map = &pid_ns->pidmap[pid/BITS_PER_PAGE];
161 /*
162 * If last_pid points into the middle of the map->page we
163 * want to scan this bitmap block twice, the second time
164 * we start with offset == 0 (or RESERVED_PIDS).
165 */
166 max_scan = DIV_ROUND_UP(pid_max, BITS_PER_PAGE) - !offset;
167 for (i = 0; i <= max_scan; ++i) {
168 if (unlikely(!map->page)) {
169 void *page = kzalloc(PAGE_SIZE, GFP_KERNEL);
170 /*
171 * Free the page if someone raced with us
172 * installing it:
173 */
174 spin_lock_irq(&pidmap_lock);
175 if (!map->page) {
176 map->page = page;
177 page = NULL;
178 }
179 spin_unlock_irq(&pidmap_lock);
180 kfree(page);
181 if (unlikely(!map->page))
182 break;
183 }
184 if (likely(atomic_read(&map->nr_free))) {
185 for ( ; ; ) {
186 if (!test_and_set_bit(offset, map->page)) {
187 atomic_dec(&map->nr_free);
188 set_last_pid(pid_ns, last, pid);
189 return pid;
190 }
191 offset = find_next_offset(map, offset);
192 if (offset >= BITS_PER_PAGE)
193 break;
194 pid = mk_pid(pid_ns, map, offset);
195 if (pid >= pid_max)
196 break;
197 }
198 }
199 if (map < &pid_ns->pidmap[(pid_max-1)/BITS_PER_PAGE]) {
200 ++map;
201 offset = 0;
202 } else {
203 map = &pid_ns->pidmap[0];
204 offset = RESERVED_PIDS;
205 if (unlikely(last == offset))
206 break;
207 }
208 pid = mk_pid(pid_ns, map, offset);
209 }
210 return -1;
211}
212
213int next_pidmap(struct pid_namespace *pid_ns, unsigned int last)
214{
215 int offset;
216 struct pidmap *map, *end;
217
218 if (last >= PID_MAX_LIMIT)
219 return -1;
220
221 offset = (last + 1) & BITS_PER_PAGE_MASK;
222 map = &pid_ns->pidmap[(last + 1)/BITS_PER_PAGE];
223 end = &pid_ns->pidmap[PIDMAP_ENTRIES];
224 for (; map < end; map++, offset = 0) {
225 if (unlikely(!map->page))
226 continue;
227 offset = find_next_bit((map)->page, BITS_PER_PAGE, offset);
228 if (offset < BITS_PER_PAGE)
229 return mk_pid(pid_ns, map, offset);
230 }
231 return -1;
232}
233
234void put_pid(struct pid *pid)
235{
236 struct pid_namespace *ns;
237
238 if (!pid)
239 return;
240
241 ns = pid->numbers[pid->level].ns;
242 if ((atomic_read(&pid->count) == 1) ||
243 atomic_dec_and_test(&pid->count)) {
244 kmem_cache_free(ns->pid_cachep, pid);
245 put_pid_ns(ns);
246 }
247}
248EXPORT_SYMBOL_GPL(put_pid);
249
250static void delayed_put_pid(struct rcu_head *rhp)
251{
252 struct pid *pid = container_of(rhp, struct pid, rcu);
253 put_pid(pid);
254}
255
256void free_pid(struct pid *pid)
257{
258 /* We can be called with write_lock_irq(&tasklist_lock) held */
259 int i;
260 unsigned long flags;
261
262 spin_lock_irqsave(&pidmap_lock, flags);
263 for (i = 0; i <= pid->level; i++) {
264 struct upid *upid = pid->numbers + i;
265 struct pid_namespace *ns = upid->ns;
266 hlist_del_rcu(&upid->pid_chain);
267 switch(--ns->nr_hashed) {
268 case 2:
269 case 1:
270 /* When all that is left in the pid namespace
271 * is the reaper wake up the reaper. The reaper
272 * may be sleeping in zap_pid_ns_processes().
273 */
274 wake_up_process(ns->child_reaper);
275 break;
276 case PIDNS_HASH_ADDING:
277 /* Handle a fork failure of the first process */
278 WARN_ON(ns->child_reaper);
279 ns->nr_hashed = 0;
280 /* fall through */
281 case 0:
282 schedule_work(&ns->proc_work);
283 break;
284 }
285 }
286 spin_unlock_irqrestore(&pidmap_lock, flags);
287
288 for (i = 0; i <= pid->level; i++)
289 free_pidmap(pid->numbers + i);
290
291 call_rcu(&pid->rcu, delayed_put_pid);
292}
293
294struct pid *alloc_pid(struct pid_namespace *ns)
295{
296 struct pid *pid;
297 enum pid_type type;
298 int i, nr;
299 struct pid_namespace *tmp;
300 struct upid *upid;
301
302 pid = kmem_cache_alloc(ns->pid_cachep, GFP_KERNEL);
303 if (!pid)
304 goto out;
305
306 tmp = ns;
307 pid->level = ns->level;
308 for (i = ns->level; i >= 0; i--) {
309 nr = alloc_pidmap(tmp);
310 if (nr < 0)
311 goto out_free;
312
313 pid->numbers[i].nr = nr;
314 pid->numbers[i].ns = tmp;
315 tmp = tmp->parent;
316 }
317
318 if (unlikely(is_child_reaper(pid))) {
319 if (pid_ns_prepare_proc(ns))
320 goto out_free;
321 }
322
323 get_pid_ns(ns);
324 atomic_set(&pid->count, 1);
325 for (type = 0; type < PIDTYPE_MAX; ++type)
326 INIT_HLIST_HEAD(&pid->tasks[type]);
327
328 upid = pid->numbers + ns->level;
329 spin_lock_irq(&pidmap_lock);
330 if (!(ns->nr_hashed & PIDNS_HASH_ADDING))
331 goto out_unlock;
332 for ( ; upid >= pid->numbers; --upid) {
333 hlist_add_head_rcu(&upid->pid_chain,
334 &pid_hash[pid_hashfn(upid->nr, upid->ns)]);
335 upid->ns->nr_hashed++;
336 }
337 spin_unlock_irq(&pidmap_lock);
338
339out:
340 return pid;
341
342out_unlock:
343 spin_unlock_irq(&pidmap_lock);
344out_free:
345 while (++i <= ns->level)
346 free_pidmap(pid->numbers + i);
347
348 kmem_cache_free(ns->pid_cachep, pid);
349 pid = NULL;
350 goto out;
351}
352
353void disable_pid_allocation(struct pid_namespace *ns)
354{
355 spin_lock_irq(&pidmap_lock);
356 ns->nr_hashed &= ~PIDNS_HASH_ADDING;
357 spin_unlock_irq(&pidmap_lock);
358}
359
360struct pid *find_pid_ns(int nr, struct pid_namespace *ns)
361{
362 struct upid *pnr;
363
364 hlist_for_each_entry_rcu(pnr,
365 &pid_hash[pid_hashfn(nr, ns)], pid_chain)
366 if (pnr->nr == nr && pnr->ns == ns)
367 return container_of(pnr, struct pid,
368 numbers[ns->level]);
369
370 return NULL;
371}
372EXPORT_SYMBOL_GPL(find_pid_ns);
373
374struct pid *find_vpid(int nr)
375{
376 return find_pid_ns(nr, task_active_pid_ns(current));
377}
378EXPORT_SYMBOL_GPL(find_vpid);
379
380/*
381 * attach_pid() must be called with the tasklist_lock write-held.
382 */
383void attach_pid(struct task_struct *task, enum pid_type type)
384{
385 struct pid_link *link = &task->pids[type];
386 hlist_add_head_rcu(&link->node, &link->pid->tasks[type]);
387}
388
389static void __change_pid(struct task_struct *task, enum pid_type type,
390 struct pid *new)
391{
392 struct pid_link *link;
393 struct pid *pid;
394 int tmp;
395
396 link = &task->pids[type];
397 pid = link->pid;
398
399 hlist_del_rcu(&link->node);
400 link->pid = new;
401
402 for (tmp = PIDTYPE_MAX; --tmp >= 0; )
403 if (!hlist_empty(&pid->tasks[tmp]))
404 return;
405
406 free_pid(pid);
407}
408
409void detach_pid(struct task_struct *task, enum pid_type type)
410{
411 __change_pid(task, type, NULL);
412}
413
414void change_pid(struct task_struct *task, enum pid_type type,
415 struct pid *pid)
416{
417 __change_pid(task, type, pid);
418 attach_pid(task, type);
419}
420
421/* transfer_pid is an optimization of attach_pid(new), detach_pid(old) */
422void transfer_pid(struct task_struct *old, struct task_struct *new,
423 enum pid_type type)
424{
425 new->pids[type].pid = old->pids[type].pid;
426 hlist_replace_rcu(&old->pids[type].node, &new->pids[type].node);
427}
428
429struct task_struct *pid_task(struct pid *pid, enum pid_type type)
430{
431 struct task_struct *result = NULL;
432 if (pid) {
433 struct hlist_node *first;
434 first = rcu_dereference_check(hlist_first_rcu(&pid->tasks[type]),
435 lockdep_tasklist_lock_is_held());
436 if (first)
437 result = hlist_entry(first, struct task_struct, pids[(type)].node);
438 }
439 return result;
440}
441EXPORT_SYMBOL(pid_task);
442
443/*
444 * Must be called under rcu_read_lock().
445 */
446struct task_struct *find_task_by_pid_ns(pid_t nr, struct pid_namespace *ns)
447{
448 rcu_lockdep_assert(rcu_read_lock_held(),
449 "find_task_by_pid_ns() needs rcu_read_lock()"
450 " protection");
451 return pid_task(find_pid_ns(nr, ns), PIDTYPE_PID);
452}
453
454struct task_struct *find_task_by_vpid(pid_t vnr)
455{
456 return find_task_by_pid_ns(vnr, task_active_pid_ns(current));
457}
458
459struct pid *get_task_pid(struct task_struct *task, enum pid_type type)
460{
461 struct pid *pid;
462 rcu_read_lock();
463 if (type != PIDTYPE_PID)
464 task = task->group_leader;
465 pid = get_pid(task->pids[type].pid);
466 rcu_read_unlock();
467 return pid;
468}
469EXPORT_SYMBOL_GPL(get_task_pid);
470
471struct task_struct *get_pid_task(struct pid *pid, enum pid_type type)
472{
473 struct task_struct *result;
474 rcu_read_lock();
475 result = pid_task(pid, type);
476 if (result)
477 get_task_struct(result);
478 rcu_read_unlock();
479 return result;
480}
481EXPORT_SYMBOL_GPL(get_pid_task);
482
483struct pid *find_get_pid(pid_t nr)
484{
485 struct pid *pid;
486
487 rcu_read_lock();
488 pid = get_pid(find_vpid(nr));
489 rcu_read_unlock();
490
491 return pid;
492}
493EXPORT_SYMBOL_GPL(find_get_pid);
494
495pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns)
496{
497 struct upid *upid;
498 pid_t nr = 0;
499
500 if (pid && ns->level <= pid->level) {
501 upid = &pid->numbers[ns->level];
502 if (upid->ns == ns)
503 nr = upid->nr;
504 }
505 return nr;
506}
507EXPORT_SYMBOL_GPL(pid_nr_ns);
508
509pid_t pid_vnr(struct pid *pid)
510{
511 return pid_nr_ns(pid, task_active_pid_ns(current));
512}
513EXPORT_SYMBOL_GPL(pid_vnr);
514
515pid_t __task_pid_nr_ns(struct task_struct *task, enum pid_type type,
516 struct pid_namespace *ns)
517{
518 pid_t nr = 0;
519
520 rcu_read_lock();
521 if (!ns)
522 ns = task_active_pid_ns(current);
523 if (likely(pid_alive(task))) {
524 if (type != PIDTYPE_PID)
525 task = task->group_leader;
526 nr = pid_nr_ns(task->pids[type].pid, ns);
527 }
528 rcu_read_unlock();
529
530 return nr;
531}
532EXPORT_SYMBOL(__task_pid_nr_ns);
533
534pid_t task_tgid_nr_ns(struct task_struct *tsk, struct pid_namespace *ns)
535{
536 return pid_nr_ns(task_tgid(tsk), ns);
537}
538EXPORT_SYMBOL(task_tgid_nr_ns);
539
540struct pid_namespace *task_active_pid_ns(struct task_struct *tsk)
541{
542 return ns_of_pid(task_pid(tsk));
543}
544EXPORT_SYMBOL_GPL(task_active_pid_ns);
545
546/*
547 * Used by proc to find the first pid that is greater than or equal to nr.
548 *
549 * If there is a pid at nr this function is exactly the same as find_pid_ns.
550 */
551struct pid *find_ge_pid(int nr, struct pid_namespace *ns)
552{
553 struct pid *pid;
554
555 do {
556 pid = find_pid_ns(nr, ns);
557 if (pid)
558 break;
559 nr = next_pidmap(ns, nr);
560 } while (nr > 0);
561
562 return pid;
563}
564
565/*
566 * The pid hash table is scaled according to the amount of memory in the
567 * machine. From a minimum of 16 slots up to 4096 slots at one gigabyte or
568 * more.
569 */
570void __init pidhash_init(void)
571{
572 unsigned int i, pidhash_size;
573
574 pid_hash = alloc_large_system_hash("PID", sizeof(*pid_hash), 0, 18,
575 HASH_EARLY | HASH_SMALL,
576 &pidhash_shift, NULL,
577 0, 4096);
578 pidhash_size = 1U << pidhash_shift;
579
580 for (i = 0; i < pidhash_size; i++)
581 INIT_HLIST_HEAD(&pid_hash[i]);
582}
583
584void __init pidmap_init(void)
585{
586 /* Veryify no one has done anything silly */
587 BUILD_BUG_ON(PID_MAX_LIMIT >= PIDNS_HASH_ADDING);
588
589 /* bump default and minimum pid_max based on number of cpus */
590 pid_max = min(pid_max_max, max_t(int, pid_max,
591 PIDS_PER_CPU_DEFAULT * num_possible_cpus()));
592 pid_max_min = max_t(int, pid_max_min,
593 PIDS_PER_CPU_MIN * num_possible_cpus());
594 pr_info("pid_max: default: %u minimum: %u\n", pid_max, pid_max_min);
595
596 init_pid_ns.pidmap[0].page = kzalloc(PAGE_SIZE, GFP_KERNEL);
597 /* Reserve PID 0. We never call free_pidmap(0) */
598 set_bit(0, init_pid_ns.pidmap[0].page);
599 atomic_dec(&init_pid_ns.pidmap[0].nr_free);
600
601 init_pid_ns.pid_cachep = KMEM_CACHE(pid,
602 SLAB_HWCACHE_ALIGN | SLAB_PANIC);
603}
1/*
2 * Generic pidhash and scalable, time-bounded PID allocator
3 *
4 * (C) 2002-2003 William Irwin, IBM
5 * (C) 2004 William Irwin, 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/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>
39
40#define pid_hashfn(nr, ns) \
41 hash_long((unsigned long)nr + (unsigned long)ns, pidhash_shift)
42static struct hlist_head *pid_hash;
43static unsigned int pidhash_shift = 4;
44struct pid init_struct_pid = INIT_STRUCT_PID;
45
46int pid_max = PID_MAX_DEFAULT;
47
48#define RESERVED_PIDS 300
49
50int pid_max_min = RESERVED_PIDS + 1;
51int pid_max_max = PID_MAX_LIMIT;
52
53#define BITS_PER_PAGE (PAGE_SIZE*8)
54#define BITS_PER_PAGE_MASK (BITS_PER_PAGE-1)
55
56static inline int mk_pid(struct pid_namespace *pid_ns,
57 struct pidmap *map, int off)
58{
59 return (map - pid_ns->pidmap)*BITS_PER_PAGE + off;
60}
61
62#define find_next_offset(map, off) \
63 find_next_zero_bit((map)->page, BITS_PER_PAGE, off)
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 = {
73 .refcount = ATOMIC_INIT(2),
74 },
75 .pidmap = {
76 [ 0 ... PIDMAP_ENTRIES-1] = { ATOMIC_INIT(BITS_PER_PAGE), NULL }
77 },
78 .last_pid = 0,
79 .level = 0,
80 .child_reaper = &init_task,
81};
82EXPORT_SYMBOL_GPL(init_pid_ns);
83
84int is_container_init(struct task_struct *tsk)
85{
86 int ret = 0;
87 struct pid *pid;
88
89 rcu_read_lock();
90 pid = task_pid(tsk);
91 if (pid != NULL && pid->numbers[pid->level].nr == 1)
92 ret = 1;
93 rcu_read_unlock();
94
95 return ret;
96}
97EXPORT_SYMBOL(is_container_init);
98
99/*
100 * Note: disable interrupts while the pidmap_lock is held as an
101 * interrupt might come in and do read_lock(&tasklist_lock).
102 *
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);
107 *
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.
111 */
112
113static __cacheline_aligned_in_smp DEFINE_SPINLOCK(pidmap_lock);
114
115static void free_pidmap(struct upid *upid)
116{
117 int nr = upid->nr;
118 struct pidmap *map = upid->ns->pidmap + nr / BITS_PER_PAGE;
119 int offset = nr & BITS_PER_PAGE_MASK;
120
121 clear_bit(offset, map->page);
122 atomic_inc(&map->nr_free);
123}
124
125/*
126 * If we started walking pids at 'base', is 'a' seen before 'b'?
127 */
128static int pid_before(int base, int a, int b)
129{
130 /*
131 * This is the same as saying
132 *
133 * (a - base + MAXUINT) % MAXUINT < (b - base + MAXUINT) % MAXUINT
134 * and that mapping orders 'a' and 'b' with respect to 'base'.
135 */
136 return (unsigned)(a - base) < (unsigned)(b - base);
137}
138
139/*
140 * We might be racing with someone else trying to set pid_ns->last_pid.
141 * We want the winner to have the "later" value, because if the
142 * "earlier" value prevails, then a pid may get reused immediately.
143 *
144 * Since pids rollover, it is not sufficient to just pick the bigger
145 * value. We have to consider where we started counting from.
146 *
147 * 'base' is the value of pid_ns->last_pid that we observed when
148 * we started looking for a pid.
149 *
150 * 'pid' is the pid that we eventually found.
151 */
152static void set_last_pid(struct pid_namespace *pid_ns, int base, int pid)
153{
154 int prev;
155 int last_write = base;
156 do {
157 prev = last_write;
158 last_write = cmpxchg(&pid_ns->last_pid, prev, pid);
159 } while ((prev != last_write) && (pid_before(base, last_write, pid)));
160}
161
162static int alloc_pidmap(struct pid_namespace *pid_ns)
163{
164 int i, offset, max_scan, pid, last = pid_ns->last_pid;
165 struct pidmap *map;
166
167 pid = last + 1;
168 if (pid >= pid_max)
169 pid = RESERVED_PIDS;
170 offset = pid & BITS_PER_PAGE_MASK;
171 map = &pid_ns->pidmap[pid/BITS_PER_PAGE];
172 /*
173 * If last_pid points into the middle of the map->page we
174 * want to scan this bitmap block twice, the second time
175 * we start with offset == 0 (or RESERVED_PIDS).
176 */
177 max_scan = DIV_ROUND_UP(pid_max, BITS_PER_PAGE) - !offset;
178 for (i = 0; i <= max_scan; ++i) {
179 if (unlikely(!map->page)) {
180 void *page = kzalloc(PAGE_SIZE, GFP_KERNEL);
181 /*
182 * Free the page if someone raced with us
183 * installing it:
184 */
185 spin_lock_irq(&pidmap_lock);
186 if (!map->page) {
187 map->page = page;
188 page = NULL;
189 }
190 spin_unlock_irq(&pidmap_lock);
191 kfree(page);
192 if (unlikely(!map->page))
193 break;
194 }
195 if (likely(atomic_read(&map->nr_free))) {
196 do {
197 if (!test_and_set_bit(offset, map->page)) {
198 atomic_dec(&map->nr_free);
199 set_last_pid(pid_ns, last, pid);
200 return pid;
201 }
202 offset = find_next_offset(map, offset);
203 pid = mk_pid(pid_ns, map, offset);
204 } while (offset < BITS_PER_PAGE && pid < pid_max);
205 }
206 if (map < &pid_ns->pidmap[(pid_max-1)/BITS_PER_PAGE]) {
207 ++map;
208 offset = 0;
209 } else {
210 map = &pid_ns->pidmap[0];
211 offset = RESERVED_PIDS;
212 if (unlikely(last == offset))
213 break;
214 }
215 pid = mk_pid(pid_ns, map, offset);
216 }
217 return -1;
218}
219
220int next_pidmap(struct pid_namespace *pid_ns, unsigned int last)
221{
222 int offset;
223 struct pidmap *map, *end;
224
225 if (last >= PID_MAX_LIMIT)
226 return -1;
227
228 offset = (last + 1) & BITS_PER_PAGE_MASK;
229 map = &pid_ns->pidmap[(last + 1)/BITS_PER_PAGE];
230 end = &pid_ns->pidmap[PIDMAP_ENTRIES];
231 for (; map < end; map++, offset = 0) {
232 if (unlikely(!map->page))
233 continue;
234 offset = find_next_bit((map)->page, BITS_PER_PAGE, offset);
235 if (offset < BITS_PER_PAGE)
236 return mk_pid(pid_ns, map, offset);
237 }
238 return -1;
239}
240
241void put_pid(struct pid *pid)
242{
243 struct pid_namespace *ns;
244
245 if (!pid)
246 return;
247
248 ns = pid->numbers[pid->level].ns;
249 if ((atomic_read(&pid->count) == 1) ||
250 atomic_dec_and_test(&pid->count)) {
251 kmem_cache_free(ns->pid_cachep, pid);
252 put_pid_ns(ns);
253 }
254}
255EXPORT_SYMBOL_GPL(put_pid);
256
257static void delayed_put_pid(struct rcu_head *rhp)
258{
259 struct pid *pid = container_of(rhp, struct pid, rcu);
260 put_pid(pid);
261}
262
263void free_pid(struct pid *pid)
264{
265 /* We can be called with write_lock_irq(&tasklist_lock) held */
266 int i;
267 unsigned long flags;
268
269 spin_lock_irqsave(&pidmap_lock, flags);
270 for (i = 0; i <= pid->level; i++)
271 hlist_del_rcu(&pid->numbers[i].pid_chain);
272 spin_unlock_irqrestore(&pidmap_lock, flags);
273
274 for (i = 0; i <= pid->level; i++)
275 free_pidmap(pid->numbers + i);
276
277 call_rcu(&pid->rcu, delayed_put_pid);
278}
279
280struct pid *alloc_pid(struct pid_namespace *ns)
281{
282 struct pid *pid;
283 enum pid_type type;
284 int i, nr;
285 struct pid_namespace *tmp;
286 struct upid *upid;
287
288 pid = kmem_cache_alloc(ns->pid_cachep, GFP_KERNEL);
289 if (!pid)
290 goto out;
291
292 tmp = ns;
293 for (i = ns->level; i >= 0; i--) {
294 nr = alloc_pidmap(tmp);
295 if (nr < 0)
296 goto out_free;
297
298 pid->numbers[i].nr = nr;
299 pid->numbers[i].ns = tmp;
300 tmp = tmp->parent;
301 }
302
303 get_pid_ns(ns);
304 pid->level = ns->level;
305 atomic_set(&pid->count, 1);
306 for (type = 0; type < PIDTYPE_MAX; ++type)
307 INIT_HLIST_HEAD(&pid->tasks[type]);
308
309 upid = pid->numbers + ns->level;
310 spin_lock_irq(&pidmap_lock);
311 for ( ; upid >= pid->numbers; --upid)
312 hlist_add_head_rcu(&upid->pid_chain,
313 &pid_hash[pid_hashfn(upid->nr, upid->ns)]);
314 spin_unlock_irq(&pidmap_lock);
315
316out:
317 return pid;
318
319out_free:
320 while (++i <= ns->level)
321 free_pidmap(pid->numbers + i);
322
323 kmem_cache_free(ns->pid_cachep, pid);
324 pid = NULL;
325 goto out;
326}
327
328struct pid *find_pid_ns(int nr, struct pid_namespace *ns)
329{
330 struct hlist_node *elem;
331 struct upid *pnr;
332
333 hlist_for_each_entry_rcu(pnr, elem,
334 &pid_hash[pid_hashfn(nr, ns)], pid_chain)
335 if (pnr->nr == nr && pnr->ns == ns)
336 return container_of(pnr, struct pid,
337 numbers[ns->level]);
338
339 return NULL;
340}
341EXPORT_SYMBOL_GPL(find_pid_ns);
342
343struct pid *find_vpid(int nr)
344{
345 return find_pid_ns(nr, current->nsproxy->pid_ns);
346}
347EXPORT_SYMBOL_GPL(find_vpid);
348
349/*
350 * attach_pid() must be called with the tasklist_lock write-held.
351 */
352void attach_pid(struct task_struct *task, enum pid_type type,
353 struct pid *pid)
354{
355 struct pid_link *link;
356
357 link = &task->pids[type];
358 link->pid = pid;
359 hlist_add_head_rcu(&link->node, &pid->tasks[type]);
360}
361
362static void __change_pid(struct task_struct *task, enum pid_type type,
363 struct pid *new)
364{
365 struct pid_link *link;
366 struct pid *pid;
367 int tmp;
368
369 link = &task->pids[type];
370 pid = link->pid;
371
372 hlist_del_rcu(&link->node);
373 link->pid = new;
374
375 for (tmp = PIDTYPE_MAX; --tmp >= 0; )
376 if (!hlist_empty(&pid->tasks[tmp]))
377 return;
378
379 free_pid(pid);
380}
381
382void detach_pid(struct task_struct *task, enum pid_type type)
383{
384 __change_pid(task, type, NULL);
385}
386
387void change_pid(struct task_struct *task, enum pid_type type,
388 struct pid *pid)
389{
390 __change_pid(task, type, pid);
391 attach_pid(task, type, pid);
392}
393
394/* transfer_pid is an optimization of attach_pid(new), detach_pid(old) */
395void transfer_pid(struct task_struct *old, struct task_struct *new,
396 enum pid_type type)
397{
398 new->pids[type].pid = old->pids[type].pid;
399 hlist_replace_rcu(&old->pids[type].node, &new->pids[type].node);
400}
401
402struct task_struct *pid_task(struct pid *pid, enum pid_type type)
403{
404 struct task_struct *result = NULL;
405 if (pid) {
406 struct hlist_node *first;
407 first = rcu_dereference_check(hlist_first_rcu(&pid->tasks[type]),
408 lockdep_tasklist_lock_is_held());
409 if (first)
410 result = hlist_entry(first, struct task_struct, pids[(type)].node);
411 }
412 return result;
413}
414EXPORT_SYMBOL(pid_task);
415
416/*
417 * Must be called under rcu_read_lock().
418 */
419struct task_struct *find_task_by_pid_ns(pid_t nr, struct pid_namespace *ns)
420{
421 rcu_lockdep_assert(rcu_read_lock_held());
422 return pid_task(find_pid_ns(nr, ns), PIDTYPE_PID);
423}
424
425struct task_struct *find_task_by_vpid(pid_t vnr)
426{
427 return find_task_by_pid_ns(vnr, current->nsproxy->pid_ns);
428}
429
430struct pid *get_task_pid(struct task_struct *task, enum pid_type type)
431{
432 struct pid *pid;
433 rcu_read_lock();
434 if (type != PIDTYPE_PID)
435 task = task->group_leader;
436 pid = get_pid(task->pids[type].pid);
437 rcu_read_unlock();
438 return pid;
439}
440EXPORT_SYMBOL_GPL(get_task_pid);
441
442struct task_struct *get_pid_task(struct pid *pid, enum pid_type type)
443{
444 struct task_struct *result;
445 rcu_read_lock();
446 result = pid_task(pid, type);
447 if (result)
448 get_task_struct(result);
449 rcu_read_unlock();
450 return result;
451}
452EXPORT_SYMBOL_GPL(get_pid_task);
453
454struct pid *find_get_pid(pid_t nr)
455{
456 struct pid *pid;
457
458 rcu_read_lock();
459 pid = get_pid(find_vpid(nr));
460 rcu_read_unlock();
461
462 return pid;
463}
464EXPORT_SYMBOL_GPL(find_get_pid);
465
466pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns)
467{
468 struct upid *upid;
469 pid_t nr = 0;
470
471 if (pid && ns->level <= pid->level) {
472 upid = &pid->numbers[ns->level];
473 if (upid->ns == ns)
474 nr = upid->nr;
475 }
476 return nr;
477}
478
479pid_t pid_vnr(struct pid *pid)
480{
481 return pid_nr_ns(pid, current->nsproxy->pid_ns);
482}
483EXPORT_SYMBOL_GPL(pid_vnr);
484
485pid_t __task_pid_nr_ns(struct task_struct *task, enum pid_type type,
486 struct pid_namespace *ns)
487{
488 pid_t nr = 0;
489
490 rcu_read_lock();
491 if (!ns)
492 ns = current->nsproxy->pid_ns;
493 if (likely(pid_alive(task))) {
494 if (type != PIDTYPE_PID)
495 task = task->group_leader;
496 nr = pid_nr_ns(task->pids[type].pid, ns);
497 }
498 rcu_read_unlock();
499
500 return nr;
501}
502EXPORT_SYMBOL(__task_pid_nr_ns);
503
504pid_t task_tgid_nr_ns(struct task_struct *tsk, struct pid_namespace *ns)
505{
506 return pid_nr_ns(task_tgid(tsk), ns);
507}
508EXPORT_SYMBOL(task_tgid_nr_ns);
509
510struct pid_namespace *task_active_pid_ns(struct task_struct *tsk)
511{
512 return ns_of_pid(task_pid(tsk));
513}
514EXPORT_SYMBOL_GPL(task_active_pid_ns);
515
516/*
517 * Used by proc to find the first pid that is greater than or equal to nr.
518 *
519 * If there is a pid at nr this function is exactly the same as find_pid_ns.
520 */
521struct pid *find_ge_pid(int nr, struct pid_namespace *ns)
522{
523 struct pid *pid;
524
525 do {
526 pid = find_pid_ns(nr, ns);
527 if (pid)
528 break;
529 nr = next_pidmap(ns, nr);
530 } while (nr > 0);
531
532 return pid;
533}
534
535/*
536 * The pid hash table is scaled according to the amount of memory in the
537 * machine. From a minimum of 16 slots up to 4096 slots at one gigabyte or
538 * more.
539 */
540void __init pidhash_init(void)
541{
542 int i, pidhash_size;
543
544 pid_hash = alloc_large_system_hash("PID", sizeof(*pid_hash), 0, 18,
545 HASH_EARLY | HASH_SMALL,
546 &pidhash_shift, NULL, 4096);
547 pidhash_size = 1 << pidhash_shift;
548
549 for (i = 0; i < pidhash_size; i++)
550 INIT_HLIST_HEAD(&pid_hash[i]);
551}
552
553void __init pidmap_init(void)
554{
555 /* bump default and minimum pid_max based on number of cpus */
556 pid_max = min(pid_max_max, max_t(int, pid_max,
557 PIDS_PER_CPU_DEFAULT * num_possible_cpus()));
558 pid_max_min = max_t(int, pid_max_min,
559 PIDS_PER_CPU_MIN * num_possible_cpus());
560 pr_info("pid_max: default: %u minimum: %u\n", pid_max, pid_max_min);
561
562 init_pid_ns.pidmap[0].page = kzalloc(PAGE_SIZE, GFP_KERNEL);
563 /* Reserve PID 0. We never call free_pidmap(0) */
564 set_bit(0, init_pid_ns.pidmap[0].page);
565 atomic_dec(&init_pid_ns.pidmap[0].nr_free);
566
567 init_pid_ns.pid_cachep = KMEM_CACHE(pid,
568 SLAB_HWCACHE_ALIGN | SLAB_PANIC);
569}