/* * 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/memblock.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\n", 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);}