Root/kernel/pid.c

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)
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}
522

Archive Download this file

Branches:
ben-wpan
ben-wpan-stefan
javiroman/ks7010
jz-2.6.34
jz-2.6.34-rc5
jz-2.6.34-rc6
jz-2.6.34-rc7
jz-2.6.35
jz-2.6.36
jz-2.6.37
jz-2.6.38
jz-2.6.39
jz-3.0
jz-3.1
jz-3.11
jz-3.12
jz-3.13
jz-3.15
jz-3.16
jz-3.18-dt
jz-3.2
jz-3.3
jz-3.4
jz-3.5
jz-3.6
jz-3.6-rc2-pwm
jz-3.9
jz-3.9-clk
jz-3.9-rc8
jz47xx
jz47xx-2.6.38
master

Tags:
od-2011-09-04
od-2011-09-18
v2.6.34-rc5
v2.6.34-rc6
v2.6.34-rc7
v3.9



interactive