Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1 | /* |
| 2 | * Generic pidhash and scalable, time-bounded PID allocator |
| 3 | * |
| 4 | * (C) 2002-2003 William Irwin, IBM |
| 5 | * (C) 2004 William Irwin, Oracle |
| 6 | * (C) 2002-2004 Ingo Molnar, Red Hat |
| 7 | * |
| 8 | * pid-structures are backing objects for tasks sharing a given ID to chain |
| 9 | * against. There is very little to them aside from hashing them and |
| 10 | * parking tasks using given ID's on a list. |
| 11 | * |
| 12 | * The hash is always changed with the tasklist_lock write-acquired, |
| 13 | * and the hash is only accessed with the tasklist_lock at least |
| 14 | * read-acquired, so there's no additional SMP locking needed here. |
| 15 | * |
| 16 | * We have a list of bitmap pages, which bitmaps represent the PID space. |
| 17 | * Allocating and freeing PIDs is completely lockless. The worst-case |
| 18 | * allocation scenario when all but one out of 1 million PIDs possible are |
| 19 | * allocated already: the scanning of 32 list entries and at most PAGE_SIZE |
| 20 | * bytes. The typical fastpath is a single successful setbit. Freeing is O(1). |
| 21 | */ |
| 22 | |
| 23 | #include <linux/mm.h> |
| 24 | #include <linux/module.h> |
| 25 | #include <linux/slab.h> |
| 26 | #include <linux/init.h> |
| 27 | #include <linux/bootmem.h> |
| 28 | #include <linux/hash.h> |
| 29 | |
| 30 | #define pid_hashfn(nr) hash_long((unsigned long)nr, pidhash_shift) |
| 31 | static struct hlist_head *pid_hash[PIDTYPE_MAX]; |
| 32 | static int pidhash_shift; |
| 33 | |
| 34 | int pid_max = PID_MAX_DEFAULT; |
| 35 | int last_pid; |
| 36 | |
| 37 | #define RESERVED_PIDS 300 |
| 38 | |
| 39 | int pid_max_min = RESERVED_PIDS + 1; |
| 40 | int pid_max_max = PID_MAX_LIMIT; |
| 41 | |
| 42 | #define PIDMAP_ENTRIES ((PID_MAX_LIMIT + 8*PAGE_SIZE - 1)/PAGE_SIZE/8) |
| 43 | #define BITS_PER_PAGE (PAGE_SIZE*8) |
| 44 | #define BITS_PER_PAGE_MASK (BITS_PER_PAGE-1) |
| 45 | #define mk_pid(map, off) (((map) - pidmap_array)*BITS_PER_PAGE + (off)) |
| 46 | #define find_next_offset(map, off) \ |
| 47 | find_next_zero_bit((map)->page, BITS_PER_PAGE, off) |
| 48 | |
| 49 | /* |
| 50 | * PID-map pages start out as NULL, they get allocated upon |
| 51 | * first use and are never deallocated. This way a low pid_max |
| 52 | * value does not cause lots of bitmaps to be allocated, but |
| 53 | * the scheme scales to up to 4 million PIDs, runtime. |
| 54 | */ |
| 55 | typedef struct pidmap { |
| 56 | atomic_t nr_free; |
| 57 | void *page; |
| 58 | } pidmap_t; |
| 59 | |
| 60 | static pidmap_t pidmap_array[PIDMAP_ENTRIES] = |
| 61 | { [ 0 ... PIDMAP_ENTRIES-1 ] = { ATOMIC_INIT(BITS_PER_PAGE), NULL } }; |
| 62 | |
| 63 | static __cacheline_aligned_in_smp DEFINE_SPINLOCK(pidmap_lock); |
| 64 | |
| 65 | fastcall void free_pidmap(int pid) |
| 66 | { |
| 67 | pidmap_t *map = pidmap_array + pid / BITS_PER_PAGE; |
| 68 | int offset = pid & BITS_PER_PAGE_MASK; |
| 69 | |
| 70 | clear_bit(offset, map->page); |
| 71 | atomic_inc(&map->nr_free); |
| 72 | } |
| 73 | |
| 74 | int alloc_pidmap(void) |
| 75 | { |
| 76 | int i, offset, max_scan, pid, last = last_pid; |
| 77 | pidmap_t *map; |
| 78 | |
| 79 | pid = last + 1; |
| 80 | if (pid >= pid_max) |
| 81 | pid = RESERVED_PIDS; |
| 82 | offset = pid & BITS_PER_PAGE_MASK; |
| 83 | map = &pidmap_array[pid/BITS_PER_PAGE]; |
| 84 | max_scan = (pid_max + BITS_PER_PAGE - 1)/BITS_PER_PAGE - !offset; |
| 85 | for (i = 0; i <= max_scan; ++i) { |
| 86 | if (unlikely(!map->page)) { |
| 87 | unsigned long page = get_zeroed_page(GFP_KERNEL); |
| 88 | /* |
| 89 | * Free the page if someone raced with us |
| 90 | * installing it: |
| 91 | */ |
| 92 | spin_lock(&pidmap_lock); |
| 93 | if (map->page) |
| 94 | free_page(page); |
| 95 | else |
| 96 | map->page = (void *)page; |
| 97 | spin_unlock(&pidmap_lock); |
| 98 | if (unlikely(!map->page)) |
| 99 | break; |
| 100 | } |
| 101 | if (likely(atomic_read(&map->nr_free))) { |
| 102 | do { |
| 103 | if (!test_and_set_bit(offset, map->page)) { |
| 104 | atomic_dec(&map->nr_free); |
| 105 | last_pid = pid; |
| 106 | return pid; |
| 107 | } |
| 108 | offset = find_next_offset(map, offset); |
| 109 | pid = mk_pid(map, offset); |
| 110 | /* |
| 111 | * find_next_offset() found a bit, the pid from it |
| 112 | * is in-bounds, and if we fell back to the last |
| 113 | * bitmap block and the final block was the same |
| 114 | * as the starting point, pid is before last_pid. |
| 115 | */ |
| 116 | } while (offset < BITS_PER_PAGE && pid < pid_max && |
| 117 | (i != max_scan || pid < last || |
| 118 | !((last+1) & BITS_PER_PAGE_MASK))); |
| 119 | } |
| 120 | if (map < &pidmap_array[(pid_max-1)/BITS_PER_PAGE]) { |
| 121 | ++map; |
| 122 | offset = 0; |
| 123 | } else { |
| 124 | map = &pidmap_array[0]; |
| 125 | offset = RESERVED_PIDS; |
| 126 | if (unlikely(last == offset)) |
| 127 | break; |
| 128 | } |
| 129 | pid = mk_pid(map, offset); |
| 130 | } |
| 131 | return -1; |
| 132 | } |
| 133 | |
| 134 | struct pid * fastcall find_pid(enum pid_type type, int nr) |
| 135 | { |
| 136 | struct hlist_node *elem; |
| 137 | struct pid *pid; |
| 138 | |
Ingo Molnar | e56d090 | 2006-01-08 01:01:37 -0800 | [diff] [blame] | 139 | hlist_for_each_entry_rcu(pid, elem, |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 140 | &pid_hash[type][pid_hashfn(nr)], pid_chain) { |
| 141 | if (pid->nr == nr) |
| 142 | return pid; |
| 143 | } |
| 144 | return NULL; |
| 145 | } |
| 146 | |
| 147 | int fastcall attach_pid(task_t *task, enum pid_type type, int nr) |
| 148 | { |
| 149 | struct pid *pid, *task_pid; |
| 150 | |
| 151 | task_pid = &task->pids[type]; |
| 152 | pid = find_pid(type, nr); |
Ingo Molnar | e56d090 | 2006-01-08 01:01:37 -0800 | [diff] [blame] | 153 | task_pid->nr = nr; |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 154 | if (pid == NULL) { |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 155 | INIT_LIST_HEAD(&task_pid->pid_list); |
Ingo Molnar | e56d090 | 2006-01-08 01:01:37 -0800 | [diff] [blame] | 156 | hlist_add_head_rcu(&task_pid->pid_chain, |
| 157 | &pid_hash[type][pid_hashfn(nr)]); |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 158 | } else { |
| 159 | INIT_HLIST_NODE(&task_pid->pid_chain); |
Ingo Molnar | e56d090 | 2006-01-08 01:01:37 -0800 | [diff] [blame] | 160 | list_add_tail_rcu(&task_pid->pid_list, &pid->pid_list); |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 161 | } |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 162 | |
| 163 | return 0; |
| 164 | } |
| 165 | |
| 166 | static fastcall int __detach_pid(task_t *task, enum pid_type type) |
| 167 | { |
| 168 | struct pid *pid, *pid_next; |
| 169 | int nr = 0; |
| 170 | |
| 171 | pid = &task->pids[type]; |
| 172 | if (!hlist_unhashed(&pid->pid_chain)) { |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 173 | |
Ingo Molnar | e56d090 | 2006-01-08 01:01:37 -0800 | [diff] [blame] | 174 | if (list_empty(&pid->pid_list)) { |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 175 | nr = pid->nr; |
Ingo Molnar | e56d090 | 2006-01-08 01:01:37 -0800 | [diff] [blame] | 176 | hlist_del_rcu(&pid->pid_chain); |
| 177 | } else { |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 178 | pid_next = list_entry(pid->pid_list.next, |
| 179 | struct pid, pid_list); |
| 180 | /* insert next pid from pid_list to hash */ |
Ingo Molnar | e56d090 | 2006-01-08 01:01:37 -0800 | [diff] [blame] | 181 | hlist_replace_rcu(&pid->pid_chain, |
| 182 | &pid_next->pid_chain); |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 183 | } |
| 184 | } |
| 185 | |
Ingo Molnar | e56d090 | 2006-01-08 01:01:37 -0800 | [diff] [blame] | 186 | list_del_rcu(&pid->pid_list); |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 187 | pid->nr = 0; |
| 188 | |
| 189 | return nr; |
| 190 | } |
| 191 | |
| 192 | void fastcall detach_pid(task_t *task, enum pid_type type) |
| 193 | { |
| 194 | int tmp, nr; |
| 195 | |
| 196 | nr = __detach_pid(task, type); |
| 197 | if (!nr) |
| 198 | return; |
| 199 | |
| 200 | for (tmp = PIDTYPE_MAX; --tmp >= 0; ) |
| 201 | if (tmp != type && find_pid(tmp, nr)) |
| 202 | return; |
| 203 | |
| 204 | free_pidmap(nr); |
| 205 | } |
| 206 | |
| 207 | task_t *find_task_by_pid_type(int type, int nr) |
| 208 | { |
| 209 | struct pid *pid; |
| 210 | |
| 211 | pid = find_pid(type, nr); |
| 212 | if (!pid) |
| 213 | return NULL; |
| 214 | |
| 215 | return pid_task(&pid->pid_list, type); |
| 216 | } |
| 217 | |
| 218 | EXPORT_SYMBOL(find_task_by_pid_type); |
| 219 | |
| 220 | /* |
| 221 | * This function switches the PIDs if a non-leader thread calls |
| 222 | * sys_execve() - this must be done without releasing the PID. |
| 223 | * (which a detach_pid() would eventually do.) |
| 224 | */ |
| 225 | void switch_exec_pids(task_t *leader, task_t *thread) |
| 226 | { |
| 227 | __detach_pid(leader, PIDTYPE_PID); |
| 228 | __detach_pid(leader, PIDTYPE_TGID); |
| 229 | __detach_pid(leader, PIDTYPE_PGID); |
| 230 | __detach_pid(leader, PIDTYPE_SID); |
| 231 | |
| 232 | __detach_pid(thread, PIDTYPE_PID); |
| 233 | __detach_pid(thread, PIDTYPE_TGID); |
| 234 | |
| 235 | leader->pid = leader->tgid = thread->pid; |
| 236 | thread->pid = thread->tgid; |
| 237 | |
| 238 | attach_pid(thread, PIDTYPE_PID, thread->pid); |
| 239 | attach_pid(thread, PIDTYPE_TGID, thread->tgid); |
| 240 | attach_pid(thread, PIDTYPE_PGID, thread->signal->pgrp); |
| 241 | attach_pid(thread, PIDTYPE_SID, thread->signal->session); |
| 242 | list_add_tail(&thread->tasks, &init_task.tasks); |
| 243 | |
| 244 | attach_pid(leader, PIDTYPE_PID, leader->pid); |
| 245 | attach_pid(leader, PIDTYPE_TGID, leader->tgid); |
| 246 | attach_pid(leader, PIDTYPE_PGID, leader->signal->pgrp); |
| 247 | attach_pid(leader, PIDTYPE_SID, leader->signal->session); |
| 248 | } |
| 249 | |
| 250 | /* |
| 251 | * The pid hash table is scaled according to the amount of memory in the |
| 252 | * machine. From a minimum of 16 slots up to 4096 slots at one gigabyte or |
| 253 | * more. |
| 254 | */ |
| 255 | void __init pidhash_init(void) |
| 256 | { |
| 257 | int i, j, pidhash_size; |
| 258 | unsigned long megabytes = nr_kernel_pages >> (20 - PAGE_SHIFT); |
| 259 | |
| 260 | pidhash_shift = max(4, fls(megabytes * 4)); |
| 261 | pidhash_shift = min(12, pidhash_shift); |
| 262 | pidhash_size = 1 << pidhash_shift; |
| 263 | |
| 264 | printk("PID hash table entries: %d (order: %d, %Zd bytes)\n", |
| 265 | pidhash_size, pidhash_shift, |
| 266 | PIDTYPE_MAX * pidhash_size * sizeof(struct hlist_head)); |
| 267 | |
| 268 | for (i = 0; i < PIDTYPE_MAX; i++) { |
| 269 | pid_hash[i] = alloc_bootmem(pidhash_size * |
| 270 | sizeof(*(pid_hash[i]))); |
| 271 | if (!pid_hash[i]) |
| 272 | panic("Could not alloc pidhash!\n"); |
| 273 | for (j = 0; j < pidhash_size; j++) |
| 274 | INIT_HLIST_HEAD(&pid_hash[i][j]); |
| 275 | } |
| 276 | } |
| 277 | |
| 278 | void __init pidmap_init(void) |
| 279 | { |
| 280 | int i; |
| 281 | |
| 282 | pidmap_array->page = (void *)get_zeroed_page(GFP_KERNEL); |
| 283 | set_bit(0, pidmap_array->page); |
| 284 | atomic_dec(&pidmap_array->nr_free); |
| 285 | |
| 286 | /* |
| 287 | * Allocate PID 0, and hash it via all PID types: |
| 288 | */ |
| 289 | |
| 290 | for (i = 0; i < PIDTYPE_MAX; i++) |
| 291 | attach_pid(current, i, 0); |
| 292 | } |