diff options
Diffstat (limited to 'kernel/pid.c')
| -rw-r--r-- | kernel/pid.c | 292 |
1 files changed, 292 insertions, 0 deletions
diff --git a/kernel/pid.c b/kernel/pid.c new file mode 100644 index 00000000000..edba31c681a --- /dev/null +++ b/kernel/pid.c @@ -0,0 +1,292 @@ +/* + * 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); +} |