[GitHub/mt8127/android_kernel_alcatel_ttab.git] / kernel / pid.c

/*
 * Generic pidhash and scalable, time-bounded PID allocator
 *
 * (C) 2002-2003 William Irwin, IBM
 * (C) 2004 William Irwin, 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).
 */

#include <linux/mm.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/init.h>
#include <linux/bootmem.h>
#include <linux/hash.h>
#include <linux/pspace.h>

#define pid_hashfn(nr) hash_long((unsigned long)nr, pidhash_shift)
static struct hlist_head *pid_hash;
static int pidhash_shift;
static kmem_cache_t *pid_cachep;

int pid_max = PID_MAX_DEFAULT;
int last_pid;

#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)
#define mk_pid(map, off)	(((map) - pidmap_array)*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.
 */
static struct pidmap pidmap_array[PIDMAP_ENTRIES] =
	 { [ 0 ... PIDMAP_ENTRIES-1 ] = { ATOMIC_INIT(BITS_PER_PAGE), NULL } };

/*
 * 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 fastcall void free_pidmap(int pid)
{
	struct pidmap *map = pidmap_array + pid / BITS_PER_PAGE;
	int offset = pid & BITS_PER_PAGE_MASK;

	clear_bit(offset, map->page);
	atomic_inc(&map->nr_free);
}

static int alloc_pidmap(void)
{
	int i, offset, max_scan, pid, last = last_pid;
	struct pidmap *map;

	pid = last + 1;
	if (pid >= pid_max)
		pid = RESERVED_PIDS;
	offset = pid & BITS_PER_PAGE_MASK;
	map = &pidmap_array[pid/BITS_PER_PAGE];
	max_scan = (pid_max + BITS_PER_PAGE - 1)/BITS_PER_PAGE - !offset;
	for (i = 0; i <= max_scan; ++i) {
		if (unlikely(!map->page)) {
			unsigned long page = get_zeroed_page(GFP_KERNEL);
			/*
			 * Free the page if someone raced with us
			 * installing it:
			 */
			spin_lock_irq(&pidmap_lock);
			if (map->page)
				free_page(page);
			else
				map->page = (void *)page;
			spin_unlock_irq(&pidmap_lock);
			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);
					last_pid = pid;
					return pid;
				}
				offset = find_next_offset(map, offset);
				pid = mk_pid(map, offset);
			/*
			 * find_next_offset() found a bit, the pid from it
			 * is in-bounds, and if we fell back to the last
			 * bitmap block and the final block was the same
			 * as the starting point, pid is before last_pid.
			 */
			} while (offset < BITS_PER_PAGE && pid < pid_max &&
					(i != max_scan || pid < last ||
					    !((last+1) & BITS_PER_PAGE_MASK)));
		}
		if (map < &pidmap_array[(pid_max-1)/BITS_PER_PAGE]) {
			++map;
			offset = 0;
		} else {
			map = &pidmap_array[0];
			offset = RESERVED_PIDS;
			if (unlikely(last == offset))
				break;
		}
		pid = mk_pid(map, offset);
	}
	return -1;
}

static int next_pidmap(int last)
{
	int offset;
	struct pidmap *map;

	offset = (last + 1) & BITS_PER_PAGE_MASK;
	map = &pidmap_array[(last + 1)/BITS_PER_PAGE];
	for (; map < &pidmap_array[PIDMAP_ENTRIES]; 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(map, offset);
	}
	return -1;
}

fastcall void put_pid(struct pid *pid)
{
	if (!pid)
		return;
	if ((atomic_read(&pid->count) == 1) ||
	     atomic_dec_and_test(&pid->count))
		kmem_cache_free(pid_cachep, pid);
}
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);
}

fastcall void free_pid(struct pid *pid)
{
	/* We can be called with write_lock_irq(&tasklist_lock) held */
	unsigned long flags;

	spin_lock_irqsave(&pidmap_lock, flags);
	hlist_del_rcu(&pid->pid_chain);
	spin_unlock_irqrestore(&pidmap_lock, flags);

	free_pidmap(pid->nr);
	call_rcu(&pid->rcu, delayed_put_pid);
}

struct pid *alloc_pid(void)
{
	struct pid *pid;
	enum pid_type type;
	int nr = -1;

	pid = kmem_cache_alloc(pid_cachep, GFP_KERNEL);
	if (!pid)
		goto out;

	nr = alloc_pidmap();
	if (nr < 0)
		goto out_free;

	atomic_set(&pid->count, 1);
	pid->nr = nr;
	for (type = 0; type < PIDTYPE_MAX; ++type)
		INIT_HLIST_HEAD(&pid->tasks[type]);

	spin_lock_irq(&pidmap_lock);
	hlist_add_head_rcu(&pid->pid_chain, &pid_hash[pid_hashfn(pid->nr)]);
	spin_unlock_irq(&pidmap_lock);

out:
	return pid;

out_free:
	kmem_cache_free(pid_cachep, pid);
	pid = NULL;
	goto out;
}

struct pid * fastcall find_pid(int nr)
{
	struct hlist_node *elem;
	struct pid *pid;

	hlist_for_each_entry_rcu(pid, elem,
			&pid_hash[pid_hashfn(nr)], pid_chain) {
		if (pid->nr == nr)
			return pid;
	}
	return NULL;
}
EXPORT_SYMBOL_GPL(find_pid);

int fastcall attach_pid(struct task_struct *task, enum pid_type type, int nr)
{
	struct pid_link *link;
	struct pid *pid;

	link = &task->pids[type];
	link->pid = pid = find_pid(nr);
	hlist_add_head_rcu(&link->node, &pid->tasks[type]);

	return 0;
}

void fastcall detach_pid(struct task_struct *task, enum pid_type type)
{
	struct pid_link *link;
	struct pid *pid;
	int tmp;

	link = &task->pids[type];
	pid = link->pid;

	hlist_del_rcu(&link->node);
	link->pid = NULL;

	for (tmp = PIDTYPE_MAX; --tmp >= 0; )
		if (!hlist_empty(&pid->tasks[tmp]))
			return;

	free_pid(pid);
}

/* transfer_pid is an optimization of attach_pid(new), detach_pid(old) */
void fastcall 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);
	old->pids[type].pid = NULL;
}

struct task_struct * fastcall pid_task(struct pid *pid, enum pid_type type)
{
	struct task_struct *result = NULL;
	if (pid) {
		struct hlist_node *first;
		first = rcu_dereference(pid->tasks[type].first);
		if (first)
			result = hlist_entry(first, struct task_struct, pids[(type)].node);
	}
	return result;
}

/*
 * Must be called under rcu_read_lock() or with tasklist_lock read-held.
 */
struct task_struct *find_task_by_pid_type(int type, int nr)
{
	return pid_task(find_pid(nr), type);
}

EXPORT_SYMBOL(find_task_by_pid_type);

struct task_struct *fastcall 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;
}

struct pid *find_get_pid(pid_t nr)
{
	struct pid *pid;

	rcu_read_lock();
	pid = get_pid(find_pid(nr));
	rcu_read_unlock();

	return pid;
}

/*
 * Used by proc to find the first pid that is greater then or equal to nr.
 *
 * If there is a pid at nr this function is exactly the same as find_pid.
 */
struct pid *find_ge_pid(int nr)
{
	struct pid *pid;

	do {
		pid = find_pid(nr);
		if (pid)
			break;
		nr = next_pidmap(nr);
	} while (nr > 0);

	return pid;
}
EXPORT_SYMBOL_GPL(find_get_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)
{
	int i, pidhash_size;
	unsigned long megabytes = nr_kernel_pages >> (20 - PAGE_SHIFT);

	pidhash_shift = max(4, fls(megabytes * 4));
	pidhash_shift = min(12, pidhash_shift);
	pidhash_size = 1 << pidhash_shift;

	printk("PID hash table entries: %d (order: %d, %Zd bytes)\n",
		pidhash_size, pidhash_shift,
		pidhash_size * sizeof(struct hlist_head));

	pid_hash = alloc_bootmem(pidhash_size *	sizeof(*(pid_hash)));
	if (!pid_hash)
		panic("Could not alloc pidhash!\n");
	for (i = 0; i < pidhash_size; i++)
		INIT_HLIST_HEAD(&pid_hash[i]);
}

void __init pidmap_init(void)
{
	pidmap_array->page = (void *)get_zeroed_page(GFP_KERNEL);
	/* Reserve PID 0. We never call free_pidmap(0) */
	set_bit(0, pidmap_array->page);
	atomic_dec(&pidmap_array->nr_free);

	pid_cachep = kmem_cache_create("pid", sizeof(struct pid),
					__alignof__(struct pid),
					SLAB_PANIC, NULL, NULL);
}
Commit	Line	Data
1da177e4 LT	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
	23	#include <linux/mm.h>
	24	#include <linux/module.h>
	25	#include <linux/slab.h>
	26	#include <linux/init.h>
	27	#include <linux/bootmem.h>
	28	#include <linux/hash.h>
aa5a6662	29	#include <linux/pspace.h>
1da177e4 LT	30
1da177e4 LT	31	#define pid_hashfn(nr) hash_long((unsigned long)nr, pidhash_shift)
92476d7f	32	static struct hlist_head *pid_hash;
1da177e4	33	static int pidhash_shift;
92476d7f	34	static kmem_cache_t *pid_cachep;
1da177e4 LT	35
	36	int pid_max = PID_MAX_DEFAULT;
	37	int last_pid;
	38
	39	#define RESERVED_PIDS 300
	40
	41	int pid_max_min = RESERVED_PIDS + 1;
	42	int pid_max_max = PID_MAX_LIMIT;
	43
1da177e4 LT	44	#define BITS_PER_PAGE (PAGE_SIZE*8)
	45	#define BITS_PER_PAGE_MASK (BITS_PER_PAGE-1)
	46	#define mk_pid(map, off) (((map) - pidmap_array)*BITS_PER_PAGE + (off))
	47	#define find_next_offset(map, off) \
	48	find_next_zero_bit((map)->page, BITS_PER_PAGE, off)
	49
	50	/*
	51	* PID-map pages start out as NULL, they get allocated upon
	52	* first use and are never deallocated. This way a low pid_max
	53	* value does not cause lots of bitmaps to be allocated, but
	54	* the scheme scales to up to 4 million PIDs, runtime.
	55	*/
6a1f3b84	56	static struct pidmap pidmap_array[PIDMAP_ENTRIES] =
1da177e4 LT	57	{ [ 0 ... PIDMAP_ENTRIES-1 ] = { ATOMIC_INIT(BITS_PER_PAGE), NULL } };
1da177e4 LT	58
92476d7f EB	59	/*
	60	* Note: disable interrupts while the pidmap_lock is held as an
	61	* interrupt might come in and do read_lock(&tasklist_lock).
	62	*
	63	* If we don't disable interrupts there is a nasty deadlock between
	64	* detach_pid()->free_pid() and another cpu that does
	65	* spin_lock(&pidmap_lock) followed by an interrupt routine that does
	66	* read_lock(&tasklist_lock);
	67	*
	68	* After we clean up the tasklist_lock and know there are no
	69	* irq handlers that take it we can leave the interrupts enabled.
	70	* For now it is easier to be safe than to prove it can't happen.
	71	*/
1da177e4 LT	72	static __cacheline_aligned_in_smp DEFINE_SPINLOCK(pidmap_lock);
1da177e4 LT	73
92476d7f	74	static fastcall void free_pidmap(int pid)
1da177e4	75	{
6a1f3b84	76	struct pidmap *map = pidmap_array + pid / BITS_PER_PAGE;
1da177e4 LT	77	int offset = pid & BITS_PER_PAGE_MASK;
	78
	79	clear_bit(offset, map->page);
	80	atomic_inc(&map->nr_free);
	81	}
	82
92476d7f	83	static int alloc_pidmap(void)
1da177e4 LT	84	{
1da177e4 LT	85	int i, offset, max_scan, pid, last = last_pid;
6a1f3b84	86	struct pidmap *map;
1da177e4 LT	87
	88	pid = last + 1;
	89	if (pid >= pid_max)
	90	pid = RESERVED_PIDS;
	91	offset = pid & BITS_PER_PAGE_MASK;
	92	map = &pidmap_array[pid/BITS_PER_PAGE];
	93	max_scan = (pid_max + BITS_PER_PAGE - 1)/BITS_PER_PAGE - !offset;
	94	for (i = 0; i <= max_scan; ++i) {
	95	if (unlikely(!map->page)) {
	96	unsigned long page = get_zeroed_page(GFP_KERNEL);
	97	/*
	98	* Free the page if someone raced with us
	99	* installing it:
	100	*/
92476d7f	101	spin_lock_irq(&pidmap_lock);
1da177e4 LT	102	if (map->page)
	103	free_page(page);
	104	else
	105	map->page = (void *)page;
92476d7f	106	spin_unlock_irq(&pidmap_lock);
1da177e4 LT	107	if (unlikely(!map->page))
	108	break;
	109	}
	110	if (likely(atomic_read(&map->nr_free))) {
	111	do {
	112	if (!test_and_set_bit(offset, map->page)) {
	113	atomic_dec(&map->nr_free);
	114	last_pid = pid;
	115	return pid;
	116	}
	117	offset = find_next_offset(map, offset);
	118	pid = mk_pid(map, offset);
	119	/*
	120	* find_next_offset() found a bit, the pid from it
	121	* is in-bounds, and if we fell back to the last
	122	* bitmap block and the final block was the same
	123	* as the starting point, pid is before last_pid.
	124	*/
	125	} while (offset < BITS_PER_PAGE && pid < pid_max &&
	126	(i != max_scan \|\| pid < last \|\|
	127	!((last+1) & BITS_PER_PAGE_MASK)));
	128	}
	129	if (map < &pidmap_array[(pid_max-1)/BITS_PER_PAGE]) {
	130	++map;
	131	offset = 0;
	132	} else {
	133	map = &pidmap_array[0];
	134	offset = RESERVED_PIDS;
	135	if (unlikely(last == offset))
	136	break;
	137	}
	138	pid = mk_pid(map, offset);
	139	}
	140	return -1;
	141	}
	142
0804ef4b EB	143	static int next_pidmap(int last)
	144	{
	145	int offset;
c88be3eb	146	struct pidmap *map;
0804ef4b EB	147
	148	offset = (last + 1) & BITS_PER_PAGE_MASK;
	149	map = &pidmap_array[(last + 1)/BITS_PER_PAGE];
	150	for (; map < &pidmap_array[PIDMAP_ENTRIES]; map++, offset = 0) {
	151	if (unlikely(!map->page))
	152	continue;
	153	offset = find_next_bit((map)->page, BITS_PER_PAGE, offset);
	154	if (offset < BITS_PER_PAGE)
	155	return mk_pid(map, offset);
	156	}
	157	return -1;
	158	}
	159
92476d7f EB	160	fastcall void put_pid(struct pid *pid)
	161	{
	162	if (!pid)
	163	return;
	164	if ((atomic_read(&pid->count) == 1) \|\|
	165	atomic_dec_and_test(&pid->count))
	166	kmem_cache_free(pid_cachep, pid);
	167	}
bbf73147	168	EXPORT_SYMBOL_GPL(put_pid);
92476d7f EB	169
	170	static void delayed_put_pid(struct rcu_head *rhp)
	171	{
	172	struct pid *pid = container_of(rhp, struct pid, rcu);
	173	put_pid(pid);
	174	}
	175
	176	fastcall void free_pid(struct pid *pid)
	177	{
	178	/* We can be called with write_lock_irq(&tasklist_lock) held */
	179	unsigned long flags;
	180
	181	spin_lock_irqsave(&pidmap_lock, flags);
	182	hlist_del_rcu(&pid->pid_chain);
	183	spin_unlock_irqrestore(&pidmap_lock, flags);
	184
	185	free_pidmap(pid->nr);
	186	call_rcu(&pid->rcu, delayed_put_pid);
	187	}
	188
	189	struct pid *alloc_pid(void)
	190	{
	191	struct pid *pid;
	192	enum pid_type type;
	193	int nr = -1;
	194
	195	pid = kmem_cache_alloc(pid_cachep, GFP_KERNEL);
	196	if (!pid)
	197	goto out;
	198
	199	nr = alloc_pidmap();
	200	if (nr < 0)
	201	goto out_free;
	202
	203	atomic_set(&pid->count, 1);
	204	pid->nr = nr;
	205	for (type = 0; type < PIDTYPE_MAX; ++type)
	206	INIT_HLIST_HEAD(&pid->tasks[type]);
	207
	208	spin_lock_irq(&pidmap_lock);
	209	hlist_add_head_rcu(&pid->pid_chain, &pid_hash[pid_hashfn(pid->nr)]);
	210	spin_unlock_irq(&pidmap_lock);
	211
	212	out:
	213	return pid;
	214
	215	out_free:
	216	kmem_cache_free(pid_cachep, pid);
	217	pid = NULL;
	218	goto out;
	219	}
	220
	221	struct pid * fastcall find_pid(int nr)
1da177e4 LT	222	{
	223	struct hlist_node *elem;
	224	struct pid *pid;
	225
e56d0903	226	hlist_for_each_entry_rcu(pid, elem,
92476d7f	227	&pid_hash[pid_hashfn(nr)], pid_chain) {
1da177e4 LT	228	if (pid->nr == nr)
	229	return pid;
	230	}
	231	return NULL;
	232	}
bbf73147	233	EXPORT_SYMBOL_GPL(find_pid);
1da177e4	234
36c8b586	235	int fastcall attach_pid(struct task_struct *task, enum pid_type type, int nr)
1da177e4	236	{
92476d7f EB	237	struct pid_link *link;
	238	struct pid *pid;
	239
92476d7f EB	240	link = &task->pids[type];
	241	link->pid = pid = find_pid(nr);
	242	hlist_add_head_rcu(&link->node, &pid->tasks[type]);
1da177e4 LT	243
	244	return 0;
	245	}
	246
36c8b586	247	void fastcall detach_pid(struct task_struct *task, enum pid_type type)
1da177e4	248	{
92476d7f EB	249	struct pid_link *link;
	250	struct pid *pid;
	251	int tmp;
1da177e4	252
92476d7f EB	253	link = &task->pids[type];
92476d7f EB	254	pid = link->pid;
1da177e4	255
92476d7f EB	256	hlist_del_rcu(&link->node);
92476d7f EB	257	link->pid = NULL;
1da177e4	258
92476d7f EB	259	for (tmp = PIDTYPE_MAX; --tmp >= 0; )
	260	if (!hlist_empty(&pid->tasks[tmp]))
	261	return;
1da177e4	262
92476d7f	263	free_pid(pid);
1da177e4 LT	264	}
1da177e4 LT	265
c18258c6 EB	266	/* transfer_pid is an optimization of attach_pid(new), detach_pid(old) */
	267	void fastcall transfer_pid(struct task_struct old, struct task_struct new,
	268	enum pid_type type)
	269	{
	270	new->pids[type].pid = old->pids[type].pid;
	271	hlist_replace_rcu(&old->pids[type].node, &new->pids[type].node);
	272	old->pids[type].pid = NULL;
	273	}
	274
92476d7f	275	struct task_struct * fastcall pid_task(struct pid *pid, enum pid_type type)
1da177e4	276	{
92476d7f EB	277	struct task_struct *result = NULL;
	278	if (pid) {
	279	struct hlist_node *first;
	280	first = rcu_dereference(pid->tasks[type].first);
	281	if (first)
	282	result = hlist_entry(first, struct task_struct, pids[(type)].node);
	283	}
	284	return result;
	285	}
1da177e4	286
92476d7f EB	287	/*
	288	* Must be called under rcu_read_lock() or with tasklist_lock read-held.
	289	*/
36c8b586	290	struct task_struct *find_task_by_pid_type(int type, int nr)
92476d7f EB	291	{
	292	return pid_task(find_pid(nr), type);
	293	}
1da177e4	294
92476d7f	295	EXPORT_SYMBOL(find_task_by_pid_type);
1da177e4	296
92476d7f EB	297	struct task_struct fastcall get_pid_task(struct pid pid, enum pid_type type)
	298	{
	299	struct task_struct *result;
	300	rcu_read_lock();
	301	result = pid_task(pid, type);
	302	if (result)
	303	get_task_struct(result);
	304	rcu_read_unlock();
	305	return result;
1da177e4 LT	306	}
1da177e4 LT	307
92476d7f	308	struct pid *find_get_pid(pid_t nr)
1da177e4 LT	309	{
	310	struct pid *pid;
	311
92476d7f EB	312	rcu_read_lock();
	313	pid = get_pid(find_pid(nr));
	314	rcu_read_unlock();
1da177e4	315
92476d7f	316	return pid;
1da177e4 LT	317	}
1da177e4 LT	318
0804ef4b EB	319	/*
	320	* Used by proc to find the first pid that is greater then or equal to nr.
	321	*
	322	* If there is a pid at nr this function is exactly the same as find_pid.
	323	*/
	324	struct pid *find_ge_pid(int nr)
	325	{
	326	struct pid *pid;
	327
	328	do {
	329	pid = find_pid(nr);
	330	if (pid)
	331	break;
	332	nr = next_pidmap(nr);
	333	} while (nr > 0);
	334
	335	return pid;
	336	}
bbf73147	337	EXPORT_SYMBOL_GPL(find_get_pid);
0804ef4b	338
1da177e4 LT	339	/*
	340	* The pid hash table is scaled according to the amount of memory in the
	341	* machine. From a minimum of 16 slots up to 4096 slots at one gigabyte or
	342	* more.
	343	*/
	344	void __init pidhash_init(void)
	345	{
92476d7f	346	int i, pidhash_size;
1da177e4 LT	347	unsigned long megabytes = nr_kernel_pages >> (20 - PAGE_SHIFT);
	348
	349	pidhash_shift = max(4, fls(megabytes * 4));
	350	pidhash_shift = min(12, pidhash_shift);
	351	pidhash_size = 1 << pidhash_shift;
	352
	353	printk("PID hash table entries: %d (order: %d, %Zd bytes)\n",
	354	pidhash_size, pidhash_shift,
92476d7f EB	355	pidhash_size * sizeof(struct hlist_head));
	356
	357	pid_hash = alloc_bootmem(pidhash_size * sizeof(*(pid_hash)));
	358	if (!pid_hash)
	359	panic("Could not alloc pidhash!\n");
	360	for (i = 0; i < pidhash_size; i++)
	361	INIT_HLIST_HEAD(&pid_hash[i]);
1da177e4 LT	362	}
	363
	364	void __init pidmap_init(void)
	365	{
1da177e4	366	pidmap_array->page = (void *)get_zeroed_page(GFP_KERNEL);
73b9ebfe	367	/* Reserve PID 0. We never call free_pidmap(0) */
1da177e4 LT	368	set_bit(0, pidmap_array->page);
1da177e4 LT	369	atomic_dec(&pidmap_array->nr_free);
92476d7f EB	370
	371	pid_cachep = kmem_cache_create("pid", sizeof(struct pid),
	372	__alignof__(struct pid),
	373	SLAB_PANIC, NULL, NULL);
1da177e4	374	}