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klist.c
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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  return (struct klist *)
51  ((unsigned long)knode->n_klist & KNODE_KLIST_MASK);
52 }
53 
54 static bool knode_dead(struct klist_node *knode)
55 {
56  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  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  *(unsigned long *)&knode->n_klist |= KNODE_DEAD;
71 }
72 
85 void klist_init(struct klist *k, void (*get)(struct klist_node *),
86  void (*put)(struct klist_node *))
87 {
88  INIT_LIST_HEAD(&k->k_list);
90  k->get = get;
91  k->put = put;
92 }
94 
95 static void add_head(struct klist *k, struct klist_node *n)
96 {
97  spin_lock(&k->k_lock);
98  list_add(&n->n_node, &k->k_list);
99  spin_unlock(&k->k_lock);
100 }
101 
102 static void add_tail(struct klist *k, struct klist_node *n)
103 {
104  spin_lock(&k->k_lock);
105  list_add_tail(&n->n_node, &k->k_list);
106  spin_unlock(&k->k_lock);
107 }
108 
109 static void klist_node_init(struct klist *k, struct klist_node *n)
110 {
111  INIT_LIST_HEAD(&n->n_node);
112  kref_init(&n->n_ref);
113  knode_set_klist(n, k);
114  if (k->get)
115  k->get(n);
116 }
117 
123 void klist_add_head(struct klist_node *n, struct klist *k)
124 {
125  klist_node_init(k, n);
126  add_head(k, n);
127 }
129 
135 void klist_add_tail(struct klist_node *n, struct klist *k)
136 {
137  klist_node_init(k, n);
138  add_tail(k, n);
139 }
141 
147 void klist_add_after(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  list_add(&n->n_node, &pos->n_node);
154  spin_unlock(&k->k_lock);
155 }
157 
163 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  list_add_tail(&n->n_node, &pos->n_node);
170  spin_unlock(&k->k_lock);
171 }
173 
174 struct klist_waiter {
175  struct list_head list;
176  struct klist_node *node;
178  int woken;
179 };
180 
181 static DEFINE_SPINLOCK(klist_remove_lock);
182 static LIST_HEAD(klist_remove_waiters);
183 
184 static void klist_release(struct kref *kref)
185 {
186  struct klist_waiter *waiter, *tmp;
187  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  list_for_each_entry_safe(waiter, tmp, &klist_remove_waiters, list) {
193  if (waiter->node != n)
194  continue;
195 
196  waiter->woken = 1;
197  mb();
198  wake_up_process(waiter->process);
199  list_del(&waiter->list);
200  }
201  spin_unlock(&klist_remove_lock);
202  knode_set_klist(n, NULL);
203 }
204 
205 static int klist_dec_and_del(struct klist_node *n)
206 {
207  return kref_put(&n->n_ref, klist_release);
208 }
209 
210 static void klist_put(struct klist_node *n, bool kill)
211 {
212  struct klist *k = knode_klist(n);
213  void (*put)(struct klist_node *) = k->put;
214 
215  spin_lock(&k->k_lock);
216  if (kill)
217  knode_kill(n);
218  if (!klist_dec_and_del(n))
219  put = NULL;
220  spin_unlock(&k->k_lock);
221  if (put)
222  put(n);
223 }
224 
229 void klist_del(struct klist_node *n)
230 {
231  klist_put(n, true);
232 }
234 
239 void klist_remove(struct klist_node *n)
240 {
241  struct klist_waiter waiter;
242 
243  waiter.node = n;
244  waiter.process = current;
245  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 (;;) {
254  if (waiter.woken)
255  break;
256  schedule();
257  }
259 }
261 
267 {
268  return (n->n_klist != NULL);
269 }
271 
281 void klist_iter_init_node(struct klist *k, struct klist_iter *i,
282  struct klist_node *n)
283 {
284  i->i_klist = k;
285  i->i_cur = n;
286  if (n)
287  kref_get(&n->n_ref);
288 }
290 
298 void klist_iter_init(struct klist *k, struct klist_iter *i)
299 {
300  klist_iter_init_node(k, i, NULL);
301 }
303 
313 {
314  if (i->i_cur) {
315  klist_put(i->i_cur, false);
316  i->i_cur = NULL;
317  }
318 }
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 
335 {
336  void (*put)(struct klist_node *) = i->i_klist->put;
337  struct klist_node *last = i->i_cur;
338  struct klist_node *next;
339 
340  spin_lock(&i->i_klist->k_lock);
341 
342  if (last) {
343  next = to_klist_node(last->n_node.next);
344  if (!klist_dec_and_del(last))
345  put = NULL;
346  } else
347  next = to_klist_node(i->i_klist->k_list.next);
348 
349  i->i_cur = NULL;
350  while (next != to_klist_node(&i->i_klist->k_list)) {
351  if (likely(!knode_dead(next))) {
352  kref_get(&next->n_ref);
353  i->i_cur = next;
354  break;
355  }
356  next = to_klist_node(next->n_node.next);
357  }
358 
359  spin_unlock(&i->i_klist->k_lock);
360 
361  if (put && last)
362  put(last);
363  return i->i_cur;
364 }