/* * 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). * * 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/module.h> #include <linux/slab.h> #include <linux/init.h> #include <linux/bootmem.h> #include <linux/hash.h> #include <linux/pid_namespace.h> #include <linux/init_task.h> #include <linux/syscalls.h> #define pid_hashfn(nr, ns) \ hash_long((unsigned long)nr + (unsigned long)ns, pidhash_shift) static struct hlist_head *pid_hash; static int pidhash_shift; struct pid init_struct_pid = INIT_STRUCT_PID; static struct kmem_cache *pid_ns_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 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, }; EXPORT_SYMBOL_GPL(init_pid_ns); int is_container_init(struct task_struct *tsk) { int ret = 0; struct pid *pid; rcu_read_lock(); pid = task_pid(tsk); if (pid != NULL && pid->numbers[pid->level].nr == 1) ret = 1; rcu_read_unlock(); return ret; } EXPORT_SYMBOL(is_container_init); /* * 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 pid_namespace *pid_ns, int pid) { struct pidmap *map = pid_ns->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 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]; 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); pid_ns->last_pid = pid; return pid; } offset = find_next_offset(map, offset); pid = mk_pid(pid_ns, 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 < &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; } static int next_pidmap(struct pid_namespace *pid_ns, int last) { int offset; struct pidmap *map, *end; 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; } fastcall 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); } fastcall 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++) hlist_del_rcu(&pid->numbers[i].pid_chain); spin_unlock_irqrestore(&pidmap_lock, flags); for (i = 0; i <= pid->level; i++) free_pidmap(pid->numbers[i].ns, pid->numbers[i].nr); 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; 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; } get_pid_ns(ns); pid->level = ns->level; atomic_set(&pid->count, 1); for (type = 0; type < PIDTYPE_MAX; ++type) INIT_HLIST_HEAD(&pid->tasks[type]); spin_lock_irq(&pidmap_lock); for (i = ns->level; i >= 0; i--) { upid = &pid->numbers[i]; hlist_add_head_rcu(&upid->pid_chain, &pid_hash[pid_hashfn(upid->nr, upid->ns)]); } spin_unlock_irq(&pidmap_lock); out: return pid; out_free: for (i++; i <= ns->level; i++) free_pidmap(pid->numbers[i].ns, pid->numbers[i].nr); kmem_cache_free(ns->pid_cachep, pid); pid = NULL; goto out; } struct pid * fastcall find_pid_ns(int nr, struct pid_namespace *ns) { struct hlist_node *elem; struct upid *pnr; hlist_for_each_entry_rcu(pnr, elem, &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, current->nsproxy->pid_ns); } EXPORT_SYMBOL_GPL(find_vpid); struct pid *find_pid(int nr) { return find_pid_ns(nr, &init_pid_ns); } EXPORT_SYMBOL_GPL(find_pid); /* * attach_pid() must be called with the tasklist_lock write-held. */ int fastcall 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]); 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_ns(int type, int nr, struct pid_namespace *ns) { return pid_task(find_pid_ns(nr, ns), type); } EXPORT_SYMBOL(find_task_by_pid_type_ns); struct task_struct *find_task_by_pid(pid_t nr) { return find_task_by_pid_type_ns(PIDTYPE_PID, nr, &init_pid_ns); } EXPORT_SYMBOL(find_task_by_pid); struct task_struct *find_task_by_vpid(pid_t vnr) { return find_task_by_pid_type_ns(PIDTYPE_PID, vnr, current->nsproxy->pid_ns); } EXPORT_SYMBOL(find_task_by_vpid); struct task_struct *find_task_by_pid_ns(pid_t nr, struct pid_namespace *ns) { return find_task_by_pid_type_ns(PIDTYPE_PID, nr, ns); } EXPORT_SYMBOL(find_task_by_pid_ns); struct pid *get_task_pid(struct task_struct *task, enum pid_type type) { struct pid *pid; rcu_read_lock(); pid = get_pid(task->pids[type].pid); rcu_read_unlock(); return pid; } 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_vpid(nr)); rcu_read_unlock(); return 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; } pid_t task_pid_nr_ns(struct task_struct *tsk, struct pid_namespace *ns) { return pid_nr_ns(task_pid(tsk), ns); } 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); pid_t task_pgrp_nr_ns(struct task_struct *tsk, struct pid_namespace *ns) { return pid_nr_ns(task_pgrp(tsk), ns); } EXPORT_SYMBOL(task_pgrp_nr_ns); pid_t task_session_nr_ns(struct task_struct *tsk, struct pid_namespace *ns) { return pid_nr_ns(task_session(tsk), ns); } EXPORT_SYMBOL(task_session_nr_ns); /* * 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_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; } EXPORT_SYMBOL_GPL(find_get_pid); struct pid_cache { int nr_ids; char name[16]; struct kmem_cache *cachep; struct list_head list; }; static LIST_HEAD(pid_caches_lh); static DEFINE_MUTEX(pid_caches_mutex); /* * creates the kmem cache to allocate pids from. * @nr_ids: the number of numerical ids this pid will have to carry */ static struct kmem_cache *create_pid_cachep(int nr_ids) { struct pid_cache *pcache; struct kmem_cache *cachep; mutex_lock(&pid_caches_mutex); list_for_each_entry (pcache, &pid_caches_lh, list) if (pcache->nr_ids == nr_ids) goto out; pcache = kmalloc(sizeof(struct pid_cache), GFP_KERNEL); if (pcache == NULL) goto err_alloc; snprintf(pcache->name, sizeof(pcache->name), "pid_%d", nr_ids); cachep = kmem_cache_create(pcache->name, sizeof(struct pid) + (nr_ids - 1) * sizeof(struct upid), 0, SLAB_HWCACHE_ALIGN, NULL); if (cachep == NULL) goto err_cachep; pcache->nr_ids = nr_ids; pcache->cachep = cachep; list_add(&pcache->list, &pid_caches_lh); out: mutex_unlock(&pid_caches_mutex); return pcache->cachep; err_cachep: kfree(pcache); err_alloc: mutex_unlock(&pid_caches_mutex); return NULL; } #ifdef CONFIG_PID_NS static struct pid_namespace *create_pid_namespace(int level) { struct pid_namespace *ns; int i; ns = kmem_cache_alloc(pid_ns_cachep, GFP_KERNEL); if (ns == NULL) goto out; ns->pidmap[0].page = kzalloc(PAGE_SIZE, GFP_KERNEL); if (!ns->pidmap[0].page) goto out_free; ns->pid_cachep = create_pid_cachep(level + 1); if (ns->pid_cachep == NULL) goto out_free_map; kref_init(&ns->kref); ns->last_pid = 0; ns->child_reaper = NULL; ns->level = level; set_bit(0, ns->pidmap[0].page); atomic_set(&ns->pidmap[0].nr_free, BITS_PER_PAGE - 1); for (i = 1; i < PIDMAP_ENTRIES; i++) { ns->pidmap[i].page = 0; atomic_set(&ns->pidmap[i].nr_free, BITS_PER_PAGE); } return ns; out_free_map: kfree(ns->pidmap[0].page); out_free: kmem_cache_free(pid_ns_cachep, ns); out: return ERR_PTR(-ENOMEM); } static void destroy_pid_namespace(struct pid_namespace *ns) { int i; for (i = 0; i < PIDMAP_ENTRIES; i++) kfree(ns->pidmap[i].page); kmem_cache_free(pid_ns_cachep, ns); } struct pid_namespace *copy_pid_ns(unsigned long flags, struct pid_namespace *old_ns) { struct pid_namespace *new_ns; BUG_ON(!old_ns); new_ns = get_pid_ns(old_ns); if (!(flags & CLONE_NEWPID)) goto out; new_ns = ERR_PTR(-EINVAL); if (flags & CLONE_THREAD) goto out_put; new_ns = create_pid_namespace(old_ns->level + 1); if (!IS_ERR(new_ns)) new_ns->parent = get_pid_ns(old_ns); out_put: put_pid_ns(old_ns); out: return new_ns; } void free_pid_ns(struct kref *kref) { struct pid_namespace *ns, *parent; ns = container_of(kref, struct pid_namespace, kref); parent = ns->parent; destroy_pid_namespace(ns); if (parent != NULL) put_pid_ns(parent); } #endif /* CONFIG_PID_NS */ void zap_pid_ns_processes(struct pid_namespace *pid_ns) { int nr; int rc; /* * The last thread in the cgroup-init thread group is terminating. * Find remaining pid_ts in the namespace, signal and wait for them * to exit. * * Note: This signals each threads in the namespace - even those that * belong to the same thread group, To avoid this, we would have * to walk the entire tasklist looking a processes in this * namespace, but that could be unnecessarily expensive if the * pid namespace has just a few processes. Or we need to * maintain a tasklist for each pid namespace. * */ read_lock(&tasklist_lock); nr = next_pidmap(pid_ns, 1); while (nr > 0) { kill_proc_info(SIGKILL, SEND_SIG_PRIV, nr); nr = next_pidmap(pid_ns, nr); } read_unlock(&tasklist_lock); do { clear_thread_flag(TIF_SIGPENDING); rc = sys_wait4(-1, NULL, __WALL, NULL); } while (rc != -ECHILD); /* Child reaper for the pid namespace is going away */ pid_ns->child_reaper = NULL; return; } /* * 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_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.pid_cachep = create_pid_cachep(1); if (init_pid_ns.pid_cachep == NULL) panic("Can't create pid_1 cachep\n"); pid_ns_cachep = KMEM_CACHE(pid_namespace, SLAB_PANIC); }