include/linux/rculist.h

   1 #ifndef _LINUX_RCULIST_H
   2 #define _LINUX_RCULIST_H
   3
   4 #ifdef __KERNEL__
   5
   6 /*
   7  * RCU-protected list version
   8  */
   9 #include <linux/list.h>
  10 #include <linux/rcupdate.h>
  11
  12 /*
  13  * Insert a new entry between two known consecutive entries.
  14  *
  15  * This is only for internal list manipulation where we know
  16  * the prev/next entries already!
  17  */
  18 static inline void __list_add_rcu(struct list_head *new,
  19                 struct list_head *prev, struct list_head *next)
  20 {
  21         new->next = next;
  22         new->prev = prev;
  23         rcu_assign_pointer(prev->next, new);
  24         next->prev = new;
  25 }
  26
  27 /**
  28  * list_add_rcu - add a new entry to rcu-protected list
  29  * @new: new entry to be added
  30  * @head: list head to add it after
  31  *
  32  * Insert a new entry after the specified head.
  33  * This is good for implementing stacks.
  34  *
  35  * The caller must take whatever precautions are necessary
  36  * (such as holding appropriate locks) to avoid racing
  37  * with another list-mutation primitive, such as list_add_rcu()
  38  * or list_del_rcu(), running on this same list.
  39  * However, it is perfectly legal to run concurrently with
  40  * the _rcu list-traversal primitives, such as
  41  * list_for_each_entry_rcu().
  42  */
  43 static inline void list_add_rcu(struct list_head *new, struct list_head *head)
  44 {
  45         __list_add_rcu(new, head, head->next);
  46 }
  47
  48 /**
  49  * list_add_tail_rcu - add a new entry to rcu-protected list
  50  * @new: new entry to be added
  51  * @head: list head to add it before
  52  *
  53  * Insert a new entry before the specified head.
  54  * This is useful for implementing queues.
  55  *
  56  * The caller must take whatever precautions are necessary
  57  * (such as holding appropriate locks) to avoid racing
  58  * with another list-mutation primitive, such as list_add_tail_rcu()
  59  * or list_del_rcu(), running on this same list.
  60  * However, it is perfectly legal to run concurrently with
  61  * the _rcu list-traversal primitives, such as
  62  * list_for_each_entry_rcu().
  63  */
  64 static inline void list_add_tail_rcu(struct list_head *new,
  65                                         struct list_head *head)
  66 {
  67         __list_add_rcu(new, head->prev, head);
  68 }
  69
  70 /**
  71  * list_del_rcu - deletes entry from list without re-initialization
  72  * @entry: the element to delete from the list.
  73  *
  74  * Note: list_empty() on entry does not return true after this,
  75  * the entry is in an undefined state. It is useful for RCU based
  76  * lockfree traversal.
  77  *
  78  * In particular, it means that we can not poison the forward
  79  * pointers that may still be used for walking the list.
  80  *
  81  * The caller must take whatever precautions are necessary
  82  * (such as holding appropriate locks) to avoid racing
  83  * with another list-mutation primitive, such as list_del_rcu()
  84  * or list_add_rcu(), running on this same list.
  85  * However, it is perfectly legal to run concurrently with
  86  * the _rcu list-traversal primitives, such as
  87  * list_for_each_entry_rcu().
  88  *
  89  * Note that the caller is not permitted to immediately free
  90  * the newly deleted entry.  Instead, either synchronize_rcu()
  91  * or call_rcu() must be used to defer freeing until an RCU
  92  * grace period has elapsed.
  93  */
  94 static inline void list_del_rcu(struct list_head *entry)
  95 {
  96         __list_del(entry->prev, entry->next);
  97         entry->prev = LIST_POISON2;
  98 }
  99
 100 /**
 101  * hlist_del_init_rcu - deletes entry from hash list with re-initialization
 102  * @n: the element to delete from the hash list.
 103  *
 104  * Note: list_unhashed() on the node return true after this. It is
 105  * useful for RCU based read lockfree traversal if the writer side
 106  * must know if the list entry is still hashed or already unhashed.
 107  *
 108  * In particular, it means that we can not poison the forward pointers
 109  * that may still be used for walking the hash list and we can only
 110  * zero the pprev pointer so list_unhashed() will return true after
 111  * this.
 112  *
 113  * The caller must take whatever precautions are necessary (such as
 114  * holding appropriate locks) to avoid racing with another
 115  * list-mutation primitive, such as hlist_add_head_rcu() or
 116  * hlist_del_rcu(), running on this same list.  However, it is
 117  * perfectly legal to run concurrently with the _rcu list-traversal
 118  * primitives, such as hlist_for_each_entry_rcu().
 119  */
 120 static inline void hlist_del_init_rcu(struct hlist_node *n)
 121 {
 122         if (!hlist_unhashed(n)) {
 123                 __hlist_del(n);
 124                 n->pprev = NULL;
 125         }
 126 }
 127
 128 /**
 129  * list_replace_rcu - replace old entry by new one
 130  * @old : the element to be replaced
 131  * @new : the new element to insert
 132  *
 133  * The @old entry will be replaced with the @new entry atomically.
 134  * Note: @old should not be empty.
 135  */
 136 static inline void list_replace_rcu(struct list_head *old,
 137                                 struct list_head *new)
 138 {
 139         new->next = old->next;
 140         new->prev = old->prev;
 141         rcu_assign_pointer(new->prev->next, new);
 142         new->next->prev = new;
 143         old->prev = LIST_POISON2;
 144 }
 145
 146 /**
 147  * list_splice_init_rcu - splice an RCU-protected list into an existing list.
 148  * @list:       the RCU-protected list to splice
 149  * @head:       the place in the list to splice the first list into
 150  * @sync:       function to sync: synchronize_rcu(), synchronize_sched(), ...
 151  *
 152  * @head can be RCU-read traversed concurrently with this function.
 153  *
 154  * Note that this function blocks.
 155  *
 156  * Important note: the caller must take whatever action is necessary to
 157  *      prevent any other updates to @head.  In principle, it is possible
 158  *      to modify the list as soon as sync() begins execution.
 159  *      If this sort of thing becomes necessary, an alternative version
 160  *      based on call_rcu() could be created.  But only if -really-
 161  *      needed -- there is no shortage of RCU API members.
 162  */
 163 static inline void list_splice_init_rcu(struct list_head *list,
 164                                         struct list_head *head,
 165                                         void (*sync)(void))
 166 {
 167         struct list_head *first = list->next;
 168         struct list_head *last = list->prev;
 169         struct list_head *at = head->next;
 170
 171         if (list_empty(head))
 172                 return;
 173
 174         /* "first" and "last" tracking list, so initialize it. */
 175
 176         INIT_LIST_HEAD(list);
 177
 178         /*
 179          * At this point, the list body still points to the source list.
 180          * Wait for any readers to finish using the list before splicing
 181          * the list body into the new list.  Any new readers will see
 182          * an empty list.
 183          */
 184
 185         sync();
 186
 187         /*
 188          * Readers are finished with the source list, so perform splice.
 189          * The order is important if the new list is global and accessible
 190          * to concurrent RCU readers.  Note that RCU readers are not
 191          * permitted to traverse the prev pointers without excluding
 192          * this function.
 193          */
 194
 195         last->next = at;
 196         rcu_assign_pointer(head->next, first);
 197         first->prev = head;
 198         at->prev = last;
 199 }
 200
 201 #define __list_for_each_rcu(pos, head) \
 202         for (pos = rcu_dereference((head)->next); \
 203                 pos != (head); \
 204                 pos = rcu_dereference(pos->next))
 205
 206 /**
 207  * list_for_each_entry_rcu      -       iterate over rcu list of given type
 208  * @pos:        the type * to use as a loop cursor.
 209  * @head:       the head for your list.
 210  * @member:     the name of the list_struct within the struct.
 211  *
 212  * This list-traversal primitive may safely run concurrently with
 213  * the _rcu list-mutation primitives such as list_add_rcu()
 214  * as long as the traversal is guarded by rcu_read_lock().
 215  */
 216 #define list_for_each_entry_rcu(pos, head, member) \
 217         for (pos = list_entry(rcu_dereference((head)->next), typeof(*pos), member); \
 218                 prefetch(pos->member.next), &pos->member != (head); \
 219                 pos = list_entry(rcu_dereference(pos->member.next), typeof(*pos), member))
 220
 221
 222 /**
 223  * list_for_each_continue_rcu
 224  * @pos:        the &struct list_head to use as a loop cursor.
 225  * @head:       the head for your list.
 226  *
 227  * Iterate over an rcu-protected list, continuing after current point.
 228  *
 229  * This list-traversal primitive may safely run concurrently with
 230  * the _rcu list-mutation primitives such as list_add_rcu()
 231  * as long as the traversal is guarded by rcu_read_lock().
 232  */
 233 #define list_for_each_continue_rcu(pos, head) \
 234         for ((pos) = rcu_dereference((pos)->next); \
 235                 prefetch((pos)->next), (pos) != (head); \
 236                 (pos) = rcu_dereference((pos)->next))
 237
 238 /**
 239  * hlist_del_rcu - deletes entry from hash list without re-initialization
 240  * @n: the element to delete from the hash list.
 241  *
 242  * Note: list_unhashed() on entry does not return true after this,
 243  * the entry is in an undefined state. It is useful for RCU based
 244  * lockfree traversal.
 245  *
 246  * In particular, it means that we can not poison the forward
 247  * pointers that may still be used for walking the hash list.
 248  *
 249  * The caller must take whatever precautions are necessary
 250  * (such as holding appropriate locks) to avoid racing
 251  * with another list-mutation primitive, such as hlist_add_head_rcu()
 252  * or hlist_del_rcu(), running on this same list.
 253  * However, it is perfectly legal to run concurrently with
 254  * the _rcu list-traversal primitives, such as
 255  * hlist_for_each_entry().
 256  */
 257 static inline void hlist_del_rcu(struct hlist_node *n)
 258 {
 259         __hlist_del(n);
 260         n->pprev = LIST_POISON2;
 261 }
 262
 263 /**
 264  * hlist_replace_rcu - replace old entry by new one
 265  * @old : the element to be replaced
 266  * @new : the new element to insert
 267  *
 268  * The @old entry will be replaced with the @new entry atomically.
 269  */
 270 static inline void hlist_replace_rcu(struct hlist_node *old,
 271                                         struct hlist_node *new)
 272 {
 273         struct hlist_node *next = old->next;
 274
 275         new->next = next;
 276         new->pprev = old->pprev;
 277         rcu_assign_pointer(*new->pprev, new);
 278         if (next)
 279                 new->next->pprev = &new->next;
 280         old->pprev = LIST_POISON2;
 281 }
 282
 283 /**
 284  * hlist_add_head_rcu
 285  * @n: the element to add to the hash list.
 286  * @h: the list to add to.
 287  *
 288  * Description:
 289  * Adds the specified element to the specified hlist,
 290  * while permitting racing traversals.
 291  *
 292  * The caller must take whatever precautions are necessary
 293  * (such as holding appropriate locks) to avoid racing
 294  * with another list-mutation primitive, such as hlist_add_head_rcu()
 295  * or hlist_del_rcu(), running on this same list.
 296  * However, it is perfectly legal to run concurrently with
 297  * the _rcu list-traversal primitives, such as
 298  * hlist_for_each_entry_rcu(), used to prevent memory-consistency
 299  * problems on Alpha CPUs.  Regardless of the type of CPU, the
 300  * list-traversal primitive must be guarded by rcu_read_lock().
 301  */
 302 static inline void hlist_add_head_rcu(struct hlist_node *n,
 303                                         struct hlist_head *h)
 304 {
 305         struct hlist_node *first = h->first;
 306
 307         n->next = first;
 308         n->pprev = &h->first;
 309         rcu_assign_pointer(h->first, n);
 310         if (first)
 311                 first->pprev = &n->next;
 312 }
 313
 314 /**
 315  * hlist_add_before_rcu
 316  * @n: the new element to add to the hash list.
 317  * @next: the existing element to add the new element before.
 318  *
 319  * Description:
 320  * Adds the specified element to the specified hlist
 321  * before the specified node while permitting racing traversals.
 322  *
 323  * The caller must take whatever precautions are necessary
 324  * (such as holding appropriate locks) to avoid racing
 325  * with another list-mutation primitive, such as hlist_add_head_rcu()
 326  * or hlist_del_rcu(), running on this same list.
 327  * However, it is perfectly legal to run concurrently with
 328  * the _rcu list-traversal primitives, such as
 329  * hlist_for_each_entry_rcu(), used to prevent memory-consistency
 330  * problems on Alpha CPUs.
 331  */
 332 static inline void hlist_add_before_rcu(struct hlist_node *n,
 333                                         struct hlist_node *next)
 334 {
 335         n->pprev = next->pprev;
 336         n->next = next;
 337         rcu_assign_pointer(*(n->pprev), n);
 338         next->pprev = &n->next;
 339 }
 340
 341 /**
 342  * hlist_add_after_rcu
 343  * @prev: the existing element to add the new element after.
 344  * @n: the new element to add to the hash list.
 345  *
 346  * Description:
 347  * Adds the specified element to the specified hlist
 348  * after the specified node while permitting racing traversals.
 349  *
 350  * The caller must take whatever precautions are necessary
 351  * (such as holding appropriate locks) to avoid racing
 352  * with another list-mutation primitive, such as hlist_add_head_rcu()
 353  * or hlist_del_rcu(), running on this same list.
 354  * However, it is perfectly legal to run concurrently with
 355  * the _rcu list-traversal primitives, such as
 356  * hlist_for_each_entry_rcu(), used to prevent memory-consistency
 357  * problems on Alpha CPUs.
 358  */
 359 static inline void hlist_add_after_rcu(struct hlist_node *prev,
 360                                        struct hlist_node *n)
 361 {
 362         n->next = prev->next;
 363         n->pprev = &prev->next;
 364         rcu_assign_pointer(prev->next, n);
 365         if (n->next)
 366                 n->next->pprev = &n->next;
 367 }
 368
 369 /**
 370  * hlist_for_each_entry_rcu - iterate over rcu list of given type
 371  * @tpos:       the type * to use as a loop cursor.
 372  * @pos:        the &struct hlist_node to use as a loop cursor.
 373  * @head:       the head for your list.
 374  * @member:     the name of the hlist_node within the struct.
 375  *
 376  * This list-traversal primitive may safely run concurrently with
 377  * the _rcu list-mutation primitives such as hlist_add_head_rcu()
 378  * as long as the traversal is guarded by rcu_read_lock().
 379  */
 380 #define hlist_for_each_entry_rcu(tpos, pos, head, member)                \
 381         for (pos = rcu_dereference((head)->first);                       \
 382                 pos && ({ prefetch(pos->next); 1; }) &&                  \
 383                 ({ tpos = hlist_entry(pos, typeof(*tpos), member); 1; }); \
 384                 pos = rcu_dereference(pos->next))
 385
 386 #endif  /* __KERNEL__ */
 387 #endif