1 /* 2 * Copyright (C) 2001 Momchil Velikov 3 * Portions Copyright (C) 2001 Christoph Hellwig 4 * Copyright (C) 2006 Nick Piggin 5 * 6 * This program is free software; you can redistribute it and/or 7 * modify it under the terms of the GNU General Public License as 8 * published by the Free Software Foundation; either version 2, or (at 9 * your option) any later version. 10 * 11 * This program is distributed in the hope that it will be useful, but 12 * WITHOUT ANY WARRANTY; without even the implied warranty of 13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 14 * General Public License for more details. 15 * 16 * You should have received a copy of the GNU General Public License 17 * along with this program; if not, write to the Free Software 18 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. 19 */ 20 #ifndef _LINUX_RADIX_TREE_H 21 #define _LINUX_RADIX_TREE_H 22 23 #include <linux/preempt.h> 24 #include <linux/types.h> 25 #include <linux/kernel.h> 26 #include <linux/rcupdate.h> 27 28 /* 29 * An indirect pointer (root->rnode pointing to a radix_tree_node, rather 30 * than a data item) is signalled by the low bit set in the root->rnode 31 * pointer. 32 * 33 * In this case root->height is > 0, but the indirect pointer tests are 34 * needed for RCU lookups (because root->height is unreliable). The only 35 * time callers need worry about this is when doing a lookup_slot under 36 * RCU. 37 * 38 * Indirect pointer in fact is also used to tag the last pointer of a node 39 * when it is shrunk, before we rcu free the node. See shrink code for 40 * details. 41 */ 42 #define RADIX_TREE_INDIRECT_PTR 1 43 44 #define radix_tree_indirect_to_ptr(ptr) \ 45 radix_tree_indirect_to_ptr((void __force *)(ptr)) 46 47 static inline int radix_tree_is_indirect_ptr(void *ptr) 48 { 49 return (int)((unsigned long)ptr & RADIX_TREE_INDIRECT_PTR); 50 } 51 52 /*** radix-tree API starts here ***/ 53 54 #define RADIX_TREE_MAX_TAGS 3 55 56 /* root tags are stored in gfp_mask, shifted by __GFP_BITS_SHIFT */ 57 struct radix_tree_root { 58 unsigned int height; 59 gfp_t gfp_mask; 60 struct radix_tree_node __rcu *rnode; 61 }; 62 63 #define RADIX_TREE_INIT(mask) { \ 64 .height = 0, \ 65 .gfp_mask = (mask), \ 66 .rnode = NULL, \ 67 } 68 69 #define RADIX_TREE(name, mask) \ 70 struct radix_tree_root name = RADIX_TREE_INIT(mask) 71 72 #define INIT_RADIX_TREE(root, mask) \ 73 do { \ 74 (root)->height = 0; \ 75 (root)->gfp_mask = (mask); \ 76 (root)->rnode = NULL; \ 77 } while (0) 78 79 /** 80 * Radix-tree synchronization 81 * 82 * The radix-tree API requires that users provide all synchronisation (with 83 * specific exceptions, noted below). 84 * 85 * Synchronization of access to the data items being stored in the tree, and 86 * management of their lifetimes must be completely managed by API users. 87 * 88 * For API usage, in general, 89 * - any function _modifying_ the tree or tags (inserting or deleting 90 * items, setting or clearing tags) must exclude other modifications, and 91 * exclude any functions reading the tree. 92 * - any function _reading_ the tree or tags (looking up items or tags, 93 * gang lookups) must exclude modifications to the tree, but may occur 94 * concurrently with other readers. 95 * 96 * The notable exceptions to this rule are the following functions: 97 * radix_tree_lookup 98 * radix_tree_lookup_slot 99 * radix_tree_tag_get 100 * radix_tree_gang_lookup 101 * radix_tree_gang_lookup_slot 102 * radix_tree_gang_lookup_tag 103 * radix_tree_gang_lookup_tag_slot 104 * radix_tree_tagged 105 * 106 * The first 7 functions are able to be called locklessly, using RCU. The 107 * caller must ensure calls to these functions are made within rcu_read_lock() 108 * regions. Other readers (lock-free or otherwise) and modifications may be 109 * running concurrently. 110 * 111 * It is still required that the caller manage the synchronization and lifetimes 112 * of the items. So if RCU lock-free lookups are used, typically this would mean 113 * that the items have their own locks, or are amenable to lock-free access; and 114 * that the items are freed by RCU (or only freed after having been deleted from 115 * the radix tree *and* a synchronize_rcu() grace period). 116 * 117 * (Note, rcu_assign_pointer and rcu_dereference are not needed to control 118 * access to data items when inserting into or looking up from the radix tree) 119 * 120 * Note that the value returned by radix_tree_tag_get() may not be relied upon 121 * if only the RCU read lock is held. Functions to set/clear tags and to 122 * delete nodes running concurrently with it may affect its result such that 123 * two consecutive reads in the same locked section may return different 124 * values. If reliability is required, modification functions must also be 125 * excluded from concurrency. 126 * 127 * radix_tree_tagged is able to be called without locking or RCU. 128 */ 129 130 /** 131 * radix_tree_deref_slot - dereference a slot 132 * @pslot: pointer to slot, returned by radix_tree_lookup_slot 133 * Returns: item that was stored in that slot with any direct pointer flag 134 * removed. 135 * 136 * For use with radix_tree_lookup_slot(). Caller must hold tree at least read 137 * locked across slot lookup and dereference. Not required if write lock is 138 * held (ie. items cannot be concurrently inserted). 139 * 140 * radix_tree_deref_retry must be used to confirm validity of the pointer if 141 * only the read lock is held. 142 */ 143 static inline void *radix_tree_deref_slot(void **pslot) 144 { 145 return rcu_dereference(*pslot); 146 } 147 148 /** 149 * radix_tree_deref_slot_protected - dereference a slot without RCU lock but with tree lock held 150 * @pslot: pointer to slot, returned by radix_tree_lookup_slot 151 * Returns: item that was stored in that slot with any direct pointer flag 152 * removed. 153 * 154 * Similar to radix_tree_deref_slot but only used during migration when a pages 155 * mapping is being moved. The caller does not hold the RCU read lock but it 156 * must hold the tree lock to prevent parallel updates. 157 */ 158 static inline void *radix_tree_deref_slot_protected(void **pslot, 159 spinlock_t *treelock) 160 { 161 return rcu_dereference_protected(*pslot, lockdep_is_held(treelock)); 162 } 163 164 /** 165 * radix_tree_deref_retry - check radix_tree_deref_slot 166 * @arg: pointer returned by radix_tree_deref_slot 167 * Returns: 0 if retry is not required, otherwise retry is required 168 * 169 * radix_tree_deref_retry must be used with radix_tree_deref_slot. 170 */ 171 static inline int radix_tree_deref_retry(void *arg) 172 { 173 return unlikely((unsigned long)arg & RADIX_TREE_INDIRECT_PTR); 174 } 175 176 /** 177 * radix_tree_replace_slot - replace item in a slot 178 * @pslot: pointer to slot, returned by radix_tree_lookup_slot 179 * @item: new item to store in the slot. 180 * 181 * For use with radix_tree_lookup_slot(). Caller must hold tree write locked 182 * across slot lookup and replacement. 183 */ 184 static inline void radix_tree_replace_slot(void **pslot, void *item) 185 { 186 BUG_ON(radix_tree_is_indirect_ptr(item)); 187 rcu_assign_pointer(*pslot, item); 188 } 189 190 int radix_tree_insert(struct radix_tree_root *, unsigned long, void *); 191 void *radix_tree_lookup(struct radix_tree_root *, unsigned long); 192 void **radix_tree_lookup_slot(struct radix_tree_root *, unsigned long); 193 void *radix_tree_delete(struct radix_tree_root *, unsigned long); 194 unsigned int 195 radix_tree_gang_lookup(struct radix_tree_root *root, void **results, 196 unsigned long first_index, unsigned int max_items); 197 unsigned int 198 radix_tree_gang_lookup_slot(struct radix_tree_root *root, void ***results, 199 unsigned long first_index, unsigned int max_items); 200 unsigned long radix_tree_next_hole(struct radix_tree_root *root, 201 unsigned long index, unsigned long max_scan); 202 unsigned long radix_tree_prev_hole(struct radix_tree_root *root, 203 unsigned long index, unsigned long max_scan); 204 int radix_tree_preload(gfp_t gfp_mask); 205 void radix_tree_init(void); 206 void *radix_tree_tag_set(struct radix_tree_root *root, 207 unsigned long index, unsigned int tag); 208 void *radix_tree_tag_clear(struct radix_tree_root *root, 209 unsigned long index, unsigned int tag); 210 int radix_tree_tag_get(struct radix_tree_root *root, 211 unsigned long index, unsigned int tag); 212 unsigned int 213 radix_tree_gang_lookup_tag(struct radix_tree_root *root, void **results, 214 unsigned long first_index, unsigned int max_items, 215 unsigned int tag); 216 unsigned int 217 radix_tree_gang_lookup_tag_slot(struct radix_tree_root *root, void ***results, 218 unsigned long first_index, unsigned int max_items, 219 unsigned int tag); 220 unsigned long radix_tree_range_tag_if_tagged(struct radix_tree_root *root, 221 unsigned long *first_indexp, unsigned long last_index, 222 unsigned long nr_to_tag, 223 unsigned int fromtag, unsigned int totag); 224 int radix_tree_tagged(struct radix_tree_root *root, unsigned int tag); 225 226 static inline void radix_tree_preload_end(void) 227 { 228 preempt_enable(); 229 } 230 231 #endif /* _LINUX_RADIX_TREE_H */ 232