/* * 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); }