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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; int retval = -ENOMEM;  pid = kmem_cache_alloc(ns->pid_cachep, GFP_KERNEL); if (!pid)  return ERR_PTR(retval);  tmp = ns; pid->level = ns->level; for (i = ns->level; i >= 0; i--) {  nr = alloc_pidmap(tmp);  if (nr < 0) {   retval = nr;   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);  return pid; out_unlock: spin_unlock_irq(&pidmap_lock); put_pid_ns(ns); out_free: while (++i <= ns->level)  free_pidmap(pid->numbers + i);  kmem_cache_free(ns->pid_cachep, pid); return ERR_PTR(retval);}

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