projects/linux·blob v3.19 · refs

608 lines · 14.9 KiB

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 <[email protected]>, OpenVZ, SWsoft Inc.
24 * (C) 2007 Sukadev Bhattiprolu <[email protected]>, 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 .ns.inum = PROC_PID_INIT_INO,
83#ifdef CONFIG_PID_NS
84 .ns.ops = &pidns_operations,
85#endif
86};
87EXPORT_SYMBOL_GPL(init_pid_ns);
88
89/*
90 * Note: disable interrupts while the pidmap_lock is held as an
91 * interrupt might come in and do read_lock(&tasklist_lock).
92 *
93 * If we don't disable interrupts there is a nasty deadlock between
94 * detach_pid()->free_pid() and another cpu that does
95 * spin_lock(&pidmap_lock) followed by an interrupt routine that does
96 * read_lock(&tasklist_lock);
97 *
98 * After we clean up the tasklist_lock and know there are no
99 * irq handlers that take it we can leave the interrupts enabled.
100 * For now it is easier to be safe than to prove it can't happen.
101 */
102
103static __cacheline_aligned_in_smp DEFINE_SPINLOCK(pidmap_lock);
104
105static void free_pidmap(struct upid *upid)
106{
107 int nr = upid->nr;
108 struct pidmap *map = upid->ns->pidmap + nr / BITS_PER_PAGE;
109 int offset = nr & BITS_PER_PAGE_MASK;
110
111 clear_bit(offset, map->page);
112 atomic_inc(&map->nr_free);
113}
114
115/*
116 * If we started walking pids at 'base', is 'a' seen before 'b'?
117 */
118static int pid_before(int base, int a, int b)
119{
120 /*
121 * This is the same as saying
122 *
123 * (a - base + MAXUINT) % MAXUINT < (b - base + MAXUINT) % MAXUINT
124 * and that mapping orders 'a' and 'b' with respect to 'base'.
125 */
126 return (unsigned)(a - base) < (unsigned)(b - base);
127}
128
129/*
130 * We might be racing with someone else trying to set pid_ns->last_pid
131 * at the pid allocation time (there's also a sysctl for this, but racing
132 * with this one is OK, see comment in kernel/pid_namespace.c about it).
133 * We want the winner to have the "later" value, because if the
134 * "earlier" value prevails, then a pid may get reused immediately.
135 *
136 * Since pids rollover, it is not sufficient to just pick the bigger
137 * value. We have to consider where we started counting from.
138 *
139 * 'base' is the value of pid_ns->last_pid that we observed when
140 * we started looking for a pid.
141 *
142 * 'pid' is the pid that we eventually found.
143 */
144static void set_last_pid(struct pid_namespace *pid_ns, int base, int pid)
145{
146 int prev;
147 int last_write = base;
148 do {
149 prev = last_write;
150 last_write = cmpxchg(&pid_ns->last_pid, prev, pid);
151 } while ((prev != last_write) && (pid_before(base, last_write, pid)));
152}
153
154static int alloc_pidmap(struct pid_namespace *pid_ns)
155{
156 int i, offset, max_scan, pid, last = pid_ns->last_pid;
157 struct pidmap *map;
158
159 pid = last + 1;
160 if (pid >= pid_max)
161 pid = RESERVED_PIDS;
162 offset = pid & BITS_PER_PAGE_MASK;
163 map = &pid_ns->pidmap[pid/BITS_PER_PAGE];
164 /*
165 * If last_pid points into the middle of the map->page we
166 * want to scan this bitmap block twice, the second time
167 * we start with offset == 0 (or RESERVED_PIDS).
168 */
169 max_scan = DIV_ROUND_UP(pid_max, BITS_PER_PAGE) - !offset;
170 for (i = 0; i <= max_scan; ++i) {
171 if (unlikely(!map->page)) {
172 void *page = kzalloc(PAGE_SIZE, GFP_KERNEL);
173 /*
174 * Free the page if someone raced with us
175 * installing it:
176 */
177 spin_lock_irq(&pidmap_lock);
178 if (!map->page) {
179 map->page = page;
180 page = NULL;
181 }
182 spin_unlock_irq(&pidmap_lock);
183 kfree(page);
184 if (unlikely(!map->page))
185 break;
186 }
187 if (likely(atomic_read(&map->nr_free))) {
188 for ( ; ; ) {
189 if (!test_and_set_bit(offset, map->page)) {
190 atomic_dec(&map->nr_free);
191 set_last_pid(pid_ns, last, pid);
192 return pid;
193 }
194 offset = find_next_offset(map, offset);
195 if (offset >= BITS_PER_PAGE)
196 break;
197 pid = mk_pid(pid_ns, map, offset);
198 if (pid >= pid_max)
199 break;
200 }
201 }
202 if (map < &pid_ns->pidmap[(pid_max-1)/BITS_PER_PAGE]) {
203 ++map;
204 offset = 0;
205 } else {
206 map = &pid_ns->pidmap[0];
207 offset = RESERVED_PIDS;
208 if (unlikely(last == offset))
209 break;
210 }
211 pid = mk_pid(pid_ns, map, offset);
212 }
213 return -1;
214}
215
216int next_pidmap(struct pid_namespace *pid_ns, unsigned int last)
217{
218 int offset;
219 struct pidmap *map, *end;
220
221 if (last >= PID_MAX_LIMIT)
222 return -1;
223
224 offset = (last + 1) & BITS_PER_PAGE_MASK;
225 map = &pid_ns->pidmap[(last + 1)/BITS_PER_PAGE];
226 end = &pid_ns->pidmap[PIDMAP_ENTRIES];
227 for (; map < end; map++, offset = 0) {
228 if (unlikely(!map->page))
229 continue;
230 offset = find_next_bit((map)->page, BITS_PER_PAGE, offset);
231 if (offset < BITS_PER_PAGE)
232 return mk_pid(pid_ns, map, offset);
233 }
234 return -1;
235}
236
237void put_pid(struct pid *pid)
238{
239 struct pid_namespace *ns;
240
241 if (!pid)
242 return;
243
244 ns = pid->numbers[pid->level].ns;
245 if ((atomic_read(&pid->count) == 1) ||
246 atomic_dec_and_test(&pid->count)) {
247 kmem_cache_free(ns->pid_cachep, pid);
248 put_pid_ns(ns);
249 }
250}
251EXPORT_SYMBOL_GPL(put_pid);
252
253static void delayed_put_pid(struct rcu_head *rhp)
254{
255 struct pid *pid = container_of(rhp, struct pid, rcu);
256 put_pid(pid);
257}
258
259void free_pid(struct pid *pid)
260{
261 /* We can be called with write_lock_irq(&tasklist_lock) held */
262 int i;
263 unsigned long flags;
264
265 spin_lock_irqsave(&pidmap_lock, flags);
266 for (i = 0; i <= pid->level; i++) {
267 struct upid *upid = pid->numbers + i;
268 struct pid_namespace *ns = upid->ns;
269 hlist_del_rcu(&upid->pid_chain);
270 switch(--ns->nr_hashed) {
271 case 2:
272 case 1:
273 /* When all that is left in the pid namespace
274 * is the reaper wake up the reaper. The reaper
275 * may be sleeping in zap_pid_ns_processes().
276 */
277 wake_up_process(ns->child_reaper);
278 break;
279 case PIDNS_HASH_ADDING:
280 /* Handle a fork failure of the first process */
281 WARN_ON(ns->child_reaper);
282 ns->nr_hashed = 0;
283 /* fall through */
284 case 0:
285 schedule_work(&ns->proc_work);
286 break;
287 }
288 }
289 spin_unlock_irqrestore(&pidmap_lock, flags);
290
291 for (i = 0; i <= pid->level; i++)
292 free_pidmap(pid->numbers + i);
293
294 call_rcu(&pid->rcu, delayed_put_pid);
295}
296
297struct pid *alloc_pid(struct pid_namespace *ns)
298{
299 struct pid *pid;
300 enum pid_type type;
301 int i, nr;
302 struct pid_namespace *tmp;
303 struct upid *upid;
304
305 pid = kmem_cache_alloc(ns->pid_cachep, GFP_KERNEL);
306 if (!pid)
307 goto out;
308
309 tmp = ns;
310 pid->level = ns->level;
311 for (i = ns->level; i >= 0; i--) {
312 nr = alloc_pidmap(tmp);
313 if (nr < 0)
314 goto out_free;
315
316 pid->numbers[i].nr = nr;
317 pid->numbers[i].ns = tmp;
318 tmp = tmp->parent;
319 }
320
321 if (unlikely(is_child_reaper(pid))) {
322 if (pid_ns_prepare_proc(ns))
323 goto out_free;
324 }
325
326 get_pid_ns(ns);
327 atomic_set(&pid->count, 1);
328 for (type = 0; type < PIDTYPE_MAX; ++type)
329 INIT_HLIST_HEAD(&pid->tasks[type]);
330
331 upid = pid->numbers + ns->level;
332 spin_lock_irq(&pidmap_lock);
333 if (!(ns->nr_hashed & PIDNS_HASH_ADDING))
334 goto out_unlock;
335 for ( ; upid >= pid->numbers; --upid) {
336 hlist_add_head_rcu(&upid->pid_chain,
337 &pid_hash[pid_hashfn(upid->nr, upid->ns)]);
338 upid->ns->nr_hashed++;
339 }
340 spin_unlock_irq(&pidmap_lock);
341
342out:
343 return pid;
344
345out_unlock:
346 spin_unlock_irq(&pidmap_lock);
347 put_pid_ns(ns);
348
349out_free:
350 while (++i <= ns->level)
351 free_pidmap(pid->numbers + i);
352
353 kmem_cache_free(ns->pid_cachep, pid);
354 pid = NULL;
355 goto out;
356}
357
358void disable_pid_allocation(struct pid_namespace *ns)
359{
360 spin_lock_irq(&pidmap_lock);
361 ns->nr_hashed &= ~PIDNS_HASH_ADDING;
362 spin_unlock_irq(&pidmap_lock);
363}
364
365struct pid *find_pid_ns(int nr, struct pid_namespace *ns)
366{
367 struct upid *pnr;
368
369 hlist_for_each_entry_rcu(pnr,
370 &pid_hash[pid_hashfn(nr, ns)], pid_chain)
371 if (pnr->nr == nr && pnr->ns == ns)
372 return container_of(pnr, struct pid,
373 numbers[ns->level]);
374
375 return NULL;
376}
377EXPORT_SYMBOL_GPL(find_pid_ns);
378
379struct pid *find_vpid(int nr)
380{
381 return find_pid_ns(nr, task_active_pid_ns(current));
382}
383EXPORT_SYMBOL_GPL(find_vpid);
384
385/*
386 * attach_pid() must be called with the tasklist_lock write-held.
387 */
388void attach_pid(struct task_struct *task, enum pid_type type)
389{
390 struct pid_link *link = &task->pids[type];
391 hlist_add_head_rcu(&link->node, &link->pid->tasks[type]);
392}
393
394static void __change_pid(struct task_struct *task, enum pid_type type,
395 struct pid *new)
396{
397 struct pid_link *link;
398 struct pid *pid;
399 int tmp;
400
401 link = &task->pids[type];
402 pid = link->pid;
403
404 hlist_del_rcu(&link->node);
405 link->pid = new;
406
407 for (tmp = PIDTYPE_MAX; --tmp >= 0; )
408 if (!hlist_empty(&pid->tasks[tmp]))
409 return;
410
411 free_pid(pid);
412}
413
414void detach_pid(struct task_struct *task, enum pid_type type)
415{
416 __change_pid(task, type, NULL);
417}
418
419void change_pid(struct task_struct *task, enum pid_type type,
420 struct pid *pid)
421{
422 __change_pid(task, type, pid);
423 attach_pid(task, type);
424}
425
426/* transfer_pid is an optimization of attach_pid(new), detach_pid(old) */
427void transfer_pid(struct task_struct *old, struct task_struct *new,
428 enum pid_type type)
429{
430 new->pids[type].pid = old->pids[type].pid;
431 hlist_replace_rcu(&old->pids[type].node, &new->pids[type].node);
432}
433
434struct task_struct *pid_task(struct pid *pid, enum pid_type type)
435{
436 struct task_struct *result = NULL;
437 if (pid) {
438 struct hlist_node *first;
439 first = rcu_dereference_check(hlist_first_rcu(&pid->tasks[type]),
440 lockdep_tasklist_lock_is_held());
441 if (first)
442 result = hlist_entry(first, struct task_struct, pids[(type)].node);
443 }
444 return result;
445}
446EXPORT_SYMBOL(pid_task);
447
448/*
449 * Must be called under rcu_read_lock().
450 */
451struct task_struct *find_task_by_pid_ns(pid_t nr, struct pid_namespace *ns)
452{
453 rcu_lockdep_assert(rcu_read_lock_held(),
454 "find_task_by_pid_ns() needs rcu_read_lock()"
455 " protection");
456 return pid_task(find_pid_ns(nr, ns), PIDTYPE_PID);
457}
458
459struct task_struct *find_task_by_vpid(pid_t vnr)
460{
461 return find_task_by_pid_ns(vnr, task_active_pid_ns(current));
462}
463
464struct pid *get_task_pid(struct task_struct *task, enum pid_type type)
465{
466 struct pid *pid;
467 rcu_read_lock();
468 if (type != PIDTYPE_PID)
469 task = task->group_leader;
470 pid = get_pid(task->pids[type].pid);
471 rcu_read_unlock();
472 return pid;
473}
474EXPORT_SYMBOL_GPL(get_task_pid);
475
476struct task_struct *get_pid_task(struct pid *pid, enum pid_type type)
477{
478 struct task_struct *result;
479 rcu_read_lock();
480 result = pid_task(pid, type);
481 if (result)
482 get_task_struct(result);
483 rcu_read_unlock();
484 return result;
485}
486EXPORT_SYMBOL_GPL(get_pid_task);
487
488struct pid *find_get_pid(pid_t nr)
489{
490 struct pid *pid;
491
492 rcu_read_lock();
493 pid = get_pid(find_vpid(nr));
494 rcu_read_unlock();
495
496 return pid;
497}
498EXPORT_SYMBOL_GPL(find_get_pid);
499
500pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns)
501{
502 struct upid *upid;
503 pid_t nr = 0;
504
505 if (pid && ns->level <= pid->level) {
506 upid = &pid->numbers[ns->level];
507 if (upid->ns == ns)
508 nr = upid->nr;
509 }
510 return nr;
511}
512EXPORT_SYMBOL_GPL(pid_nr_ns);
513
514pid_t pid_vnr(struct pid *pid)
515{
516 return pid_nr_ns(pid, task_active_pid_ns(current));
517}
518EXPORT_SYMBOL_GPL(pid_vnr);
519
520pid_t __task_pid_nr_ns(struct task_struct *task, enum pid_type type,
521 struct pid_namespace *ns)
522{
523 pid_t nr = 0;
524
525 rcu_read_lock();
526 if (!ns)
527 ns = task_active_pid_ns(current);
528 if (likely(pid_alive(task))) {
529 if (type != PIDTYPE_PID)
530 task = task->group_leader;
531 nr = pid_nr_ns(task->pids[type].pid, ns);
532 }
533 rcu_read_unlock();
534
535 return nr;
536}
537EXPORT_SYMBOL(__task_pid_nr_ns);
538
539pid_t task_tgid_nr_ns(struct task_struct *tsk, struct pid_namespace *ns)
540{
541 return pid_nr_ns(task_tgid(tsk), ns);
542}
543EXPORT_SYMBOL(task_tgid_nr_ns);
544
545struct pid_namespace *task_active_pid_ns(struct task_struct *tsk)
546{
547 return ns_of_pid(task_pid(tsk));
548}
549EXPORT_SYMBOL_GPL(task_active_pid_ns);
550
551/*
552 * Used by proc to find the first pid that is greater than or equal to nr.
553 *
554 * If there is a pid at nr this function is exactly the same as find_pid_ns.
555 */
556struct pid *find_ge_pid(int nr, struct pid_namespace *ns)
557{
558 struct pid *pid;
559
560 do {
561 pid = find_pid_ns(nr, ns);
562 if (pid)
563 break;
564 nr = next_pidmap(ns, nr);
565 } while (nr > 0);
566
567 return pid;
568}
569
570/*
571 * The pid hash table is scaled according to the amount of memory in the
572 * machine. From a minimum of 16 slots up to 4096 slots at one gigabyte or
573 * more.
574 */
575void __init pidhash_init(void)
576{
577 unsigned int i, pidhash_size;
578
579 pid_hash = alloc_large_system_hash("PID", sizeof(*pid_hash), 0, 18,
580 HASH_EARLY | HASH_SMALL,
581 &pidhash_shift, NULL,
582 0, 4096);
583 pidhash_size = 1U << pidhash_shift;
584
585 for (i = 0; i < pidhash_size; i++)
586 INIT_HLIST_HEAD(&pid_hash[i]);
587}
588
589void __init pidmap_init(void)
590{
591 /* Veryify no one has done anything silly */
592 BUILD_BUG_ON(PID_MAX_LIMIT >= PIDNS_HASH_ADDING);
593
594 /* bump default and minimum pid_max based on number of cpus */
595 pid_max = min(pid_max_max, max_t(int, pid_max,
596 PIDS_PER_CPU_DEFAULT * num_possible_cpus()));
597 pid_max_min = max_t(int, pid_max_min,
598 PIDS_PER_CPU_MIN * num_possible_cpus());
599 pr_info("pid_max: default: %u minimum: %u\n", pid_max, pid_max_min);
600
601 init_pid_ns.pidmap[0].page = kzalloc(PAGE_SIZE, GFP_KERNEL);
602 /* Reserve PID 0. We never call free_pidmap(0) */
603 set_bit(0, init_pid_ns.pidmap[0].page);
604 atomic_dec(&init_pid_ns.pidmap[0].nr_free);
605
606 init_pid_ns.pid_cachep = KMEM_CACHE(pid,
607 SLAB_HWCACHE_ALIGN | SLAB_PANIC);
608}