/*

* Generic pidhash and scalable, time-bounded PID allocator

*

* (C) 2002-2003 Nadia Yvette Chambers, IBM

* (C) 2004 Nadia Yvette Chambers, Oracle

* (C) 2002-2004 Ingo Molnar, Red Hat

*

* pid-structures are backing objects for tasks sharing a given ID to chain

* against. There is very little to them aside from hashing them and

* parking tasks using given ID's on a list.

*

* The hash is always changed with the tasklist_lock write-acquired,

* and the hash is only accessed with the tasklist_lock at least

* read-acquired, so there's no additional SMP locking needed here.

*

* We have a list of bitmap pages, which bitmaps represent the PID space.

* Allocating and freeing PIDs is completely lockless. The worst-case

* allocation scenario when all but one out of 1 million PIDs possible are

* allocated already: the scanning of 32 list entries and at most PAGE_SIZE

* bytes. The typical fastpath is a single successful setbit. Freeing is O(1).

*

* Pid namespaces:

* (C) 2007 Pavel Emelyanov <xemul@openvz.org>, OpenVZ, SWsoft Inc.

* (C) 2007 Sukadev Bhattiprolu <sukadev@us.ibm.com>, IBM

* Many thanks to Oleg Nesterov for comments and help

*

*/

#include <linux/mm.h>

#include <linux/export.h>

#include <linux/slab.h>

#include <linux/init.h>

#include <linux/rculist.h>

#include <linux/bootmem.h>

#include <linux/hash.h>

#include <linux/pid_namespace.h>

#include <linux/init_task.h>

#include <linux/syscalls.h>

#include <linux/proc_fs.h>

#define pid_hashfn(nr, ns) \

hash_long((unsigned long)nr + (unsigned long)ns, pidhash_shift)

static struct hlist_head *pid_hash;

static unsigned int pidhash_shift = 4;

struct pid init_struct_pid = INIT_STRUCT_PID;

int pid_max = PID_MAX_DEFAULT;

#define RESERVED_PIDS 300

int pid_max_min = RESERVED_PIDS + 1;

int pid_max_max = PID_MAX_LIMIT;

#define BITS_PER_PAGE (PAGE_SIZE*8)

#define BITS_PER_PAGE_MASK (BITS_PER_PAGE-1)

static inline int mk_pid(struct pid_namespace *pid_ns,

struct pidmap *map, int off)

{

return (map - pid_ns->pidmap)*BITS_PER_PAGE + off;

}

#define find_next_offset(map, off) \

find_next_zero_bit((map)->page, BITS_PER_PAGE, off)

/*

* PID-map pages start out as NULL, they get allocated upon

* first use and are never deallocated. This way a low pid_max

* value does not cause lots of bitmaps to be allocated, but

* the scheme scales to up to 4 million PIDs, runtime.

*/

struct pid_namespace init_pid_ns = {

.kref = {

.refcount = ATOMIC_INIT(2),

},

.pidmap = {

[ 0 ... PIDMAP_ENTRIES-1] = { ATOMIC_INIT(BITS_PER_PAGE), NULL }

},

.last_pid = 0,

.level = 0,

.child_reaper = &init_task,

.user_ns = &init_user_ns,

.proc_inum = PROC_PID_INIT_INO,

};

EXPORT_SYMBOL_GPL(init_pid_ns);

/*

* Note: disable interrupts while the pidmap_lock is held as an

* interrupt might come in and do read_lock(&tasklist_lock).

*

* If we don't disable interrupts there is a nasty deadlock between

* detach_pid()->free_pid() and another cpu that does

* spin_lock(&pidmap_lock) followed by an interrupt routine that does

* read_lock(&tasklist_lock);

*

* After we clean up the tasklist_lock and know there are no

* irq handlers that take it we can leave the interrupts enabled.

* For now it is easier to be safe than to prove it can't happen.

*/

static __cacheline_aligned_in_smp DEFINE_SPINLOCK(pidmap_lock);

static void free_pidmap(struct upid *upid)

{

int nr = upid->nr;

struct pidmap *map = upid->ns->pidmap + nr / BITS_PER_PAGE;

int offset = nr & BITS_PER_PAGE_MASK;

clear_bit(offset, map->page);

atomic_inc(&map->nr_free);

}

/*

* If we started walking pids at 'base', is 'a' seen before 'b'?

*/

static int pid_before(int base, int a, int b)

{

/*

* This is the same as saying

*

* (a - base + MAXUINT) % MAXUINT < (b - base + MAXUINT) % MAXUINT

* and that mapping orders 'a' and 'b' with respect to 'base'.

*/

return (unsigned)(a - base) < (unsigned)(b - base);

}

/*

* We might be racing with someone else trying to set pid_ns->last_pid

* at the pid allocation time (there's also a sysctl for this, but racing

* with this one is OK, see comment in kernel/pid_namespace.c about it).

* We want the winner to have the "later" value, because if the

* "earlier" value prevails, then a pid may get reused immediately.

*

* Since pids rollover, it is not sufficient to just pick the bigger

* value. We have to consider where we started counting from.

*

* 'base' is the value of pid_ns->last_pid that we observed when

* we started looking for a pid.

*

* 'pid' is the pid that we eventually found.

*/

static void set_last_pid(struct pid_namespace *pid_ns, int base, int pid)

{

int prev;

int last_write = base;

do {

prev = last_write;

last_write = cmpxchg(&pid_ns->last_pid, prev, pid);

} while ((prev != last_write) && (pid_before(base, last_write, pid)));

}

static int alloc_pidmap(struct pid_namespace *pid_ns)

{

int i, offset, max_scan, pid, last = pid_ns->last_pid;

struct pidmap *map;

pid = last + 1;

if (pid >= pid_max)

pid = RESERVED_PIDS;

offset = pid & BITS_PER_PAGE_MASK;

map = &pid_ns->pidmap[pid/BITS_PER_PAGE];

/*

* If last_pid points into the middle of the map->page we

* want to scan this bitmap block twice, the second time

* we start with offset == 0 (or RESERVED_PIDS).

*/

max_scan = DIV_ROUND_UP(pid_max, BITS_PER_PAGE) - !offset;

for (i = 0; i <= max_scan; ++i) {

if (unlikely(!map->page)) {

void *page = kzalloc(PAGE_SIZE, GFP_KERNEL);

/*

* Free the page if someone raced with us

* installing it:

*/

spin_lock_irq(&pidmap_lock);

if (!map->page) {

map->page = page;

page = NULL;

}

spin_unlock_irq(&pidmap_lock);

kfree(page);

if (unlikely(!map->page))

break;

}

if (likely(atomic_read(&map->nr_free))) {

do {

if (!test_and_set_bit(offset, map->page)) {

atomic_dec(&map->nr_free);

set_last_pid(pid_ns, last, pid);

return pid;

}

offset = find_next_offset(map, offset);

pid = mk_pid(pid_ns, map, offset);

} while (offset < BITS_PER_PAGE && pid < pid_max);

}

if (map < &pid_ns->pidmap[(pid_max-1)/BITS_PER_PAGE]) {

++map;

offset = 0;

} else {

map = &pid_ns->pidmap[0];

offset = RESERVED_PIDS;

if (unlikely(last == offset))

break;

}

pid = mk_pid(pid_ns, map, offset);

}

return -1;

}

int next_pidmap(struct pid_namespace *pid_ns, unsigned int last)

{

int offset;

struct pidmap *map, *end;

if (last >= PID_MAX_LIMIT)

return -1;

offset = (last + 1) & BITS_PER_PAGE_MASK;

map = &pid_ns->pidmap[(last + 1)/BITS_PER_PAGE];

end = &pid_ns->pidmap[PIDMAP_ENTRIES];

for (; map < end; map++, offset = 0) {

if (unlikely(!map->page))

continue;

offset = find_next_bit((map)->page, BITS_PER_PAGE, offset);

if (offset < BITS_PER_PAGE)

return mk_pid(pid_ns, map, offset);

}

return -1;

}

void put_pid(struct pid *pid)

{

struct pid_namespace *ns;

if (!pid)

return;

ns = pid->numbers[pid->level].ns;

if ((atomic_read(&pid->count) == 1) ||

atomic_dec_and_test(&pid->count)) {

kmem_cache_free(ns->pid_cachep, pid);

put_pid_ns(ns);

}

}

EXPORT_SYMBOL_GPL(put_pid);

static void delayed_put_pid(struct rcu_head *rhp)

{

struct pid *pid = container_of(rhp, struct pid, rcu);

put_pid(pid);

}

void free_pid(struct pid *pid)

{

/* We can be called with write_lock_irq(&tasklist_lock) held */

int i;

unsigned long flags;

spin_lock_irqsave(&pidmap_lock, flags);

for (i = 0; i <= pid->level; i++) {

struct upid *upid = pid->numbers + i;

struct pid_namespace *ns = upid->ns;

hlist_del_rcu(&upid->pid_chain);

switch(--ns->nr_hashed) {

case 1:

/* When all that is left in the pid namespace

* is the reaper wake up the reaper. The reaper

* may be sleeping in zap_pid_ns_processes().

*/

wake_up_process(ns->child_reaper);

break;

case 0:

ns->nr_hashed = -1;

schedule_work(&ns->proc_work);

break;

}

}

spin_unlock_irqrestore(&pidmap_lock, flags);

for (i = 0; i <= pid->level; i++)

free_pidmap(pid->numbers + i);

call_rcu(&pid->rcu, delayed_put_pid);

}

struct pid *alloc_pid(struct pid_namespace *ns)

{

struct pid *pid;

enum pid_type type;

int i, nr;

struct pid_namespace *tmp;

struct upid *upid;

pid = kmem_cache_alloc(ns->pid_cachep, GFP_KERNEL);

if (!pid)

goto out;

tmp = ns;

pid->level = ns->level;

for (i = ns->level; i >= 0; i--) {

nr = alloc_pidmap(tmp);

if (nr < 0)

goto out_free;

pid->numbers[i].nr = nr;

pid->numbers[i].ns = tmp;

tmp = tmp->parent;

}

if (unlikely(is_child_reaper(pid))) {

if (pid_ns_prepare_proc(ns))

goto out_free;

}

get_pid_ns(ns);

atomic_set(&pid->count, 1);

for (type = 0; type < PIDTYPE_MAX; ++type)

INIT_HLIST_HEAD(&pid->tasks[type]);

upid = pid->numbers + ns->level;

spin_lock_irq(&pidmap_lock);

if (ns->nr_hashed < 0)

goto out_unlock;

for ( ; upid >= pid->numbers; --upid) {

hlist_add_head_rcu(&upid->pid_chain,

&pid_hash[pid_hashfn(upid->nr, upid->ns)]);

upid->ns->nr_hashed++;

}

spin_unlock_irq(&pidmap_lock);

out:

return pid;

out_unlock:

spin_unlock(&pidmap_lock);

out_free:

while (++i <= ns->level)

free_pidmap(pid->numbers + i);

kmem_cache_free(ns->pid_cachep, pid);

pid = NULL;

goto out;

}

struct pid *find_pid_ns(int nr, struct pid_namespace *ns)

{

struct hlist_node *elem;

struct upid *pnr;

hlist_for_each_entry_rcu(pnr, elem,

&pid_hash[pid_hashfn(nr, ns)], pid_chain)

if (pnr->nr == nr && pnr->ns == ns)

return container_of(pnr, struct pid,

numbers[ns->level]);

return NULL;

}

EXPORT_SYMBOL_GPL(find_pid_ns);

struct pid *find_vpid(int nr)

{

return find_pid_ns(nr, task_active_pid_ns(current));

}

EXPORT_SYMBOL_GPL(find_vpid);

/*

* attach_pid() must be called with the tasklist_lock write-held.

*/

void attach_pid(struct task_struct *task, enum pid_type type,

struct pid *pid)

{

struct pid_link *link;

link = &task->pids[type];

link->pid = pid;

hlist_add_head_rcu(&link->node, &pid->tasks[type]);

}

static void __change_pid(struct task_struct *task, enum pid_type type,

struct pid *new)

{

struct pid_link *link;

struct pid *pid;

int tmp;

link = &task->pids[type];

pid = link->pid;

hlist_del_rcu(&link->node);

link->pid = new;

for (tmp = PIDTYPE_MAX; --tmp >= 0; )

if (!hlist_empty(&pid->tasks[tmp]))

return;

free_pid(pid);

}

void detach_pid(struct task_struct *task, enum pid_type type)

{

__change_pid(task, type, NULL);

}

void change_pid(struct task_struct *task, enum pid_type type,

struct pid *pid)

{

__change_pid(task, type, pid);

attach_pid(task, type, pid);

}

/* transfer_pid is an optimization of attach_pid(new), detach_pid(old) */

void transfer_pid(struct task_struct *old, struct task_struct *new,

enum pid_type type)

{

new->pids[type].pid = old->pids[type].pid;

hlist_replace_rcu(&old->pids[type].node, &new->pids[type].node);

}

struct task_struct *pid_task(struct pid *pid, enum pid_type type)

{

struct task_struct *result = NULL;

if (pid) {

struct hlist_node *first;

first = rcu_dereference_check(hlist_first_rcu(&pid->tasks[type]),

lockdep_tasklist_lock_is_held());

if (first)

result = hlist_entry(first, struct task_struct, pids[(type)].node);

}

return result;

}

EXPORT_SYMBOL(pid_task);

/*

* Must be called under rcu_read_lock().

*/

struct task_struct *find_task_by_pid_ns(pid_t nr, struct pid_namespace *ns)

{

rcu_lockdep_assert(rcu_read_lock_held(),

"find_task_by_pid_ns() needs rcu_read_lock()"

" protection");

return pid_task(find_pid_ns(nr, ns), PIDTYPE_PID);

}

struct task_struct *find_task_by_vpid(pid_t vnr)

{

return find_task_by_pid_ns(vnr, task_active_pid_ns(current));

}

struct pid *get_task_pid(struct task_struct *task, enum pid_type type)

{

struct pid *pid;

rcu_read_lock();

if (type != PIDTYPE_PID)

task = task->group_leader;

pid = get_pid(task->pids[type].pid);

rcu_read_unlock();

return pid;

}

EXPORT_SYMBOL_GPL(get_task_pid);

struct task_struct *get_pid_task(struct pid *pid, enum pid_type type)

{

struct task_struct *result;

rcu_read_lock();

result = pid_task(pid, type);

if (result)

get_task_struct(result);

rcu_read_unlock();

return result;

}

EXPORT_SYMBOL_GPL(get_pid_task);

struct pid *find_get_pid(pid_t nr)

{

struct pid *pid;

rcu_read_lock();

pid = get_pid(find_vpid(nr));

rcu_read_unlock();

return pid;

}

EXPORT_SYMBOL_GPL(find_get_pid);

pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns)

{

struct upid *upid;

pid_t nr = 0;

if (pid && ns->level <= pid->level) {

upid = &pid->numbers[ns->level];

if (upid->ns == ns)

nr = upid->nr;

}

return nr;

}

EXPORT_SYMBOL_GPL(pid_nr_ns);

pid_t pid_vnr(struct pid *pid)

{

return pid_nr_ns(pid, task_active_pid_ns(current));

}

EXPORT_SYMBOL_GPL(pid_vnr);

pid_t __task_pid_nr_ns(struct task_struct *task, enum pid_type type,

struct pid_namespace *ns)

{

pid_t nr = 0;

rcu_read_lock();

if (!ns)

ns = task_active_pid_ns(current);

if (likely(pid_alive(task))) {

if (type != PIDTYPE_PID)

task = task->group_leader;

nr = pid_nr_ns(task->pids[type].pid, ns);

}

rcu_read_unlock();

return nr;

}

EXPORT_SYMBOL(__task_pid_nr_ns);

pid_t task_tgid_nr_ns(struct task_struct *tsk, struct pid_namespace *ns)

{

return pid_nr_ns(task_tgid(tsk), ns);

}

EXPORT_SYMBOL(task_tgid_nr_ns);

struct pid_namespace *task_active_pid_ns(struct task_struct *tsk)

{

return ns_of_pid(task_pid(tsk));

}

EXPORT_SYMBOL_GPL(task_active_pid_ns);

/*

* Used by proc to find the first pid that is greater than or equal to nr.

*

* If there is a pid at nr this function is exactly the same as find_pid_ns.

*/

struct pid *find_ge_pid(int nr, struct pid_namespace *ns)

{

struct pid *pid;

do {

pid = find_pid_ns(nr, ns);

if (pid)

break;

nr = next_pidmap(ns, nr);

} while (nr > 0);

return pid;

}

/*

* The pid hash table is scaled according to the amount of memory in the

* machine. From a minimum of 16 slots up to 4096 slots at one gigabyte or

* more.

*/

void __init pidhash_init(void)

{

unsigned int i, pidhash_size;

pid_hash = alloc_large_system_hash("PID", sizeof(*pid_hash), 0, 18,

HASH_EARLY | HASH_SMALL,

&pidhash_shift, NULL,

0, 4096);

pidhash_size = 1U << pidhash_shift;

for (i = 0; i < pidhash_size; i++)

INIT_HLIST_HEAD(&pid_hash[i]);

}

void __init pidmap_init(void)

{

/* bump default and minimum pid_max based on number of cpus */

pid_max = min(pid_max_max, max_t(int, pid_max,

PIDS_PER_CPU_DEFAULT * num_possible_cpus()));

pid_max_min = max_t(int, pid_max_min,

PIDS_PER_CPU_MIN * num_possible_cpus());

pr_info("pid_max: default: %u minimum: %u\n", pid_max, pid_max_min);

init_pid_ns.pidmap[0].page = kzalloc(PAGE_SIZE, GFP_KERNEL);

/* Reserve PID 0. We never call free_pidmap(0) */

set_bit(0, init_pid_ns.pidmap[0].page);

atomic_dec(&init_pid_ns.pidmap[0].nr_free);

init_pid_ns.nr_hashed = 1;

init_pid_ns.pid_cachep = KMEM_CACHE(pid,

SLAB_HWCACHE_ALIGN | SLAB_PANIC);

}