[linux.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>

#define pid_hashfn(nr) hash_long((unsigned long)nr, pidhash_shift)
static struct hlist_head *pid_hash[PIDTYPE_MAX];
static int pidhash_shift;

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 PIDMAP_ENTRIES		((PID_MAX_LIMIT + 8*PAGE_SIZE - 1)/PAGE_SIZE/8)
#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.
 */
typedef struct pidmap {
	atomic_t nr_free;
	void *page;
} pidmap_t;

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

static  __cacheline_aligned_in_smp DEFINE_SPINLOCK(pidmap_lock);

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

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

int alloc_pidmap(void)
{
	int i, offset, max_scan, pid, last = last_pid;
	pidmap_t *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(&pidmap_lock);
			if (map->page)
				free_page(page);
			else
				map->page = (void *)page;
			spin_unlock(&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;
}

struct pid * fastcall find_pid(enum pid_type type, int nr)
{
	struct hlist_node *elem;
	struct pid *pid;

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

int fastcall attach_pid(task_t *task, enum pid_type type, int nr)
{
	struct pid *pid, *task_pid;

	task_pid = &task->pids[type];
	pid = find_pid(type, nr);
	task_pid->nr = nr;
	if (pid == NULL) {
		INIT_LIST_HEAD(&task_pid->pid_list);
		hlist_add_head_rcu(&task_pid->pid_chain,
				   &pid_hash[type][pid_hashfn(nr)]);
	} else {
		INIT_HLIST_NODE(&task_pid->pid_chain);
		list_add_tail_rcu(&task_pid->pid_list, &pid->pid_list);
	}

	return 0;
}

static fastcall int __detach_pid(task_t *task, enum pid_type type)
{
	struct pid *pid, *pid_next;
	int nr = 0;

	pid = &task->pids[type];
	if (!hlist_unhashed(&pid->pid_chain)) {

		if (list_empty(&pid->pid_list)) {
			nr = pid->nr;
			hlist_del_rcu(&pid->pid_chain);
		} else {
			pid_next = list_entry(pid->pid_list.next,
						struct pid, pid_list);
			/* insert next pid from pid_list to hash */
			hlist_replace_rcu(&pid->pid_chain,
					  &pid_next->pid_chain);
		}
	}

	list_del_rcu(&pid->pid_list);
	pid->nr = 0;

	return nr;
}

void fastcall detach_pid(task_t *task, enum pid_type type)
{
	int tmp, nr;

	nr = __detach_pid(task, type);
	if (!nr)
		return;

	for (tmp = PIDTYPE_MAX; --tmp >= 0; )
		if (tmp != type && find_pid(tmp, nr))
			return;

	free_pidmap(nr);
}

task_t *find_task_by_pid_type(int type, int nr)
{
	struct pid *pid;

	pid = find_pid(type, nr);
	if (!pid)
		return NULL;

	return pid_task(&pid->pid_list, type);
}

EXPORT_SYMBOL(find_task_by_pid_type);

/*
 * This function switches the PIDs if a non-leader thread calls
 * sys_execve() - this must be done without releasing the PID.
 * (which a detach_pid() would eventually do.)
 */
void switch_exec_pids(task_t *leader, task_t *thread)
{
	__detach_pid(leader, PIDTYPE_PID);
	__detach_pid(leader, PIDTYPE_TGID);
	__detach_pid(leader, PIDTYPE_PGID);
	__detach_pid(leader, PIDTYPE_SID);

	__detach_pid(thread, PIDTYPE_PID);
	__detach_pid(thread, PIDTYPE_TGID);

	leader->pid = leader->tgid = thread->pid;
	thread->pid = thread->tgid;

	attach_pid(thread, PIDTYPE_PID, thread->pid);
	attach_pid(thread, PIDTYPE_TGID, thread->tgid);
	attach_pid(thread, PIDTYPE_PGID, thread->signal->pgrp);
	attach_pid(thread, PIDTYPE_SID, thread->signal->session);
	list_add_tail(&thread->tasks, &init_task.tasks);

	attach_pid(leader, PIDTYPE_PID, leader->pid);
	attach_pid(leader, PIDTYPE_TGID, leader->tgid);
	attach_pid(leader, PIDTYPE_PGID, leader->signal->pgrp);
	attach_pid(leader, PIDTYPE_SID, leader->signal->session);
}

/*
 * 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, j, 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,
		PIDTYPE_MAX * pidhash_size * sizeof(struct hlist_head));

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

void __init pidmap_init(void)
{
	int i;

	pidmap_array->page = (void *)get_zeroed_page(GFP_KERNEL);
	set_bit(0, pidmap_array->page);
	atomic_dec(&pidmap_array->nr_free);

	/*
	 * Allocate PID 0, and hash it via all PID types:
	 */

	for (i = 0; i < PIDTYPE_MAX; i++)
		attach_pid(current, i, 0);
}
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>
	29
	30	#define pid_hashfn(nr) hash_long((unsigned long)nr, pidhash_shift)
	31	static struct hlist_head *pid_hash[PIDTYPE_MAX];
	32	static int pidhash_shift;
	33
	34	int pid_max = PID_MAX_DEFAULT;
	35	int last_pid;
	36
	37	#define RESERVED_PIDS 300
	38
	39	int pid_max_min = RESERVED_PIDS + 1;
	40	int pid_max_max = PID_MAX_LIMIT;
	41
	42	#define PIDMAP_ENTRIES ((PID_MAX_LIMIT + 8*PAGE_SIZE - 1)/PAGE_SIZE/8)
	43	#define BITS_PER_PAGE (PAGE_SIZE*8)
	44	#define BITS_PER_PAGE_MASK (BITS_PER_PAGE-1)
	45	#define mk_pid(map, off) (((map) - pidmap_array)*BITS_PER_PAGE + (off))
	46	#define find_next_offset(map, off) \
	47	find_next_zero_bit((map)->page, BITS_PER_PAGE, off)
	48
	49	/*
	50	* PID-map pages start out as NULL, they get allocated upon
	51	* first use and are never deallocated. This way a low pid_max
	52	* value does not cause lots of bitmaps to be allocated, but
	53	* the scheme scales to up to 4 million PIDs, runtime.
	54	*/
	55	typedef struct pidmap {
	56	atomic_t nr_free;
	57	void *page;
	58	} pidmap_t;
	59
	60	static pidmap_t pidmap_array[PIDMAP_ENTRIES] =
	61	{ [ 0 ... PIDMAP_ENTRIES-1 ] = { ATOMIC_INIT(BITS_PER_PAGE), NULL } };
	62
	63	static __cacheline_aligned_in_smp DEFINE_SPINLOCK(pidmap_lock);
	64
65	fastcall void free_pidmap(int pid)
66	{
67	pidmap_t *map = pidmap_array + pid / BITS_PER_PAGE;
68	int offset = pid & BITS_PER_PAGE_MASK;
69
70	clear_bit(offset, map->page);
71	atomic_inc(&map->nr_free);
72	}
73
74	int alloc_pidmap(void)
75	{
76	int i, offset, max_scan, pid, last = last_pid;
77	pidmap_t *map;
78
79	pid = last + 1;
80	if (pid >= pid_max)
81	pid = RESERVED_PIDS;
82	offset = pid & BITS_PER_PAGE_MASK;
83	map = &pidmap_array[pid/BITS_PER_PAGE];
84	max_scan = (pid_max + BITS_PER_PAGE - 1)/BITS_PER_PAGE - !offset;
85	for (i = 0; i <= max_scan; ++i) {
86	if (unlikely(!map->page)) {
87	unsigned long page = get_zeroed_page(GFP_KERNEL);
88	/*
89	* Free the page if someone raced with us
90	* installing it:
91	*/
92	spin_lock(&pidmap_lock);
93	if (map->page)
94	free_page(page);
95	else
96	map->page = (void *)page;
97	spin_unlock(&pidmap_lock);
98	if (unlikely(!map->page))
99	break;
100	}
101	if (likely(atomic_read(&map->nr_free))) {
102	do {
103	if (!test_and_set_bit(offset, map->page)) {
104	atomic_dec(&map->nr_free);
105	last_pid = pid;
106	return pid;
107	}
108	offset = find_next_offset(map, offset);
109	pid = mk_pid(map, offset);
110	/*
111	* find_next_offset() found a bit, the pid from it
112	* is in-bounds, and if we fell back to the last
113	* bitmap block and the final block was the same
114	* as the starting point, pid is before last_pid.
115	*/
116	} while (offset < BITS_PER_PAGE && pid < pid_max &&
117	(i != max_scan \|\| pid < last \|\|
118	!((last+1) & BITS_PER_PAGE_MASK)));
119	}
120	if (map < &pidmap_array[(pid_max-1)/BITS_PER_PAGE]) {
121	++map;
122	offset = 0;
123	} else {
124	map = &pidmap_array[0];
125	offset = RESERVED_PIDS;
126	if (unlikely(last == offset))
127	break;
128	}
129	pid = mk_pid(map, offset);
130	}
131	return -1;
132	}
133
134	struct pid * fastcall find_pid(enum pid_type type, int nr)
135	{
136	struct hlist_node *elem;
137	struct pid *pid;
138
e56d0903	139	hlist_for_each_entry_rcu(pid, elem,
1da177e4 LT	140	&pid_hash[type][pid_hashfn(nr)], pid_chain) {
	141	if (pid->nr == nr)
	142	return pid;
	143	}
	144	return NULL;
	145	}
	146
	147	int fastcall attach_pid(task_t *task, enum pid_type type, int nr)
	148	{
	149	struct pid pid, task_pid;
	150
	151	task_pid = &task->pids[type];
	152	pid = find_pid(type, nr);
e56d0903	153	task_pid->nr = nr;
1da177e4	154	if (pid == NULL) {
1da177e4	155	INIT_LIST_HEAD(&task_pid->pid_list);
e56d0903 IM	156	hlist_add_head_rcu(&task_pid->pid_chain,
e56d0903 IM	157	&pid_hash[type][pid_hashfn(nr)]);
1da177e4 LT	158	} else {
1da177e4 LT	159	INIT_HLIST_NODE(&task_pid->pid_chain);
e56d0903	160	list_add_tail_rcu(&task_pid->pid_list, &pid->pid_list);
1da177e4	161	}
1da177e4 LT	162
	163	return 0;
	164	}
	165
	166	static fastcall int __detach_pid(task_t *task, enum pid_type type)
	167	{
	168	struct pid pid, pid_next;
	169	int nr = 0;
	170
	171	pid = &task->pids[type];
	172	if (!hlist_unhashed(&pid->pid_chain)) {
1da177e4	173
e56d0903	174	if (list_empty(&pid->pid_list)) {
1da177e4	175	nr = pid->nr;
e56d0903 IM	176	hlist_del_rcu(&pid->pid_chain);
e56d0903 IM	177	} else {
1da177e4 LT	178	pid_next = list_entry(pid->pid_list.next,
	179	struct pid, pid_list);
	180	/* insert next pid from pid_list to hash */
e56d0903 IM	181	hlist_replace_rcu(&pid->pid_chain,
e56d0903 IM	182	&pid_next->pid_chain);
1da177e4 LT	183	}
	184	}
	185
e56d0903	186	list_del_rcu(&pid->pid_list);
1da177e4 LT	187	pid->nr = 0;
	188
	189	return nr;
	190	}
	191
	192	void fastcall detach_pid(task_t *task, enum pid_type type)
	193	{
	194	int tmp, nr;
	195
	196	nr = __detach_pid(task, type);
	197	if (!nr)
	198	return;
	199
	200	for (tmp = PIDTYPE_MAX; --tmp >= 0; )
	201	if (tmp != type && find_pid(tmp, nr))
	202	return;
	203
	204	free_pidmap(nr);
	205	}
	206
	207	task_t *find_task_by_pid_type(int type, int nr)
	208	{
	209	struct pid *pid;
	210
	211	pid = find_pid(type, nr);
	212	if (!pid)
	213	return NULL;
	214
	215	return pid_task(&pid->pid_list, type);
	216	}
	217
	218	EXPORT_SYMBOL(find_task_by_pid_type);
	219
	220	/*
	221	* This function switches the PIDs if a non-leader thread calls
	222	* sys_execve() - this must be done without releasing the PID.
	223	* (which a detach_pid() would eventually do.)
	224	*/
	225	void switch_exec_pids(task_t leader, task_t thread)
	226	{
	227	__detach_pid(leader, PIDTYPE_PID);
	228	__detach_pid(leader, PIDTYPE_TGID);
	229	__detach_pid(leader, PIDTYPE_PGID);
	230	__detach_pid(leader, PIDTYPE_SID);
	231
	232	__detach_pid(thread, PIDTYPE_PID);
	233	__detach_pid(thread, PIDTYPE_TGID);
	234
	235	leader->pid = leader->tgid = thread->pid;
	236	thread->pid = thread->tgid;
	237
	238	attach_pid(thread, PIDTYPE_PID, thread->pid);
	239	attach_pid(thread, PIDTYPE_TGID, thread->tgid);
	240	attach_pid(thread, PIDTYPE_PGID, thread->signal->pgrp);
	241	attach_pid(thread, PIDTYPE_SID, thread->signal->session);
	242	list_add_tail(&thread->tasks, &init_task.tasks);
	243
	244	attach_pid(leader, PIDTYPE_PID, leader->pid);
	245	attach_pid(leader, PIDTYPE_TGID, leader->tgid);
	246	attach_pid(leader, PIDTYPE_PGID, leader->signal->pgrp);
	247	attach_pid(leader, PIDTYPE_SID, leader->signal->session);
	248	}
	249
	250	/*
251	* The pid hash table is scaled according to the amount of memory in the
252	* machine. From a minimum of 16 slots up to 4096 slots at one gigabyte or
253	* more.
254	*/
255	void __init pidhash_init(void)
256	{
257	int i, j, pidhash_size;
258	unsigned long megabytes = nr_kernel_pages >> (20 - PAGE_SHIFT);
259
260	pidhash_shift = max(4, fls(megabytes * 4));
261	pidhash_shift = min(12, pidhash_shift);
262	pidhash_size = 1 << pidhash_shift;
263
264	printk("PID hash table entries: %d (order: %d, %Zd bytes)\n",
265	pidhash_size, pidhash_shift,
266	PIDTYPE_MAX * pidhash_size * sizeof(struct hlist_head));
267
268	for (i = 0; i < PIDTYPE_MAX; i++) {
269	pid_hash[i] = alloc_bootmem(pidhash_size *
270	sizeof(*(pid_hash[i])));
271	if (!pid_hash[i])
272	panic("Could not alloc pidhash!\n");
273	for (j = 0; j < pidhash_size; j++)
274	INIT_HLIST_HEAD(&pid_hash[i][j]);
275	}
276	}
277
278	void __init pidmap_init(void)
279	{
280	int i;
281
282	pidmap_array->page = (void *)get_zeroed_page(GFP_KERNEL);
283	set_bit(0, pidmap_array->page);
284	atomic_dec(&pidmap_array->nr_free);
285
286	/*
287	* Allocate PID 0, and hash it via all PID types:
288	*/
289
290	for (i = 0; i < PIDTYPE_MAX; i++)
291	attach_pid(current, i, 0);
292	}