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1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * klist.c - Routines for manipulating klists.
4 *
5 * Copyright (C) 2005 Patrick Mochel
6 *
7 * This klist interface provides a couple of structures that wrap around
8 * struct list_head to provide explicit list "head" (struct klist) and list
9 * "node" (struct klist_node) objects. For struct klist, a spinlock is
10 * included that protects access to the actual list itself. struct
11 * klist_node provides a pointer to the klist that owns it and a kref
12 * reference count that indicates the number of current users of that node
13 * in the list.
14 *
15 * The entire point is to provide an interface for iterating over a list
16 * that is safe and allows for modification of the list during the
17 * iteration (e.g. insertion and removal), including modification of the
18 * current node on the list.
19 *
20 * It works using a 3rd object type - struct klist_iter - that is declared
21 * and initialized before an iteration. klist_next() is used to acquire the
22 * next element in the list. It returns NULL if there are no more items.
23 * Internally, that routine takes the klist's lock, decrements the
24 * reference count of the previous klist_node and increments the count of
25 * the next klist_node. It then drops the lock and returns.
26 *
27 * There are primitives for adding and removing nodes to/from a klist.
28 * When deleting, klist_del() will simply decrement the reference count.
29 * Only when the count goes to 0 is the node removed from the list.
30 * klist_remove() will try to delete the node from the list and block until
31 * it is actually removed. This is useful for objects (like devices) that
32 * have been removed from the system and must be freed (but must wait until
33 * all accessors have finished).
34 */
35
36#include <linux/klist.h>
37#include <linux/export.h>
38#include <linux/sched.h>
39
40/*
41 * Use the lowest bit of n_klist to mark deleted nodes and exclude
42 * dead ones from iteration.
43 */
44#define KNODE_DEAD 1LU
45#define KNODE_KLIST_MASK ~KNODE_DEAD
46
47static struct klist *knode_klist(struct klist_node *knode)
48{
49 return (struct klist *)
50 ((unsigned long)knode->n_klist & KNODE_KLIST_MASK);
51}
52
53static bool knode_dead(struct klist_node *knode)
54{
55 return (unsigned long)knode->n_klist & KNODE_DEAD;
56}
57
58static void knode_set_klist(struct klist_node *knode, struct klist *klist)
59{
60 knode->n_klist = klist;
61 /* no knode deserves to start its life dead */
62 WARN_ON(knode_dead(knode));
63}
64
65static void knode_kill(struct klist_node *knode)
66{
67 /* and no knode should die twice ever either, see we're very humane */
68 WARN_ON(knode_dead(knode));
69 *(unsigned long *)&knode->n_klist |= KNODE_DEAD;
70}
71
72/**
73 * klist_init - Initialize a klist structure.
74 * @k: The klist we're initializing.
75 * @get: The get function for the embedding object (NULL if none)
76 * @put: The put function for the embedding object (NULL if none)
77 *
78 * Initialises the klist structure. If the klist_node structures are
79 * going to be embedded in refcounted objects (necessary for safe
80 * deletion) then the get/put arguments are used to initialise
81 * functions that take and release references on the embedding
82 * objects.
83 */
84void klist_init(struct klist *k, void (*get)(struct klist_node *),
85 void (*put)(struct klist_node *))
86{
87 INIT_LIST_HEAD(&k->k_list);
88 spin_lock_init(&k->k_lock);
89 k->get = get;
90 k->put = put;
91}
92EXPORT_SYMBOL_GPL(klist_init);
93
94static void add_head(struct klist *k, struct klist_node *n)
95{
96 spin_lock(&k->k_lock);
97 list_add(&n->n_node, &k->k_list);
98 spin_unlock(&k->k_lock);
99}
100
101static void add_tail(struct klist *k, struct klist_node *n)
102{
103 spin_lock(&k->k_lock);
104 list_add_tail(&n->n_node, &k->k_list);
105 spin_unlock(&k->k_lock);
106}
107
108static void klist_node_init(struct klist *k, struct klist_node *n)
109{
110 INIT_LIST_HEAD(&n->n_node);
111 kref_init(&n->n_ref);
112 knode_set_klist(n, k);
113 if (k->get)
114 k->get(n);
115}
116
117/**
118 * klist_add_head - Initialize a klist_node and add it to front.
119 * @n: node we're adding.
120 * @k: klist it's going on.
121 */
122void klist_add_head(struct klist_node *n, struct klist *k)
123{
124 klist_node_init(k, n);
125 add_head(k, n);
126}
127EXPORT_SYMBOL_GPL(klist_add_head);
128
129/**
130 * klist_add_tail - Initialize a klist_node and add it to back.
131 * @n: node we're adding.
132 * @k: klist it's going on.
133 */
134void klist_add_tail(struct klist_node *n, struct klist *k)
135{
136 klist_node_init(k, n);
137 add_tail(k, n);
138}
139EXPORT_SYMBOL_GPL(klist_add_tail);
140
141/**
142 * klist_add_behind - Init a klist_node and add it after an existing node
143 * @n: node we're adding.
144 * @pos: node to put @n after
145 */
146void klist_add_behind(struct klist_node *n, struct klist_node *pos)
147{
148 struct klist *k = knode_klist(pos);
149
150 klist_node_init(k, n);
151 spin_lock(&k->k_lock);
152 list_add(&n->n_node, &pos->n_node);
153 spin_unlock(&k->k_lock);
154}
155EXPORT_SYMBOL_GPL(klist_add_behind);
156
157/**
158 * klist_add_before - Init a klist_node and add it before an existing node
159 * @n: node we're adding.
160 * @pos: node to put @n after
161 */
162void klist_add_before(struct klist_node *n, struct klist_node *pos)
163{
164 struct klist *k = knode_klist(pos);
165
166 klist_node_init(k, n);
167 spin_lock(&k->k_lock);
168 list_add_tail(&n->n_node, &pos->n_node);
169 spin_unlock(&k->k_lock);
170}
171EXPORT_SYMBOL_GPL(klist_add_before);
172
173struct klist_waiter {
174 struct list_head list;
175 struct klist_node *node;
176 struct task_struct *process;
177 int woken;
178};
179
180static DEFINE_SPINLOCK(klist_remove_lock);
181static LIST_HEAD(klist_remove_waiters);
182
183static void klist_release(struct kref *kref)
184{
185 struct klist_waiter *waiter, *tmp;
186 struct klist_node *n = container_of(kref, struct klist_node, n_ref);
187
188 WARN_ON(!knode_dead(n));
189 list_del(&n->n_node);
190 spin_lock(&klist_remove_lock);
191 list_for_each_entry_safe(waiter, tmp, &klist_remove_waiters, list) {
192 if (waiter->node != n)
193 continue;
194
195 list_del(&waiter->list);
196 waiter->woken = 1;
197 mb();
198 wake_up_process(waiter->process);
199 }
200 spin_unlock(&klist_remove_lock);
201 knode_set_klist(n, NULL);
202}
203
204static int klist_dec_and_del(struct klist_node *n)
205{
206 return kref_put(&n->n_ref, klist_release);
207}
208
209static void klist_put(struct klist_node *n, bool kill)
210{
211 struct klist *k = knode_klist(n);
212 void (*put)(struct klist_node *) = k->put;
213
214 spin_lock(&k->k_lock);
215 if (kill)
216 knode_kill(n);
217 if (!klist_dec_and_del(n))
218 put = NULL;
219 spin_unlock(&k->k_lock);
220 if (put)
221 put(n);
222}
223
224/**
225 * klist_del - Decrement the reference count of node and try to remove.
226 * @n: node we're deleting.
227 */
228void klist_del(struct klist_node *n)
229{
230 klist_put(n, true);
231}
232EXPORT_SYMBOL_GPL(klist_del);
233
234/**
235 * klist_remove - Decrement the refcount of node and wait for it to go away.
236 * @n: node we're removing.
237 */
238void klist_remove(struct klist_node *n)
239{
240 struct klist_waiter waiter;
241
242 waiter.node = n;
243 waiter.process = current;
244 waiter.woken = 0;
245 spin_lock(&klist_remove_lock);
246 list_add(&waiter.list, &klist_remove_waiters);
247 spin_unlock(&klist_remove_lock);
248
249 klist_del(n);
250
251 for (;;) {
252 set_current_state(TASK_UNINTERRUPTIBLE);
253 if (waiter.woken)
254 break;
255 schedule();
256 }
257 __set_current_state(TASK_RUNNING);
258}
259EXPORT_SYMBOL_GPL(klist_remove);
260
261/**
262 * klist_node_attached - Say whether a node is bound to a list or not.
263 * @n: Node that we're testing.
264 */
265int klist_node_attached(struct klist_node *n)
266{
267 return (n->n_klist != NULL);
268}
269EXPORT_SYMBOL_GPL(klist_node_attached);
270
271/**
272 * klist_iter_init_node - Initialize a klist_iter structure.
273 * @k: klist we're iterating.
274 * @i: klist_iter we're filling.
275 * @n: node to start with.
276 *
277 * Similar to klist_iter_init(), but starts the action off with @n,
278 * instead of with the list head.
279 */
280void klist_iter_init_node(struct klist *k, struct klist_iter *i,
281 struct klist_node *n)
282{
283 i->i_klist = k;
284 i->i_cur = NULL;
285 if (n && kref_get_unless_zero(&n->n_ref))
286 i->i_cur = n;
287}
288EXPORT_SYMBOL_GPL(klist_iter_init_node);
289
290/**
291 * klist_iter_init - Iniitalize a klist_iter structure.
292 * @k: klist we're iterating.
293 * @i: klist_iter structure we're filling.
294 *
295 * Similar to klist_iter_init_node(), but start with the list head.
296 */
297void klist_iter_init(struct klist *k, struct klist_iter *i)
298{
299 klist_iter_init_node(k, i, NULL);
300}
301EXPORT_SYMBOL_GPL(klist_iter_init);
302
303/**
304 * klist_iter_exit - Finish a list iteration.
305 * @i: Iterator structure.
306 *
307 * Must be called when done iterating over list, as it decrements the
308 * refcount of the current node. Necessary in case iteration exited before
309 * the end of the list was reached, and always good form.
310 */
311void klist_iter_exit(struct klist_iter *i)
312{
313 if (i->i_cur) {
314 klist_put(i->i_cur, false);
315 i->i_cur = NULL;
316 }
317}
318EXPORT_SYMBOL_GPL(klist_iter_exit);
319
320static struct klist_node *to_klist_node(struct list_head *n)
321{
322 return container_of(n, struct klist_node, n_node);
323}
324
325/**
326 * klist_prev - Ante up prev node in list.
327 * @i: Iterator structure.
328 *
329 * First grab list lock. Decrement the reference count of the previous
330 * node, if there was one. Grab the prev node, increment its reference
331 * count, drop the lock, and return that prev node.
332 */
333struct klist_node *klist_prev(struct klist_iter *i)
334{
335 void (*put)(struct klist_node *) = i->i_klist->put;
336 struct klist_node *last = i->i_cur;
337 struct klist_node *prev;
338 unsigned long flags;
339
340 spin_lock_irqsave(&i->i_klist->k_lock, flags);
341
342 if (last) {
343 prev = to_klist_node(last->n_node.prev);
344 if (!klist_dec_and_del(last))
345 put = NULL;
346 } else
347 prev = to_klist_node(i->i_klist->k_list.prev);
348
349 i->i_cur = NULL;
350 while (prev != to_klist_node(&i->i_klist->k_list)) {
351 if (likely(!knode_dead(prev))) {
352 kref_get(&prev->n_ref);
353 i->i_cur = prev;
354 break;
355 }
356 prev = to_klist_node(prev->n_node.prev);
357 }
358
359 spin_unlock_irqrestore(&i->i_klist->k_lock, flags);
360
361 if (put && last)
362 put(last);
363 return i->i_cur;
364}
365EXPORT_SYMBOL_GPL(klist_prev);
366
367/**
368 * klist_next - Ante up next node in list.
369 * @i: Iterator structure.
370 *
371 * First grab list lock. Decrement the reference count of the previous
372 * node, if there was one. Grab the next node, increment its reference
373 * count, drop the lock, and return that next node.
374 */
375struct klist_node *klist_next(struct klist_iter *i)
376{
377 void (*put)(struct klist_node *) = i->i_klist->put;
378 struct klist_node *last = i->i_cur;
379 struct klist_node *next;
380 unsigned long flags;
381
382 spin_lock_irqsave(&i->i_klist->k_lock, flags);
383
384 if (last) {
385 next = to_klist_node(last->n_node.next);
386 if (!klist_dec_and_del(last))
387 put = NULL;
388 } else
389 next = to_klist_node(i->i_klist->k_list.next);
390
391 i->i_cur = NULL;
392 while (next != to_klist_node(&i->i_klist->k_list)) {
393 if (likely(!knode_dead(next))) {
394 kref_get(&next->n_ref);
395 i->i_cur = next;
396 break;
397 }
398 next = to_klist_node(next->n_node.next);
399 }
400
401 spin_unlock_irqrestore(&i->i_klist->k_lock, flags);
402
403 if (put && last)
404 put(last);
405 return i->i_cur;
406}
407EXPORT_SYMBOL_GPL(klist_next);