lib/sbitmap.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * Copyright (C) 2016 Facebook
   4  * Copyright (C) 2013-2014 Jens Axboe
   5  */
   6
   7 #include <linux/sched.h>
   8 #include <linux/random.h>
   9 #include <linux/sbitmap.h>
  10 #include <linux/seq_file.h>
  11
  12 /*
  13  * See if we have deferred clears that we can batch move
  14  */
  15 static inline bool sbitmap_deferred_clear(struct sbitmap_word *map)
  16 {
  17         unsigned long mask;
  18
  19         if (!READ_ONCE(map->cleared))
  20                 return false;
  21
  22         /*
  23          * First get a stable cleared mask, setting the old mask to 0.
  24          */
  25         mask = xchg(&map->cleared, 0);
  26
  27         /*
  28          * Now clear the masked bits in our free word
  29          */
  30         atomic_long_andnot(mask, (atomic_long_t *)&map->word);
  31         BUILD_BUG_ON(sizeof(atomic_long_t) != sizeof(map->word));
  32         return true;
  33 }
  34
  35 int sbitmap_init_node(struct sbitmap *sb, unsigned int depth, int shift,
  36                       gfp_t flags, int node)
  37 {
  38         unsigned int bits_per_word;
  39         unsigned int i;
  40
  41         if (shift < 0) {
  42                 shift = ilog2(BITS_PER_LONG);
  43                 /*
  44                  * If the bitmap is small, shrink the number of bits per word so
  45                  * we spread over a few cachelines, at least. If less than 4
  46                  * bits, just forget about it, it's not going to work optimally
  47                  * anyway.
  48                  */
  49                 if (depth >= 4) {
  50                         while ((4U << shift) > depth)
  51                                 shift--;
  52                 }
  53         }
  54         bits_per_word = 1U << shift;
  55         if (bits_per_word > BITS_PER_LONG)
  56                 return -EINVAL;
  57
  58         sb->shift = shift;
  59         sb->depth = depth;
  60         sb->map_nr = DIV_ROUND_UP(sb->depth, bits_per_word);
  61
  62         if (depth == 0) {
  63                 sb->map = NULL;
  64                 return 0;
  65         }
  66
  67         sb->map = kcalloc_node(sb->map_nr, sizeof(*sb->map), flags, node);
  68         if (!sb->map)
  69                 return -ENOMEM;
  70
  71         for (i = 0; i < sb->map_nr; i++) {
  72                 sb->map[i].depth = min(depth, bits_per_word);
  73                 depth -= sb->map[i].depth;
  74         }
  75         return 0;
  76 }
  77 EXPORT_SYMBOL_GPL(sbitmap_init_node);
  78
  79 void sbitmap_resize(struct sbitmap *sb, unsigned int depth)
  80 {
  81         unsigned int bits_per_word = 1U << sb->shift;
  82         unsigned int i;
  83
  84         for (i = 0; i < sb->map_nr; i++)
  85                 sbitmap_deferred_clear(&sb->map[i]);
  86
  87         sb->depth = depth;
  88         sb->map_nr = DIV_ROUND_UP(sb->depth, bits_per_word);
  89
  90         for (i = 0; i < sb->map_nr; i++) {
  91                 sb->map[i].depth = min(depth, bits_per_word);
  92                 depth -= sb->map[i].depth;
  93         }
  94 }
  95 EXPORT_SYMBOL_GPL(sbitmap_resize);
  96
  97 static int __sbitmap_get_word(unsigned long *word, unsigned long depth,
  98                               unsigned int hint, bool wrap)
  99 {
 100         int nr;
 101
 102         /* don't wrap if starting from 0 */
 103         wrap = wrap && hint;
 104
 105         while (1) {
 106                 nr = find_next_zero_bit(word, depth, hint);
 107                 if (unlikely(nr >= depth)) {
 108                         /*
 109                          * We started with an offset, and we didn't reset the
 110                          * offset to 0 in a failure case, so start from 0 to
 111                          * exhaust the map.
 112                          */
 113                         if (hint && wrap) {
 114                                 hint = 0;
 115                                 continue;
 116                         }
 117                         return -1;
 118                 }
 119
 120                 if (!test_and_set_bit_lock(nr, word))
 121                         break;
 122
 123                 hint = nr + 1;
 124                 if (hint >= depth - 1)
 125                         hint = 0;
 126         }
 127
 128         return nr;
 129 }
 130
 131 static int sbitmap_find_bit_in_index(struct sbitmap *sb, int index,
 132                                      unsigned int alloc_hint, bool round_robin)
 133 {
 134         struct sbitmap_word *map = &sb->map[index];
 135         int nr;
 136
 137         do {
 138                 nr = __sbitmap_get_word(&map->word, map->depth, alloc_hint,
 139                                         !round_robin);
 140                 if (nr != -1)
 141                         break;
 142                 if (!sbitmap_deferred_clear(map))
 143                         break;
 144         } while (1);
 145
 146         return nr;
 147 }
 148
 149 int sbitmap_get(struct sbitmap *sb, unsigned int alloc_hint, bool round_robin)
 150 {
 151         unsigned int i, index;
 152         int nr = -1;
 153
 154         index = SB_NR_TO_INDEX(sb, alloc_hint);
 155
 156         /*
 157          * Unless we're doing round robin tag allocation, just use the
 158          * alloc_hint to find the right word index. No point in looping
 159          * twice in find_next_zero_bit() for that case.
 160          */
 161         if (round_robin)
 162                 alloc_hint = SB_NR_TO_BIT(sb, alloc_hint);
 163         else
 164                 alloc_hint = 0;
 165
 166         for (i = 0; i < sb->map_nr; i++) {
 167                 nr = sbitmap_find_bit_in_index(sb, index, alloc_hint,
 168                                                 round_robin);
 169                 if (nr != -1) {
 170                         nr += index << sb->shift;
 171                         break;
 172                 }
 173
 174                 /* Jump to next index. */
 175                 alloc_hint = 0;
 176                 if (++index >= sb->map_nr)
 177                         index = 0;
 178         }
 179
 180         return nr;
 181 }
 182 EXPORT_SYMBOL_GPL(sbitmap_get);
 183
 184 int sbitmap_get_shallow(struct sbitmap *sb, unsigned int alloc_hint,
 185                         unsigned long shallow_depth)
 186 {
 187         unsigned int i, index;
 188         int nr = -1;
 189
 190         index = SB_NR_TO_INDEX(sb, alloc_hint);
 191
 192         for (i = 0; i < sb->map_nr; i++) {
 193 again:
 194                 nr = __sbitmap_get_word(&sb->map[index].word,
 195                                         min(sb->map[index].depth, shallow_depth),
 196                                         SB_NR_TO_BIT(sb, alloc_hint), true);
 197                 if (nr != -1) {
 198                         nr += index << sb->shift;
 199                         break;
 200                 }
 201
 202                 if (sbitmap_deferred_clear(&sb->map[index]))
 203                         goto again;
 204
 205                 /* Jump to next index. */
 206                 index++;
 207                 alloc_hint = index << sb->shift;
 208
 209                 if (index >= sb->map_nr) {
 210                         index = 0;
 211                         alloc_hint = 0;
 212                 }
 213         }
 214
 215         return nr;
 216 }
 217 EXPORT_SYMBOL_GPL(sbitmap_get_shallow);
 218
 219 bool sbitmap_any_bit_set(const struct sbitmap *sb)
 220 {
 221         unsigned int i;
 222
 223         for (i = 0; i < sb->map_nr; i++) {
 224                 if (sb->map[i].word & ~sb->map[i].cleared)
 225                         return true;
 226         }
 227         return false;
 228 }
 229 EXPORT_SYMBOL_GPL(sbitmap_any_bit_set);
 230
 231 static unsigned int __sbitmap_weight(const struct sbitmap *sb, bool set)
 232 {
 233         unsigned int i, weight = 0;
 234
 235         for (i = 0; i < sb->map_nr; i++) {
 236                 const struct sbitmap_word *word = &sb->map[i];
 237
 238                 if (set)
 239                         weight += bitmap_weight(&word->word, word->depth);
 240                 else
 241                         weight += bitmap_weight(&word->cleared, word->depth);
 242         }
 243         return weight;
 244 }
 245
 246 static unsigned int sbitmap_weight(const struct sbitmap *sb)
 247 {
 248         return __sbitmap_weight(sb, true);
 249 }
 250
 251 static unsigned int sbitmap_cleared(const struct sbitmap *sb)
 252 {
 253         return __sbitmap_weight(sb, false);
 254 }
 255
 256 void sbitmap_show(struct sbitmap *sb, struct seq_file *m)
 257 {
 258         seq_printf(m, "depth=%u\n", sb->depth);
 259         seq_printf(m, "busy=%u\n", sbitmap_weight(sb) - sbitmap_cleared(sb));
 260         seq_printf(m, "cleared=%u\n", sbitmap_cleared(sb));
 261         seq_printf(m, "bits_per_word=%u\n", 1U << sb->shift);
 262         seq_printf(m, "map_nr=%u\n", sb->map_nr);
 263 }
 264 EXPORT_SYMBOL_GPL(sbitmap_show);
 265
 266 static inline void emit_byte(struct seq_file *m, unsigned int offset, u8 byte)
 267 {
 268         if ((offset & 0xf) == 0) {
 269                 if (offset != 0)
 270                         seq_putc(m, '\n');
 271                 seq_printf(m, "%08x:", offset);
 272         }
 273         if ((offset & 0x1) == 0)
 274                 seq_putc(m, ' ');
 275         seq_printf(m, "%02x", byte);
 276 }
 277
 278 void sbitmap_bitmap_show(struct sbitmap *sb, struct seq_file *m)
 279 {
 280         u8 byte = 0;
 281         unsigned int byte_bits = 0;
 282         unsigned int offset = 0;
 283         int i;
 284
 285         for (i = 0; i < sb->map_nr; i++) {
 286                 unsigned long word = READ_ONCE(sb->map[i].word);
 287                 unsigned long cleared = READ_ONCE(sb->map[i].cleared);
 288                 unsigned int word_bits = READ_ONCE(sb->map[i].depth);
 289
 290                 word &= ~cleared;
 291
 292                 while (word_bits > 0) {
 293                         unsigned int bits = min(8 - byte_bits, word_bits);
 294
 295                         byte |= (word & (BIT(bits) - 1)) << byte_bits;
 296                         byte_bits += bits;
 297                         if (byte_bits == 8) {
 298                                 emit_byte(m, offset, byte);
 299                                 byte = 0;
 300                                 byte_bits = 0;
 301                                 offset++;
 302                         }
 303                         word >>= bits;
 304                         word_bits -= bits;
 305                 }
 306         }
 307         if (byte_bits) {
 308                 emit_byte(m, offset, byte);
 309                 offset++;
 310         }
 311         if (offset)
 312                 seq_putc(m, '\n');
 313 }
 314 EXPORT_SYMBOL_GPL(sbitmap_bitmap_show);
 315
 316 static unsigned int sbq_calc_wake_batch(struct sbitmap_queue *sbq,
 317                                         unsigned int depth)
 318 {
 319         unsigned int wake_batch;
 320         unsigned int shallow_depth;
 321
 322         /*
 323          * For each batch, we wake up one queue. We need to make sure that our
 324          * batch size is small enough that the full depth of the bitmap,
 325          * potentially limited by a shallow depth, is enough to wake up all of
 326          * the queues.
 327          *
 328          * Each full word of the bitmap has bits_per_word bits, and there might
 329          * be a partial word. There are depth / bits_per_word full words and
 330          * depth % bits_per_word bits left over. In bitwise arithmetic:
 331          *
 332          * bits_per_word = 1 << shift
 333          * depth / bits_per_word = depth >> shift
 334          * depth % bits_per_word = depth & ((1 << shift) - 1)
 335          *
 336          * Each word can be limited to sbq->min_shallow_depth bits.
 337          */
 338         shallow_depth = min(1U << sbq->sb.shift, sbq->min_shallow_depth);
 339         depth = ((depth >> sbq->sb.shift) * shallow_depth +
 340                  min(depth & ((1U << sbq->sb.shift) - 1), shallow_depth));
 341         wake_batch = clamp_t(unsigned int, depth / SBQ_WAIT_QUEUES, 1,
 342                              SBQ_WAKE_BATCH);
 343
 344         return wake_batch;
 345 }
 346
 347 int sbitmap_queue_init_node(struct sbitmap_queue *sbq, unsigned int depth,
 348                             int shift, bool round_robin, gfp_t flags, int node)
 349 {
 350         int ret;
 351         int i;
 352
 353         ret = sbitmap_init_node(&sbq->sb, depth, shift, flags, node);
 354         if (ret)
 355                 return ret;
 356
 357         sbq->alloc_hint = alloc_percpu_gfp(unsigned int, flags);
 358         if (!sbq->alloc_hint) {
 359                 sbitmap_free(&sbq->sb);
 360                 return -ENOMEM;
 361         }
 362
 363         if (depth && !round_robin) {
 364                 for_each_possible_cpu(i)
 365                         *per_cpu_ptr(sbq->alloc_hint, i) = prandom_u32() % depth;
 366         }
 367
 368         sbq->min_shallow_depth = UINT_MAX;
 369         sbq->wake_batch = sbq_calc_wake_batch(sbq, depth);
 370         atomic_set(&sbq->wake_index, 0);
 371         atomic_set(&sbq->ws_active, 0);
 372
 373         sbq->ws = kzalloc_node(SBQ_WAIT_QUEUES * sizeof(*sbq->ws), flags, node);
 374         if (!sbq->ws) {
 375                 free_percpu(sbq->alloc_hint);
 376                 sbitmap_free(&sbq->sb);
 377                 return -ENOMEM;
 378         }
 379
 380         for (i = 0; i < SBQ_WAIT_QUEUES; i++) {
 381                 init_waitqueue_head(&sbq->ws[i].wait);
 382                 atomic_set(&sbq->ws[i].wait_cnt, sbq->wake_batch);
 383         }
 384
 385         sbq->round_robin = round_robin;
 386         return 0;
 387 }
 388 EXPORT_SYMBOL_GPL(sbitmap_queue_init_node);
 389
 390 static void sbitmap_queue_update_wake_batch(struct sbitmap_queue *sbq,
 391                                             unsigned int depth)
 392 {
 393         unsigned int wake_batch = sbq_calc_wake_batch(sbq, depth);
 394         int i;
 395
 396         if (sbq->wake_batch != wake_batch) {
 397                 WRITE_ONCE(sbq->wake_batch, wake_batch);
 398                 /*
 399                  * Pairs with the memory barrier in sbitmap_queue_wake_up()
 400                  * to ensure that the batch size is updated before the wait
 401                  * counts.
 402                  */
 403                 smp_mb();
 404                 for (i = 0; i < SBQ_WAIT_QUEUES; i++)
 405                         atomic_set(&sbq->ws[i].wait_cnt, 1);
 406         }
 407 }
 408
 409 void sbitmap_queue_resize(struct sbitmap_queue *sbq, unsigned int depth)
 410 {
 411         sbitmap_queue_update_wake_batch(sbq, depth);
 412         sbitmap_resize(&sbq->sb, depth);
 413 }
 414 EXPORT_SYMBOL_GPL(sbitmap_queue_resize);
 415
 416 int __sbitmap_queue_get(struct sbitmap_queue *sbq)
 417 {
 418         unsigned int hint, depth;
 419         int nr;
 420
 421         hint = this_cpu_read(*sbq->alloc_hint);
 422         depth = READ_ONCE(sbq->sb.depth);
 423         if (unlikely(hint >= depth)) {
 424                 hint = depth ? prandom_u32() % depth : 0;
 425                 this_cpu_write(*sbq->alloc_hint, hint);
 426         }
 427         nr = sbitmap_get(&sbq->sb, hint, sbq->round_robin);
 428
 429         if (nr == -1) {
 430                 /* If the map is full, a hint won't do us much good. */
 431                 this_cpu_write(*sbq->alloc_hint, 0);
 432         } else if (nr == hint || unlikely(sbq->round_robin)) {
 433                 /* Only update the hint if we used it. */
 434                 hint = nr + 1;
 435                 if (hint >= depth - 1)
 436                         hint = 0;
 437                 this_cpu_write(*sbq->alloc_hint, hint);
 438         }
 439
 440         return nr;
 441 }
 442 EXPORT_SYMBOL_GPL(__sbitmap_queue_get);
 443
 444 int __sbitmap_queue_get_shallow(struct sbitmap_queue *sbq,
 445                                 unsigned int shallow_depth)
 446 {
 447         unsigned int hint, depth;
 448         int nr;
 449
 450         WARN_ON_ONCE(shallow_depth < sbq->min_shallow_depth);
 451
 452         hint = this_cpu_read(*sbq->alloc_hint);
 453         depth = READ_ONCE(sbq->sb.depth);
 454         if (unlikely(hint >= depth)) {
 455                 hint = depth ? prandom_u32() % depth : 0;
 456                 this_cpu_write(*sbq->alloc_hint, hint);
 457         }
 458         nr = sbitmap_get_shallow(&sbq->sb, hint, shallow_depth);
 459
 460         if (nr == -1) {
 461                 /* If the map is full, a hint won't do us much good. */
 462                 this_cpu_write(*sbq->alloc_hint, 0);
 463         } else if (nr == hint || unlikely(sbq->round_robin)) {
 464                 /* Only update the hint if we used it. */
 465                 hint = nr + 1;
 466                 if (hint >= depth - 1)
 467                         hint = 0;
 468                 this_cpu_write(*sbq->alloc_hint, hint);
 469         }
 470
 471         return nr;
 472 }
 473 EXPORT_SYMBOL_GPL(__sbitmap_queue_get_shallow);
 474
 475 void sbitmap_queue_min_shallow_depth(struct sbitmap_queue *sbq,
 476                                      unsigned int min_shallow_depth)
 477 {
 478         sbq->min_shallow_depth = min_shallow_depth;
 479         sbitmap_queue_update_wake_batch(sbq, sbq->sb.depth);
 480 }
 481 EXPORT_SYMBOL_GPL(sbitmap_queue_min_shallow_depth);
 482
 483 static struct sbq_wait_state *sbq_wake_ptr(struct sbitmap_queue *sbq)
 484 {
 485         int i, wake_index;
 486
 487         if (!atomic_read(&sbq->ws_active))
 488                 return NULL;
 489
 490         wake_index = atomic_read(&sbq->wake_index);
 491         for (i = 0; i < SBQ_WAIT_QUEUES; i++) {
 492                 struct sbq_wait_state *ws = &sbq->ws[wake_index];
 493
 494                 if (waitqueue_active(&ws->wait)) {
 495                         if (wake_index != atomic_read(&sbq->wake_index))
 496                                 atomic_set(&sbq->wake_index, wake_index);
 497                         return ws;
 498                 }
 499
 500                 wake_index = sbq_index_inc(wake_index);
 501         }
 502
 503         return NULL;
 504 }
 505
 506 static bool __sbq_wake_up(struct sbitmap_queue *sbq)
 507 {
 508         struct sbq_wait_state *ws;
 509         unsigned int wake_batch;
 510         int wait_cnt;
 511
 512         ws = sbq_wake_ptr(sbq);
 513         if (!ws)
 514                 return false;
 515
 516         wait_cnt = atomic_dec_return(&ws->wait_cnt);
 517         if (wait_cnt <= 0) {
 518                 int ret;
 519
 520                 wake_batch = READ_ONCE(sbq->wake_batch);
 521
 522                 /*
 523                  * Pairs with the memory barrier in sbitmap_queue_resize() to
 524                  * ensure that we see the batch size update before the wait
 525                  * count is reset.
 526                  */
 527                 smp_mb__before_atomic();
 528
 529                 /*
 530                  * For concurrent callers of this, the one that failed the
 531                  * atomic_cmpxhcg() race should call this function again
 532                  * to wakeup a new batch on a different 'ws'.
 533                  */
 534                 ret = atomic_cmpxchg(&ws->wait_cnt, wait_cnt, wake_batch);
 535                 if (ret == wait_cnt) {
 536                         sbq_index_atomic_inc(&sbq->wake_index);
 537                         wake_up_nr(&ws->wait, wake_batch);
 538                         return false;
 539                 }
 540
 541                 return true;
 542         }
 543
 544         return false;
 545 }
 546
 547 void sbitmap_queue_wake_up(struct sbitmap_queue *sbq)
 548 {
 549         while (__sbq_wake_up(sbq))
 550                 ;
 551 }
 552 EXPORT_SYMBOL_GPL(sbitmap_queue_wake_up);
 553
 554 void sbitmap_queue_clear(struct sbitmap_queue *sbq, unsigned int nr,
 555                          unsigned int cpu)
 556 {
 557         /*
 558          * Once the clear bit is set, the bit may be allocated out.
 559          *
 560          * Orders READ/WRITE on the asssociated instance(such as request
 561          * of blk_mq) by this bit for avoiding race with re-allocation,
 562          * and its pair is the memory barrier implied in __sbitmap_get_word.
 563          *
 564          * One invariant is that the clear bit has to be zero when the bit
 565          * is in use.
 566          */
 567         smp_mb__before_atomic();
 568         sbitmap_deferred_clear_bit(&sbq->sb, nr);
 569
 570         /*
 571          * Pairs with the memory barrier in set_current_state() to ensure the
 572          * proper ordering of clear_bit_unlock()/waitqueue_active() in the waker
 573          * and test_and_set_bit_lock()/prepare_to_wait()/finish_wait() in the
 574          * waiter. See the comment on waitqueue_active().
 575          */
 576         smp_mb__after_atomic();
 577         sbitmap_queue_wake_up(sbq);
 578
 579         if (likely(!sbq->round_robin && nr < sbq->sb.depth))
 580                 *per_cpu_ptr(sbq->alloc_hint, cpu) = nr;
 581 }
 582 EXPORT_SYMBOL_GPL(sbitmap_queue_clear);
 583
 584 void sbitmap_queue_wake_all(struct sbitmap_queue *sbq)
 585 {
 586         int i, wake_index;
 587
 588         /*
 589          * Pairs with the memory barrier in set_current_state() like in
 590          * sbitmap_queue_wake_up().
 591          */
 592         smp_mb();
 593         wake_index = atomic_read(&sbq->wake_index);
 594         for (i = 0; i < SBQ_WAIT_QUEUES; i++) {
 595                 struct sbq_wait_state *ws = &sbq->ws[wake_index];
 596
 597                 if (waitqueue_active(&ws->wait))
 598                         wake_up(&ws->wait);
 599
 600                 wake_index = sbq_index_inc(wake_index);
 601         }
 602 }
 603 EXPORT_SYMBOL_GPL(sbitmap_queue_wake_all);
 604
 605 void sbitmap_queue_show(struct sbitmap_queue *sbq, struct seq_file *m)
 606 {
 607         bool first;
 608         int i;
 609
 610         sbitmap_show(&sbq->sb, m);
 611
 612         seq_puts(m, "alloc_hint={");
 613         first = true;
 614         for_each_possible_cpu(i) {
 615                 if (!first)
 616                         seq_puts(m, ", ");
 617                 first = false;
 618                 seq_printf(m, "%u", *per_cpu_ptr(sbq->alloc_hint, i));
 619         }
 620         seq_puts(m, "}\n");
 621
 622         seq_printf(m, "wake_batch=%u\n", sbq->wake_batch);
 623         seq_printf(m, "wake_index=%d\n", atomic_read(&sbq->wake_index));
 624         seq_printf(m, "ws_active=%d\n", atomic_read(&sbq->ws_active));
 625
 626         seq_puts(m, "ws={\n");
 627         for (i = 0; i < SBQ_WAIT_QUEUES; i++) {
 628                 struct sbq_wait_state *ws = &sbq->ws[i];
 629
 630                 seq_printf(m, "\t{.wait_cnt=%d, .wait=%s},\n",
 631                            atomic_read(&ws->wait_cnt),
 632                            waitqueue_active(&ws->wait) ? "active" : "inactive");
 633         }
 634         seq_puts(m, "}\n");
 635
 636         seq_printf(m, "round_robin=%d\n", sbq->round_robin);
 637         seq_printf(m, "min_shallow_depth=%u\n", sbq->min_shallow_depth);
 638 }
 639 EXPORT_SYMBOL_GPL(sbitmap_queue_show);
 640
 641 void sbitmap_add_wait_queue(struct sbitmap_queue *sbq,
 642                             struct sbq_wait_state *ws,
 643                             struct sbq_wait *sbq_wait)
 644 {
 645         if (!sbq_wait->sbq) {
 646                 sbq_wait->sbq = sbq;
 647                 atomic_inc(&sbq->ws_active);
 648                 add_wait_queue(&ws->wait, &sbq_wait->wait);
 649         }
 650 }
 651 EXPORT_SYMBOL_GPL(sbitmap_add_wait_queue);
 652
 653 void sbitmap_del_wait_queue(struct sbq_wait *sbq_wait)
 654 {
 655         list_del_init(&sbq_wait->wait.entry);
 656         if (sbq_wait->sbq) {
 657                 atomic_dec(&sbq_wait->sbq->ws_active);
 658                 sbq_wait->sbq = NULL;
 659         }
 660 }
 661 EXPORT_SYMBOL_GPL(sbitmap_del_wait_queue);
 662
 663 void sbitmap_prepare_to_wait(struct sbitmap_queue *sbq,
 664                              struct sbq_wait_state *ws,
 665                              struct sbq_wait *sbq_wait, int state)
 666 {
 667         if (!sbq_wait->sbq) {
 668                 atomic_inc(&sbq->ws_active);
 669                 sbq_wait->sbq = sbq;
 670         }
 671         prepare_to_wait_exclusive(&ws->wait, &sbq_wait->wait, state);
 672 }
 673 EXPORT_SYMBOL_GPL(sbitmap_prepare_to_wait);
 674
 675 void sbitmap_finish_wait(struct sbitmap_queue *sbq, struct sbq_wait_state *ws,
 676                          struct sbq_wait *sbq_wait)
 677 {
 678         finish_wait(&ws->wait, &sbq_wait->wait);
 679         if (sbq_wait->sbq) {
 680                 atomic_dec(&sbq->ws_active);
 681                 sbq_wait->sbq = NULL;
 682         }
 683 }
 684 EXPORT_SYMBOL_GPL(sbitmap_finish_wait);