| /* |
| * Generic pidhash and scalable, time-bounded PID allocator |
| * |
| * (C) 2002-2003 Nadia Yvette Chambers, IBM |
| * (C) 2004 Nadia Yvette Chambers, 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). |
| * |
| * Pid namespaces: |
| * (C) 2007 Pavel Emelyanov <xemul@openvz.org>, OpenVZ, SWsoft Inc. |
| * (C) 2007 Sukadev Bhattiprolu <sukadev@us.ibm.com>, IBM |
| * Many thanks to Oleg Nesterov for comments and help |
| * |
| */ |
| |
| #include <linux/mm.h> |
| #include <linux/export.h> |
| #include <linux/slab.h> |
| #include <linux/init.h> |
| #include <linux/rculist.h> |
| #include <linux/bootmem.h> |
| #include <linux/hash.h> |
| #include <linux/pid_namespace.h> |
| #include <linux/init_task.h> |
| #include <linux/syscalls.h> |
| #include <linux/proc_ns.h> |
| #include <linux/proc_fs.h> |
| |
| #define pid_hashfn(nr, ns) \ |
| hash_long((unsigned long)nr + (unsigned long)ns, pidhash_shift) |
| static struct hlist_head *pid_hash; |
| static unsigned int pidhash_shift = 4; |
| struct pid init_struct_pid = INIT_STRUCT_PID; |
| |
| int pid_max = PID_MAX_DEFAULT; |
| |
| #define RESERVED_PIDS 300 |
| |
| int pid_max_min = RESERVED_PIDS + 1; |
| int pid_max_max = PID_MAX_LIMIT; |
| |
| static inline int mk_pid(struct pid_namespace *pid_ns, |
| struct pidmap *map, int off) |
| { |
| return (map - pid_ns->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 pid_namespace init_pid_ns = { |
| .kref = { |
| .refcount = ATOMIC_INIT(2), |
| }, |
| .pidmap = { |
| [ 0 ... PIDMAP_ENTRIES-1] = { ATOMIC_INIT(BITS_PER_PAGE), NULL } |
| }, |
| .last_pid = 0, |
| .level = 0, |
| .child_reaper = &init_task, |
| .user_ns = &init_user_ns, |
| .proc_inum = PROC_PID_INIT_INO, |
| }; |
| EXPORT_SYMBOL_GPL(init_pid_ns); |
| |
| /* |
| * 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 void free_pidmap(struct upid *upid) |
| { |
| int nr = upid->nr; |
| struct pidmap *map = upid->ns->pidmap + nr / BITS_PER_PAGE; |
| int offset = nr & BITS_PER_PAGE_MASK; |
| |
| clear_bit(offset, map->page); |
| atomic_inc(&map->nr_free); |
| } |
| |
| /* |
| * If we started walking pids at 'base', is 'a' seen before 'b'? |
| */ |
| static int pid_before(int base, int a, int b) |
| { |
| /* |
| * This is the same as saying |
| * |
| * (a - base + MAXUINT) % MAXUINT < (b - base + MAXUINT) % MAXUINT |
| * and that mapping orders 'a' and 'b' with respect to 'base'. |
| */ |
| return (unsigned)(a - base) < (unsigned)(b - base); |
| } |
| |
| /* |
| * We might be racing with someone else trying to set pid_ns->last_pid |
| * at the pid allocation time (there's also a sysctl for this, but racing |
| * with this one is OK, see comment in kernel/pid_namespace.c about it). |
| * We want the winner to have the "later" value, because if the |
| * "earlier" value prevails, then a pid may get reused immediately. |
| * |
| * Since pids rollover, it is not sufficient to just pick the bigger |
| * value. We have to consider where we started counting from. |
| * |
| * 'base' is the value of pid_ns->last_pid that we observed when |
| * we started looking for a pid. |
| * |
| * 'pid' is the pid that we eventually found. |
| */ |
| static void set_last_pid(struct pid_namespace *pid_ns, int base, int pid) |
| { |
| int prev; |
| int last_write = base; |
| do { |
| prev = last_write; |
| last_write = cmpxchg(&pid_ns->last_pid, prev, pid); |
| } while ((prev != last_write) && (pid_before(base, last_write, pid))); |
| } |
| |
| static int alloc_pidmap(struct pid_namespace *pid_ns) |
| { |
| int i, offset, max_scan, pid, last = pid_ns->last_pid; |
| struct pidmap *map; |
| |
| pid = last + 1; |
| if (pid >= pid_max) |
| pid = RESERVED_PIDS; |
| offset = pid & BITS_PER_PAGE_MASK; |
| map = &pid_ns->pidmap[pid/BITS_PER_PAGE]; |
| /* |
| * If last_pid points into the middle of the map->page we |
| * want to scan this bitmap block twice, the second time |
| * we start with offset == 0 (or RESERVED_PIDS). |
| */ |
| max_scan = DIV_ROUND_UP(pid_max, 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) { |
| map->page = page; |
| page = NULL; |
| } |
| spin_unlock_irq(&pidmap_lock); |
| kfree(page); |
| if (unlikely(!map->page)) |
| break; |
| } |
| if (likely(atomic_read(&map->nr_free))) { |
| for ( ; ; ) { |
| if (!test_and_set_bit(offset, map->page)) { |
| atomic_dec(&map->nr_free); |
| set_last_pid(pid_ns, last, pid); |
| return pid; |
| } |
| offset = find_next_offset(map, offset); |
| if (offset >= BITS_PER_PAGE) |
| break; |
| pid = mk_pid(pid_ns, map, offset); |
| if (pid >= pid_max) |
| break; |
| } |
| } |
| if (map < &pid_ns->pidmap[(pid_max-1)/BITS_PER_PAGE]) { |
| ++map; |
| offset = 0; |
| } else { |
| map = &pid_ns->pidmap[0]; |
| offset = RESERVED_PIDS; |
| if (unlikely(last == offset)) |
| break; |
| } |
| pid = mk_pid(pid_ns, map, offset); |
| } |
| return -1; |
| } |
| |
| int next_pidmap(struct pid_namespace *pid_ns, unsigned int last) |
| { |
| int offset; |
| struct pidmap *map, *end; |
| |
| if (last >= PID_MAX_LIMIT) |
| return -1; |
| |
| offset = (last + 1) & BITS_PER_PAGE_MASK; |
| map = &pid_ns->pidmap[(last + 1)/BITS_PER_PAGE]; |
| end = &pid_ns->pidmap[PIDMAP_ENTRIES]; |
| for (; map < end; 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(pid_ns, map, offset); |
| } |
| return -1; |
| } |
| |
| void put_pid(struct pid *pid) |
| { |
| struct pid_namespace *ns; |
| |
| if (!pid) |
| return; |
| |
| ns = pid->numbers[pid->level].ns; |
| if ((atomic_read(&pid->count) == 1) || |
| atomic_dec_and_test(&pid->count)) { |
| kmem_cache_free(ns->pid_cachep, pid); |
| put_pid_ns(ns); |
| } |
| } |
| 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); |
| } |
| |
| void free_pid(struct pid *pid) |
| { |
| /* We can be called with write_lock_irq(&tasklist_lock) held */ |
| int i; |
| unsigned long flags; |
| |
| spin_lock_irqsave(&pidmap_lock, flags); |
| for (i = 0; i <= pid->level; i++) { |
| struct upid *upid = pid->numbers + i; |
| struct pid_namespace *ns = upid->ns; |
| hlist_del_rcu(&upid->pid_chain); |
| switch(--ns->nr_hashed) { |
| case 2: |
| case 1: |
| /* When all that is left in the pid namespace |
| * is the reaper wake up the reaper. The reaper |
| * may be sleeping in zap_pid_ns_processes(). |
| */ |
| wake_up_process(ns->child_reaper); |
| break; |
| case 0: |
| schedule_work(&ns->proc_work); |
| break; |
| } |
| } |
| spin_unlock_irqrestore(&pidmap_lock, flags); |
| |
| for (i = 0; i <= pid->level; i++) |
| free_pidmap(pid->numbers + i); |
| |
| call_rcu(&pid->rcu, delayed_put_pid); |
| } |
| |
| struct pid *alloc_pid(struct pid_namespace *ns) |
| { |
| struct pid *pid; |
| enum pid_type type; |
| int i, nr; |
| struct pid_namespace *tmp; |
| struct upid *upid; |
| |
| pid = kmem_cache_alloc(ns->pid_cachep, GFP_KERNEL); |
| if (!pid) |
| goto out; |
| |
| tmp = ns; |
| pid->level = ns->level; |
| for (i = ns->level; i >= 0; i--) { |
| nr = alloc_pidmap(tmp); |
| if (nr < 0) |
| goto out_free; |
| |
| pid->numbers[i].nr = nr; |
| pid->numbers[i].ns = tmp; |
| tmp = tmp->parent; |
| } |
| |
| if (unlikely(is_child_reaper(pid))) { |
| if (pid_ns_prepare_proc(ns)) |
| goto out_free; |
| } |
| |
| get_pid_ns(ns); |
| atomic_set(&pid->count, 1); |
| for (type = 0; type < PIDTYPE_MAX; ++type) |
| INIT_HLIST_HEAD(&pid->tasks[type]); |
| |
| upid = pid->numbers + ns->level; |
| spin_lock_irq(&pidmap_lock); |
| if (!(ns->nr_hashed & PIDNS_HASH_ADDING)) |
| goto out_unlock; |
| for ( ; upid >= pid->numbers; --upid) { |
| hlist_add_head_rcu(&upid->pid_chain, |
| &pid_hash[pid_hashfn(upid->nr, upid->ns)]); |
| upid->ns->nr_hashed++; |
| } |
| spin_unlock_irq(&pidmap_lock); |
| |
| out: |
| return pid; |
| |
| out_unlock: |
| spin_unlock_irq(&pidmap_lock); |
| out_free: |
| while (++i <= ns->level) |
| free_pidmap(pid->numbers + i); |
| |
| kmem_cache_free(ns->pid_cachep, pid); |
| pid = NULL; |
| goto out; |
| } |
| |
| void disable_pid_allocation(struct pid_namespace *ns) |
| { |
| spin_lock_irq(&pidmap_lock); |
| ns->nr_hashed &= ~PIDNS_HASH_ADDING; |
| spin_unlock_irq(&pidmap_lock); |
| } |
| |
| struct pid *find_pid_ns(int nr, struct pid_namespace *ns) |
| { |
| struct upid *pnr; |
| |
| hlist_for_each_entry_rcu(pnr, |
| &pid_hash[pid_hashfn(nr, ns)], pid_chain) |
| if (pnr->nr == nr && pnr->ns == ns) |
| return container_of(pnr, struct pid, |
| numbers[ns->level]); |
| |
| return NULL; |
| } |
| EXPORT_SYMBOL_GPL(find_pid_ns); |
| |
| struct pid *find_vpid(int nr) |
| { |
| return find_pid_ns(nr, task_active_pid_ns(current)); |
| } |
| EXPORT_SYMBOL_GPL(find_vpid); |
| |
| /* |
| * attach_pid() must be called with the tasklist_lock write-held. |
| */ |
| void attach_pid(struct task_struct *task, enum pid_type type, |
| struct pid *pid) |
| { |
| struct pid_link *link; |
| |
| link = &task->pids[type]; |
| link->pid = pid; |
| hlist_add_head_rcu(&link->node, &pid->tasks[type]); |
| } |
| |
| static void __change_pid(struct task_struct *task, enum pid_type type, |
| struct pid *new) |
| { |
| struct pid_link *link; |
| struct pid *pid; |
| int tmp; |
| |
| link = &task->pids[type]; |
| pid = link->pid; |
| |
| hlist_del_rcu(&link->node); |
| link->pid = new; |
| |
| for (tmp = PIDTYPE_MAX; --tmp >= 0; ) |
| if (!hlist_empty(&pid->tasks[tmp])) |
| return; |
| |
| free_pid(pid); |
| } |
| |
| void detach_pid(struct task_struct *task, enum pid_type type) |
| { |
| __change_pid(task, type, NULL); |
| } |
| |
| void change_pid(struct task_struct *task, enum pid_type type, |
| struct pid *pid) |
| { |
| __change_pid(task, type, pid); |
| attach_pid(task, type, pid); |
| } |
| |
| /* transfer_pid is an optimization of attach_pid(new), detach_pid(old) */ |
| void 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); |
| } |
| EXPORT_SYMBOL(find_task_by_vpid); |
| |
| struct task_struct *pid_task(struct pid *pid, enum pid_type type) |
| { |
| struct task_struct *result = NULL; |
| if (pid) { |
| struct hlist_node *first; |
| first = rcu_dereference_check(hlist_first_rcu(&pid->tasks[type]), |
| lockdep_tasklist_lock_is_held()); |
| if (first) |
| result = hlist_entry(first, struct task_struct, pids[(type)].node); |
| } |
| return result; |
| } |
| EXPORT_SYMBOL(pid_task); |
| |
| /* |
| * Must be called under rcu_read_lock(). |
| */ |
| struct task_struct *find_task_by_pid_ns(pid_t nr, struct pid_namespace *ns) |
| { |
| rcu_lockdep_assert(rcu_read_lock_held(), |
| "find_task_by_pid_ns() needs rcu_read_lock()" |
| " protection"); |
| return pid_task(find_pid_ns(nr, ns), PIDTYPE_PID); |
| } |
| |
| struct task_struct *find_task_by_vpid(pid_t vnr) |
| { |
| return find_task_by_pid_ns(vnr, task_active_pid_ns(current)); |
| } |
| |
| struct pid *get_task_pid(struct task_struct *task, enum pid_type type) |
| { |
| struct pid *pid; |
| rcu_read_lock(); |
| if (type != PIDTYPE_PID) |
| task = task->group_leader; |
| pid = get_pid(task->pids[type].pid); |
| rcu_read_unlock(); |
| return pid; |
| } |
| EXPORT_SYMBOL_GPL(get_task_pid); |
| |
| struct task_struct *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; |
| } |
| EXPORT_SYMBOL_GPL(get_pid_task); |
| |
| struct pid *find_get_pid(pid_t nr) |
| { |
| struct pid *pid; |
| |
| rcu_read_lock(); |
| pid = get_pid(find_vpid(nr)); |
| rcu_read_unlock(); |
| |
| return pid; |
| } |
| EXPORT_SYMBOL_GPL(find_get_pid); |
| |
| pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns) |
| { |
| struct upid *upid; |
| pid_t nr = 0; |
| |
| if (pid && ns->level <= pid->level) { |
| upid = &pid->numbers[ns->level]; |
| if (upid->ns == ns) |
| nr = upid->nr; |
| } |
| return nr; |
| } |
| EXPORT_SYMBOL_GPL(pid_nr_ns); |
| |
| pid_t pid_vnr(struct pid *pid) |
| { |
| return pid_nr_ns(pid, task_active_pid_ns(current)); |
| } |
| EXPORT_SYMBOL_GPL(pid_vnr); |
| |
| pid_t __task_pid_nr_ns(struct task_struct *task, enum pid_type type, |
| struct pid_namespace *ns) |
| { |
| pid_t nr = 0; |
| |
| rcu_read_lock(); |
| if (!ns) |
| ns = task_active_pid_ns(current); |
| if (likely(pid_alive(task))) { |
| if (type != PIDTYPE_PID) |
| task = task->group_leader; |
| nr = pid_nr_ns(task->pids[type].pid, ns); |
| } |
| rcu_read_unlock(); |
| |
| return nr; |
| } |
| EXPORT_SYMBOL(__task_pid_nr_ns); |
| |
| pid_t task_tgid_nr_ns(struct task_struct *tsk, struct pid_namespace *ns) |
| { |
| return pid_nr_ns(task_tgid(tsk), ns); |
| } |
| EXPORT_SYMBOL(task_tgid_nr_ns); |
| |
| struct pid_namespace *task_active_pid_ns(struct task_struct *tsk) |
| { |
| return ns_of_pid(task_pid(tsk)); |
| } |
| EXPORT_SYMBOL_GPL(task_active_pid_ns); |
| |
| /* |
| * Used by proc to find the first pid that is greater than or equal to nr. |
| * |
| * If there is a pid at nr this function is exactly the same as find_pid_ns. |
| */ |
| struct pid *find_ge_pid(int nr, struct pid_namespace *ns) |
| { |
| struct pid *pid; |
| |
| do { |
| pid = find_pid_ns(nr, ns); |
| if (pid) |
| break; |
| nr = next_pidmap(ns, nr); |
| } while (nr > 0); |
| |
| return 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) |
| { |
| unsigned int i, pidhash_size; |
| |
| pid_hash = alloc_large_system_hash("PID", sizeof(*pid_hash), 0, 18, |
| HASH_EARLY | HASH_SMALL, |
| &pidhash_shift, NULL, |
| 0, 4096); |
| pidhash_size = 1U << pidhash_shift; |
| |
| for (i = 0; i < pidhash_size; i++) |
| INIT_HLIST_HEAD(&pid_hash[i]); |
| } |
| |
| void __init pidmap_init(void) |
| { |
| /* Veryify no one has done anything silly */ |
| BUILD_BUG_ON(PID_MAX_LIMIT >= PIDNS_HASH_ADDING); |
| |
| /* bump default and minimum pid_max based on number of cpus */ |
| pid_max = min(pid_max_max, max_t(int, pid_max, |
| PIDS_PER_CPU_DEFAULT * num_possible_cpus())); |
| pid_max_min = max_t(int, pid_max_min, |
| PIDS_PER_CPU_MIN * num_possible_cpus()); |
| pr_info("pid_max: default: %u minimum: %u\n", pid_max, pid_max_min); |
| |
| init_pid_ns.pidmap[0].page = kzalloc(PAGE_SIZE, GFP_KERNEL); |
| /* Reserve PID 0. We never call free_pidmap(0) */ |
| set_bit(0, init_pid_ns.pidmap[0].page); |
| atomic_dec(&init_pid_ns.pidmap[0].nr_free); |
| init_pid_ns.nr_hashed = PIDNS_HASH_ADDING; |
| |
| init_pid_ns.pid_cachep = KMEM_CACHE(pid, |
| SLAB_HWCACHE_ALIGN | SLAB_PANIC); |
| } |