git.sesse.net Git - bcachefs-tools-debian/blob - linux/six.c

   1 // SPDX-License-Identifier: GPL-2.0
   2
   3 #include <linux/export.h>
   4 #include <linux/log2.h>
   5 #include <linux/percpu.h>
   6 #include <linux/preempt.h>
   7 #include <linux/rcupdate.h>
   8 #include <linux/sched.h>
   9 #include <linux/sched/clock.h>
  10 #include <linux/sched/rt.h>
  11 #include <linux/six.h>
  12 #include <linux/slab.h>
  13
  14 #ifdef DEBUG
  15 #define EBUG_ON(cond)           BUG_ON(cond)
  16 #else
  17 #define EBUG_ON(cond)           do {} while (0)
  18 #endif
  19
  20 #define six_acquire(l, t, r)    lock_acquire(l, 0, t, r, 1, NULL, _RET_IP_)
  21 #define six_release(l)          lock_release(l, _RET_IP_)
  22
  23 static void do_six_unlock_type(struct six_lock *lock, enum six_lock_type type);
  24
  25 struct six_lock_vals {
  26         /* Value we add to the lock in order to take the lock: */
  27         u64                     lock_val;
  28
  29         /* If the lock has this value (used as a mask), taking the lock fails: */
  30         u64                     lock_fail;
  31
  32         /* Value we add to the lock in order to release the lock: */
  33         u64                     unlock_val;
  34
  35         /* Mask that indicates lock is held for this type: */
  36         u64                     held_mask;
  37
  38         /* Waitlist we wakeup when releasing the lock: */
  39         enum six_lock_type      unlock_wakeup;
  40 };
  41
  42 #define __SIX_LOCK_HELD_read    __SIX_VAL(read_lock, ~0)
  43 #define __SIX_LOCK_HELD_intent  __SIX_VAL(intent_lock, ~0)
  44 #define __SIX_LOCK_HELD_write   __SIX_VAL(seq, 1)
  45
  46 #define LOCK_VALS {                                                     \
  47         [SIX_LOCK_read] = {                                             \
  48                 .lock_val       = __SIX_VAL(read_lock, 1),              \
  49                 .lock_fail      = __SIX_LOCK_HELD_write + __SIX_VAL(write_locking, 1),\
  50                 .unlock_val     = -__SIX_VAL(read_lock, 1),             \
  51                 .held_mask      = __SIX_LOCK_HELD_read,                 \
  52                 .unlock_wakeup  = SIX_LOCK_write,                       \
  53         },                                                              \
  54         [SIX_LOCK_intent] = {                                           \
  55                 .lock_val       = __SIX_VAL(intent_lock, 1),            \
  56                 .lock_fail      = __SIX_LOCK_HELD_intent,               \
  57                 .unlock_val     = -__SIX_VAL(intent_lock, 1),           \
  58                 .held_mask      = __SIX_LOCK_HELD_intent,               \
  59                 .unlock_wakeup  = SIX_LOCK_intent,                      \
  60         },                                                              \
  61         [SIX_LOCK_write] = {                                            \
  62                 .lock_val       = __SIX_VAL(seq, 1),                    \
  63                 .lock_fail      = __SIX_LOCK_HELD_read,                 \
  64                 .unlock_val     = __SIX_VAL(seq, 1),                    \
  65                 .held_mask      = __SIX_LOCK_HELD_write,                \
  66                 .unlock_wakeup  = SIX_LOCK_read,                        \
  67         },                                                              \
  68 }
  69
  70 static inline void six_set_owner(struct six_lock *lock, enum six_lock_type type,
  71                                  union six_lock_state old,
  72                                  struct task_struct *owner)
  73 {
  74         if (type != SIX_LOCK_intent)
  75                 return;
  76
  77         if (!old.intent_lock) {
  78                 EBUG_ON(lock->owner);
  79                 lock->owner = owner;
  80         } else {
  81                 EBUG_ON(lock->owner != current);
  82         }
  83 }
  84
  85 static inline unsigned pcpu_read_count(struct six_lock *lock)
  86 {
  87         unsigned read_count = 0;
  88         int cpu;
  89
  90         for_each_possible_cpu(cpu)
  91                 read_count += *per_cpu_ptr(lock->readers, cpu);
  92         return read_count;
  93 }
  94
  95 /* This is probably up there with the more evil things I've done */
  96 #define waitlist_bitnr(id) ilog2((((union six_lock_state) { .waiters = 1 << (id) }).l))
  97
  98 static int __do_six_trylock_type(struct six_lock *lock,
  99                                  enum six_lock_type type,
 100                                  struct task_struct *task,
 101                                  bool try)
 102 {
 103         const struct six_lock_vals l[] = LOCK_VALS;
 104         union six_lock_state old, new;
 105         int ret;
 106         u64 v;
 107
 108         EBUG_ON(type == SIX_LOCK_write && lock->owner != task);
 109         EBUG_ON(type == SIX_LOCK_write && (lock->state.seq & 1));
 110         EBUG_ON(type == SIX_LOCK_write && (try != !(lock->state.write_locking)));
 111
 112         /*
 113          * Percpu reader mode:
 114          *
 115          * The basic idea behind this algorithm is that you can implement a lock
 116          * between two threads without any atomics, just memory barriers:
 117          *
 118          * For two threads you'll need two variables, one variable for "thread a
 119          * has the lock" and another for "thread b has the lock".
 120          *
 121          * To take the lock, a thread sets its variable indicating that it holds
 122          * the lock, then issues a full memory barrier, then reads from the
 123          * other thread's variable to check if the other thread thinks it has
 124          * the lock. If we raced, we backoff and retry/sleep.
 125          */
 126
 127         if (type == SIX_LOCK_read && lock->readers) {
 128                 preempt_disable();
 129                 this_cpu_inc(*lock->readers); /* signal that we own lock */
 130
 131                 smp_mb();
 132
 133                 old.v = READ_ONCE(lock->state.v);
 134                 ret = !(old.v & l[type].lock_fail);
 135
 136                 this_cpu_sub(*lock->readers, !ret);
 137                 preempt_enable();
 138
 139                 /*
 140                  * If we failed because a writer was trying to take the
 141                  * lock, issue a wakeup because we might have caused a
 142                  * spurious trylock failure:
 143                  */
 144                 if (old.write_locking)
 145                         ret = -1 - SIX_LOCK_write;
 146         } else if (type == SIX_LOCK_write && lock->readers) {
 147                 if (try) {
 148                         atomic64_add(__SIX_VAL(write_locking, 1),
 149                                      &lock->state.counter);
 150                         smp_mb__after_atomic();
 151                 }
 152
 153                 ret = !pcpu_read_count(lock);
 154
 155                 /*
 156                  * On success, we increment lock->seq; also we clear
 157                  * write_locking unless we failed from the lock path:
 158                  */
 159                 v = 0;
 160                 if (ret)
 161                         v += __SIX_VAL(seq, 1);
 162                 if (ret || try)
 163                         v -= __SIX_VAL(write_locking, 1);
 164
 165                 if (!ret && !try && !(lock->state.waiters & (1 << SIX_LOCK_write)))
 166                         v += __SIX_VAL(waiters, 1 << SIX_LOCK_write);
 167
 168                 if (try && !ret) {
 169                         old.v = atomic64_add_return(v, &lock->state.counter);
 170                         if (old.waiters & (1 << SIX_LOCK_read))
 171                                 ret = -1 - SIX_LOCK_read;
 172                 } else {
 173                         atomic64_add(v, &lock->state.counter);
 174                 }
 175         } else {
 176                 v = READ_ONCE(lock->state.v);
 177                 do {
 178                         new.v = old.v = v;
 179
 180                         if (!(old.v & l[type].lock_fail)) {
 181                                 new.v += l[type].lock_val;
 182
 183                                 if (type == SIX_LOCK_write)
 184                                         new.write_locking = 0;
 185                         } else if (!try && !(new.waiters & (1 << type)))
 186                                 new.waiters |= 1 << type;
 187                         else
 188                                 break; /* waiting bit already set */
 189                 } while ((v = atomic64_cmpxchg_acquire(&lock->state.counter,
 190                                         old.v, new.v)) != old.v);
 191
 192                 ret = !(old.v & l[type].lock_fail);
 193
 194                 EBUG_ON(ret && !(lock->state.v & l[type].held_mask));
 195         }
 196
 197         if (ret > 0)
 198                 six_set_owner(lock, type, old, task);
 199
 200         EBUG_ON(type == SIX_LOCK_write && (try || ret > 0) && (lock->state.write_locking));
 201
 202         return ret;
 203 }
 204
 205 static inline void __six_lock_wakeup(struct six_lock *lock, enum six_lock_type lock_type)
 206 {
 207         struct six_lock_waiter *w, *next;
 208         struct task_struct *task;
 209         bool saw_one;
 210         int ret;
 211 again:
 212         ret = 0;
 213         saw_one = false;
 214         raw_spin_lock(&lock->wait_lock);
 215
 216         list_for_each_entry_safe(w, next, &lock->wait_list, list) {
 217                 if (w->lock_want != lock_type)
 218                         continue;
 219
 220                 if (saw_one && lock_type != SIX_LOCK_read)
 221                         goto unlock;
 222                 saw_one = true;
 223
 224                 ret = __do_six_trylock_type(lock, lock_type, w->task, false);
 225                 if (ret <= 0)
 226                         goto unlock;
 227
 228                 __list_del(w->list.prev, w->list.next);
 229                 task = w->task;
 230                 /*
 231                  * Do no writes to @w besides setting lock_acquired - otherwise
 232                  * we would need a memory barrier:
 233                  */
 234                 barrier();
 235                 w->lock_acquired = true;
 236                 wake_up_process(task);
 237         }
 238
 239         clear_bit(waitlist_bitnr(lock_type), (unsigned long *) &lock->state.v);
 240 unlock:
 241         raw_spin_unlock(&lock->wait_lock);
 242
 243         if (ret < 0) {
 244                 lock_type = -ret - 1;
 245                 goto again;
 246         }
 247 }
 248
 249 static inline void six_lock_wakeup(struct six_lock *lock,
 250                                    union six_lock_state state,
 251                                    enum six_lock_type lock_type)
 252 {
 253         if (lock_type == SIX_LOCK_write && state.read_lock)
 254                 return;
 255
 256         if (!(state.waiters & (1 << lock_type)))
 257                 return;
 258
 259         __six_lock_wakeup(lock, lock_type);
 260 }
 261
 262 static bool do_six_trylock_type(struct six_lock *lock,
 263                                 enum six_lock_type type,
 264                                 bool try)
 265 {
 266         int ret;
 267
 268         ret = __do_six_trylock_type(lock, type, current, try);
 269         if (ret < 0)
 270                 __six_lock_wakeup(lock, -ret - 1);
 271
 272         return ret > 0;
 273 }
 274
 275 __always_inline __flatten
 276 static bool __six_trylock_type(struct six_lock *lock, enum six_lock_type type)
 277 {
 278         if (!do_six_trylock_type(lock, type, true))
 279                 return false;
 280
 281         if (type != SIX_LOCK_write)
 282                 six_acquire(&lock->dep_map, 1, type == SIX_LOCK_read);
 283         return true;
 284 }
 285
 286 __always_inline __flatten
 287 static bool __six_relock_type(struct six_lock *lock, enum six_lock_type type,
 288                               unsigned seq)
 289 {
 290         const struct six_lock_vals l[] = LOCK_VALS;
 291         union six_lock_state old;
 292         u64 v;
 293
 294         EBUG_ON(type == SIX_LOCK_write);
 295
 296         if (type == SIX_LOCK_read &&
 297             lock->readers) {
 298                 bool ret;
 299
 300                 preempt_disable();
 301                 this_cpu_inc(*lock->readers);
 302
 303                 smp_mb();
 304
 305                 old.v = READ_ONCE(lock->state.v);
 306                 ret = !(old.v & l[type].lock_fail) && old.seq == seq;
 307
 308                 this_cpu_sub(*lock->readers, !ret);
 309                 preempt_enable();
 310
 311                 /*
 312                  * Similar to the lock path, we may have caused a spurious write
 313                  * lock fail and need to issue a wakeup:
 314                  */
 315                 if (old.write_locking)
 316                         six_lock_wakeup(lock, old, SIX_LOCK_write);
 317
 318                 if (ret)
 319                         six_acquire(&lock->dep_map, 1, type == SIX_LOCK_read);
 320
 321                 return ret;
 322         }
 323
 324         v = READ_ONCE(lock->state.v);
 325         do {
 326                 old.v = v;
 327
 328                 if (old.seq != seq || old.v & l[type].lock_fail)
 329                         return false;
 330         } while ((v = atomic64_cmpxchg_acquire(&lock->state.counter,
 331                                 old.v,
 332                                 old.v + l[type].lock_val)) != old.v);
 333
 334         six_set_owner(lock, type, old, current);
 335         if (type != SIX_LOCK_write)
 336                 six_acquire(&lock->dep_map, 1, type == SIX_LOCK_read);
 337         return true;
 338 }
 339
 340 #ifdef CONFIG_LOCK_SPIN_ON_OWNER
 341
 342 static inline bool six_optimistic_spin(struct six_lock *lock,
 343                                        struct six_lock_waiter *wait)
 344 {
 345         struct task_struct *owner, *task = current;
 346
 347         switch (wait->lock_want) {
 348         case SIX_LOCK_read:
 349                 break;
 350         case SIX_LOCK_intent:
 351                 if (lock->wait_list.next != &wait->list)
 352                         return false;
 353                 break;
 354         case SIX_LOCK_write:
 355                 return false;
 356         }
 357
 358         rcu_read_lock();
 359         owner = READ_ONCE(lock->owner);
 360
 361         while (owner && lock->owner == owner) {
 362                 /*
 363                  * Ensure we emit the owner->on_cpu, dereference _after_
 364                  * checking lock->owner still matches owner. If that fails,
 365                  * owner might point to freed memory. If it still matches,
 366                  * the rcu_read_lock() ensures the memory stays valid.
 367                  */
 368                 barrier();
 369
 370                 /*
 371                  * If we're an RT task that will live-lock because we won't let
 372                  * the owner complete.
 373                  */
 374                 if (wait->lock_acquired ||
 375                     !owner->on_cpu ||
 376                     rt_task(task) ||
 377                     need_resched())
 378                         break;
 379
 380                 cpu_relax();
 381         }
 382         rcu_read_unlock();
 383
 384         return wait->lock_acquired;
 385 }
 386
 387 #else /* CONFIG_LOCK_SPIN_ON_OWNER */
 388
 389 static inline bool six_optimistic_spin(struct six_lock *lock,
 390                                        struct six_lock_waiter *wait)
 391 {
 392         return false;
 393 }
 394
 395 #endif
 396
 397 noinline
 398 static int __six_lock_type_slowpath(struct six_lock *lock, enum six_lock_type type,
 399                                     struct six_lock_waiter *wait,
 400                                     six_lock_should_sleep_fn should_sleep_fn, void *p)
 401 {
 402         union six_lock_state old;
 403         int ret = 0;
 404
 405         if (type == SIX_LOCK_write) {
 406                 EBUG_ON(lock->state.write_locking);
 407                 atomic64_add(__SIX_VAL(write_locking, 1), &lock->state.counter);
 408                 smp_mb__after_atomic();
 409         }
 410
 411         lock_contended(&lock->dep_map, _RET_IP_);
 412
 413         wait->task              = current;
 414         wait->lock_want         = type;
 415         wait->lock_acquired     = false;
 416
 417         raw_spin_lock(&lock->wait_lock);
 418         if (!(lock->state.waiters & (1 << type)))
 419                 set_bit(waitlist_bitnr(type), (unsigned long *) &lock->state.v);
 420         /*
 421          * Retry taking the lock after taking waitlist lock, have raced with an
 422          * unlock:
 423          */
 424         ret = __do_six_trylock_type(lock, type, current, false);
 425         if (ret <= 0) {
 426                 wait->start_time = local_clock();
 427
 428                 if (!list_empty(&lock->wait_list)) {
 429                         struct six_lock_waiter *last =
 430                                 list_last_entry(&lock->wait_list,
 431                                         struct six_lock_waiter, list);
 432
 433                         if (time_before_eq64(wait->start_time, last->start_time))
 434                                 wait->start_time = last->start_time + 1;
 435                 }
 436
 437                 list_add_tail(&wait->list, &lock->wait_list);
 438         }
 439         raw_spin_unlock(&lock->wait_lock);
 440
 441         if (unlikely(ret > 0)) {
 442                 ret = 0;
 443                 goto out;
 444         }
 445
 446         if (unlikely(ret < 0)) {
 447                 __six_lock_wakeup(lock, -ret - 1);
 448                 ret = 0;
 449         }
 450
 451         if (six_optimistic_spin(lock, wait))
 452                 goto out;
 453
 454         while (1) {
 455                 set_current_state(TASK_UNINTERRUPTIBLE);
 456
 457                 if (wait->lock_acquired)
 458                         break;
 459
 460                 ret = should_sleep_fn ? should_sleep_fn(lock, p) : 0;
 461                 if (unlikely(ret)) {
 462                         raw_spin_lock(&lock->wait_lock);
 463                         if (!wait->lock_acquired)
 464                                 list_del(&wait->list);
 465                         raw_spin_unlock(&lock->wait_lock);
 466
 467                         if (wait->lock_acquired)
 468                                 do_six_unlock_type(lock, type);
 469                         break;
 470                 }
 471
 472                 schedule();
 473         }
 474
 475         __set_current_state(TASK_RUNNING);
 476 out:
 477         if (ret && type == SIX_LOCK_write && lock->state.write_locking) {
 478                 old.v = atomic64_sub_return(__SIX_VAL(write_locking, 1),
 479                                             &lock->state.counter);
 480                 six_lock_wakeup(lock, old, SIX_LOCK_read);
 481         }
 482
 483         return ret;
 484 }
 485
 486 __always_inline __flatten
 487 static int __six_lock_type_waiter(struct six_lock *lock, enum six_lock_type type,
 488                          struct six_lock_waiter *wait,
 489                          six_lock_should_sleep_fn should_sleep_fn, void *p)
 490 {
 491         int ret;
 492
 493         wait->start_time = 0;
 494
 495         if (type != SIX_LOCK_write)
 496                 six_acquire(&lock->dep_map, 0, type == SIX_LOCK_read);
 497
 498         ret = do_six_trylock_type(lock, type, true) ? 0
 499                 : __six_lock_type_slowpath(lock, type, wait, should_sleep_fn, p);
 500
 501         if (ret && type != SIX_LOCK_write)
 502                 six_release(&lock->dep_map);
 503         if (!ret)
 504                 lock_acquired(&lock->dep_map, _RET_IP_);
 505
 506         return ret;
 507 }
 508
 509 __always_inline
 510 static int __six_lock_type(struct six_lock *lock, enum six_lock_type type,
 511                            six_lock_should_sleep_fn should_sleep_fn, void *p)
 512 {
 513         struct six_lock_waiter wait;
 514
 515         return __six_lock_type_waiter(lock, type, &wait, should_sleep_fn, p);
 516 }
 517
 518 __always_inline __flatten
 519 static void do_six_unlock_type(struct six_lock *lock, enum six_lock_type type)
 520 {
 521         const struct six_lock_vals l[] = LOCK_VALS;
 522         union six_lock_state state;
 523
 524         if (type == SIX_LOCK_intent)
 525                 lock->owner = NULL;
 526
 527         if (type == SIX_LOCK_read &&
 528             lock->readers) {
 529                 smp_mb(); /* unlock barrier */
 530                 this_cpu_dec(*lock->readers);
 531                 smp_mb(); /* between unlocking and checking for waiters */
 532                 state.v = READ_ONCE(lock->state.v);
 533         } else {
 534                 EBUG_ON(!(lock->state.v & l[type].held_mask));
 535                 state.v = atomic64_add_return_release(l[type].unlock_val,
 536                                                       &lock->state.counter);
 537         }
 538
 539         six_lock_wakeup(lock, state, l[type].unlock_wakeup);
 540 }
 541
 542 __always_inline __flatten
 543 static void __six_unlock_type(struct six_lock *lock, enum six_lock_type type)
 544 {
 545         EBUG_ON(type == SIX_LOCK_write &&
 546                 !(lock->state.v & __SIX_LOCK_HELD_intent));
 547         EBUG_ON((type == SIX_LOCK_write ||
 548                  type == SIX_LOCK_intent) &&
 549                 lock->owner != current);
 550
 551         if (type != SIX_LOCK_write)
 552                 six_release(&lock->dep_map);
 553
 554         if (type == SIX_LOCK_intent &&
 555             lock->intent_lock_recurse) {
 556                 --lock->intent_lock_recurse;
 557                 return;
 558         }
 559
 560         do_six_unlock_type(lock, type);
 561 }
 562
 563 #define __SIX_LOCK(type)                                                \
 564 bool six_trylock_##type(struct six_lock *lock)                          \
 565 {                                                                       \
 566         return __six_trylock_type(lock, SIX_LOCK_##type);               \
 567 }                                                                       \
 568 EXPORT_SYMBOL_GPL(six_trylock_##type);                                  \
 569                                                                         \
 570 bool six_relock_##type(struct six_lock *lock, u32 seq)                  \
 571 {                                                                       \
 572         return __six_relock_type(lock, SIX_LOCK_##type, seq);           \
 573 }                                                                       \
 574 EXPORT_SYMBOL_GPL(six_relock_##type);                                   \
 575                                                                         \
 576 int six_lock_##type(struct six_lock *lock,                              \
 577                     six_lock_should_sleep_fn should_sleep_fn, void *p)  \
 578 {                                                                       \
 579         return __six_lock_type(lock, SIX_LOCK_##type, should_sleep_fn, p);\
 580 }                                                                       \
 581 EXPORT_SYMBOL_GPL(six_lock_##type);                                     \
 582                                                                         \
 583 int six_lock_waiter_##type(struct six_lock *lock,                       \
 584                            struct six_lock_waiter *wait,                \
 585                            six_lock_should_sleep_fn should_sleep_fn, void *p)\
 586 {                                                                       \
 587         return __six_lock_type_waiter(lock, SIX_LOCK_##type, wait, should_sleep_fn, p);\
 588 }                                                                       \
 589 EXPORT_SYMBOL_GPL(six_lock_waiter_##type);                              \
 590                                                                         \
 591 void six_unlock_##type(struct six_lock *lock)                           \
 592 {                                                                       \
 593         __six_unlock_type(lock, SIX_LOCK_##type);                       \
 594 }                                                                       \
 595 EXPORT_SYMBOL_GPL(six_unlock_##type);
 596
 597 __SIX_LOCK(read)
 598 __SIX_LOCK(intent)
 599 __SIX_LOCK(write)
 600
 601 #undef __SIX_LOCK
 602
 603 /* Convert from intent to read: */
 604 void six_lock_downgrade(struct six_lock *lock)
 605 {
 606         six_lock_increment(lock, SIX_LOCK_read);
 607         six_unlock_intent(lock);
 608 }
 609 EXPORT_SYMBOL_GPL(six_lock_downgrade);
 610
 611 bool six_lock_tryupgrade(struct six_lock *lock)
 612 {
 613         union six_lock_state old, new;
 614         u64 v = READ_ONCE(lock->state.v);
 615
 616         do {
 617                 new.v = old.v = v;
 618
 619                 if (new.intent_lock)
 620                         return false;
 621
 622                 if (!lock->readers) {
 623                         EBUG_ON(!new.read_lock);
 624                         new.read_lock--;
 625                 }
 626
 627                 new.intent_lock = 1;
 628         } while ((v = atomic64_cmpxchg_acquire(&lock->state.counter,
 629                                 old.v, new.v)) != old.v);
 630
 631         if (lock->readers)
 632                 this_cpu_dec(*lock->readers);
 633
 634         six_set_owner(lock, SIX_LOCK_intent, old, current);
 635
 636         return true;
 637 }
 638 EXPORT_SYMBOL_GPL(six_lock_tryupgrade);
 639
 640 bool six_trylock_convert(struct six_lock *lock,
 641                          enum six_lock_type from,
 642                          enum six_lock_type to)
 643 {
 644         EBUG_ON(to == SIX_LOCK_write || from == SIX_LOCK_write);
 645
 646         if (to == from)
 647                 return true;
 648
 649         if (to == SIX_LOCK_read) {
 650                 six_lock_downgrade(lock);
 651                 return true;
 652         } else {
 653                 return six_lock_tryupgrade(lock);
 654         }
 655 }
 656 EXPORT_SYMBOL_GPL(six_trylock_convert);
 657
 658 /*
 659  * Increment read/intent lock count, assuming we already have it read or intent
 660  * locked:
 661  */
 662 void six_lock_increment(struct six_lock *lock, enum six_lock_type type)
 663 {
 664         const struct six_lock_vals l[] = LOCK_VALS;
 665
 666         six_acquire(&lock->dep_map, 0, type == SIX_LOCK_read);
 667
 668         /* XXX: assert already locked, and that we don't overflow: */
 669
 670         switch (type) {
 671         case SIX_LOCK_read:
 672                 if (lock->readers) {
 673                         this_cpu_inc(*lock->readers);
 674                 } else {
 675                         EBUG_ON(!lock->state.read_lock &&
 676                                 !lock->state.intent_lock);
 677                         atomic64_add(l[type].lock_val, &lock->state.counter);
 678                 }
 679                 break;
 680         case SIX_LOCK_intent:
 681                 EBUG_ON(!lock->state.intent_lock);
 682                 lock->intent_lock_recurse++;
 683                 break;
 684         case SIX_LOCK_write:
 685                 BUG();
 686                 break;
 687         }
 688 }
 689 EXPORT_SYMBOL_GPL(six_lock_increment);
 690
 691 void six_lock_wakeup_all(struct six_lock *lock)
 692 {
 693         union six_lock_state state = lock->state;
 694         struct six_lock_waiter *w;
 695
 696         six_lock_wakeup(lock, state, SIX_LOCK_read);
 697         six_lock_wakeup(lock, state, SIX_LOCK_intent);
 698         six_lock_wakeup(lock, state, SIX_LOCK_write);
 699
 700         raw_spin_lock(&lock->wait_lock);
 701         list_for_each_entry(w, &lock->wait_list, list)
 702                 wake_up_process(w->task);
 703         raw_spin_unlock(&lock->wait_lock);
 704 }
 705 EXPORT_SYMBOL_GPL(six_lock_wakeup_all);
 706
 707 void six_lock_pcpu_free(struct six_lock *lock)
 708 {
 709         BUG_ON(lock->readers && pcpu_read_count(lock));
 710         BUG_ON(lock->state.read_lock);
 711
 712         free_percpu(lock->readers);
 713         lock->readers = NULL;
 714 }
 715 EXPORT_SYMBOL_GPL(six_lock_pcpu_free);
 716
 717 void six_lock_pcpu_alloc(struct six_lock *lock)
 718 {
 719 #ifdef __KERNEL__
 720         if (!lock->readers)
 721                 lock->readers = alloc_percpu(unsigned);
 722 #endif
 723 }
 724 EXPORT_SYMBOL_GPL(six_lock_pcpu_alloc);
 725
 726 /*
 727  * Returns lock held counts, for both read and intent
 728  */
 729 struct six_lock_count six_lock_counts(struct six_lock *lock)
 730 {
 731         struct six_lock_count ret;
 732
 733         ret.n[SIX_LOCK_read]    = 0;
 734         ret.n[SIX_LOCK_intent]  = lock->state.intent_lock + lock->intent_lock_recurse;
 735         ret.n[SIX_LOCK_write]   = lock->state.seq & 1;
 736
 737         if (!lock->readers)
 738                 ret.n[SIX_LOCK_read] += lock->state.read_lock;
 739         else {
 740                 int cpu;
 741
 742                 for_each_possible_cpu(cpu)
 743                         ret.n[SIX_LOCK_read] += *per_cpu_ptr(lock->readers, cpu);
 744         }
 745
 746         return ret;
 747 }
 748 EXPORT_SYMBOL_GPL(six_lock_counts);