/* * 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(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);	if (pid == NULL) {		hlist_add_head(&task_pid->pid_chain,				&pid_hash[type][pid_hashfn(nr)]);		INIT_LIST_HEAD(&task_pid->pid_list);	} else {		INIT_HLIST_NODE(&task_pid->pid_chain);		list_add_tail(&task_pid->pid_list, &pid->pid_list);	}	task_pid->nr = nr; 	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)) {		hlist_del(&pid->pid_chain); 		if (list_empty(&pid->pid_list))			nr = pid->nr;		else {			pid_next = list_entry(pid->pid_list.next,						struct pid, pid_list);			/* insert next pid from pid_list to hash */			hlist_add_head(&pid_next->pid_chain,				&pid_hash[type][pid_hashfn(pid_next->nr)]);		}	} 	list_del(&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);}