lib/rculist.h

   1 /*
   2  * Copyright (c) 2008, 2009, 2010, 2011, 2013, 2014 Nicira, Inc.
   3  *
   4  * Licensed under the Apache License, Version 2.0 (the "License");
   5  * you may not use this file except in compliance with the License.
   6  * You may obtain a copy of the License at:
   7  *
   8  *     http://www.apache.org/licenses/LICENSE-2.0
   9  *
  10  * Unless required by applicable law or agreed to in writing, software
  11  * distributed under the License is distributed on an "AS IS" BASIS,
  12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  13  * See the License for the specific language governing permissions and
  14  * limitations under the License.
  15  */
  16 #ifndef RCULIST_H
  17 #define RCULIST_H 1
  18
  19 /* A single writer multiple RCU-reader doubly linked list.
  20  *
  21  * RCU readers may iterate over the list at the same time as a writer is
  22  * modifying the list.  Multiple writers can be supported by use of mutual
  23  * exclusion, but rculist does not provide that, as the user of rculist
  24  * typically does that already.
  25  *
  26  * To be RCU-friendly, the struct rculist instances must be freed via
  27  * ovsrcu_postpone().
  28  *
  29  * The API is almost the same as for struct list, with the following exeptions:
  30  *
  31  * - The 'prev' pointer may not be accessed by the user.
  32  * - The 'next' pointer should be accessed via rculist_next() by readers, and
  33  *   rculist_next_protected() by the writer.
  34  * - No rculist_moved(): due to the memory management limitation stated above,
  35  *   rculist instances may not be reallocated, as realloc may instantly free
  36  *   the old memory.
  37  * - rculist_front() returns a const pointer to accommodate for an RCU reader.
  38  * - rculist_splice_hidden(): Spliced elements may not have been visible to
  39  *   RCU readers before the operation.
  40  * - rculist_poison(): Immediately poisons the 'prev' pointer, and schedules
  41  *   ovsrcu_postpone() to poison the 'next' pointer.  This issues a memory
  42  *   write operation to the list element, hopefully crashing the program if
  43  *   the list node was freed or re-used too early.
  44  *
  45  * The following functions are variations of the struct list functions with
  46  * similar names, but are now restricted to the writer use:
  47  *
  48  * - rculist_back_protected()
  49  * - rculist_is_short_protected()
  50  * - rculist_is_singleton_protected()
  51  */
  52
  53 #include <stdbool.h>
  54 #include <stddef.h>
  55 #include "ovs-rcu.h"
  56 #include "util.h"
  57
  58 /* A non-existing mutex to make it more difficult for an user to accidentally
  59  * keep using the 'prev' pointer.  This may be helpful when porting code from
  60  * struct list to rculist. */
  61 extern struct ovs_mutex rculist_fake_mutex;
  62
  63 /* Doubly linked list head or element. */
  64 struct rculist {
  65     /* Previous list element. */
  66     struct rculist *prev OVS_GUARDED_BY(rculist_fake_mutex);
  67
  68     /* Next list element. */
  69     OVSRCU_TYPE(struct rculist *) next;
  70 };
  71
  72 /* Easier access to 'next' member. */
  73 static inline const struct rculist *rculist_next(const struct rculist *);
  74 static inline struct rculist *rculist_next_protected(const struct rculist *);
  75
  76 /* List initialization. */
  77 #define RCULIST_INITIALIZER(LIST) { LIST, OVSRCU_INITIALIZER(LIST) }
  78
  79 static inline void rculist_init(struct rculist *list);
  80 static inline void rculist_poison(struct rculist *elem);
  81
  82 /* List insertion. */
  83 static inline void rculist_insert(struct rculist *list, struct rculist *elem);
  84 static inline void rculist_splice_hidden(struct rculist *before,
  85                                          struct rculist *first,
  86                                          struct rculist *last);
  87 static inline void rculist_push_front(struct rculist *list,
  88                                       struct rculist *elem);
  89 static inline void rculist_push_back(struct rculist *list,
  90                                      struct rculist *elem);
  91 static inline void rculist_replace(struct rculist *replacement,
  92                                    struct rculist *replaced);
  93 static inline void rculist_move(struct rculist *dst, struct rculist *src);
  94
  95 /* List removal. */
  96 static inline struct rculist *rculist_remove(struct rculist *elem);
  97 static inline struct rculist *rculist_pop_front(struct rculist *list);
  98 static inline struct rculist *rculist_pop_back(struct rculist *list);
  99
 100 /* List elements. */
 101 static inline const struct rculist *rculist_front(const struct rculist *);
 102 static inline struct rculist *rculist_back_protected(const struct rculist *);
 103
 104 /* List properties. */
 105 static inline size_t rculist_size(const struct rculist *);
 106 static inline bool rculist_is_empty(const struct rculist *);
 107 static inline bool rculist_is_singleton_protected(const struct rculist *);
 108 static inline bool rculist_is_short_protected(const struct rculist *);
 109
 110 \f
 111 /* Inline implementations. */
 112
 113 static inline const struct rculist *
 114 rculist_next(const struct rculist *list)
 115 {
 116     return ovsrcu_get(struct rculist *, &list->next);
 117 }
 118
 119 static inline struct rculist *
 120 rculist_next_protected(const struct rculist *list)
 121
 122 {
 123     return ovsrcu_get_protected(struct rculist *, &list->next);
 124 }
 125
 126 static inline void
 127 rculist_init(struct rculist *list)
 128     OVS_NO_THREAD_SAFETY_ANALYSIS
 129 {
 130     list->prev = list;
 131     ovsrcu_init(&list->next, list);
 132 }
 133
 134 #define RCULIST_POISON (struct rculist *)(UINTPTR_MAX / 0xf * 0xc)
 135
 136 void rculist_poison__(struct rculist *list);
 137
 138 /* Initializes 'list' with pointers that will (probably) cause segfaults if
 139  * dereferenced and, better yet, show up clearly in a debugger. */
 140 static inline void
 141 rculist_poison(struct rculist *list)
 142     OVS_NO_THREAD_SAFETY_ANALYSIS
 143 {
 144     list->prev = RCULIST_POISON;
 145     ovsrcu_postpone(rculist_poison__, list);
 146 }
 147
 148 /* rculist insertion. */
 149 static inline void
 150 rculist_insert(struct rculist *before, struct rculist *elem)
 151     OVS_NO_THREAD_SAFETY_ANALYSIS
 152 {
 153     elem->prev = before->prev;
 154     ovsrcu_set_hidden(&elem->next, before);
 155     ovsrcu_set(&before->prev->next, elem);
 156     before->prev = elem;
 157 }
 158
 159 /* Removes elements 'first' though 'last' (exclusive) from their current list,
 160  * which may NOT be visible to any other threads (== be hidden from them),
 161  * then inserts them just before 'before'. */
 162 static inline void
 163 rculist_splice_hidden(struct rculist *before, struct rculist *first,
 164                       struct rculist *last)
 165     OVS_NO_THREAD_SAFETY_ANALYSIS
 166 {
 167     struct rculist *last_next;
 168
 169     if (first == last) {
 170         return;
 171     }
 172     last = last->prev;
 173
 174     /* Cleanly remove 'first'...'last' from its current list. */
 175     last_next = rculist_next_protected(last);
 176     last_next->prev = first->prev;
 177     ovsrcu_set_hidden(&first->prev->next, last_next);
 178
 179     /* Splice 'first'...'last' into new list. */
 180     first->prev = before->prev;
 181     ovsrcu_set(&last->next, before);
 182     ovsrcu_set(&before->prev->next, first);
 183     before->prev = last;
 184 }
 185
 186 /* Inserts 'elem' at the beginning of 'list', so that it becomes the front in
 187  * 'list'. */
 188 static inline void
 189 rculist_push_front(struct rculist *list, struct rculist *elem)
 190 {
 191     rculist_insert(rculist_next_protected(list), elem);
 192 }
 193
 194 /* Inserts 'elem' at the end of 'list', so that it becomes the back in
 195  * 'list'. */
 196 static inline void
 197 rculist_push_back(struct rculist *list, struct rculist *elem)
 198 {
 199     rculist_insert(list, elem);
 200 }
 201
 202 /* Puts 'element' in the position currently occupied by 'position'.
 203  *
 204  * Afterward, 'position' is not linked to from the list any more, but still
 205  * links to the nodes in the list, and may still be referenced by other threads
 206  * until all other threads quiesce.  The replaced node ('position') may not be
 207  * re-inserted, re-initialized, or deleted until after all other threads have
 208  * quiesced (use ovsrcu_postpone). */
 209 static inline void
 210 rculist_replace(struct rculist *element, struct rculist *position)
 211     OVS_NO_THREAD_SAFETY_ANALYSIS
 212 {
 213     struct rculist *position_next = rculist_next_protected(position);
 214
 215     ovsrcu_set_hidden(&element->next, position_next);
 216     position_next->prev = element;
 217     element->prev = position->prev;
 218     ovsrcu_set(&element->prev->next, element);
 219
 220 #ifndef NDEBUG
 221     rculist_poison(position); /* XXX: Some overhead due to ovsrcu_postpone() */
 222 #endif
 223 }
 224
 225 /* Initializes 'dst' with the contents of 'src', compensating for moving it
 226  * around in memory.  The effect is that, if 'src' was the head of a list, now
 227  * 'dst' is the head of a list containing the same elements.
 228  *
 229  * Memory for 'src' must be kept around until the next RCU quiescent period.
 230  * rculist cannot be simply reallocated, so there is no rculist_moved(). */
 231 static inline void
 232 rculist_move(struct rculist *dst, struct rculist *src)
 233     OVS_NO_THREAD_SAFETY_ANALYSIS
 234 {
 235     if (!rculist_is_empty(src)) {
 236         struct rculist *src_next = rculist_next_protected(src);
 237
 238         dst->prev = src->prev;
 239         ovsrcu_set_hidden(&dst->next, src_next);
 240
 241         src_next->prev = dst;
 242         ovsrcu_set(&src->prev->next, dst);
 243     } else {
 244         rculist_init(dst);
 245     }
 246
 247 #ifndef NDEBUG
 248     rculist_poison(src); /* XXX: Some overhead due to ovsrcu_postpone() */
 249 #endif
 250 }
 251
 252 /* Removes 'elem' from its list and returns the element that followed it.
 253  * Has no effect when 'elem' is initialized, but not in a list.
 254  * Undefined behavior if 'elem' is not initialized.
 255  *
 256  * Afterward, 'elem' is not linked to from the list any more, but still links
 257  * to the nodes in the list, and may still be referenced by other threads until
 258  * all other threads quiesce.  The removed node ('elem') may not be
 259  * re-inserted, re-initialized, or deleted until after all other threads have
 260  * quiesced (use ovsrcu_postpone).
 261  */
 262 static inline struct rculist *
 263 rculist_remove(struct rculist *elem)
 264     OVS_NO_THREAD_SAFETY_ANALYSIS
 265 {
 266     struct rculist *elem_next = rculist_next_protected(elem);
 267
 268     elem_next->prev = elem->prev;
 269     ovsrcu_set(&elem->prev->next, elem_next);
 270
 271 #ifndef NDEBUG
 272     rculist_poison(elem); /* XXX: Some overhead due to ovsrcu_postpone() */
 273 #endif
 274     return elem_next;
 275 }
 276
 277 /* Removes the front element from 'list' and returns it.  Undefined behavior if
 278  * 'list' is empty before removal.
 279  *
 280  * Afterward, teh returned former first node is not linked to from the list any
 281  * more, but still links to the nodes in the list, and may still be referenced
 282  * by other threads until all other threads quiesce.  The returned node may not
 283  * be re-inserted, re-initialized, or deleted until after all other threads
 284  * have quiesced (use ovsrcu_postpone). */
 285 static inline struct rculist *
 286 rculist_pop_front(struct rculist *list)
 287     OVS_NO_THREAD_SAFETY_ANALYSIS
 288 {
 289     struct rculist *front = rculist_next_protected(list);
 290     rculist_remove(front);
 291     return front;
 292 }
 293
 294 /* Removes the back element from 'list' and returns it.
 295  * Undefined behavior if 'list' is empty before removal.
 296  *
 297  * Afterward, teh returned former last node is not linked to from the list any
 298  * more, but still links to the nodes in the list, and may still be referenced
 299  * by other threads until all other threads quiesce.  The returned node may not
 300  * be re-inserted, re-initialized, or deleted until after all other threads
 301  * have quiesced (use ovsrcu_postpone). */
 302 static inline struct rculist *
 303 rculist_pop_back(struct rculist *list)
 304     OVS_NO_THREAD_SAFETY_ANALYSIS
 305 {
 306     struct rculist *back = list->prev;
 307     rculist_remove(back);
 308     return back;
 309 }
 310
 311 /* Returns the front element in 'list_'.
 312  * Undefined behavior if 'list_' is empty. */
 313 static inline const struct rculist *
 314 rculist_front(const struct rculist *list)
 315 {
 316     ovs_assert(!rculist_is_empty(list));
 317
 318     return rculist_next(list);
 319 }
 320
 321 /* Returns the back element in 'list_'.
 322  * Returns the 'list_' itself, if 'list_' is empty. */
 323 static inline struct rculist *
 324 rculist_back_protected(const struct rculist *list)
 325     OVS_NO_THREAD_SAFETY_ANALYSIS
 326 {
 327     return CONST_CAST(struct rculist *, list)->prev;
 328 }
 329
 330 /* Returns the number of elements in 'list'.
 331  * Runs in O(n) in the number of elements. */
 332 static inline size_t
 333 rculist_size(const struct rculist *list)
 334 {
 335     const struct rculist *e;
 336     size_t cnt = 0;
 337
 338     for (e = rculist_next(list); e != list; e = rculist_next(e)) {
 339         cnt++;
 340     }
 341     return cnt;
 342 }
 343
 344 /* Returns true if 'list' is empty, false otherwise. */
 345 static inline bool
 346 rculist_is_empty(const struct rculist *list)
 347 {
 348     return rculist_next(list) == list;
 349 }
 350
 351 /* Returns true if 'list' has 0 or 1 elements, false otherwise. */
 352 static inline bool
 353 rculist_is_short_protected(const struct rculist *list)
 354     OVS_NO_THREAD_SAFETY_ANALYSIS
 355 {
 356     return rculist_next_protected(list) == list->prev;
 357 }
 358
 359 /* Returns true if 'list' has exactly 1 element, false otherwise. */
 360 static inline bool
 361 rculist_is_singleton_protected(const struct rculist *list)
 362     OVS_NO_THREAD_SAFETY_ANALYSIS
 363 {
 364     const struct rculist *list_next = rculist_next_protected(list);
 365
 366     return list_next == list->prev && list_next != list;
 367 }
 368
 369 #define RCULIST_FOR_EACH(ITER, MEMBER, RCULIST)                         \
 370     for (INIT_CONTAINER(ITER, rculist_next(RCULIST), MEMBER);           \
 371          &(ITER)->MEMBER != (RCULIST);                                  \
 372          ASSIGN_CONTAINER(ITER, rculist_next(&(ITER)->MEMBER), MEMBER))
 373 #define RCULIST_FOR_EACH_CONTINUE(ITER, MEMBER, RCULIST)                \
 374     for (ASSIGN_CONTAINER(ITER, rculist_next(&(ITER)->MEMBER), MEMBER); \
 375          &(ITER)->MEMBER != (RCULIST);                                  \
 376          ASSIGN_CONTAINER(ITER, rculist_next(&(ITER)->MEMBER), MEMBER))
 377
 378 #define RCULIST_FOR_EACH_REVERSE_PROTECTED(ITER, MEMBER, RCULIST)       \
 379     for (INIT_CONTAINER(ITER, (RCULIST)->prev, MEMBER);                 \
 380          &(ITER)->MEMBER != (RCULIST);                                  \
 381          ASSIGN_CONTAINER(ITER, (ITER)->MEMBER.prev, MEMBER))
 382 #define RCULIST_FOR_EACH_REVERSE_PROTECTED_CONTINUE(ITER, MEMBER, RCULIST) \
 383     for (ASSIGN_CONTAINER(ITER, (ITER)->MEMBER.prev, MEMBER);           \
 384          &(ITER)->MEMBER != (RCULIST);                                  \
 385          ASSIGN_CONTAINER(ITER, (ITER)->MEMBER.prev, MEMBER))
 386
 387 #define RCULIST_FOR_EACH_PROTECTED(ITER, MEMBER, RCULIST)               \
 388     for (INIT_CONTAINER(ITER, rculist_next_protected(RCULIST), MEMBER); \
 389          &(ITER)->MEMBER != (RCULIST);                                  \
 390          ASSIGN_CONTAINER(ITER, rculist_next_protected(&(ITER)->MEMBER), \
 391                           MEMBER))
 392
 393 #define RCULIST_FOR_EACH_SAFE_PROTECTED(ITER, NEXT, MEMBER, RCULIST)    \
 394     for (INIT_CONTAINER(ITER, rculist_next_protected(RCULIST), MEMBER); \
 395          (&(ITER)->MEMBER != (RCULIST)                                  \
 396           ? INIT_CONTAINER(NEXT, rculist_next_protected(&(ITER)->MEMBER), \
 397                            MEMBER), 1 : 0);                             \
 398          (ITER) = (NEXT))
 399
 400 #endif /* rculist.h */