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1// SPDX-License-Identifier: GPL-2.0-only2/*3 * klist.c - Routines for manipulating klists.4 *5 * Copyright (C) 2005 Patrick Mochel6 *7 * This klist interface provides a couple of structures that wrap around8 * struct list_head to provide explicit list "head" (struct klist) and list9 * "node" (struct klist_node) objects. For struct klist, a spinlock is10 * included that protects access to the actual list itself. struct11 * klist_node provides a pointer to the klist that owns it and a kref12 * reference count that indicates the number of current users of that node13 * in the list.14 *15 * The entire point is to provide an interface for iterating over a list16 * that is safe and allows for modification of the list during the17 * iteration (e.g. insertion and removal), including modification of the18 * current node on the list.19 *20 * It works using a 3rd object type - struct klist_iter - that is declared21 * and initialized before an iteration. klist_next() is used to acquire the22 * next element in the list. It returns NULL if there are no more items.23 * Internally, that routine takes the klist's lock, decrements the24 * reference count of the previous klist_node and increments the count of25 * 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 until31 * it is actually removed. This is useful for objects (like devices) that32 * have been removed from the system and must be freed (but must wait until33 * 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 exclude42 * dead ones from iteration.43 */44#define KNODE_DEAD 1LU45#define KNODE_KLIST_MASK ~KNODE_DEAD46 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 are79 * going to be embedded in refcounted objects (necessary for safe80 * deletion) then the get/put arguments are used to initialise81 * functions that take and release references on the embedding82 * 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 HWJS_SUSPENDS 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 node143 * @n: node we're adding.144 * @pos: node to put @n after145 */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 node159 * @n: node we're adding.160 * @pos: node to put @n after161 */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 HWJS_SUSPENDS 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 HWJS_SUSPENDS int klist_dec_and_del(struct klist_node *n)205{206 return kref_put(&n->n_ref, klist_release);207}208 209static HWJS_SUSPENDS 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 the308 * refcount of the current node. Necessary in case iteration exited before309 * 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 previous330 * node, if there was one. Grab the prev node, increment its reference331 * 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 } else347 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 previous372 * node, if there was one. Grab the next node, increment its reference373 * 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 } else389 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);408