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Linux/lib/klist.c

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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 
 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 
 53 static bool knode_dead(struct klist_node *knode)
 54 {
 55         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         knode->n_klist = klist;
 61         /* no knode deserves to start its life dead */
 62         WARN_ON(knode_dead(knode));
 63 }
 64 
 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  */
 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 
 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 
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 
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  */
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  */
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  */
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  */
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 
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 
204 static int klist_dec_and_del(struct klist_node *n)
205 {
206         return kref_put(&n->n_ref, klist_release);
207 }
208 
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  */
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  */
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  */
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  */
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  */
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  */
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 
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  */
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  */
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 

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