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 
knode_klist(struct klist_node * knode)47 static struct klist *knode_klist(struct klist_node *knode)
48 {
49 	return (struct klist *)
50 		((unsigned long)knode->n_klist & KNODE_KLIST_MASK);
51 }
52 
knode_dead(struct klist_node * knode)53 static bool knode_dead(struct klist_node *knode)
54 {
55 	return (unsigned long)knode->n_klist & KNODE_DEAD;
56 }
57 
knode_set_klist(struct klist_node * knode,struct klist * klist)58 static 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 
knode_kill(struct klist_node * knode)65 static 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  */
klist_init(struct klist * k,void (* get)(struct klist_node *),void (* put)(struct klist_node *))84 void 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 }
92 EXPORT_SYMBOL_GPL(klist_init);
93 
add_head(struct klist * k,struct klist_node * n)94 static 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 
add_tail(struct klist * k,struct klist_node * n)101 static 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 
klist_node_init(struct klist * k,struct klist_node * n)108 static 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  */
klist_add_head(struct klist_node * n,struct klist * k)122 void klist_add_head(struct klist_node *n, struct klist *k)
123 {
124 	klist_node_init(k, n);
125 	add_head(k, n);
126 }
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  */
klist_add_tail(struct klist_node * n,struct klist * k)134 void klist_add_tail(struct klist_node *n, struct klist *k)
135 {
136 	klist_node_init(k, n);
137 	add_tail(k, n);
138 }
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  */
klist_add_behind(struct klist_node * n,struct klist_node * pos)146 void 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 }
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  */
klist_add_before(struct klist_node * n,struct klist_node * pos)162 void 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 }
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 
klist_release(struct kref * kref)183 static 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 
klist_dec_and_del(struct klist_node * n)204 static int klist_dec_and_del(struct klist_node *n)
205 {
206 	return kref_put(&n->n_ref, klist_release);
207 }
208 
klist_put(struct klist_node * n,bool kill)209 static 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  */
klist_del(struct klist_node * n)228 void klist_del(struct klist_node *n)
229 {
230 	klist_put(n, true);
231 }
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  */
klist_remove(struct klist_node * n)238 void 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 }
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  */
klist_node_attached(struct klist_node * n)265 int klist_node_attached(struct klist_node *n)
266 {
267 	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  */
klist_iter_init_node(struct klist * k,struct klist_iter * i,struct klist_node * n)280 void 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 }
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  */
klist_iter_init(struct klist * k,struct klist_iter * i)297 void klist_iter_init(struct klist *k, struct klist_iter *i)
298 {
299 	klist_iter_init_node(k, i, NULL);
300 }
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  */
klist_iter_exit(struct klist_iter * i)311 void 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 }
318 EXPORT_SYMBOL_GPL(klist_iter_exit);
319 
to_klist_node(struct list_head * n)320 static 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  */
klist_prev(struct klist_iter * i)333 struct 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 }
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  */
klist_next(struct klist_iter * i)375 struct 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 }
407 EXPORT_SYMBOL_GPL(klist_next);
408