lib/idr.c

   1 #include <linux/bitmap.h>
   2 #include <linux/bug.h>
   3 #include <linux/export.h>
   4 #include <linux/idr.h>
   5 #include <linux/slab.h>
   6 #include <linux/spinlock.h>
   7
   8 DEFINE_PER_CPU(struct ida_bitmap *, ida_bitmap);
   9 static DEFINE_SPINLOCK(simple_ida_lock);
  10
  11 /**
  12  * idr_alloc_u32() - Allocate an ID.
  13  * @idr: IDR handle.
  14  * @ptr: Pointer to be associated with the new ID.
  15  * @nextid: Pointer to an ID.
  16  * @max: The maximum ID to allocate (inclusive).
  17  * @gfp: Memory allocation flags.
  18  *
  19  * Allocates an unused ID in the range specified by @nextid and @max.
  20  * Note that @max is inclusive whereas the @end parameter to idr_alloc()
  21  * is exclusive.  The new ID is assigned to @nextid before the pointer
  22  * is inserted into the IDR, so if @nextid points into the object pointed
  23  * to by @ptr, a concurrent lookup will not find an uninitialised ID.
  24  *
  25  * The caller should provide their own locking to ensure that two
  26  * concurrent modifications to the IDR are not possible.  Read-only
  27  * accesses to the IDR may be done under the RCU read lock or may
  28  * exclude simultaneous writers.
  29  *
  30  * Return: 0 if an ID was allocated, -ENOMEM if memory allocation failed,
  31  * or -ENOSPC if no free IDs could be found.  If an error occurred,
  32  * @nextid is unchanged.
  33  */
  34 int idr_alloc_u32(struct idr *idr, void *ptr, u32 *nextid,
  35                         unsigned long max, gfp_t gfp)
  36 {
  37         struct radix_tree_iter iter;
  38         void __rcu **slot;
  39         int base = idr->idr_base;
  40         int id = *nextid;
  41
  42         if (WARN_ON_ONCE(radix_tree_is_internal_node(ptr)))
  43                 return -EINVAL;
  44         if (WARN_ON_ONCE(!(idr->idr_rt.gfp_mask & ROOT_IS_IDR)))
  45                 idr->idr_rt.gfp_mask |= IDR_RT_MARKER;
  46
  47         id = (id < base) ? 0 : id - base;
  48         radix_tree_iter_init(&iter, id);
  49         slot = idr_get_free(&idr->idr_rt, &iter, gfp, max - base);
  50         if (IS_ERR(slot))
  51                 return PTR_ERR(slot);
  52
  53         *nextid = iter.index + base;
  54         /* there is a memory barrier inside radix_tree_iter_replace() */
  55         radix_tree_iter_replace(&idr->idr_rt, &iter, slot, ptr);
  56         radix_tree_iter_tag_clear(&idr->idr_rt, &iter, IDR_FREE);
  57
  58         return 0;
  59 }
  60 EXPORT_SYMBOL_GPL(idr_alloc_u32);
  61
  62 /**
  63  * idr_alloc() - Allocate an ID.
  64  * @idr: IDR handle.
  65  * @ptr: Pointer to be associated with the new ID.
  66  * @start: The minimum ID (inclusive).
  67  * @end: The maximum ID (exclusive).
  68  * @gfp: Memory allocation flags.
  69  *
  70  * Allocates an unused ID in the range specified by @start and @end.  If
  71  * @end is <= 0, it is treated as one larger than %INT_MAX.  This allows
  72  * callers to use @start + N as @end as long as N is within integer range.
  73  *
  74  * The caller should provide their own locking to ensure that two
  75  * concurrent modifications to the IDR are not possible.  Read-only
  76  * accesses to the IDR may be done under the RCU read lock or may
  77  * exclude simultaneous writers.
  78  *
  79  * Return: The newly allocated ID, -ENOMEM if memory allocation failed,
  80  * or -ENOSPC if no free IDs could be found.
  81  */
  82 int idr_alloc(struct idr *idr, void *ptr, int start, int end, gfp_t gfp)
  83 {
  84         u32 id = start;
  85         int ret;
  86
  87         if (WARN_ON_ONCE(start < 0))
  88                 return -EINVAL;
  89
  90         ret = idr_alloc_u32(idr, ptr, &id, end > 0 ? end - 1 : INT_MAX, gfp);
  91         if (ret)
  92                 return ret;
  93
  94         return id;
  95 }
  96 EXPORT_SYMBOL_GPL(idr_alloc);
  97
  98 /**
  99  * idr_alloc_cyclic() - Allocate an ID cyclically.
 100  * @idr: IDR handle.
 101  * @ptr: Pointer to be associated with the new ID.
 102  * @start: The minimum ID (inclusive).
 103  * @end: The maximum ID (exclusive).
 104  * @gfp: Memory allocation flags.
 105  *
 106  * Allocates an unused ID in the range specified by @nextid and @end.  If
 107  * @end is <= 0, it is treated as one larger than %INT_MAX.  This allows
 108  * callers to use @start + N as @end as long as N is within integer range.
 109  * The search for an unused ID will start at the last ID allocated and will
 110  * wrap around to @start if no free IDs are found before reaching @end.
 111  *
 112  * The caller should provide their own locking to ensure that two
 113  * concurrent modifications to the IDR are not possible.  Read-only
 114  * accesses to the IDR may be done under the RCU read lock or may
 115  * exclude simultaneous writers.
 116  *
 117  * Return: The newly allocated ID, -ENOMEM if memory allocation failed,
 118  * or -ENOSPC if no free IDs could be found.
 119  */
 120 int idr_alloc_cyclic(struct idr *idr, void *ptr, int start, int end, gfp_t gfp)
 121 {
 122         u32 id = idr->idr_next;
 123         int err, max = end > 0 ? end - 1 : INT_MAX;
 124
 125         if ((int)id < start)
 126                 id = start;
 127
 128         err = idr_alloc_u32(idr, ptr, &id, max, gfp);
 129         if ((err == -ENOSPC) && (id > start)) {
 130                 id = start;
 131                 err = idr_alloc_u32(idr, ptr, &id, max, gfp);
 132         }
 133         if (err)
 134                 return err;
 135
 136         idr->idr_next = id + 1;
 137         return id;
 138 }
 139 EXPORT_SYMBOL(idr_alloc_cyclic);
 140
 141 /**
 142  * idr_remove() - Remove an ID from the IDR.
 143  * @idr: IDR handle.
 144  * @id: Pointer ID.
 145  *
 146  * Removes this ID from the IDR.  If the ID was not previously in the IDR,
 147  * this function returns %NULL.
 148  *
 149  * Since this function modifies the IDR, the caller should provide their
 150  * own locking to ensure that concurrent modification of the same IDR is
 151  * not possible.
 152  *
 153  * Return: The pointer formerly associated with this ID.
 154  */
 155 void *idr_remove(struct idr *idr, unsigned long id)
 156 {
 157         return radix_tree_delete_item(&idr->idr_rt, id - idr->idr_base, NULL);
 158 }
 159 EXPORT_SYMBOL_GPL(idr_remove);
 160
 161 /**
 162  * idr_find() - Return pointer for given ID.
 163  * @idr: IDR handle.
 164  * @id: Pointer ID.
 165  *
 166  * Looks up the pointer associated with this ID.  A %NULL pointer may
 167  * indicate that @id is not allocated or that the %NULL pointer was
 168  * associated with this ID.
 169  *
 170  * This function can be called under rcu_read_lock(), given that the leaf
 171  * pointers lifetimes are correctly managed.
 172  *
 173  * Return: The pointer associated with this ID.
 174  */
 175 void *idr_find(const struct idr *idr, unsigned long id)
 176 {
 177         return radix_tree_lookup(&idr->idr_rt, id - idr->idr_base);
 178 }
 179 EXPORT_SYMBOL_GPL(idr_find);
 180
 181 /**
 182  * idr_for_each() - Iterate through all stored pointers.
 183  * @idr: IDR handle.
 184  * @fn: Function to be called for each pointer.
 185  * @data: Data passed to callback function.
 186  *
 187  * The callback function will be called for each entry in @idr, passing
 188  * the ID, the entry and @data.
 189  *
 190  * If @fn returns anything other than %0, the iteration stops and that
 191  * value is returned from this function.
 192  *
 193  * idr_for_each() can be called concurrently with idr_alloc() and
 194  * idr_remove() if protected by RCU.  Newly added entries may not be
 195  * seen and deleted entries may be seen, but adding and removing entries
 196  * will not cause other entries to be skipped, nor spurious ones to be seen.
 197  */
 198 int idr_for_each(const struct idr *idr,
 199                 int (*fn)(int id, void *p, void *data), void *data)
 200 {
 201         struct radix_tree_iter iter;
 202         void __rcu **slot;
 203         int base = idr->idr_base;
 204
 205         radix_tree_for_each_slot(slot, &idr->idr_rt, &iter, 0) {
 206                 int ret;
 207
 208                 if (WARN_ON_ONCE(iter.index > INT_MAX))
 209                         break;
 210                 ret = fn(iter.index + base, rcu_dereference_raw(*slot), data);
 211                 if (ret)
 212                         return ret;
 213         }
 214
 215         return 0;
 216 }
 217 EXPORT_SYMBOL(idr_for_each);
 218
 219 /**
 220  * idr_get_next() - Find next populated entry.
 221  * @idr: IDR handle.
 222  * @nextid: Pointer to an ID.
 223  *
 224  * Returns the next populated entry in the tree with an ID greater than
 225  * or equal to the value pointed to by @nextid.  On exit, @nextid is updated
 226  * to the ID of the found value.  To use in a loop, the value pointed to by
 227  * nextid must be incremented by the user.
 228  */
 229 void *idr_get_next(struct idr *idr, int *nextid)
 230 {
 231         struct radix_tree_iter iter;
 232         void __rcu **slot;
 233         int base = idr->idr_base;
 234         int id = *nextid;
 235
 236         id = (id < base) ? 0 : id - base;
 237         slot = radix_tree_iter_find(&idr->idr_rt, &iter, id);
 238         if (!slot)
 239                 return NULL;
 240         id = iter.index + base;
 241
 242         if (WARN_ON_ONCE(id > INT_MAX))
 243                 return NULL;
 244
 245         *nextid = id;
 246         return rcu_dereference_raw(*slot);
 247 }
 248 EXPORT_SYMBOL(idr_get_next);
 249
 250 /**
 251  * idr_get_next_ul() - Find next populated entry.
 252  * @idr: IDR handle.
 253  * @nextid: Pointer to an ID.
 254  *
 255  * Returns the next populated entry in the tree with an ID greater than
 256  * or equal to the value pointed to by @nextid.  On exit, @nextid is updated
 257  * to the ID of the found value.  To use in a loop, the value pointed to by
 258  * nextid must be incremented by the user.
 259  */
 260 void *idr_get_next_ul(struct idr *idr, unsigned long *nextid)
 261 {
 262         struct radix_tree_iter iter;
 263         void __rcu **slot;
 264         unsigned long base = idr->idr_base;
 265         unsigned long id = *nextid;
 266
 267         id = (id < base) ? 0 : id - base;
 268         slot = radix_tree_iter_find(&idr->idr_rt, &iter, id);
 269         if (!slot)
 270                 return NULL;
 271
 272         *nextid = iter.index + base;
 273         return rcu_dereference_raw(*slot);
 274 }
 275 EXPORT_SYMBOL(idr_get_next_ul);
 276
 277 /**
 278  * idr_replace() - replace pointer for given ID.
 279  * @idr: IDR handle.
 280  * @ptr: New pointer to associate with the ID.
 281  * @id: ID to change.
 282  *
 283  * Replace the pointer registered with an ID and return the old value.
 284  * This function can be called under the RCU read lock concurrently with
 285  * idr_alloc() and idr_remove() (as long as the ID being removed is not
 286  * the one being replaced!).
 287  *
 288  * Returns: the old value on success.  %-ENOENT indicates that @id was not
 289  * found.  %-EINVAL indicates that @ptr was not valid.
 290  */
 291 void *idr_replace(struct idr *idr, void *ptr, unsigned long id)
 292 {
 293         struct radix_tree_node *node;
 294         void __rcu **slot = NULL;
 295         void *entry;
 296
 297         if (WARN_ON_ONCE(radix_tree_is_internal_node(ptr)))
 298                 return ERR_PTR(-EINVAL);
 299         id -= idr->idr_base;
 300
 301         entry = __radix_tree_lookup(&idr->idr_rt, id, &node, &slot);
 302         if (!slot || radix_tree_tag_get(&idr->idr_rt, id, IDR_FREE))
 303                 return ERR_PTR(-ENOENT);
 304
 305         __radix_tree_replace(&idr->idr_rt, node, slot, ptr, NULL);
 306
 307         return entry;
 308 }
 309 EXPORT_SYMBOL(idr_replace);
 310
 311 /**
 312  * DOC: IDA description
 313  *
 314  * The IDA is an ID allocator which does not provide the ability to
 315  * associate an ID with a pointer.  As such, it only needs to store one
 316  * bit per ID, and so is more space efficient than an IDR.  To use an IDA,
 317  * define it using DEFINE_IDA() (or embed a &struct ida in a data structure,
 318  * then initialise it using ida_init()).  To allocate a new ID, call
 319  * ida_simple_get().  To free an ID, call ida_simple_remove().
 320  *
 321  * If you have more complex locking requirements, use a loop around
 322  * ida_pre_get() and ida_get_new() to allocate a new ID.  Then use
 323  * ida_remove() to free an ID.  You must make sure that ida_get_new() and
 324  * ida_remove() cannot be called at the same time as each other for the
 325  * same IDA.
 326  *
 327  * You can also use ida_get_new_above() if you need an ID to be allocated
 328  * above a particular number.  ida_destroy() can be used to dispose of an
 329  * IDA without needing to free the individual IDs in it.  You can use
 330  * ida_is_empty() to find out whether the IDA has any IDs currently allocated.
 331  *
 332  * IDs are currently limited to the range [0-INT_MAX].  If this is an awkward
 333  * limitation, it should be quite straightforward to raise the maximum.
 334  */
 335
 336 /*
 337  * Developer's notes:
 338  *
 339  * The IDA uses the functionality provided by the IDR & radix tree to store
 340  * bitmaps in each entry.  The IDR_FREE tag means there is at least one bit
 341  * free, unlike the IDR where it means at least one entry is free.
 342  *
 343  * I considered telling the radix tree that each slot is an order-10 node
 344  * and storing the bit numbers in the radix tree, but the radix tree can't
 345  * allow a single multiorder entry at index 0, which would significantly
 346  * increase memory consumption for the IDA.  So instead we divide the index
 347  * by the number of bits in the leaf bitmap before doing a radix tree lookup.
 348  *
 349  * As an optimisation, if there are only a few low bits set in any given
 350  * leaf, instead of allocating a 128-byte bitmap, we use the 'exceptional
 351  * entry' functionality of the radix tree to store BITS_PER_LONG - 2 bits
 352  * directly in the entry.  By being really tricksy, we could store
 353  * BITS_PER_LONG - 1 bits, but there're diminishing returns after optimising
 354  * for 0-3 allocated IDs.
 355  *
 356  * We allow the radix tree 'exceptional' count to get out of date.  Nothing
 357  * in the IDA nor the radix tree code checks it.  If it becomes important
 358  * to maintain an accurate exceptional count, switch the rcu_assign_pointer()
 359  * calls to radix_tree_iter_replace() which will correct the exceptional
 360  * count.
 361  *
 362  * The IDA always requires a lock to alloc/free.  If we add a 'test_bit'
 363  * equivalent, it will still need locking.  Going to RCU lookup would require
 364  * using RCU to free bitmaps, and that's not trivial without embedding an
 365  * RCU head in the bitmap, which adds a 2-pointer overhead to each 128-byte
 366  * bitmap, which is excessive.
 367  */
 368
 369 #define IDA_MAX (0x80000000U / IDA_BITMAP_BITS - 1)
 370
 371 /**
 372  * ida_get_new_above - allocate new ID above or equal to a start id
 373  * @ida: ida handle
 374  * @start: id to start search at
 375  * @id: pointer to the allocated handle
 376  *
 377  * Allocate new ID above or equal to @start.  It should be called
 378  * with any required locks to ensure that concurrent calls to
 379  * ida_get_new_above() / ida_get_new() / ida_remove() are not allowed.
 380  * Consider using ida_simple_get() if you do not have complex locking
 381  * requirements.
 382  *
 383  * If memory is required, it will return %-EAGAIN, you should unlock
 384  * and go back to the ida_pre_get() call.  If the ida is full, it will
 385  * return %-ENOSPC.  On success, it will return 0.
 386  *
 387  * @id returns a value in the range @start ... %0x7fffffff.
 388  */
 389 int ida_get_new_above(struct ida *ida, int start, int *id)
 390 {
 391         struct radix_tree_root *root = &ida->ida_rt;
 392         void __rcu **slot;
 393         struct radix_tree_iter iter;
 394         struct ida_bitmap *bitmap;
 395         unsigned long index;
 396         unsigned bit, ebit;
 397         int new;
 398
 399         index = start / IDA_BITMAP_BITS;
 400         bit = start % IDA_BITMAP_BITS;
 401         ebit = bit + RADIX_TREE_EXCEPTIONAL_SHIFT;
 402
 403         slot = radix_tree_iter_init(&iter, index);
 404         for (;;) {
 405                 if (slot)
 406                         slot = radix_tree_next_slot(slot, &iter,
 407                                                 RADIX_TREE_ITER_TAGGED);
 408                 if (!slot) {
 409                         slot = idr_get_free(root, &iter, GFP_NOWAIT, IDA_MAX);
 410                         if (IS_ERR(slot)) {
 411                                 if (slot == ERR_PTR(-ENOMEM))
 412                                         return -EAGAIN;
 413                                 return PTR_ERR(slot);
 414                         }
 415                 }
 416                 if (iter.index > index) {
 417                         bit = 0;
 418                         ebit = RADIX_TREE_EXCEPTIONAL_SHIFT;
 419                 }
 420                 new = iter.index * IDA_BITMAP_BITS;
 421                 bitmap = rcu_dereference_raw(*slot);
 422                 if (radix_tree_exception(bitmap)) {
 423                         unsigned long tmp = (unsigned long)bitmap;
 424                         ebit = find_next_zero_bit(&tmp, BITS_PER_LONG, ebit);
 425                         if (ebit < BITS_PER_LONG) {
 426                                 tmp |= 1UL << ebit;
 427                                 rcu_assign_pointer(*slot, (void *)tmp);
 428                                 *id = new + ebit - RADIX_TREE_EXCEPTIONAL_SHIFT;
 429                                 return 0;
 430                         }
 431                         bitmap = this_cpu_xchg(ida_bitmap, NULL);
 432                         if (!bitmap)
 433                                 return -EAGAIN;
 434                         memset(bitmap, 0, sizeof(*bitmap));
 435                         bitmap->bitmap[0] = tmp >> RADIX_TREE_EXCEPTIONAL_SHIFT;
 436                         rcu_assign_pointer(*slot, bitmap);
 437                 }
 438
 439                 if (bitmap) {
 440                         bit = find_next_zero_bit(bitmap->bitmap,
 441                                                         IDA_BITMAP_BITS, bit);
 442                         new += bit;
 443                         if (new < 0)
 444                                 return -ENOSPC;
 445                         if (bit == IDA_BITMAP_BITS)
 446                                 continue;
 447
 448                         __set_bit(bit, bitmap->bitmap);
 449                         if (bitmap_full(bitmap->bitmap, IDA_BITMAP_BITS))
 450                                 radix_tree_iter_tag_clear(root, &iter,
 451                                                                 IDR_FREE);
 452                 } else {
 453                         new += bit;
 454                         if (new < 0)
 455                                 return -ENOSPC;
 456                         if (ebit < BITS_PER_LONG) {
 457                                 bitmap = (void *)((1UL << ebit) |
 458                                                 RADIX_TREE_EXCEPTIONAL_ENTRY);
 459                                 radix_tree_iter_replace(root, &iter, slot,
 460                                                 bitmap);
 461                                 *id = new;
 462                                 return 0;
 463                         }
 464                         bitmap = this_cpu_xchg(ida_bitmap, NULL);
 465                         if (!bitmap)
 466                                 return -EAGAIN;
 467                         memset(bitmap, 0, sizeof(*bitmap));
 468                         __set_bit(bit, bitmap->bitmap);
 469                         radix_tree_iter_replace(root, &iter, slot, bitmap);
 470                 }
 471
 472                 *id = new;
 473                 return 0;
 474         }
 475 }
 476 EXPORT_SYMBOL(ida_get_new_above);
 477
 478 /**
 479  * ida_remove - Free the given ID
 480  * @ida: ida handle
 481  * @id: ID to free
 482  *
 483  * This function should not be called at the same time as ida_get_new_above().
 484  */
 485 void ida_remove(struct ida *ida, int id)
 486 {
 487         unsigned long index = id / IDA_BITMAP_BITS;
 488         unsigned offset = id % IDA_BITMAP_BITS;
 489         struct ida_bitmap *bitmap;
 490         unsigned long *btmp;
 491         struct radix_tree_iter iter;
 492         void __rcu **slot;
 493
 494         slot = radix_tree_iter_lookup(&ida->ida_rt, &iter, index);
 495         if (!slot)
 496                 goto err;
 497
 498         bitmap = rcu_dereference_raw(*slot);
 499         if (radix_tree_exception(bitmap)) {
 500                 btmp = (unsigned long *)slot;
 501                 offset += RADIX_TREE_EXCEPTIONAL_SHIFT;
 502                 if (offset >= BITS_PER_LONG)
 503                         goto err;
 504         } else {
 505                 btmp = bitmap->bitmap;
 506         }
 507         if (!test_bit(offset, btmp))
 508                 goto err;
 509
 510         __clear_bit(offset, btmp);
 511         radix_tree_iter_tag_set(&ida->ida_rt, &iter, IDR_FREE);
 512         if (radix_tree_exception(bitmap)) {
 513                 if (rcu_dereference_raw(*slot) ==
 514                                         (void *)RADIX_TREE_EXCEPTIONAL_ENTRY)
 515                         radix_tree_iter_delete(&ida->ida_rt, &iter, slot);
 516         } else if (bitmap_empty(btmp, IDA_BITMAP_BITS)) {
 517                 kfree(bitmap);
 518                 radix_tree_iter_delete(&ida->ida_rt, &iter, slot);
 519         }
 520         return;
 521  err:
 522         WARN(1, "ida_remove called for id=%d which is not allocated.\n", id);
 523 }
 524 EXPORT_SYMBOL(ida_remove);
 525
 526 /**
 527  * ida_destroy - Free the contents of an ida
 528  * @ida: ida handle
 529  *
 530  * Calling this function releases all resources associated with an IDA.  When
 531  * this call returns, the IDA is empty and can be reused or freed.  The caller
 532  * should not allow ida_remove() or ida_get_new_above() to be called at the
 533  * same time.
 534  */
 535 void ida_destroy(struct ida *ida)
 536 {
 537         struct radix_tree_iter iter;
 538         void __rcu **slot;
 539
 540         radix_tree_for_each_slot(slot, &ida->ida_rt, &iter, 0) {
 541                 struct ida_bitmap *bitmap = rcu_dereference_raw(*slot);
 542                 if (!radix_tree_exception(bitmap))
 543                         kfree(bitmap);
 544                 radix_tree_iter_delete(&ida->ida_rt, &iter, slot);
 545         }
 546 }
 547 EXPORT_SYMBOL(ida_destroy);
 548
 549 /**
 550  * ida_simple_get - get a new id.
 551  * @ida: the (initialized) ida.
 552  * @start: the minimum id (inclusive, < 0x8000000)
 553  * @end: the maximum id (exclusive, < 0x8000000 or 0)
 554  * @gfp_mask: memory allocation flags
 555  *
 556  * Allocates an id in the range start <= id < end, or returns -ENOSPC.
 557  * On memory allocation failure, returns -ENOMEM.
 558  *
 559  * Compared to ida_get_new_above() this function does its own locking, and
 560  * should be used unless there are special requirements.
 561  *
 562  * Use ida_simple_remove() to get rid of an id.
 563  */
 564 int ida_simple_get(struct ida *ida, unsigned int start, unsigned int end,
 565                    gfp_t gfp_mask)
 566 {
 567         int ret, id;
 568         unsigned int max;
 569         unsigned long flags;
 570
 571         BUG_ON((int)start < 0);
 572         BUG_ON((int)end < 0);
 573
 574         if (end == 0)
 575                 max = 0x80000000;
 576         else {
 577                 BUG_ON(end < start);
 578                 max = end - 1;
 579         }
 580
 581 again:
 582         if (!ida_pre_get(ida, gfp_mask))
 583                 return -ENOMEM;
 584
 585         spin_lock_irqsave(&simple_ida_lock, flags);
 586         ret = ida_get_new_above(ida, start, &id);
 587         if (!ret) {
 588                 if (id > max) {
 589                         ida_remove(ida, id);
 590                         ret = -ENOSPC;
 591                 } else {
 592                         ret = id;
 593                 }
 594         }
 595         spin_unlock_irqrestore(&simple_ida_lock, flags);
 596
 597         if (unlikely(ret == -EAGAIN))
 598                 goto again;
 599
 600         return ret;
 601 }
 602 EXPORT_SYMBOL(ida_simple_get);
 603
 604 /**
 605  * ida_simple_remove - remove an allocated id.
 606  * @ida: the (initialized) ida.
 607  * @id: the id returned by ida_simple_get.
 608  *
 609  * Use to release an id allocated with ida_simple_get().
 610  *
 611  * Compared to ida_remove() this function does its own locking, and should be
 612  * used unless there are special requirements.
 613  */
 614 void ida_simple_remove(struct ida *ida, unsigned int id)
 615 {
 616         unsigned long flags;
 617
 618         BUG_ON((int)id < 0);
 619         spin_lock_irqsave(&simple_ida_lock, flags);
 620         ida_remove(ida, id);
 621         spin_unlock_irqrestore(&simple_ida_lock, flags);
 622 }
 623 EXPORT_SYMBOL(ida_simple_remove);