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#include <linux/sched/task.h>
42#include <linux/idr.h>
43
44struct pid init_struct_pid = {
45 .count = ATOMIC_INIT(1),
46 .tasks = {
47 { .first = NULL },
48 { .first = NULL },
49 { .first = NULL },
50 },
51 .level = 0,
52 .numbers = { {
53 .nr = 0,
54 .ns = &init_pid_ns,
55 }, }
56};
57
58int pid_max = PID_MAX_DEFAULT;
59
60#define RESERVED_PIDS 300
61
62int pid_max_min = RESERVED_PIDS + 1;
63int pid_max_max = PID_MAX_LIMIT;
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 = KREF_INIT(2),
73 .idr = IDR_INIT(init_pid_ns.idr),
74 .pid_allocated = PIDNS_ADDING,
75 .level = 0,
76 .child_reaper = &init_task,
77 .user_ns = &init_user_ns,
78 .ns.inum = PROC_PID_INIT_INO,
79#ifdef CONFIG_PID_NS
80 .ns.ops = &pidns_operations,
81#endif
82};
83EXPORT_SYMBOL_GPL(init_pid_ns);
84
85/*
86 * Note: disable interrupts while the pidmap_lock is held as an
87 * interrupt might come in and do read_lock(&tasklist_lock).
88 *
89 * If we don't disable interrupts there is a nasty deadlock between
90 * detach_pid()->free_pid() and another cpu that does
91 * spin_lock(&pidmap_lock) followed by an interrupt routine that does
92 * read_lock(&tasklist_lock);
93 *
94 * After we clean up the tasklist_lock and know there are no
95 * irq handlers that take it we can leave the interrupts enabled.
96 * For now it is easier to be safe than to prove it can't happen.
97 */
98
99static __cacheline_aligned_in_smp DEFINE_SPINLOCK(pidmap_lock);
100
101void put_pid(struct pid *pid)
102{
103 struct pid_namespace *ns;
104
105 if (!pid)
106 return;
107
108 ns = pid->numbers[pid->level].ns;
109 if ((atomic_read(&pid->count) == 1) ||
110 atomic_dec_and_test(&pid->count)) {
111 kmem_cache_free(ns->pid_cachep, pid);
112 put_pid_ns(ns);
113 }
114}
115EXPORT_SYMBOL_GPL(put_pid);
116
117static void delayed_put_pid(struct rcu_head *rhp)
118{
119 struct pid *pid = container_of(rhp, struct pid, rcu);
120 put_pid(pid);
121}
122
123void free_pid(struct pid *pid)
124{
125 /* We can be called with write_lock_irq(&tasklist_lock) held */
126 int i;
127 unsigned long flags;
128
129 spin_lock_irqsave(&pidmap_lock, flags);
130 for (i = 0; i <= pid->level; i++) {
131 struct upid *upid = pid->numbers + i;
132 struct pid_namespace *ns = upid->ns;
133 switch (--ns->pid_allocated) {
134 case 2:
135 case 1:
136 /* When all that is left in the pid namespace
137 * is the reaper wake up the reaper. The reaper
138 * may be sleeping in zap_pid_ns_processes().
139 */
140 wake_up_process(ns->child_reaper);
141 break;
142 case PIDNS_ADDING:
143 /* Handle a fork failure of the first process */
144 WARN_ON(ns->child_reaper);
145 ns->pid_allocated = 0;
146 /* fall through */
147 case 0:
148 schedule_work(&ns->proc_work);
149 break;
150 }
151
152 idr_remove(&ns->idr, upid->nr);
153 }
154 spin_unlock_irqrestore(&pidmap_lock, flags);
155
156 call_rcu(&pid->rcu, delayed_put_pid);
157}
158
159struct pid *alloc_pid(struct pid_namespace *ns)
160{
161 struct pid *pid;
162 enum pid_type type;
163 int i, nr;
164 struct pid_namespace *tmp;
165 struct upid *upid;
166 int retval = -ENOMEM;
167
168 pid = kmem_cache_alloc(ns->pid_cachep, GFP_KERNEL);
169 if (!pid)
170 return ERR_PTR(retval);
171
172 tmp = ns;
173 pid->level = ns->level;
174
175 for (i = ns->level; i >= 0; i--) {
176 int pid_min = 1;
177
178 idr_preload(GFP_KERNEL);
179 spin_lock_irq(&pidmap_lock);
180
181 /*
182 * init really needs pid 1, but after reaching the maximum
183 * wrap back to RESERVED_PIDS
184 */
185 if (idr_get_cursor(&tmp->idr) > RESERVED_PIDS)
186 pid_min = RESERVED_PIDS;
187
188 /*
189 * Store a null pointer so find_pid_ns does not find
190 * a partially initialized PID (see below).
191 */
192 nr = idr_alloc_cyclic(&tmp->idr, NULL, pid_min,
193 pid_max, GFP_ATOMIC);
194 spin_unlock_irq(&pidmap_lock);
195 idr_preload_end();
196
197 if (nr < 0) {
198 retval = nr;
199 goto out_free;
200 }
201
202 pid->numbers[i].nr = nr;
203 pid->numbers[i].ns = tmp;
204 tmp = tmp->parent;
205 }
206
207 if (unlikely(is_child_reaper(pid))) {
208 if (pid_ns_prepare_proc(ns))
209 goto out_free;
210 }
211
212 get_pid_ns(ns);
213 atomic_set(&pid->count, 1);
214 for (type = 0; type < PIDTYPE_MAX; ++type)
215 INIT_HLIST_HEAD(&pid->tasks[type]);
216
217 upid = pid->numbers + ns->level;
218 spin_lock_irq(&pidmap_lock);
219 if (!(ns->pid_allocated & PIDNS_ADDING))
220 goto out_unlock;
221 for ( ; upid >= pid->numbers; --upid) {
222 /* Make the PID visible to find_pid_ns. */
223 idr_replace(&upid->ns->idr, pid, upid->nr);
224 upid->ns->pid_allocated++;
225 }
226 spin_unlock_irq(&pidmap_lock);
227
228 return pid;
229
230out_unlock:
231 spin_unlock_irq(&pidmap_lock);
232 put_pid_ns(ns);
233
234out_free:
235 spin_lock_irq(&pidmap_lock);
236 while (++i <= ns->level)
237 idr_remove(&ns->idr, (pid->numbers + i)->nr);
238
239 /* On failure to allocate the first pid, reset the state */
240 if (ns->pid_allocated == PIDNS_ADDING)
241 idr_set_cursor(&ns->idr, 0);
242
243 spin_unlock_irq(&pidmap_lock);
244
245 kmem_cache_free(ns->pid_cachep, pid);
246 return ERR_PTR(retval);
247}
248
249void disable_pid_allocation(struct pid_namespace *ns)
250{
251 spin_lock_irq(&pidmap_lock);
252 ns->pid_allocated &= ~PIDNS_ADDING;
253 spin_unlock_irq(&pidmap_lock);
254}
255
256struct pid *find_pid_ns(int nr, struct pid_namespace *ns)
257{
258 return idr_find(&ns->idr, nr);
259}
260EXPORT_SYMBOL_GPL(find_pid_ns);
261
262struct pid *find_vpid(int nr)
263{
264 return find_pid_ns(nr, task_active_pid_ns(current));
265}
266EXPORT_SYMBOL_GPL(find_vpid);
267
268static struct pid **task_pid_ptr(struct task_struct *task, enum pid_type type)
269{
270 return (type == PIDTYPE_PID) ?
271 &task->thread_pid :
272 &task->signal->pids[type];
273}
274
275/*
276 * attach_pid() must be called with the tasklist_lock write-held.
277 */
278void attach_pid(struct task_struct *task, enum pid_type type)
279{
280 struct pid *pid = *task_pid_ptr(task, type);
281 hlist_add_head_rcu(&task->pid_links[type], &pid->tasks[type]);
282}
283
284static void __change_pid(struct task_struct *task, enum pid_type type,
285 struct pid *new)
286{
287 struct pid **pid_ptr = task_pid_ptr(task, type);
288 struct pid *pid;
289 int tmp;
290
291 pid = *pid_ptr;
292
293 hlist_del_rcu(&task->pid_links[type]);
294 *pid_ptr = new;
295
296 for (tmp = PIDTYPE_MAX; --tmp >= 0; )
297 if (!hlist_empty(&pid->tasks[tmp]))
298 return;
299
300 free_pid(pid);
301}
302
303void detach_pid(struct task_struct *task, enum pid_type type)
304{
305 __change_pid(task, type, NULL);
306}
307
308void change_pid(struct task_struct *task, enum pid_type type,
309 struct pid *pid)
310{
311 __change_pid(task, type, pid);
312 attach_pid(task, type);
313}
314
315/* transfer_pid is an optimization of attach_pid(new), detach_pid(old) */
316void transfer_pid(struct task_struct *old, struct task_struct *new,
317 enum pid_type type)
318{
319 if (type == PIDTYPE_PID)
320 new->thread_pid = old->thread_pid;
321 hlist_replace_rcu(&old->pid_links[type], &new->pid_links[type]);
322}
323
324struct task_struct *pid_task(struct pid *pid, enum pid_type type)
325{
326 struct task_struct *result = NULL;
327 if (pid) {
328 struct hlist_node *first;
329 first = rcu_dereference_check(hlist_first_rcu(&pid->tasks[type]),
330 lockdep_tasklist_lock_is_held());
331 if (first)
332 result = hlist_entry(first, struct task_struct, pid_links[(type)]);
333 }
334 return result;
335}
336EXPORT_SYMBOL(pid_task);
337
338/*
339 * Must be called under rcu_read_lock().
340 */
341struct task_struct *find_task_by_pid_ns(pid_t nr, struct pid_namespace *ns)
342{
343 RCU_LOCKDEP_WARN(!rcu_read_lock_held(),
344 "find_task_by_pid_ns() needs rcu_read_lock() protection");
345 return pid_task(find_pid_ns(nr, ns), PIDTYPE_PID);
346}
347
348struct task_struct *find_task_by_vpid(pid_t vnr)
349{
350 return find_task_by_pid_ns(vnr, task_active_pid_ns(current));
351}
352
353struct task_struct *find_get_task_by_vpid(pid_t nr)
354{
355 struct task_struct *task;
356
357 rcu_read_lock();
358 task = find_task_by_vpid(nr);
359 if (task)
360 get_task_struct(task);
361 rcu_read_unlock();
362
363 return task;
364}
365
366struct pid *get_task_pid(struct task_struct *task, enum pid_type type)
367{
368 struct pid *pid;
369 rcu_read_lock();
370 pid = get_pid(rcu_dereference(*task_pid_ptr(task, type)));
371 rcu_read_unlock();
372 return pid;
373}
374EXPORT_SYMBOL_GPL(get_task_pid);
375
376struct task_struct *get_pid_task(struct pid *pid, enum pid_type type)
377{
378 struct task_struct *result;
379 rcu_read_lock();
380 result = pid_task(pid, type);
381 if (result)
382 get_task_struct(result);
383 rcu_read_unlock();
384 return result;
385}
386EXPORT_SYMBOL_GPL(get_pid_task);
387
388struct pid *find_get_pid(pid_t nr)
389{
390 struct pid *pid;
391
392 rcu_read_lock();
393 pid = get_pid(find_vpid(nr));
394 rcu_read_unlock();
395
396 return pid;
397}
398EXPORT_SYMBOL_GPL(find_get_pid);
399
400pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns)
401{
402 struct upid *upid;
403 pid_t nr = 0;
404
405 if (pid && ns->level <= pid->level) {
406 upid = &pid->numbers[ns->level];
407 if (upid->ns == ns)
408 nr = upid->nr;
409 }
410 return nr;
411}
412EXPORT_SYMBOL_GPL(pid_nr_ns);
413
414pid_t pid_vnr(struct pid *pid)
415{
416 return pid_nr_ns(pid, task_active_pid_ns(current));
417}
418EXPORT_SYMBOL_GPL(pid_vnr);
419
420pid_t __task_pid_nr_ns(struct task_struct *task, enum pid_type type,
421 struct pid_namespace *ns)
422{
423 pid_t nr = 0;
424
425 rcu_read_lock();
426 if (!ns)
427 ns = task_active_pid_ns(current);
428 if (likely(pid_alive(task)))
429 nr = pid_nr_ns(rcu_dereference(*task_pid_ptr(task, type)), ns);
430 rcu_read_unlock();
431
432 return nr;
433}
434EXPORT_SYMBOL(__task_pid_nr_ns);
435
436struct pid_namespace *task_active_pid_ns(struct task_struct *tsk)
437{
438 return ns_of_pid(task_pid(tsk));
439}
440EXPORT_SYMBOL_GPL(task_active_pid_ns);
441
442/*
443 * Used by proc to find the first pid that is greater than or equal to nr.
444 *
445 * If there is a pid at nr this function is exactly the same as find_pid_ns.
446 */
447struct pid *find_ge_pid(int nr, struct pid_namespace *ns)
448{
449 return idr_get_next(&ns->idr, &nr);
450}
451
452void __init pid_idr_init(void)
453{
454 /* Verify no one has done anything silly: */
455 BUILD_BUG_ON(PID_MAX_LIMIT >= PIDNS_ADDING);
456
457 /* bump default and minimum pid_max based on number of cpus */
458 pid_max = min(pid_max_max, max_t(int, pid_max,
459 PIDS_PER_CPU_DEFAULT * num_possible_cpus()));
460 pid_max_min = max_t(int, pid_max_min,
461 PIDS_PER_CPU_MIN * num_possible_cpus());
462 pr_info("pid_max: default: %u minimum: %u\n", pid_max, pid_max_min);
463
464 idr_init(&init_pid_ns.idr);
465
466 init_pid_ns.pid_cachep = KMEM_CACHE(pid,
467 SLAB_HWCACHE_ALIGN | SLAB_PANIC | SLAB_ACCOUNT);
468}
469