klist.c 10.3 KB
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406
/*
 * klist.c - Routines for manipulating klists.
 *
 * Copyright (C) 2005 Patrick Mochel
 *
 * This file is released under the GPL v2.
 *
 * This klist interface provides a couple of structures that wrap around
 * struct list_head to provide explicit list "head" (struct klist) and list
 * "node" (struct klist_node) objects. For struct klist, a spinlock is
 * included that protects access to the actual list itself. struct
 * klist_node provides a pointer to the klist that owns it and a kref
 * reference count that indicates the number of current users of that node
 * in the list.
 *
 * The entire point is to provide an interface for iterating over a list
 * that is safe and allows for modification of the list during the
 * iteration (e.g. insertion and removal), including modification of the
 * current node on the list.
 *
 * It works using a 3rd object type - struct klist_iter - that is declared
 * and initialized before an iteration. klist_next() is used to acquire the
 * next element in the list. It returns NULL if there are no more items.
 * Internally, that routine takes the klist's lock, decrements the
 * reference count of the previous klist_node and increments the count of
 * the next klist_node. It then drops the lock and returns.
 *
 * There are primitives for adding and removing nodes to/from a klist.
 * When deleting, klist_del() will simply decrement the reference count.
 * Only when the count goes to 0 is the node removed from the list.
 * klist_remove() will try to delete the node from the list and block until
 * it is actually removed. This is useful for objects (like devices) that
 * have been removed from the system and must be freed (but must wait until
 * all accessors have finished).
 */

#include <linux/klist.h>
#include <linux/export.h>
#include <linux/sched.h>

/*
 * Use the lowest bit of n_klist to mark deleted nodes and exclude
 * dead ones from iteration.
 */
#define KNODE_DEAD		1LU
#define KNODE_KLIST_MASK	~KNODE_DEAD

static struct klist *knode_klist(struct klist_node *knode)
{
	return (struct klist *)
		((unsigned long)knode->n_klist & KNODE_KLIST_MASK);
}

static bool knode_dead(struct klist_node *knode)
{
	return (unsigned long)knode->n_klist & KNODE_DEAD;
}

static void knode_set_klist(struct klist_node *knode, struct klist *klist)
{
	knode->n_klist = klist;
	/* no knode deserves to start its life dead */
	WARN_ON(knode_dead(knode));
}

static void knode_kill(struct klist_node *knode)
{
	/* and no knode should die twice ever either, see we're very humane */
	WARN_ON(knode_dead(knode));
	*(unsigned long *)&knode->n_klist |= KNODE_DEAD;
}

/**
 * klist_init - Initialize a klist structure.
 * @k: The klist we're initializing.
 * @get: The get function for the embedding object (NULL if none)
 * @put: The put function for the embedding object (NULL if none)
 *
 * Initialises the klist structure.  If the klist_node structures are
 * going to be embedded in refcounted objects (necessary for safe
 * deletion) then the get/put arguments are used to initialise
 * functions that take and release references on the embedding
 * objects.
 */
void klist_init(struct klist *k, void (*get)(struct klist_node *),
		void (*put)(struct klist_node *))
{
	INIT_LIST_HEAD(&k->k_list);
	spin_lock_init(&k->k_lock);
	k->get = get;
	k->put = put;
}
EXPORT_SYMBOL_GPL(klist_init);

static void add_head(struct klist *k, struct klist_node *n)
{
	spin_lock(&k->k_lock);
	list_add(&n->n_node, &k->k_list);
	spin_unlock(&k->k_lock);
}

static void add_tail(struct klist *k, struct klist_node *n)
{
	spin_lock(&k->k_lock);
	list_add_tail(&n->n_node, &k->k_list);
	spin_unlock(&k->k_lock);
}

static void klist_node_init(struct klist *k, struct klist_node *n)
{
	INIT_LIST_HEAD(&n->n_node);
	kref_init(&n->n_ref);
	knode_set_klist(n, k);
	if (k->get)
		k->get(n);
}

/**
 * klist_add_head - Initialize a klist_node and add it to front.
 * @n: node we're adding.
 * @k: klist it's going on.
 */
void klist_add_head(struct klist_node *n, struct klist *k)
{
	klist_node_init(k, n);
	add_head(k, n);
}
EXPORT_SYMBOL_GPL(klist_add_head);

/**
 * klist_add_tail - Initialize a klist_node and add it to back.
 * @n: node we're adding.
 * @k: klist it's going on.
 */
void klist_add_tail(struct klist_node *n, struct klist *k)
{
	klist_node_init(k, n);
	add_tail(k, n);
}
EXPORT_SYMBOL_GPL(klist_add_tail);

/**
 * klist_add_behind - Init a klist_node and add it after an existing node
 * @n: node we're adding.
 * @pos: node to put @n after
 */
void klist_add_behind(struct klist_node *n, struct klist_node *pos)
{
	struct klist *k = knode_klist(pos);

	klist_node_init(k, n);
	spin_lock(&k->k_lock);
	list_add(&n->n_node, &pos->n_node);
	spin_unlock(&k->k_lock);
}
EXPORT_SYMBOL_GPL(klist_add_behind);

/**
 * klist_add_before - Init a klist_node and add it before an existing node
 * @n: node we're adding.
 * @pos: node to put @n after
 */
void klist_add_before(struct klist_node *n, struct klist_node *pos)
{
	struct klist *k = knode_klist(pos);

	klist_node_init(k, n);
	spin_lock(&k->k_lock);
	list_add_tail(&n->n_node, &pos->n_node);
	spin_unlock(&k->k_lock);
}
EXPORT_SYMBOL_GPL(klist_add_before);

struct klist_waiter {
	struct list_head list;
	struct klist_node *node;
	struct task_struct *process;
	int woken;
};

static DEFINE_SPINLOCK(klist_remove_lock);
static LIST_HEAD(klist_remove_waiters);

static void klist_release(struct kref *kref)
{
	struct klist_waiter *waiter, *tmp;
	struct klist_node *n = container_of(kref, struct klist_node, n_ref);

	WARN_ON(!knode_dead(n));
	list_del(&n->n_node);
	spin_lock(&klist_remove_lock);
	list_for_each_entry_safe(waiter, tmp, &klist_remove_waiters, list) {
		if (waiter->node != n)
			continue;

		list_del(&waiter->list);
		waiter->woken = 1;
		mb();
		wake_up_process(waiter->process);
	}
	spin_unlock(&klist_remove_lock);
	knode_set_klist(n, NULL);
}

static int klist_dec_and_del(struct klist_node *n)
{
	return kref_put(&n->n_ref, klist_release);
}

static void klist_put(struct klist_node *n, bool kill)
{
	struct klist *k = knode_klist(n);
	void (*put)(struct klist_node *) = k->put;

	spin_lock(&k->k_lock);
	if (kill)
		knode_kill(n);
	if (!klist_dec_and_del(n))
		put = NULL;
	spin_unlock(&k->k_lock);
	if (put)
		put(n);
}

/**
 * klist_del - Decrement the reference count of node and try to remove.
 * @n: node we're deleting.
 */
void klist_del(struct klist_node *n)
{
	klist_put(n, true);
}
EXPORT_SYMBOL_GPL(klist_del);

/**
 * klist_remove - Decrement the refcount of node and wait for it to go away.
 * @n: node we're removing.
 */
void klist_remove(struct klist_node *n)
{
	struct klist_waiter waiter;

	waiter.node = n;
	waiter.process = current;
	waiter.woken = 0;
	spin_lock(&klist_remove_lock);
	list_add(&waiter.list, &klist_remove_waiters);
	spin_unlock(&klist_remove_lock);

	klist_del(n);

	for (;;) {
		set_current_state(TASK_UNINTERRUPTIBLE);
		if (waiter.woken)
			break;
		schedule();
	}
	__set_current_state(TASK_RUNNING);
}
EXPORT_SYMBOL_GPL(klist_remove);

/**
 * klist_node_attached - Say whether a node is bound to a list or not.
 * @n: Node that we're testing.
 */
int klist_node_attached(struct klist_node *n)
{
	return (n->n_klist != NULL);
}
EXPORT_SYMBOL_GPL(klist_node_attached);

/**
 * klist_iter_init_node - Initialize a klist_iter structure.
 * @k: klist we're iterating.
 * @i: klist_iter we're filling.
 * @n: node to start with.
 *
 * Similar to klist_iter_init(), but starts the action off with @n,
 * instead of with the list head.
 */
void klist_iter_init_node(struct klist *k, struct klist_iter *i,
			  struct klist_node *n)
{
	i->i_klist = k;
	i->i_cur = NULL;
	if (n && kref_get_unless_zero(&n->n_ref))
		i->i_cur = n;
}
EXPORT_SYMBOL_GPL(klist_iter_init_node);

/**
 * klist_iter_init - Iniitalize a klist_iter structure.
 * @k: klist we're iterating.
 * @i: klist_iter structure we're filling.
 *
 * Similar to klist_iter_init_node(), but start with the list head.
 */
void klist_iter_init(struct klist *k, struct klist_iter *i)
{
	klist_iter_init_node(k, i, NULL);
}
EXPORT_SYMBOL_GPL(klist_iter_init);

/**
 * klist_iter_exit - Finish a list iteration.
 * @i: Iterator structure.
 *
 * Must be called when done iterating over list, as it decrements the
 * refcount of the current node. Necessary in case iteration exited before
 * the end of the list was reached, and always good form.
 */
void klist_iter_exit(struct klist_iter *i)
{
	if (i->i_cur) {
		klist_put(i->i_cur, false);
		i->i_cur = NULL;
	}
}
EXPORT_SYMBOL_GPL(klist_iter_exit);

static struct klist_node *to_klist_node(struct list_head *n)
{
	return container_of(n, struct klist_node, n_node);
}

/**
 * klist_prev - Ante up prev node in list.
 * @i: Iterator structure.
 *
 * First grab list lock. Decrement the reference count of the previous
 * node, if there was one. Grab the prev node, increment its reference
 * count, drop the lock, and return that prev node.
 */
struct klist_node *klist_prev(struct klist_iter *i)
{
	void (*put)(struct klist_node *) = i->i_klist->put;
	struct klist_node *last = i->i_cur;
	struct klist_node *prev;

	spin_lock(&i->i_klist->k_lock);

	if (last) {
		prev = to_klist_node(last->n_node.prev);
		if (!klist_dec_and_del(last))
			put = NULL;
	} else
		prev = to_klist_node(i->i_klist->k_list.prev);

	i->i_cur = NULL;
	while (prev != to_klist_node(&i->i_klist->k_list)) {
		if (likely(!knode_dead(prev))) {
			kref_get(&prev->n_ref);
			i->i_cur = prev;
			break;
		}
		prev = to_klist_node(prev->n_node.prev);
	}

	spin_unlock(&i->i_klist->k_lock);

	if (put && last)
		put(last);
	return i->i_cur;
}
EXPORT_SYMBOL_GPL(klist_prev);

/**
 * klist_next - Ante up next node in list.
 * @i: Iterator structure.
 *
 * First grab list lock. Decrement the reference count of the previous
 * node, if there was one. Grab the next node, increment its reference
 * count, drop the lock, and return that next node.
 */
struct klist_node *klist_next(struct klist_iter *i)
{
	void (*put)(struct klist_node *) = i->i_klist->put;
	struct klist_node *last = i->i_cur;
	struct klist_node *next;

	spin_lock(&i->i_klist->k_lock);

	if (last) {
		next = to_klist_node(last->n_node.next);
		if (!klist_dec_and_del(last))
			put = NULL;
	} else
		next = to_klist_node(i->i_klist->k_list.next);

	i->i_cur = NULL;
	while (next != to_klist_node(&i->i_klist->k_list)) {
		if (likely(!knode_dead(next))) {
			kref_get(&next->n_ref);
			i->i_cur = next;
			break;
		}
		next = to_klist_node(next->n_node.next);
	}

	spin_unlock(&i->i_klist->k_lock);

	if (put && last)
		put(last);
	return i->i_cur;
}
EXPORT_SYMBOL_GPL(klist_next);