kernel/pid.c - linux/kernel/git/davem/net-next - Git at Google

 /*
  * 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;
 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 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 } };

 /*
  * 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)
 {
 	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);
 }

 static 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_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;
 }

 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);
 }

 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;
 }

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

 	WARN_ON(!task->pid); /* to be removed soon */
 	WARN_ON(!nr); /* to be removed soon */

 	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(task_t *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);
 }

 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.
  */
 task_t *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;
 }

 /*
  * 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);
 }
	/*
	* 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;
	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 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 } };

	/*
	* 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)
	{
	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);
	}

	static 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_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;
	}

	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);
	}

	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;
	}

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

	WARN_ON(!task->pid); /* to be removed soon */
	WARN_ON(!nr); /* to be removed soon */

	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(task_t *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);
	}

	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.
	*/
	task_t *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;
	}

	/*
	* 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);
	}