/*
   * 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>

  #include <linux/sched/task.h>

  #include <linux/idr.h>

  struct pid init_struct_pid = {
  	.count 		= ATOMIC_INIT(1),
  	.tasks		= {
  		{ .first = NULL },
  		{ .first = NULL },
  		{ .first = NULL },
  	},
  	.level		= 0,
  	.numbers	= { {
  		.nr		= 0,
  		.ns		= &init_pid_ns,
  	}, }
  };

  
  int pid_max = PID_MAX_DEFAULT;

  
  #define RESERVED_PIDS		300
  
  int pid_max_min = RESERVED_PIDS + 1;
  int pid_max_max = PID_MAX_LIMIT;

  /*
   * 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 = KREF_INIT(2),

  	.idr = IDR_INIT(init_pid_ns.idr),

  	.pid_allocated = PIDNS_ADDING,

  	.level = 0,
  	.child_reaper = &init_task,

  	.user_ns = &init_user_ns,

  	.ns.inum = PROC_PID_INIT_INO,

  #ifdef CONFIG_PID_NS
  	.ns.ops = &pidns_operations,
  #endif

  };

  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);

  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;

  		switch (--ns->pid_allocated) {

  		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 PIDNS_ADDING:

  			/* Handle a fork failure of the first process */
  			WARN_ON(ns->child_reaper);

  			ns->pid_allocated = 0;

  			/* fall through */

  		case 0:

  			schedule_work(&ns->proc_work);
  			break;

  		}

  
  		idr_remove(&ns->idr, upid->nr);

  	}

  	spin_unlock_irqrestore(&pidmap_lock, flags);

  	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;

  	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--) {

  		int pid_min = 1;
  
  		idr_preload(GFP_KERNEL);
  		spin_lock_irq(&pidmap_lock);
  
  		/*
  		 * init really needs pid 1, but after reaching the maximum
  		 * wrap back to RESERVED_PIDS
  		 */
  		if (idr_get_cursor(&tmp->idr) > RESERVED_PIDS)
  			pid_min = RESERVED_PIDS;
  
  		/*
  		 * Store a null pointer so find_pid_ns does not find
  		 * a partially initialized PID (see below).
  		 */
  		nr = idr_alloc_cyclic(&tmp->idr, NULL, pid_min,
  				      pid_max, GFP_ATOMIC);
  		spin_unlock_irq(&pidmap_lock);
  		idr_preload_end();

  		if (nr < 0) {

  			retval = (nr == -ENOSPC) ? -EAGAIN : 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->pid_allocated & PIDNS_ADDING))

  		goto out_unlock;

  	for ( ; upid >= pid->numbers; --upid) {

  		/* Make the PID visible to find_pid_ns. */
  		idr_replace(&upid->ns->idr, pid, upid->nr);

  		upid->ns->pid_allocated++;

  	}

  	spin_unlock_irq(&pidmap_lock);

  	return pid;

  out_unlock:

  	spin_unlock_irq(&pidmap_lock);

  	put_pid_ns(ns);

  out_free:

  	spin_lock_irq(&pidmap_lock);

  	while (++i <= ns->level) {
  		upid = pid->numbers + i;
  		idr_remove(&upid->ns->idr, upid->nr);
  	}

  	/* On failure to allocate the first pid, reset the state */
  	if (ns->pid_allocated == PIDNS_ADDING)
  		idr_set_cursor(&ns->idr, 0);

  	spin_unlock_irq(&pidmap_lock);

  	kmem_cache_free(ns->pid_cachep, pid);

  	return ERR_PTR(retval);

  }

  void disable_pid_allocation(struct pid_namespace *ns)
  {
  	spin_lock_irq(&pidmap_lock);

  	ns->pid_allocated &= ~PIDNS_ADDING;

  	spin_unlock_irq(&pidmap_lock);
  }

  struct pid *find_pid_ns(int nr, struct pid_namespace *ns)

  {

  	return idr_find(&ns->idr, nr);

  }

  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);

  static struct pid **task_pid_ptr(struct task_struct *task, enum pid_type type)
  {
  	return (type == PIDTYPE_PID) ?
  		&task->thread_pid :

  		&task->signal->pids[type];
  }

  /*
   * 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 = *task_pid_ptr(task, type);
  	hlist_add_head_rcu(&task->pid_links[type], &pid->tasks[type]);

  }

  static void __change_pid(struct task_struct *task, enum pid_type type,
  			struct pid *new)

  {

  	struct pid **pid_ptr = task_pid_ptr(task, type);

  	struct pid *pid;
  	int tmp;

  	pid = *pid_ptr;

  	hlist_del_rcu(&task->pid_links[type]);
  	*pid_ptr = 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);

  }

  /* 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)
  {

  	if (type == PIDTYPE_PID)
  		new->thread_pid = old->thread_pid;
  	hlist_replace_rcu(&old->pid_links[type], &new->pid_links[type]);

  }

  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, pid_links[(type)]);

  	}
  	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_WARN(!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 task_struct *find_get_task_by_vpid(pid_t nr)
  {
  	struct task_struct *task;
  
  	rcu_read_lock();
  	task = find_task_by_vpid(nr);
  	if (task)
  		get_task_struct(task);
  	rcu_read_unlock();
  
  	return task;
  }

  struct pid *get_task_pid(struct task_struct *task, enum pid_type type)
  {
  	struct pid *pid;
  	rcu_read_lock();

  	pid = get_pid(rcu_dereference(*task_pid_ptr(task, type)));

  	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)))
  		nr = pid_nr_ns(rcu_dereference(*task_pid_ptr(task, type)), ns);

  	rcu_read_unlock();
  
  	return nr;

  }

  EXPORT_SYMBOL(__task_pid_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)

  {

  	return idr_get_next(&ns->idr, &nr);

  }

  void __init pid_idr_init(void)

  {

  	/* Verify no one has done anything silly: */

  	BUILD_BUG_ON(PID_MAX_LIMIT >= PIDNS_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
  ", pid_max, pid_max_min);

  	idr_init(&init_pid_ns.idr);

  	init_pid_ns.pid_cachep = KMEM_CACHE(pid,

  			SLAB_HWCACHE_ALIGN | SLAB_PANIC | SLAB_ACCOUNT);

  }