projects/linux·blob v2.6.32-rc1 · refs

521 lines · 12.3 KiB

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 <[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/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
125static int alloc_pidmap(struct pid_namespace *pid_ns)
126{
127 int i, offset, max_scan, pid, last = pid_ns->last_pid;
128 struct pidmap *map;
129
130 pid = last + 1;
131 if (pid >= pid_max)
132 pid = RESERVED_PIDS;
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);
139 /*
140 * Free the page if someone raced with us
141 * installing it:
142 */
143 spin_lock_irq(&pidmap_lock);
144 if (map->page)
145 kfree(page);
146 else
147 map->page = page;
148 spin_unlock_irq(&pidmap_lock);
149 if (unlikely(!map->page))
150 break;
151 }
152 if (likely(atomic_read(&map->nr_free))) {
153 do {
154 if (!test_and_set_bit(offset, map->page)) {
155 atomic_dec(&map->nr_free);
156 pid_ns->last_pid = pid;
157 return pid;
158 }
159 offset = find_next_offset(map, offset);
160 pid = mk_pid(pid_ns, map, offset);
161 /*
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.
166 */
167 } while (offset < BITS_PER_PAGE && pid < pid_max &&
168 (i != max_scan || pid < last ||
169 !((last+1) & BITS_PER_PAGE_MASK)));
170 }
171 if (map < &pid_ns->pidmap[(pid_max-1)/BITS_PER_PAGE]) {
172 ++map;
173 offset = 0;
174 } else {
175 map = &pid_ns->pidmap[0];
176 offset = RESERVED_PIDS;
177 if (unlikely(last == offset))
178 break;
179 }
180 pid = mk_pid(pid_ns, map, offset);
181 }
182 return -1;
183}
184
185int next_pidmap(struct pid_namespace *pid_ns, int last)
186{
187 int offset;
188 struct pidmap *map, *end;
189
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))
195 continue;
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);
199 }
200 return -1;
201}
202
203void put_pid(struct pid *pid)
204{
205 struct pid_namespace *ns;
206
207 if (!pid)
208 return;
209
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);
214 put_pid_ns(ns);
215 }
216}
217EXPORT_SYMBOL_GPL(put_pid);
218
219static void delayed_put_pid(struct rcu_head *rhp)
220{
221 struct pid *pid = container_of(rhp, struct pid, rcu);
222 put_pid(pid);
223}
224
225void free_pid(struct pid *pid)
226{
227 /* We can be called with write_lock_irq(&tasklist_lock) held */
228 int i;
229 unsigned long flags;
230
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);
235
236 for (i = 0; i <= pid->level; i++)
237 free_pidmap(pid->numbers + i);
238
239 call_rcu(&pid->rcu, delayed_put_pid);
240}
241
242struct pid *alloc_pid(struct pid_namespace *ns)
243{
244 struct pid *pid;
245 enum pid_type type;
246 int i, nr;
247 struct pid_namespace *tmp;
248 struct upid *upid;
249
250 pid = kmem_cache_alloc(ns->pid_cachep, GFP_KERNEL);
251 if (!pid)
252 goto out;
253
254 tmp = ns;
255 for (i = ns->level; i >= 0; i--) {
256 nr = alloc_pidmap(tmp);
257 if (nr < 0)
258 goto out_free;
259
260 pid->numbers[i].nr = nr;
261 pid->numbers[i].ns = tmp;
262 tmp = tmp->parent;
263 }
264
265 get_pid_ns(ns);
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]);
270
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)]);
276 }
277 spin_unlock_irq(&pidmap_lock);
278
279out:
280 return pid;
281
282out_free:
283 while (++i <= ns->level)
284 free_pidmap(pid->numbers + i);
285
286 kmem_cache_free(ns->pid_cachep, pid);
287 pid = NULL;
288 goto out;
289}
290
291struct pid *find_pid_ns(int nr, struct pid_namespace *ns)
292{
293 struct hlist_node *elem;
294 struct upid *pnr;
295
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,
300 numbers[ns->level]);
301
302 return NULL;
303}
304EXPORT_SYMBOL_GPL(find_pid_ns);
305
306struct pid *find_vpid(int nr)
307{
308 return find_pid_ns(nr, current->nsproxy->pid_ns);
309}
310EXPORT_SYMBOL_GPL(find_vpid);
311
312/*
313 * attach_pid() must be called with the tasklist_lock write-held.
314 */
315void attach_pid(struct task_struct *task, enum pid_type type,
316 struct pid *pid)
317{
318 struct pid_link *link;
319
320 link = &task->pids[type];
321 link->pid = pid;
322 hlist_add_head_rcu(&link->node, &pid->tasks[type]);
323}
324
325static void __change_pid(struct task_struct *task, enum pid_type type,
326 struct pid *new)
327{
328 struct pid_link *link;
329 struct pid *pid;
330 int tmp;
331
332 link = &task->pids[type];
333 pid = link->pid;
334
335 hlist_del_rcu(&link->node);
336 link->pid = new;
337
338 for (tmp = PIDTYPE_MAX; --tmp >= 0; )
339 if (!hlist_empty(&pid->tasks[tmp]))
340 return;
341
342 free_pid(pid);
343}
344
345void detach_pid(struct task_struct *task, enum pid_type type)
346{
347 __change_pid(task, type, NULL);
348}
349
350void change_pid(struct task_struct *task, enum pid_type type,
351 struct pid *pid)
352{
353 __change_pid(task, type, pid);
354 attach_pid(task, type, pid);
355}
356
357/* transfer_pid is an optimization of attach_pid(new), detach_pid(old) */
358void transfer_pid(struct task_struct *old, struct task_struct *new,
359 enum pid_type type)
360{
361 new->pids[type].pid = old->pids[type].pid;
362 hlist_replace_rcu(&old->pids[type].node, &new->pids[type].node);
363}
364
365struct task_struct *pid_task(struct pid *pid, enum pid_type type)
366{
367 struct task_struct *result = NULL;
368 if (pid) {
369 struct hlist_node *first;
370 first = rcu_dereference(pid->tasks[type].first);
371 if (first)
372 result = hlist_entry(first, struct task_struct, pids[(type)].node);
373 }
374 return result;
375}
376EXPORT_SYMBOL(pid_task);
377
378/*
379 * Must be called under rcu_read_lock() or with tasklist_lock read-held.
380 */
381struct task_struct *find_task_by_pid_ns(pid_t nr, struct pid_namespace *ns)
382{
383 return pid_task(find_pid_ns(nr, ns), PIDTYPE_PID);
384}
385
386struct task_struct *find_task_by_vpid(pid_t vnr)
387{
388 return find_task_by_pid_ns(vnr, current->nsproxy->pid_ns);
389}
390
391struct pid *get_task_pid(struct task_struct *task, enum pid_type type)
392{
393 struct pid *pid;
394 rcu_read_lock();
395 if (type != PIDTYPE_PID)
396 task = task->group_leader;
397 pid = get_pid(task->pids[type].pid);
398 rcu_read_unlock();
399 return pid;
400}
401
402struct task_struct *get_pid_task(struct pid *pid, enum pid_type type)
403{
404 struct task_struct *result;
405 rcu_read_lock();
406 result = pid_task(pid, type);
407 if (result)
408 get_task_struct(result);
409 rcu_read_unlock();
410 return result;
411}
412
413struct pid *find_get_pid(pid_t nr)
414{
415 struct pid *pid;
416
417 rcu_read_lock();
418 pid = get_pid(find_vpid(nr));
419 rcu_read_unlock();
420
421 return pid;
422}
423EXPORT_SYMBOL_GPL(find_get_pid);
424
425pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns)
426{
427 struct upid *upid;
428 pid_t nr = 0;
429
430 if (pid && ns->level <= pid->level) {
431 upid = &pid->numbers[ns->level];
432 if (upid->ns == ns)
433 nr = upid->nr;
434 }
435 return nr;
436}
437
438pid_t pid_vnr(struct pid *pid)
439{
440 return pid_nr_ns(pid, current->nsproxy->pid_ns);
441}
442EXPORT_SYMBOL_GPL(pid_vnr);
443
444pid_t __task_pid_nr_ns(struct task_struct *task, enum pid_type type,
445 struct pid_namespace *ns)
446{
447 pid_t nr = 0;
448
449 rcu_read_lock();
450 if (!ns)
451 ns = current->nsproxy->pid_ns;
452 if (likely(pid_alive(task))) {
453 if (type != PIDTYPE_PID)
454 task = task->group_leader;
455 nr = pid_nr_ns(task->pids[type].pid, ns);
456 }
457 rcu_read_unlock();
458
459 return nr;
460}
461EXPORT_SYMBOL(__task_pid_nr_ns);
462
463pid_t task_tgid_nr_ns(struct task_struct *tsk, struct pid_namespace *ns)
464{
465 return pid_nr_ns(task_tgid(tsk), ns);
466}
467EXPORT_SYMBOL(task_tgid_nr_ns);
468
469struct pid_namespace *task_active_pid_ns(struct task_struct *tsk)
470{
471 return ns_of_pid(task_pid(tsk));
472}
473EXPORT_SYMBOL_GPL(task_active_pid_ns);
474
475/*
476 * Used by proc to find the first pid that is greater than or equal to nr.
477 *
478 * If there is a pid at nr this function is exactly the same as find_pid_ns.
479 */
480struct pid *find_ge_pid(int nr, struct pid_namespace *ns)
481{
482 struct pid *pid;
483
484 do {
485 pid = find_pid_ns(nr, ns);
486 if (pid)
487 break;
488 nr = next_pidmap(ns, nr);
489 } while (nr > 0);
490
491 return pid;
492}
493
494/*
495 * The pid hash table is scaled according to the amount of memory in the
496 * machine. From a minimum of 16 slots up to 4096 slots at one gigabyte or
497 * more.
498 */
499void __init pidhash_init(void)
500{
501 int i, pidhash_size;
502
503 pid_hash = alloc_large_system_hash("PID", sizeof(*pid_hash), 0, 18,
504 HASH_EARLY | HASH_SMALL,
505 &pidhash_shift, NULL, 4096);
506 pidhash_size = 1 << pidhash_shift;
507
508 for (i = 0; i < pidhash_size; i++)
509 INIT_HLIST_HEAD(&pid_hash[i]);
510}
511
512void __init pidmap_init(void)
513{
514 init_pid_ns.pidmap[0].page = kzalloc(PAGE_SIZE, GFP_KERNEL);
515 /* Reserve PID 0. We never call free_pidmap(0) */
516 set_bit(0, init_pid_ns.pidmap[0].page);
517 atomic_dec(&init_pid_ns.pidmap[0].nr_free);
518
519 init_pid_ns.pid_cachep = KMEM_CACHE(pid,
520 SLAB_HWCACHE_ALIGN | SLAB_PANIC);
521}