projects/linux·blob v5.2-rc7 · refs

470 lines · 11.2 KiB

1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * Generic pidhash and scalable, time-bounded PID allocator
4 *
5 * (C) 2002-2003 Nadia Yvette Chambers, IBM
6 * (C) 2004 Nadia Yvette Chambers, Oracle
7 * (C) 2002-2004 Ingo Molnar, Red Hat
8 *
9 * pid-structures are backing objects for tasks sharing a given ID to chain
10 * against. There is very little to them aside from hashing them and
11 * parking tasks using given ID's on a list.
12 *
13 * The hash is always changed with the tasklist_lock write-acquired,
14 * and the hash is only accessed with the tasklist_lock at least
15 * read-acquired, so there's no additional SMP locking needed here.
16 *
17 * We have a list of bitmap pages, which bitmaps represent the PID space.
18 * Allocating and freeing PIDs is completely lockless. The worst-case
19 * allocation scenario when all but one out of 1 million PIDs possible are
20 * allocated already: the scanning of 32 list entries and at most PAGE_SIZE
21 * bytes. The typical fastpath is a single successful setbit. Freeing is O(1).
22 *
23 * Pid namespaces:
24 * (C) 2007 Pavel Emelyanov <[email protected]>, OpenVZ, SWsoft Inc.
25 * (C) 2007 Sukadev Bhattiprolu <[email protected]>, IBM
26 * Many thanks to Oleg Nesterov for comments and help
27 *
28 */
29
30#include <linux/mm.h>
31#include <linux/export.h>
32#include <linux/slab.h>
33#include <linux/init.h>
34#include <linux/rculist.h>
35#include <linux/memblock.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 == -ENOSPC) ? -EAGAIN : 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 upid = pid->numbers + i;
238 idr_remove(&upid->ns->idr, upid->nr);
239 }
240
241 /* On failure to allocate the first pid, reset the state */
242 if (ns->pid_allocated == PIDNS_ADDING)
243 idr_set_cursor(&ns->idr, 0);
244
245 spin_unlock_irq(&pidmap_lock);
246
247 kmem_cache_free(ns->pid_cachep, pid);
248 return ERR_PTR(retval);
249}
250
251void disable_pid_allocation(struct pid_namespace *ns)
252{
253 spin_lock_irq(&pidmap_lock);
254 ns->pid_allocated &= ~PIDNS_ADDING;
255 spin_unlock_irq(&pidmap_lock);
256}
257
258struct pid *find_pid_ns(int nr, struct pid_namespace *ns)
259{
260 return idr_find(&ns->idr, nr);
261}
262EXPORT_SYMBOL_GPL(find_pid_ns);
263
264struct pid *find_vpid(int nr)
265{
266 return find_pid_ns(nr, task_active_pid_ns(current));
267}
268EXPORT_SYMBOL_GPL(find_vpid);
269
270static struct pid **task_pid_ptr(struct task_struct *task, enum pid_type type)
271{
272 return (type == PIDTYPE_PID) ?
273 &task->thread_pid :
274 &task->signal->pids[type];
275}
276
277/*
278 * attach_pid() must be called with the tasklist_lock write-held.
279 */
280void attach_pid(struct task_struct *task, enum pid_type type)
281{
282 struct pid *pid = *task_pid_ptr(task, type);
283 hlist_add_head_rcu(&task->pid_links[type], &pid->tasks[type]);
284}
285
286static void __change_pid(struct task_struct *task, enum pid_type type,
287 struct pid *new)
288{
289 struct pid **pid_ptr = task_pid_ptr(task, type);
290 struct pid *pid;
291 int tmp;
292
293 pid = *pid_ptr;
294
295 hlist_del_rcu(&task->pid_links[type]);
296 *pid_ptr = new;
297
298 for (tmp = PIDTYPE_MAX; --tmp >= 0; )
299 if (!hlist_empty(&pid->tasks[tmp]))
300 return;
301
302 free_pid(pid);
303}
304
305void detach_pid(struct task_struct *task, enum pid_type type)
306{
307 __change_pid(task, type, NULL);
308}
309
310void change_pid(struct task_struct *task, enum pid_type type,
311 struct pid *pid)
312{
313 __change_pid(task, type, pid);
314 attach_pid(task, type);
315}
316
317/* transfer_pid is an optimization of attach_pid(new), detach_pid(old) */
318void transfer_pid(struct task_struct *old, struct task_struct *new,
319 enum pid_type type)
320{
321 if (type == PIDTYPE_PID)
322 new->thread_pid = old->thread_pid;
323 hlist_replace_rcu(&old->pid_links[type], &new->pid_links[type]);
324}
325
326struct task_struct *pid_task(struct pid *pid, enum pid_type type)
327{
328 struct task_struct *result = NULL;
329 if (pid) {
330 struct hlist_node *first;
331 first = rcu_dereference_check(hlist_first_rcu(&pid->tasks[type]),
332 lockdep_tasklist_lock_is_held());
333 if (first)
334 result = hlist_entry(first, struct task_struct, pid_links[(type)]);
335 }
336 return result;
337}
338EXPORT_SYMBOL(pid_task);
339
340/*
341 * Must be called under rcu_read_lock().
342 */
343struct task_struct *find_task_by_pid_ns(pid_t nr, struct pid_namespace *ns)
344{
345 RCU_LOCKDEP_WARN(!rcu_read_lock_held(),
346 "find_task_by_pid_ns() needs rcu_read_lock() protection");
347 return pid_task(find_pid_ns(nr, ns), PIDTYPE_PID);
348}
349
350struct task_struct *find_task_by_vpid(pid_t vnr)
351{
352 return find_task_by_pid_ns(vnr, task_active_pid_ns(current));
353}
354
355struct task_struct *find_get_task_by_vpid(pid_t nr)
356{
357 struct task_struct *task;
358
359 rcu_read_lock();
360 task = find_task_by_vpid(nr);
361 if (task)
362 get_task_struct(task);
363 rcu_read_unlock();
364
365 return task;
366}
367
368struct pid *get_task_pid(struct task_struct *task, enum pid_type type)
369{
370 struct pid *pid;
371 rcu_read_lock();
372 pid = get_pid(rcu_dereference(*task_pid_ptr(task, type)));
373 rcu_read_unlock();
374 return pid;
375}
376EXPORT_SYMBOL_GPL(get_task_pid);
377
378struct task_struct *get_pid_task(struct pid *pid, enum pid_type type)
379{
380 struct task_struct *result;
381 rcu_read_lock();
382 result = pid_task(pid, type);
383 if (result)
384 get_task_struct(result);
385 rcu_read_unlock();
386 return result;
387}
388EXPORT_SYMBOL_GPL(get_pid_task);
389
390struct pid *find_get_pid(pid_t nr)
391{
392 struct pid *pid;
393
394 rcu_read_lock();
395 pid = get_pid(find_vpid(nr));
396 rcu_read_unlock();
397
398 return pid;
399}
400EXPORT_SYMBOL_GPL(find_get_pid);
401
402pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns)
403{
404 struct upid *upid;
405 pid_t nr = 0;
406
407 if (pid && ns->level <= pid->level) {
408 upid = &pid->numbers[ns->level];
409 if (upid->ns == ns)
410 nr = upid->nr;
411 }
412 return nr;
413}
414EXPORT_SYMBOL_GPL(pid_nr_ns);
415
416pid_t pid_vnr(struct pid *pid)
417{
418 return pid_nr_ns(pid, task_active_pid_ns(current));
419}
420EXPORT_SYMBOL_GPL(pid_vnr);
421
422pid_t __task_pid_nr_ns(struct task_struct *task, enum pid_type type,
423 struct pid_namespace *ns)
424{
425 pid_t nr = 0;
426
427 rcu_read_lock();
428 if (!ns)
429 ns = task_active_pid_ns(current);
430 if (likely(pid_alive(task)))
431 nr = pid_nr_ns(rcu_dereference(*task_pid_ptr(task, type)), ns);
432 rcu_read_unlock();
433
434 return nr;
435}
436EXPORT_SYMBOL(__task_pid_nr_ns);
437
438struct pid_namespace *task_active_pid_ns(struct task_struct *tsk)
439{
440 return ns_of_pid(task_pid(tsk));
441}
442EXPORT_SYMBOL_GPL(task_active_pid_ns);
443
444/*
445 * Used by proc to find the first pid that is greater than or equal to nr.
446 *
447 * If there is a pid at nr this function is exactly the same as find_pid_ns.
448 */
449struct pid *find_ge_pid(int nr, struct pid_namespace *ns)
450{
451 return idr_get_next(&ns->idr, &nr);
452}
453
454void __init pid_idr_init(void)
455{
456 /* Verify no one has done anything silly: */
457 BUILD_BUG_ON(PID_MAX_LIMIT >= PIDNS_ADDING);
458
459 /* bump default and minimum pid_max based on number of cpus */
460 pid_max = min(pid_max_max, max_t(int, pid_max,
461 PIDS_PER_CPU_DEFAULT * num_possible_cpus()));
462 pid_max_min = max_t(int, pid_max_min,
463 PIDS_PER_CPU_MIN * num_possible_cpus());
464 pr_info("pid_max: default: %u minimum: %u\n", pid_max, pid_max_min);
465
466 idr_init(&init_pid_ns.idr);
467
468 init_pid_ns.pid_cachep = KMEM_CACHE(pid,
469 SLAB_HWCACHE_ALIGN | SLAB_PANIC | SLAB_ACCOUNT);
470}