Root/
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) |
42 | static struct hlist_head *pid_hash; |
43 | static unsigned int pidhash_shift = 4; |
44 | struct pid init_struct_pid = INIT_STRUCT_PID; |
45 | |
46 | int pid_max = PID_MAX_DEFAULT; |
47 | |
48 | #define RESERVED_PIDS 300 |
49 | |
50 | int pid_max_min = RESERVED_PIDS + 1; |
51 | int 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 | |
56 | static 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 | */ |
71 | struct 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 | }; |
82 | EXPORT_SYMBOL_GPL(init_pid_ns); |
83 | |
84 | int 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 | } |
97 | EXPORT_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 | |
113 | static __cacheline_aligned_in_smp DEFINE_SPINLOCK(pidmap_lock); |
114 | |
115 | static 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 | */ |
128 | static 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 | */ |
152 | static 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 | |
162 | static 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 | |
220 | int next_pidmap(struct pid_namespace *pid_ns, int last) |
221 | { |
222 | int offset; |
223 | struct pidmap *map, *end; |
224 | |
225 | offset = (last + 1) & BITS_PER_PAGE_MASK; |
226 | map = &pid_ns->pidmap[(last + 1)/BITS_PER_PAGE]; |
227 | end = &pid_ns->pidmap[PIDMAP_ENTRIES]; |
228 | for (; map < end; map++, offset = 0) { |
229 | if (unlikely(!map->page)) |
230 | continue; |
231 | offset = find_next_bit((map)->page, BITS_PER_PAGE, offset); |
232 | if (offset < BITS_PER_PAGE) |
233 | return mk_pid(pid_ns, map, offset); |
234 | } |
235 | return -1; |
236 | } |
237 | |
238 | void put_pid(struct pid *pid) |
239 | { |
240 | struct pid_namespace *ns; |
241 | |
242 | if (!pid) |
243 | return; |
244 | |
245 | ns = pid->numbers[pid->level].ns; |
246 | if ((atomic_read(&pid->count) == 1) || |
247 | atomic_dec_and_test(&pid->count)) { |
248 | kmem_cache_free(ns->pid_cachep, pid); |
249 | put_pid_ns(ns); |
250 | } |
251 | } |
252 | EXPORT_SYMBOL_GPL(put_pid); |
253 | |
254 | static void delayed_put_pid(struct rcu_head *rhp) |
255 | { |
256 | struct pid *pid = container_of(rhp, struct pid, rcu); |
257 | put_pid(pid); |
258 | } |
259 | |
260 | void free_pid(struct pid *pid) |
261 | { |
262 | /* We can be called with write_lock_irq(&tasklist_lock) held */ |
263 | int i; |
264 | unsigned long flags; |
265 | |
266 | spin_lock_irqsave(&pidmap_lock, flags); |
267 | for (i = 0; i <= pid->level; i++) |
268 | hlist_del_rcu(&pid->numbers[i].pid_chain); |
269 | spin_unlock_irqrestore(&pidmap_lock, flags); |
270 | |
271 | for (i = 0; i <= pid->level; i++) |
272 | free_pidmap(pid->numbers + i); |
273 | |
274 | call_rcu(&pid->rcu, delayed_put_pid); |
275 | } |
276 | |
277 | struct pid *alloc_pid(struct pid_namespace *ns) |
278 | { |
279 | struct pid *pid; |
280 | enum pid_type type; |
281 | int i, nr; |
282 | struct pid_namespace *tmp; |
283 | struct upid *upid; |
284 | |
285 | pid = kmem_cache_alloc(ns->pid_cachep, GFP_KERNEL); |
286 | if (!pid) |
287 | goto out; |
288 | |
289 | tmp = ns; |
290 | for (i = ns->level; i >= 0; i--) { |
291 | nr = alloc_pidmap(tmp); |
292 | if (nr < 0) |
293 | goto out_free; |
294 | |
295 | pid->numbers[i].nr = nr; |
296 | pid->numbers[i].ns = tmp; |
297 | tmp = tmp->parent; |
298 | } |
299 | |
300 | get_pid_ns(ns); |
301 | pid->level = ns->level; |
302 | atomic_set(&pid->count, 1); |
303 | for (type = 0; type < PIDTYPE_MAX; ++type) |
304 | INIT_HLIST_HEAD(&pid->tasks[type]); |
305 | |
306 | upid = pid->numbers + ns->level; |
307 | spin_lock_irq(&pidmap_lock); |
308 | for ( ; upid >= pid->numbers; --upid) |
309 | hlist_add_head_rcu(&upid->pid_chain, |
310 | &pid_hash[pid_hashfn(upid->nr, upid->ns)]); |
311 | spin_unlock_irq(&pidmap_lock); |
312 | |
313 | out: |
314 | return pid; |
315 | |
316 | out_free: |
317 | while (++i <= ns->level) |
318 | free_pidmap(pid->numbers + i); |
319 | |
320 | kmem_cache_free(ns->pid_cachep, pid); |
321 | pid = NULL; |
322 | goto out; |
323 | } |
324 | |
325 | struct pid *find_pid_ns(int nr, struct pid_namespace *ns) |
326 | { |
327 | struct hlist_node *elem; |
328 | struct upid *pnr; |
329 | |
330 | hlist_for_each_entry_rcu(pnr, elem, |
331 | &pid_hash[pid_hashfn(nr, ns)], pid_chain) |
332 | if (pnr->nr == nr && pnr->ns == ns) |
333 | return container_of(pnr, struct pid, |
334 | numbers[ns->level]); |
335 | |
336 | return NULL; |
337 | } |
338 | EXPORT_SYMBOL_GPL(find_pid_ns); |
339 | |
340 | struct pid *find_vpid(int nr) |
341 | { |
342 | return find_pid_ns(nr, current->nsproxy->pid_ns); |
343 | } |
344 | EXPORT_SYMBOL_GPL(find_vpid); |
345 | |
346 | /* |
347 | * attach_pid() must be called with the tasklist_lock write-held. |
348 | */ |
349 | void attach_pid(struct task_struct *task, enum pid_type type, |
350 | struct pid *pid) |
351 | { |
352 | struct pid_link *link; |
353 | |
354 | link = &task->pids[type]; |
355 | link->pid = pid; |
356 | hlist_add_head_rcu(&link->node, &pid->tasks[type]); |
357 | } |
358 | |
359 | static void __change_pid(struct task_struct *task, enum pid_type type, |
360 | struct pid *new) |
361 | { |
362 | struct pid_link *link; |
363 | struct pid *pid; |
364 | int tmp; |
365 | |
366 | link = &task->pids[type]; |
367 | pid = link->pid; |
368 | |
369 | hlist_del_rcu(&link->node); |
370 | link->pid = new; |
371 | |
372 | for (tmp = PIDTYPE_MAX; --tmp >= 0; ) |
373 | if (!hlist_empty(&pid->tasks[tmp])) |
374 | return; |
375 | |
376 | free_pid(pid); |
377 | } |
378 | |
379 | void detach_pid(struct task_struct *task, enum pid_type type) |
380 | { |
381 | __change_pid(task, type, NULL); |
382 | } |
383 | |
384 | void change_pid(struct task_struct *task, enum pid_type type, |
385 | struct pid *pid) |
386 | { |
387 | __change_pid(task, type, pid); |
388 | attach_pid(task, type, pid); |
389 | } |
390 | |
391 | /* transfer_pid is an optimization of attach_pid(new), detach_pid(old) */ |
392 | void transfer_pid(struct task_struct *old, struct task_struct *new, |
393 | enum pid_type type) |
394 | { |
395 | new->pids[type].pid = old->pids[type].pid; |
396 | hlist_replace_rcu(&old->pids[type].node, &new->pids[type].node); |
397 | } |
398 | |
399 | struct task_struct *pid_task(struct pid *pid, enum pid_type type) |
400 | { |
401 | struct task_struct *result = NULL; |
402 | if (pid) { |
403 | struct hlist_node *first; |
404 | first = rcu_dereference_check(hlist_first_rcu(&pid->tasks[type]), |
405 | rcu_read_lock_held() || |
406 | lockdep_tasklist_lock_is_held()); |
407 | if (first) |
408 | result = hlist_entry(first, struct task_struct, pids[(type)].node); |
409 | } |
410 | return result; |
411 | } |
412 | EXPORT_SYMBOL(pid_task); |
413 | |
414 | /* |
415 | * Must be called under rcu_read_lock(). |
416 | */ |
417 | struct task_struct *find_task_by_pid_ns(pid_t nr, struct pid_namespace *ns) |
418 | { |
419 | rcu_lockdep_assert(rcu_read_lock_held()); |
420 | return pid_task(find_pid_ns(nr, ns), PIDTYPE_PID); |
421 | } |
422 | |
423 | struct task_struct *find_task_by_vpid(pid_t vnr) |
424 | { |
425 | return find_task_by_pid_ns(vnr, current->nsproxy->pid_ns); |
426 | } |
427 | |
428 | struct pid *get_task_pid(struct task_struct *task, enum pid_type type) |
429 | { |
430 | struct pid *pid; |
431 | rcu_read_lock(); |
432 | if (type != PIDTYPE_PID) |
433 | task = task->group_leader; |
434 | pid = get_pid(task->pids[type].pid); |
435 | rcu_read_unlock(); |
436 | return pid; |
437 | } |
438 | |
439 | struct task_struct *get_pid_task(struct pid *pid, enum pid_type type) |
440 | { |
441 | struct task_struct *result; |
442 | rcu_read_lock(); |
443 | result = pid_task(pid, type); |
444 | if (result) |
445 | get_task_struct(result); |
446 | rcu_read_unlock(); |
447 | return result; |
448 | } |
449 | |
450 | struct pid *find_get_pid(pid_t nr) |
451 | { |
452 | struct pid *pid; |
453 | |
454 | rcu_read_lock(); |
455 | pid = get_pid(find_vpid(nr)); |
456 | rcu_read_unlock(); |
457 | |
458 | return pid; |
459 | } |
460 | EXPORT_SYMBOL_GPL(find_get_pid); |
461 | |
462 | pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns) |
463 | { |
464 | struct upid *upid; |
465 | pid_t nr = 0; |
466 | |
467 | if (pid && ns->level <= pid->level) { |
468 | upid = &pid->numbers[ns->level]; |
469 | if (upid->ns == ns) |
470 | nr = upid->nr; |
471 | } |
472 | return nr; |
473 | } |
474 | |
475 | pid_t pid_vnr(struct pid *pid) |
476 | { |
477 | return pid_nr_ns(pid, current->nsproxy->pid_ns); |
478 | } |
479 | EXPORT_SYMBOL_GPL(pid_vnr); |
480 | |
481 | pid_t __task_pid_nr_ns(struct task_struct *task, enum pid_type type, |
482 | struct pid_namespace *ns) |
483 | { |
484 | pid_t nr = 0; |
485 | |
486 | rcu_read_lock(); |
487 | if (!ns) |
488 | ns = current->nsproxy->pid_ns; |
489 | if (likely(pid_alive(task))) { |
490 | if (type != PIDTYPE_PID) |
491 | task = task->group_leader; |
492 | nr = pid_nr_ns(task->pids[type].pid, ns); |
493 | } |
494 | rcu_read_unlock(); |
495 | |
496 | return nr; |
497 | } |
498 | EXPORT_SYMBOL(__task_pid_nr_ns); |
499 | |
500 | pid_t task_tgid_nr_ns(struct task_struct *tsk, struct pid_namespace *ns) |
501 | { |
502 | return pid_nr_ns(task_tgid(tsk), ns); |
503 | } |
504 | EXPORT_SYMBOL(task_tgid_nr_ns); |
505 | |
506 | struct pid_namespace *task_active_pid_ns(struct task_struct *tsk) |
507 | { |
508 | return ns_of_pid(task_pid(tsk)); |
509 | } |
510 | EXPORT_SYMBOL_GPL(task_active_pid_ns); |
511 | |
512 | /* |
513 | * Used by proc to find the first pid that is greater than or equal to nr. |
514 | * |
515 | * If there is a pid at nr this function is exactly the same as find_pid_ns. |
516 | */ |
517 | struct pid *find_ge_pid(int nr, struct pid_namespace *ns) |
518 | { |
519 | struct pid *pid; |
520 | |
521 | do { |
522 | pid = find_pid_ns(nr, ns); |
523 | if (pid) |
524 | break; |
525 | nr = next_pidmap(ns, nr); |
526 | } while (nr > 0); |
527 | |
528 | return pid; |
529 | } |
530 | |
531 | /* |
532 | * The pid hash table is scaled according to the amount of memory in the |
533 | * machine. From a minimum of 16 slots up to 4096 slots at one gigabyte or |
534 | * more. |
535 | */ |
536 | void __init pidhash_init(void) |
537 | { |
538 | int i, pidhash_size; |
539 | |
540 | pid_hash = alloc_large_system_hash("PID", sizeof(*pid_hash), 0, 18, |
541 | HASH_EARLY | HASH_SMALL, |
542 | &pidhash_shift, NULL, 4096); |
543 | pidhash_size = 1 << pidhash_shift; |
544 | |
545 | for (i = 0; i < pidhash_size; i++) |
546 | INIT_HLIST_HEAD(&pid_hash[i]); |
547 | } |
548 | |
549 | void __init pidmap_init(void) |
550 | { |
551 | /* bump default and minimum pid_max based on number of cpus */ |
552 | pid_max = min(pid_max_max, max_t(int, pid_max, |
553 | PIDS_PER_CPU_DEFAULT * num_possible_cpus())); |
554 | pid_max_min = max_t(int, pid_max_min, |
555 | PIDS_PER_CPU_MIN * num_possible_cpus()); |
556 | pr_info("pid_max: default: %u minimum: %u\n", pid_max, pid_max_min); |
557 | |
558 | init_pid_ns.pidmap[0].page = kzalloc(PAGE_SIZE, GFP_KERNEL); |
559 | /* Reserve PID 0. We never call free_pidmap(0) */ |
560 | set_bit(0, init_pid_ns.pidmap[0].page); |
561 | atomic_dec(&init_pid_ns.pidmap[0].nr_free); |
562 | |
563 | init_pid_ns.pid_cachep = KMEM_CACHE(pid, |
564 | SLAB_HWCACHE_ALIGN | SLAB_PANIC); |
565 | } |
566 |
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