// SPDX-License-Identifier: GPL-2.0-only
/*
* klist.c - Routines for manipulating klists.
*
* Copyright (C) 2005 Patrick Mochel
*
* This klist interface provides a couple of structures that wrap around
* struct list_head to provide explicit list "head" (struct klist) and list
* "node" (struct klist_node) objects. For struct klist, a spinlock is
* included that protects access to the actual list itself. struct
* klist_node provides a pointer to the klist that owns it and a kref
* reference count that indicates the number of current users of that node
* in the list.
*
* The entire point is to provide an interface for iterating over a list
* that is safe and allows for modification of the list during the
* iteration (e.g. insertion and removal), including modification of the
* current node on the list.
*
* It works using a 3rd object type - struct klist_iter - that is declared
* and initialized before an iteration. klist_next() is used to acquire the
* next element in the list. It returns NULL if there are no more items.
* Internally, that routine takes the klist's lock, decrements the
* reference count of the previous klist_node and increments the count of
* the next klist_node. It then drops the lock and returns.
*
* There are primitives for adding and removing nodes to/from a klist.
* When deleting, klist_del() will simply decrement the reference count.
* Only when the count goes to 0 is the node removed from the list.
* klist_remove() will try to delete the node from the list and block until
* it is actually removed. This is useful for objects (like devices) that
* have been removed from the system and must be freed (but must wait until
* all accessors have finished).
*/
#include <linux/klist.h>
#include <linux/export.h>
#include <linux/sched.h>
/*
* Use the lowest bit of n_klist to mark deleted nodes and exclude
* dead ones from iteration.
*/
#define KNODE_DEAD 1LU
#define KNODE_KLIST_MASK ~KNODE_DEAD
static struct klist *knode_klist(struct klist_node *knode)
{
return (struct klist *)
((unsigned long)knode->n_klist & KNODE_KLIST_MASK);
}
static bool knode_dead(struct klist_node *knode)
{
return (unsigned long)knode->n_klist & KNODE_DEAD;
}
static void knode_set_klist(struct klist_node *knode, struct klist *klist)
{
knode->n_klist = klist;
/* no knode deserves to start its life dead */
WARN_ON(knode_dead(knode));
}
static void knode_kill(struct klist_node *knode)
{
/* and no knode should die twice ever either, see we're very humane */
WARN_ON(knode_dead(knode));
*(unsigned long *)&knode->n_klist |= KNODE_DEAD;
}
/**
* klist_init - Initialize a klist structure.
* @k: The klist we're initializing.
* @get: The get function for the embedding object (NULL if none)
* @put: The put function for the embedding object (NULL if none)
*
* Initialises the klist structure. If the klist_node structures are
* going to be embedded in refcounted objects (necessary for safe
* deletion) then the get/put arguments are used to initialise
* functions that take and release references on the embedding
* objects.
*/
void klist_init(struct klist *k, void (*get)(struct klist_node *),
void (*put)(struct klist_node *))
{
INIT_LIST_HEAD(&k->k_list);
spin_lock_init(&k->k_lock);
k->get = get;
k->put = put;
}
EXPORT_SYMBOL_GPL(klist_init);
static void add_head(struct klist *k, struct klist_node *n)
{
spin_lock(&k->k_lock);
list_add(&n->n_node, &k->k_list);
spin_unlock(&k->k_lock);
}
static void add_tail(struct klist *k, struct klist_node *n)
{
spin_lock(&k->k_lock);
list_add_tail(&n->n_node, &k->k_list);
spin_unlock(&k->k_lock);
}
static void klist_node_init(struct klist *k, struct klist_node *n)
{
INIT_LIST_HEAD(&n->n_node);
kref_init(&n->n_ref);
knode_set_klist(n, k);
if (k->get)
k->get(n);
}
/**
* klist_add_head - Initialize a klist_node and add it to front.
* @n: node we're adding.
* @k: klist it's going on.
*/
void klist_add_head(struct klist_node *n, struct klist *k)
{
klist_node_init(k, n);
add_head(k, n);
}
EXPORT_SYMBOL_GPL(klist_add_head);
/**
* klist_add_tail - Initialize a klist_node and add it to back.
* @n: node we're adding.
* @k: klist it's going on.
*/
void klist_add_tail(struct klist_node *n, struct klist *k)
{
klist_node_init(k, n);
add_tail(k, n);
}
EXPORT_SYMBOL_GPL(klist_add_tail);
/**
* klist_add_behind - Init a klist_node and add it after an existing node
* @n: node we're adding.
* @pos: node to put @n after
*/
void klist_add_behind(struct klist_node *n, struct klist_node *pos)
{
struct klist *k = knode_klist(pos);
klist_node_init(k, n);
spin_lock(&k->k_lock);
list_add(&n->n_node, &pos->n_node);
spin_unlock(&k->k_lock);
}
EXPORT_SYMBOL_GPL(klist_add_behind);
/**
* klist_add_before - Init a klist_node and add it before an existing node
* @n: node we're adding.
* @pos: node to put @n after
*/
void klist_add_before(struct klist_node *n, struct klist_node *pos)
{
struct klist *k = knode_klist(pos);
klist_node_init(k, n);
spin_lock(&k->k_lock);
list_add_tail(&n->n_node, &pos->n_node);
spin_unlock(&k->k_lock);
}
EXPORT_SYMBOL_GPL(klist_add_before);
struct klist_waiter {
struct list_head list;
struct klist_node *node;
struct task_struct *process;
int woken;
};
static DEFINE_SPINLOCK(klist_remove_lock);
static LIST_HEAD(klist_remove_waiters);
static void klist_release(struct kref *kref)
{
struct klist_waiter *waiter, *tmp;
struct klist_node *n = container_of(kref, struct klist_node, n_ref);
WARN_ON(!knode_dead(n));
list_del(&n->n_node);
spin_lock(&klist_remove_lock);
list_for_each_entry_safe(waiter, tmp, &klist_remove_waiters, list) {
if (waiter->node != n)
continue;
list_del(&waiter->list);
waiter->woken = 1;
mb();
wake_up_process(waiter->process);
}
spin_unlock(&klist_remove_lock);
knode_set_klist(n, NULL);
}
static int klist_dec_and_del(struct klist_node *n)
{
return kref_put(&n->n_ref, klist_release);
}
static void klist_put(struct klist_node *n, bool kill)
{
struct klist *k = knode_klist(n);
void (*put)(struct klist_node *) = k->put;
spin_lock(&k->k_lock);
if (kill)
knode_kill(n);
if (!klist_dec_and_del(n))
put = NULL;
spin_unlock(&k->k_lock);
if (put)
put(n);
}
/**
* klist_del - Decrement the reference count of node and try to remove.
* @n: node we're deleting.
*/
void klist_del(struct klist_node *n)
{
klist_put(n, true);
}
EXPORT_SYMBOL_GPL(klist_del);
/**
* klist_remove - Decrement the refcount of node and wait for it to go away.
* @n: node we're removing.
*/
void klist_remove(struct klist_node *n)
{
struct klist_waiter waiter;
waiter.node = n;
waiter.process = current;
waiter.woken = 0;
spin_lock(&klist_remove_lock);
list_add(&waiter.list, &klist_remove_waiters);
spin_unlock(&klist_remove_lock);
klist_del(n);
for (;;) {
set_current_state(TASK_UNINTERRUPTIBLE);
if (waiter.woken)
break;
schedule();
}
__set_current_state(TASK_RUNNING);
}
EXPORT_SYMBOL_GPL(klist_remove);
/**
* klist_node_attached - Say whether a node is bound to a list or not.
* @n: Node that we're testing.
*/
int klist_node_attached(struct klist_node *n)
{
return (n->n_klist != NULL);
}
EXPORT_SYMBOL_GPL(klist_node_attached);
/**
* klist_iter_init_node - Initialize a klist_iter structure.
* @k: klist we're iterating.
* @i: klist_iter we're filling.
* @n: node to start with.
*
* Similar to klist_iter_init(), but starts the action off with @n,
* instead of with the list head.
*/
void klist_iter_init_node(struct klist *k, struct klist_iter *i,
struct klist_node *n)
{
i->i_klist = k;
i->i_cur = NULL;
if (n && kref_get_unless_zero(&n->n_ref))
i->i_cur = n;
}
EXPORT_SYMBOL_GPL(klist_iter_init_node);
/**
* klist_iter_init - Iniitalize a klist_iter structure.
* @k: klist we're iterating.
* @i: klist_iter structure we're filling.
*
* Similar to klist_iter_init_node(), but start with the list head.
*/
void klist_iter_init(struct klist *k, struct klist_iter *i)
{
klist_iter_init_node(k, i, NULL);
}
EXPORT_SYMBOL_GPL(klist_iter_init);
/**
* klist_iter_exit - Finish a list iteration.
* @i: Iterator structure.
*
* Must be called when done iterating over list, as it decrements the
* refcount of the current node. Necessary in case iteration exited before
* the end of the list was reached, and always good form.
*/
void klist_iter_exit(struct klist_iter *i)
{
if (i->i_cur) {
klist_put(i->i_cur, false);
i->i_cur = NULL;
}
}
EXPORT_SYMBOL_GPL(klist_iter_exit);
static struct klist_node *to_klist_node(struct list_head *n)
{
return container_of(n, struct klist_node, n_node);
}
/**
* klist_prev - Ante up prev node in list.
* @i: Iterator structure.
*
* First grab list lock. Decrement the reference count of the previous
* node, if there was one. Grab the prev node, increment its reference
* count, drop the lock, and return that prev node.
*/
struct klist_node *klist_prev(struct klist_iter *i)
{
void (*put)(struct klist_node *) = i->i_klist->put;
struct klist_node *last = i->i_cur;
struct klist_node *prev;
unsigned long flags;
spin_lock_irqsave(&i->i_klist->k_lock, flags);
if (last) {
prev = to_klist_node(last->n_node.prev);
if (!klist_dec_and_del(last))
put = NULL;
} else
prev = to_klist_node(i->i_klist->k_list.prev);
i->i_cur = NULL;
while (prev != to_klist_node(&i->i_klist->k_list)) {
if (likely(!knode_dead(prev))) {
kref_get(&prev->n_ref);
i->i_cur = prev;
break;
}
prev = to_klist_node(prev->n_node.prev);
}
spin_unlock_irqrestore(&i->i_klist->k_lock, flags);
if (put && last)
put(last);
return i->i_cur;
}
EXPORT_SYMBOL_GPL(klist_prev);
/**
* klist_next - Ante up next node in list.
* @i: Iterator structure.
*
* First grab list lock. Decrement the reference count of the previous
* node, if there was one. Grab the next node, increment its reference
* count, drop the lock, and return that next node.
*/
struct klist_node *klist_next(struct klist_iter *i)
{
void (*put)(struct klist_node *) = i->i_klist->put;
struct klist_node *last = i->i_cur;
struct klist_node *next;
unsigned long flags;
spin_lock_irqsave(&i->i_klist->k_lock, flags);
if (last) {
next = to_klist_node(last->n_node.next);
if (!klist_dec_and_del(last))
put = NULL;
} else
next = to_klist_node(i->i_klist->k_list.next);
i->i_cur = NULL;
while (next != to_klist_node(&i->i_klist->k_list)) {
if (likely(!knode_dead(next))) {
kref_get(&next->n_ref);
i->i_cur = next;
break;
}
next = to_klist_node(next->n_node.next);
}
spin_unlock_irqrestore(&i->i_klist->k_lock, flags);
if (put && last)
put(last);
return i->i_cur;
}
EXPORT_SYMBOL_GPL(klist_next);
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