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/*

 * 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;

}