Line data Source code
1 : /*
2 : * klist.c - Routines for manipulating klists.
3 : *
4 : * Copyright (C) 2005 Patrick Mochel
5 : *
6 : * This file is released under the GPL v2.
7 : *
8 : * This klist interface provides a couple of structures that wrap around
9 : * struct list_head to provide explicit list "head" (struct klist) and list
10 : * "node" (struct klist_node) objects. For struct klist, a spinlock is
11 : * included that protects access to the actual list itself. struct
12 : * klist_node provides a pointer to the klist that owns it and a kref
13 : * reference count that indicates the number of current users of that node
14 : * in the list.
15 : *
16 : * The entire point is to provide an interface for iterating over a list
17 : * that is safe and allows for modification of the list during the
18 : * iteration (e.g. insertion and removal), including modification of the
19 : * current node on the list.
20 : *
21 : * It works using a 3rd object type - struct klist_iter - that is declared
22 : * and initialized before an iteration. klist_next() is used to acquire the
23 : * next element in the list. It returns NULL if there are no more items.
24 : * Internally, that routine takes the klist's lock, decrements the
25 : * reference count of the previous klist_node and increments the count of
26 : * the next klist_node. It then drops the lock and returns.
27 : *
28 : * There are primitives for adding and removing nodes to/from a klist.
29 : * When deleting, klist_del() will simply decrement the reference count.
30 : * Only when the count goes to 0 is the node removed from the list.
31 : * klist_remove() will try to delete the node from the list and block until
32 : * it is actually removed. This is useful for objects (like devices) that
33 : * have been removed from the system and must be freed (but must wait until
34 : * all accessors have finished).
35 : */
36 :
37 : #include <linux/klist.h>
38 : #include <linux/export.h>
39 : #include <linux/sched.h>
40 :
41 : /*
42 : * Use the lowest bit of n_klist to mark deleted nodes and exclude
43 : * dead ones from iteration.
44 : */
45 : #define KNODE_DEAD 1LU
46 : #define KNODE_KLIST_MASK ~KNODE_DEAD
47 :
48 : static struct klist *knode_klist(struct klist_node *knode)
49 : {
50 70 : return (struct klist *)
51 70 : ((unsigned long)knode->n_klist & KNODE_KLIST_MASK);
52 : }
53 :
54 : static bool knode_dead(struct klist_node *knode)
55 : {
56 64107 : return (unsigned long)knode->n_klist & KNODE_DEAD;
57 : }
58 :
59 : static void knode_set_klist(struct klist_node *knode, struct klist *klist)
60 : {
61 439 : knode->n_klist = klist;
62 : /* no knode deserves to start its life dead */
63 : WARN_ON(knode_dead(knode));
64 : }
65 :
66 : static void knode_kill(struct klist_node *knode)
67 : {
68 : /* and no knode should die twice ever either, see we're very humane */
69 : WARN_ON(knode_dead(knode));
70 24 : *(unsigned long *)&knode->n_klist |= KNODE_DEAD;
71 : }
72 :
73 : /**
74 : * klist_init - Initialize a klist structure.
75 : * @k: The klist we're initializing.
76 : * @get: The get function for the embedding object (NULL if none)
77 : * @put: The put function for the embedding object (NULL if none)
78 : *
79 : * Initialises the klist structure. If the klist_node structures are
80 : * going to be embedded in refcounted objects (necessary for safe
81 : * deletion) then the get/put arguments are used to initialise
82 : * functions that take and release references on the embedding
83 : * objects.
84 : */
85 384 : void klist_init(struct klist *k, void (*get)(struct klist_node *),
86 : void (*put)(struct klist_node *))
87 : {
88 384 : INIT_LIST_HEAD(&k->k_list);
89 : spin_lock_init(&k->k_lock);
90 384 : k->get = get;
91 384 : k->put = put;
92 384 : }
93 : EXPORT_SYMBOL_GPL(klist_init);
94 :
95 0 : static void add_head(struct klist *k, struct klist_node *n)
96 : {
97 : spin_lock(&k->k_lock);
98 0 : list_add(&n->n_node, &k->k_list);
99 : spin_unlock(&k->k_lock);
100 0 : }
101 :
102 415 : static void add_tail(struct klist *k, struct klist_node *n)
103 : {
104 : spin_lock(&k->k_lock);
105 415 : list_add_tail(&n->n_node, &k->k_list);
106 : spin_unlock(&k->k_lock);
107 415 : }
108 :
109 : static void klist_node_init(struct klist *k, struct klist_node *n)
110 : {
111 415 : INIT_LIST_HEAD(&n->n_node);
112 : kref_init(&n->n_ref);
113 : knode_set_klist(n, k);
114 415 : if (k->get)
115 342 : k->get(n);
116 : }
117 :
118 : /**
119 : * klist_add_head - Initialize a klist_node and add it to front.
120 : * @n: node we're adding.
121 : * @k: klist it's going on.
122 : */
123 0 : void klist_add_head(struct klist_node *n, struct klist *k)
124 : {
125 : klist_node_init(k, n);
126 0 : add_head(k, n);
127 0 : }
128 : EXPORT_SYMBOL_GPL(klist_add_head);
129 :
130 : /**
131 : * klist_add_tail - Initialize a klist_node and add it to back.
132 : * @n: node we're adding.
133 : * @k: klist it's going on.
134 : */
135 415 : void klist_add_tail(struct klist_node *n, struct klist *k)
136 : {
137 : klist_node_init(k, n);
138 415 : add_tail(k, n);
139 415 : }
140 : EXPORT_SYMBOL_GPL(klist_add_tail);
141 :
142 : /**
143 : * klist_add_behind - Init a klist_node and add it after an existing node
144 : * @n: node we're adding.
145 : * @pos: node to put @n after
146 : */
147 0 : void klist_add_behind(struct klist_node *n, struct klist_node *pos)
148 : {
149 : struct klist *k = knode_klist(pos);
150 :
151 : klist_node_init(k, n);
152 : spin_lock(&k->k_lock);
153 0 : list_add(&n->n_node, &pos->n_node);
154 : spin_unlock(&k->k_lock);
155 0 : }
156 : EXPORT_SYMBOL_GPL(klist_add_behind);
157 :
158 : /**
159 : * klist_add_before - Init a klist_node and add it before an existing node
160 : * @n: node we're adding.
161 : * @pos: node to put @n after
162 : */
163 0 : void klist_add_before(struct klist_node *n, struct klist_node *pos)
164 : {
165 : struct klist *k = knode_klist(pos);
166 :
167 : klist_node_init(k, n);
168 : spin_lock(&k->k_lock);
169 0 : list_add_tail(&n->n_node, &pos->n_node);
170 : spin_unlock(&k->k_lock);
171 0 : }
172 : EXPORT_SYMBOL_GPL(klist_add_before);
173 :
174 : struct klist_waiter {
175 : struct list_head list;
176 : struct klist_node *node;
177 : struct task_struct *process;
178 : int woken;
179 : };
180 :
181 : static DEFINE_SPINLOCK(klist_remove_lock);
182 : static LIST_HEAD(klist_remove_waiters);
183 :
184 24 : static void klist_release(struct kref *kref)
185 : {
186 : struct klist_waiter *waiter, *tmp;
187 24 : struct klist_node *n = container_of(kref, struct klist_node, n_ref);
188 :
189 : WARN_ON(!knode_dead(n));
190 : list_del(&n->n_node);
191 : spin_lock(&klist_remove_lock);
192 27 : list_for_each_entry_safe(waiter, tmp, &klist_remove_waiters, list) {
193 3 : if (waiter->node != n)
194 0 : continue;
195 :
196 : list_del(&waiter->list);
197 3 : waiter->woken = 1;
198 3 : mb();
199 3 : wake_up_process(waiter->process);
200 : }
201 : spin_unlock(&klist_remove_lock);
202 : knode_set_klist(n, NULL);
203 24 : }
204 :
205 64131 : static int klist_dec_and_del(struct klist_node *n)
206 : {
207 128262 : return kref_put(&n->n_ref, klist_release);
208 : }
209 :
210 70 : static void klist_put(struct klist_node *n, bool kill)
211 : {
212 : struct klist *k = knode_klist(n);
213 70 : void (*put)(struct klist_node *) = k->put;
214 :
215 : spin_lock(&k->k_lock);
216 70 : if (kill)
217 : knode_kill(n);
218 70 : if (!klist_dec_and_del(n))
219 : put = NULL;
220 : spin_unlock(&k->k_lock);
221 70 : if (put)
222 21 : put(n);
223 70 : }
224 :
225 : /**
226 : * klist_del - Decrement the reference count of node and try to remove.
227 : * @n: node we're deleting.
228 : */
229 21 : void klist_del(struct klist_node *n)
230 : {
231 24 : klist_put(n, true);
232 21 : }
233 : EXPORT_SYMBOL_GPL(klist_del);
234 :
235 : /**
236 : * klist_remove - Decrement the refcount of node and wait for it to go away.
237 : * @n: node we're removing.
238 : */
239 3 : void klist_remove(struct klist_node *n)
240 : {
241 : struct klist_waiter waiter;
242 :
243 3 : waiter.node = n;
244 3 : waiter.process = current;
245 3 : waiter.woken = 0;
246 : spin_lock(&klist_remove_lock);
247 : list_add(&waiter.list, &klist_remove_waiters);
248 : spin_unlock(&klist_remove_lock);
249 :
250 : klist_del(n);
251 :
252 : for (;;) {
253 3 : set_current_state(TASK_UNINTERRUPTIBLE);
254 3 : if (waiter.woken)
255 : break;
256 0 : schedule();
257 0 : }
258 3 : __set_current_state(TASK_RUNNING);
259 3 : }
260 : EXPORT_SYMBOL_GPL(klist_remove);
261 :
262 : /**
263 : * klist_node_attached - Say whether a node is bound to a list or not.
264 : * @n: Node that we're testing.
265 : */
266 39 : int klist_node_attached(struct klist_node *n)
267 : {
268 39 : return (n->n_klist != NULL);
269 : }
270 : EXPORT_SYMBOL_GPL(klist_node_attached);
271 :
272 : /**
273 : * klist_iter_init_node - Initialize a klist_iter structure.
274 : * @k: klist we're iterating.
275 : * @i: klist_iter we're filling.
276 : * @n: node to start with.
277 : *
278 : * Similar to klist_iter_init(), but starts the action off with @n,
279 : * instead of with the list head.
280 : */
281 1054 : void klist_iter_init_node(struct klist *k, struct klist_iter *i,
282 : struct klist_node *n)
283 : {
284 1054 : i->i_klist = k;
285 1054 : i->i_cur = n;
286 1054 : if (n)
287 : kref_get(&n->n_ref);
288 1054 : }
289 : EXPORT_SYMBOL_GPL(klist_iter_init_node);
290 :
291 : /**
292 : * klist_iter_init - Iniitalize a klist_iter structure.
293 : * @k: klist we're iterating.
294 : * @i: klist_iter structure we're filling.
295 : *
296 : * Similar to klist_iter_init_node(), but start with the list head.
297 : */
298 0 : void klist_iter_init(struct klist *k, struct klist_iter *i)
299 : {
300 : klist_iter_init_node(k, i, NULL);
301 0 : }
302 : EXPORT_SYMBOL_GPL(klist_iter_init);
303 :
304 : /**
305 : * klist_iter_exit - Finish a list iteration.
306 : * @i: Iterator structure.
307 : *
308 : * Must be called when done iterating over list, as it decrements the
309 : * refcount of the current node. Necessary in case iteration exited before
310 : * the end of the list was reached, and always good form.
311 : */
312 1054 : void klist_iter_exit(struct klist_iter *i)
313 : {
314 1054 : if (i->i_cur) {
315 46 : klist_put(i->i_cur, false);
316 46 : i->i_cur = NULL;
317 : }
318 1054 : }
319 : EXPORT_SYMBOL_GPL(klist_iter_exit);
320 :
321 : static struct klist_node *to_klist_node(struct list_head *n)
322 : {
323 : return container_of(n, struct klist_node, n_node);
324 : }
325 :
326 : /**
327 : * klist_next - Ante up next node in list.
328 : * @i: Iterator structure.
329 : *
330 : * First grab list lock. Decrement the reference count of the previous
331 : * node, if there was one. Grab the next node, increment its reference
332 : * count, drop the lock, and return that next node.
333 : */
334 65115 : struct klist_node *klist_next(struct klist_iter *i)
335 : {
336 65115 : void (*put)(struct klist_node *) = i->i_klist->put;
337 65115 : struct klist_node *last = i->i_cur;
338 64107 : struct klist_node *next;
339 :
340 : spin_lock(&i->i_klist->k_lock);
341 :
342 65115 : if (last) {
343 64061 : next = to_klist_node(last->n_node.next);
344 64061 : if (!klist_dec_and_del(last))
345 : put = NULL;
346 : } else
347 1054 : next = to_klist_node(i->i_klist->k_list.next);
348 :
349 65115 : i->i_cur = NULL;
350 130230 : while (next != to_klist_node(&i->i_klist->k_list)) {
351 64107 : if (likely(!knode_dead(next))) {
352 : kref_get(&next->n_ref);
353 64107 : i->i_cur = next;
354 64107 : break;
355 : }
356 0 : next = to_klist_node(next->n_node.next);
357 : }
358 :
359 : spin_unlock(&i->i_klist->k_lock);
360 :
361 65115 : if (put && last)
362 0 : put(last);
363 65115 : return i->i_cur;
364 : }
365 : EXPORT_SYMBOL_GPL(klist_next);
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