| /* |
| * 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> |
| #include <linux/pspace.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; |
| |
| #define RESERVED_PIDS 300 |
| |
| int pid_max_min = RESERVED_PIDS + 1; |
| int pid_max_max = PID_MAX_LIMIT; |
| |
| #define BITS_PER_PAGE (PAGE_SIZE*8) |
| #define BITS_PER_PAGE_MASK (BITS_PER_PAGE-1) |
| |
| static inline int mk_pid(struct pspace *pspace, struct pidmap *map, int off) |
| { |
| return (map - pspace->pidmap)*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. |
| */ |
| struct pspace init_pspace = { |
| .pidmap = { |
| [ 0 ... PIDMAP_ENTRIES-1] = { ATOMIC_INIT(BITS_PER_PAGE), NULL } |
| }, |
| .last_pid = 0 |
| }; |
| |
| /* |
| * 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(struct pspace *pspace, int pid) |
| { |
| struct pidmap *map = pspace->pidmap + 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(struct pspace *pspace) |
| { |
| int i, offset, max_scan, pid, last = pspace->last_pid; |
| struct pidmap *map; |
| |
| pid = last + 1; |
| if (pid >= pid_max) |
| pid = RESERVED_PIDS; |
| offset = pid & BITS_PER_PAGE_MASK; |
| map = &pspace->pidmap[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)) { |
| void *page = kzalloc(PAGE_SIZE, GFP_KERNEL); |
| /* |
| * Free the page if someone raced with us |
| * installing it: |
| */ |
| spin_lock_irq(&pidmap_lock); |
| if (map->page) |
| kfree(page); |
| else |
| map->page = 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); |
| pspace->last_pid = pid; |
| return pid; |
| } |
| offset = find_next_offset(map, offset); |
| pid = mk_pid(pspace, 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 < &pspace->pidmap[(pid_max-1)/BITS_PER_PAGE]) { |
| ++map; |
| offset = 0; |
| } else { |
| map = &pspace->pidmap[0]; |
| offset = RESERVED_PIDS; |
| if (unlikely(last == offset)) |
| break; |
| } |
| pid = mk_pid(pspace, map, offset); |
| } |
| return -1; |
| } |
| |
| static int next_pidmap(int last) |
| { |
| int offset; |
| struct pidmap *map; |
| |
| offset = (last + 1) & BITS_PER_PAGE_MASK; |
| map = &pidmap_array[(last + 1)/BITS_PER_PAGE]; |
| for (; map < &pidmap_array[PIDMAP_ENTRIES]; map++, offset = 0) { |
| if (unlikely(!map->page)) |
| continue; |
| offset = find_next_bit((map)->page, BITS_PER_PAGE, offset); |
| if (offset < BITS_PER_PAGE) |
| return 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); |
| } |
| EXPORT_SYMBOL_GPL(put_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(&init_pspace, 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(&init_pspace); |
| 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; |
| } |
| EXPORT_SYMBOL_GPL(find_pid); |
| |
| int fastcall attach_pid(struct task_struct *task, enum pid_type type, int nr) |
| { |
| struct pid_link *link; |
| struct pid *pid; |
| |
| 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(struct task_struct *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); |
| } |
| |
| /* transfer_pid is an optimization of attach_pid(new), detach_pid(old) */ |
| void fastcall transfer_pid(struct task_struct *old, struct task_struct *new, |
| enum pid_type type) |
| { |
| new->pids[type].pid = old->pids[type].pid; |
| hlist_replace_rcu(&old->pids[type].node, &new->pids[type].node); |
| old->pids[type].pid = NULL; |
| } |
| |
| 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. |
| */ |
| struct task_struct *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; |
| } |
| |
| /* |
| * Used by proc to find the first pid that is greater then or equal to nr. |
| * |
| * If there is a pid at nr this function is exactly the same as find_pid. |
| */ |
| struct pid *find_ge_pid(int nr) |
| { |
| struct pid *pid; |
| |
| do { |
| pid = find_pid(nr); |
| if (pid) |
| break; |
| nr = next_pidmap(nr); |
| } while (nr > 0); |
| |
| return pid; |
| } |
| EXPORT_SYMBOL_GPL(find_get_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) |
| { |
| init_pspace.pidmap[0].page = kzalloc(PAGE_SIZE, GFP_KERNEL); |
| /* Reserve PID 0. We never call free_pidmap(0) */ |
| set_bit(0, init_pspace.pidmap[0].page); |
| atomic_dec(&init_pspace.pidmap[0].nr_free); |
| |
| pid_cachep = kmem_cache_create("pid", sizeof(struct pid), |
| __alignof__(struct pid), |
| SLAB_PANIC, NULL, NULL); |
| } |