Line data Source code
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 :
47 : static struct klist *knode_klist(struct klist_node *knode)
48 : {
49 91 : return (struct klist *)
50 91 : ((unsigned long)knode->n_klist & KNODE_KLIST_MASK);
51 : }
52 :
53 : static bool knode_dead(struct klist_node *knode)
54 : {
55 950 : return (unsigned long)knode->n_klist & KNODE_DEAD;
56 : }
57 :
58 : static void knode_set_klist(struct klist_node *knode, struct klist *klist)
59 : {
60 727 : knode->n_klist = klist;
61 : /* no knode deserves to start its life dead */
62 1363 : WARN_ON(knode_dead(knode));
63 : }
64 :
65 91 : static void knode_kill(struct klist_node *knode)
66 : {
67 : /* and no knode should die twice ever either, see we're very humane */
68 182 : WARN_ON(knode_dead(knode));
69 91 : *(unsigned long *)&knode->n_klist |= KNODE_DEAD;
70 91 : }
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 : */
84 630 : void klist_init(struct klist *k, void (*get)(struct klist_node *),
85 : void (*put)(struct klist_node *))
86 : {
87 1260 : INIT_LIST_HEAD(&k->k_list);
88 630 : spin_lock_init(&k->k_lock);
89 630 : k->get = get;
90 630 : k->put = put;
91 630 : }
92 : EXPORT_SYMBOL_GPL(klist_init);
93 :
94 : static void add_head(struct klist *k, struct klist_node *n)
95 : {
96 0 : spin_lock(&k->k_lock);
97 0 : list_add(&n->n_node, &k->k_list);
98 0 : spin_unlock(&k->k_lock);
99 : }
100 :
101 : static void add_tail(struct klist *k, struct klist_node *n)
102 : {
103 1272 : spin_lock(&k->k_lock);
104 1272 : list_add_tail(&n->n_node, &k->k_list);
105 1272 : spin_unlock(&k->k_lock);
106 : }
107 :
108 636 : static void klist_node_init(struct klist *k, struct klist_node *n)
109 : {
110 1272 : INIT_LIST_HEAD(&n->n_node);
111 1272 : kref_init(&n->n_ref);
112 1272 : knode_set_klist(n, k);
113 636 : if (k->get)
114 576 : k->get(n);
115 636 : }
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 : */
122 0 : void klist_add_head(struct klist_node *n, struct klist *k)
123 : {
124 0 : klist_node_init(k, n);
125 0 : add_head(k, n);
126 0 : }
127 : EXPORT_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 : */
134 636 : void klist_add_tail(struct klist_node *n, struct klist *k)
135 : {
136 636 : klist_node_init(k, n);
137 636 : add_tail(k, n);
138 636 : }
139 : EXPORT_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 : */
146 0 : void klist_add_behind(struct klist_node *n, struct klist_node *pos)
147 : {
148 0 : struct klist *k = knode_klist(pos);
149 :
150 0 : klist_node_init(k, n);
151 0 : spin_lock(&k->k_lock);
152 0 : list_add(&n->n_node, &pos->n_node);
153 0 : spin_unlock(&k->k_lock);
154 0 : }
155 : EXPORT_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 : */
162 0 : void klist_add_before(struct klist_node *n, struct klist_node *pos)
163 : {
164 0 : struct klist *k = knode_klist(pos);
165 :
166 0 : klist_node_init(k, n);
167 0 : spin_lock(&k->k_lock);
168 0 : list_add_tail(&n->n_node, &pos->n_node);
169 0 : spin_unlock(&k->k_lock);
170 0 : }
171 : EXPORT_SYMBOL_GPL(klist_add_before);
172 :
173 : struct klist_waiter {
174 : struct list_head list;
175 : struct klist_node *node;
176 : struct task_struct *process;
177 : int woken;
178 : };
179 :
180 : static DEFINE_SPINLOCK(klist_remove_lock);
181 : static LIST_HEAD(klist_remove_waiters);
182 :
183 91 : static void klist_release(struct kref *kref)
184 : {
185 : struct klist_waiter *waiter, *tmp;
186 91 : struct klist_node *n = container_of(kref, struct klist_node, n_ref);
187 :
188 182 : WARN_ON(!knode_dead(n));
189 182 : list_del(&n->n_node);
190 91 : spin_lock(&klist_remove_lock);
191 136 : list_for_each_entry_safe(waiter, tmp, &klist_remove_waiters, list) {
192 45 : if (waiter->node != n)
193 0 : continue;
194 :
195 90 : list_del(&waiter->list);
196 45 : waiter->woken = 1;
197 45 : mb();
198 45 : wake_up_process(waiter->process);
199 : }
200 91 : spin_unlock(&klist_remove_lock);
201 182 : knode_set_klist(n, NULL);
202 91 : }
203 :
204 223 : static int klist_dec_and_del(struct klist_node *n)
205 : {
206 446 : return kref_put(&n->n_ref, klist_release);
207 : }
208 :
209 91 : static void klist_put(struct klist_node *n, bool kill)
210 : {
211 182 : struct klist *k = knode_klist(n);
212 91 : void (*put)(struct klist_node *) = k->put;
213 :
214 182 : spin_lock(&k->k_lock);
215 91 : if (kill)
216 91 : knode_kill(n);
217 91 : if (!klist_dec_and_del(n))
218 0 : put = NULL;
219 182 : spin_unlock(&k->k_lock);
220 91 : if (put)
221 46 : put(n);
222 91 : }
223 :
224 : /**
225 : * klist_del - Decrement the reference count of node and try to remove.
226 : * @n: node we're deleting.
227 : */
228 46 : void klist_del(struct klist_node *n)
229 : {
230 91 : klist_put(n, true);
231 46 : }
232 : EXPORT_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 : */
238 45 : void klist_remove(struct klist_node *n)
239 : {
240 : struct klist_waiter waiter;
241 :
242 45 : waiter.node = n;
243 45 : waiter.process = current;
244 45 : waiter.woken = 0;
245 45 : spin_lock(&klist_remove_lock);
246 45 : list_add(&waiter.list, &klist_remove_waiters);
247 45 : spin_unlock(&klist_remove_lock);
248 :
249 : klist_del(n);
250 :
251 : for (;;) {
252 45 : set_current_state(TASK_UNINTERRUPTIBLE);
253 45 : if (waiter.woken)
254 : break;
255 0 : schedule();
256 : }
257 45 : __set_current_state(TASK_RUNNING);
258 45 : }
259 : EXPORT_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 : */
265 44 : int klist_node_attached(struct klist_node *n)
266 : {
267 44 : return (n->n_klist != NULL);
268 : }
269 : EXPORT_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 : */
280 96 : void klist_iter_init_node(struct klist *k, struct klist_iter *i,
281 : struct klist_node *n)
282 : {
283 96 : i->i_klist = k;
284 96 : i->i_cur = NULL;
285 96 : if (n && kref_get_unless_zero(&n->n_ref))
286 0 : i->i_cur = n;
287 96 : }
288 : EXPORT_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 : */
297 0 : void klist_iter_init(struct klist *k, struct klist_iter *i)
298 : {
299 0 : klist_iter_init_node(k, i, NULL);
300 0 : }
301 : EXPORT_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 : */
311 96 : void klist_iter_exit(struct klist_iter *i)
312 : {
313 96 : if (i->i_cur) {
314 0 : klist_put(i->i_cur, false);
315 0 : i->i_cur = NULL;
316 : }
317 96 : }
318 : EXPORT_SYMBOL_GPL(klist_iter_exit);
319 :
320 : static struct klist_node *to_klist_node(struct list_head *n)
321 : {
322 456 : 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 : */
333 0 : struct klist_node *klist_prev(struct klist_iter *i)
334 : {
335 0 : void (*put)(struct klist_node *) = i->i_klist->put;
336 0 : struct klist_node *last = i->i_cur;
337 : struct klist_node *prev;
338 : unsigned long flags;
339 :
340 0 : spin_lock_irqsave(&i->i_klist->k_lock, flags);
341 :
342 0 : if (last) {
343 0 : prev = to_klist_node(last->n_node.prev);
344 0 : if (!klist_dec_and_del(last))
345 0 : put = NULL;
346 : } else
347 0 : prev = to_klist_node(i->i_klist->k_list.prev);
348 :
349 0 : i->i_cur = NULL;
350 0 : while (prev != to_klist_node(&i->i_klist->k_list)) {
351 0 : if (likely(!knode_dead(prev))) {
352 0 : kref_get(&prev->n_ref);
353 0 : i->i_cur = prev;
354 0 : break;
355 : }
356 0 : prev = to_klist_node(prev->n_node.prev);
357 : }
358 :
359 0 : spin_unlock_irqrestore(&i->i_klist->k_lock, flags);
360 :
361 0 : if (put && last)
362 0 : put(last);
363 0 : return i->i_cur;
364 : }
365 : EXPORT_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 : */
375 228 : struct klist_node *klist_next(struct klist_iter *i)
376 : {
377 228 : void (*put)(struct klist_node *) = i->i_klist->put;
378 228 : struct klist_node *last = i->i_cur;
379 : struct klist_node *next;
380 : unsigned long flags;
381 :
382 228 : spin_lock_irqsave(&i->i_klist->k_lock, flags);
383 :
384 228 : if (last) {
385 264 : next = to_klist_node(last->n_node.next);
386 132 : if (!klist_dec_and_del(last))
387 132 : put = NULL;
388 : } else
389 192 : next = to_klist_node(i->i_klist->k_list.next);
390 :
391 228 : i->i_cur = NULL;
392 684 : while (next != to_klist_node(&i->i_klist->k_list)) {
393 264 : if (likely(!knode_dead(next))) {
394 264 : kref_get(&next->n_ref);
395 132 : i->i_cur = next;
396 132 : break;
397 : }
398 0 : next = to_klist_node(next->n_node.next);
399 : }
400 :
401 456 : spin_unlock_irqrestore(&i->i_klist->k_lock, flags);
402 :
403 228 : if (put && last)
404 0 : put(last);
405 228 : return i->i_cur;
406 : }
407 : EXPORT_SYMBOL_GPL(klist_next);
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