/* * 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);}