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18#include <linux/types.h>
19#include <linux/kernel.h>
20#include <linux/sched.h>
21#include <linux/sched/rt.h>
22#include <linux/sched/task.h>
23#include <linux/sched/debug.h>
24#include <linux/sched/wake_q.h>
25#include <linux/sched/signal.h>
26#include <linux/sched/clock.h>
27#include <linux/export.h>
28#include <linux/rwsem.h>
29#include <linux/atomic.h>
30
31#include "rwsem.h"
32#include "lock_events.h"
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98
99#define RWSEM_READER_OWNED (1UL << 0)
100#define RWSEM_RD_NONSPINNABLE (1UL << 1)
101#define RWSEM_WR_NONSPINNABLE (1UL << 2)
102#define RWSEM_NONSPINNABLE (RWSEM_RD_NONSPINNABLE | RWSEM_WR_NONSPINNABLE)
103#define RWSEM_OWNER_FLAGS_MASK (RWSEM_READER_OWNED | RWSEM_NONSPINNABLE)
104
105#ifdef CONFIG_DEBUG_RWSEMS
106# define DEBUG_RWSEMS_WARN_ON(c, sem) do { \
107 if (!debug_locks_silent && \
108 WARN_ONCE(c, "DEBUG_RWSEMS_WARN_ON(%s): count = 0x%lx, owner = 0x%lx, curr 0x%lx, list %sempty\n",\
109 #c, atomic_long_read(&(sem)->count), \
110 atomic_long_read(&(sem)->owner), (long)current, \
111 list_empty(&(sem)->wait_list) ? "" : "not ")) \
112 debug_locks_off(); \
113 } while (0)
114#else
115# define DEBUG_RWSEMS_WARN_ON(c, sem)
116#endif
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154#define RWSEM_WRITER_LOCKED (1UL << 0)
155#define RWSEM_FLAG_WAITERS (1UL << 1)
156#define RWSEM_FLAG_HANDOFF (1UL << 2)
157#define RWSEM_FLAG_READFAIL (1UL << (BITS_PER_LONG - 1))
158
159#define RWSEM_READER_SHIFT 8
160#define RWSEM_READER_BIAS (1UL << RWSEM_READER_SHIFT)
161#define RWSEM_READER_MASK (~(RWSEM_READER_BIAS - 1))
162#define RWSEM_WRITER_MASK RWSEM_WRITER_LOCKED
163#define RWSEM_LOCK_MASK (RWSEM_WRITER_MASK|RWSEM_READER_MASK)
164#define RWSEM_READ_FAILED_MASK (RWSEM_WRITER_MASK|RWSEM_FLAG_WAITERS|\
165 RWSEM_FLAG_HANDOFF|RWSEM_FLAG_READFAIL)
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172
173
174static inline void rwsem_set_owner(struct rw_semaphore *sem)
175{
176 atomic_long_set(&sem->owner, (long)current);
177}
178
179static inline void rwsem_clear_owner(struct rw_semaphore *sem)
180{
181 atomic_long_set(&sem->owner, 0);
182}
183
184
185
186
187static inline bool rwsem_test_oflags(struct rw_semaphore *sem, long flags)
188{
189 return atomic_long_read(&sem->owner) & flags;
190}
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200
201
202static inline void __rwsem_set_reader_owned(struct rw_semaphore *sem,
203 struct task_struct *owner)
204{
205 unsigned long val = (unsigned long)owner | RWSEM_READER_OWNED |
206 (atomic_long_read(&sem->owner) & RWSEM_RD_NONSPINNABLE);
207
208 atomic_long_set(&sem->owner, val);
209}
210
211static inline void rwsem_set_reader_owned(struct rw_semaphore *sem)
212{
213 __rwsem_set_reader_owned(sem, current);
214}
215
216
217
218
219static inline bool is_rwsem_reader_owned(struct rw_semaphore *sem)
220{
221#ifdef CONFIG_DEBUG_RWSEMS
222
223
224
225 long count = atomic_long_read(&sem->count);
226
227 if (count & RWSEM_WRITER_MASK)
228 return false;
229#endif
230 return rwsem_test_oflags(sem, RWSEM_READER_OWNED);
231}
232
233#ifdef CONFIG_DEBUG_RWSEMS
234
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238
239
240static inline void rwsem_clear_reader_owned(struct rw_semaphore *sem)
241{
242 unsigned long val = atomic_long_read(&sem->owner);
243
244 while ((val & ~RWSEM_OWNER_FLAGS_MASK) == (unsigned long)current) {
245 if (atomic_long_try_cmpxchg(&sem->owner, &val,
246 val & RWSEM_OWNER_FLAGS_MASK))
247 return;
248 }
249}
250#else
251static inline void rwsem_clear_reader_owned(struct rw_semaphore *sem)
252{
253}
254#endif
255
256
257
258
259
260static inline void rwsem_set_nonspinnable(struct rw_semaphore *sem)
261{
262 unsigned long owner = atomic_long_read(&sem->owner);
263
264 do {
265 if (!(owner & RWSEM_READER_OWNED))
266 break;
267 if (owner & RWSEM_NONSPINNABLE)
268 break;
269 } while (!atomic_long_try_cmpxchg(&sem->owner, &owner,
270 owner | RWSEM_NONSPINNABLE));
271}
272
273static inline bool rwsem_read_trylock(struct rw_semaphore *sem)
274{
275 long cnt = atomic_long_add_return_acquire(RWSEM_READER_BIAS, &sem->count);
276 if (WARN_ON_ONCE(cnt < 0))
277 rwsem_set_nonspinnable(sem);
278 return !(cnt & RWSEM_READ_FAILED_MASK);
279}
280
281
282
283
284static inline struct task_struct *rwsem_owner(struct rw_semaphore *sem)
285{
286 return (struct task_struct *)
287 (atomic_long_read(&sem->owner) & ~RWSEM_OWNER_FLAGS_MASK);
288}
289
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292
293
294static inline struct task_struct *
295rwsem_owner_flags(struct rw_semaphore *sem, unsigned long *pflags)
296{
297 unsigned long owner = atomic_long_read(&sem->owner);
298
299 *pflags = owner & RWSEM_OWNER_FLAGS_MASK;
300 return (struct task_struct *)(owner & ~RWSEM_OWNER_FLAGS_MASK);
301}
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323void __init_rwsem(struct rw_semaphore *sem, const char *name,
324 struct lock_class_key *key)
325{
326#ifdef CONFIG_DEBUG_LOCK_ALLOC
327
328
329
330 debug_check_no_locks_freed((void *)sem, sizeof(*sem));
331 lockdep_init_map(&sem->dep_map, name, key, 0);
332#endif
333 atomic_long_set(&sem->count, RWSEM_UNLOCKED_VALUE);
334 raw_spin_lock_init(&sem->wait_lock);
335 INIT_LIST_HEAD(&sem->wait_list);
336 atomic_long_set(&sem->owner, 0L);
337#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
338 osq_lock_init(&sem->osq);
339#endif
340}
341EXPORT_SYMBOL(__init_rwsem);
342
343enum rwsem_waiter_type {
344 RWSEM_WAITING_FOR_WRITE,
345 RWSEM_WAITING_FOR_READ
346};
347
348struct rwsem_waiter {
349 struct list_head list;
350 struct task_struct *task;
351 enum rwsem_waiter_type type;
352 unsigned long timeout;
353 unsigned long last_rowner;
354};
355#define rwsem_first_waiter(sem) \
356 list_first_entry(&sem->wait_list, struct rwsem_waiter, list)
357
358enum rwsem_wake_type {
359 RWSEM_WAKE_ANY,
360 RWSEM_WAKE_READERS,
361 RWSEM_WAKE_READ_OWNED
362};
363
364enum writer_wait_state {
365 WRITER_NOT_FIRST,
366 WRITER_FIRST,
367 WRITER_HANDOFF
368};
369
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373
374
375#define RWSEM_WAIT_TIMEOUT DIV_ROUND_UP(HZ, 250)
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382
383#define MAX_READERS_WAKEUP 0x100
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397static void rwsem_mark_wake(struct rw_semaphore *sem,
398 enum rwsem_wake_type wake_type,
399 struct wake_q_head *wake_q)
400{
401 struct rwsem_waiter *waiter, *tmp;
402 long oldcount, woken = 0, adjustment = 0;
403 struct list_head wlist;
404
405 lockdep_assert_held(&sem->wait_lock);
406
407
408
409
410
411 waiter = rwsem_first_waiter(sem);
412
413 if (waiter->type == RWSEM_WAITING_FOR_WRITE) {
414 if (wake_type == RWSEM_WAKE_ANY) {
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418
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420
421
422 wake_q_add(wake_q, waiter->task);
423 lockevent_inc(rwsem_wake_writer);
424 }
425
426 return;
427 }
428
429
430
431
432 if (unlikely(atomic_long_read(&sem->count) < 0))
433 return;
434
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436
437
438
439
440 if (wake_type != RWSEM_WAKE_READ_OWNED) {
441 struct task_struct *owner;
442
443 adjustment = RWSEM_READER_BIAS;
444 oldcount = atomic_long_fetch_add(adjustment, &sem->count);
445 if (unlikely(oldcount & RWSEM_WRITER_MASK)) {
446
447
448
449
450
451 if (!(oldcount & RWSEM_FLAG_HANDOFF) &&
452 time_after(jiffies, waiter->timeout)) {
453 adjustment -= RWSEM_FLAG_HANDOFF;
454 lockevent_inc(rwsem_rlock_handoff);
455 }
456
457 atomic_long_add(-adjustment, &sem->count);
458 return;
459 }
460
461
462
463
464
465
466 owner = waiter->task;
467 if (waiter->last_rowner & RWSEM_RD_NONSPINNABLE) {
468 owner = (void *)((unsigned long)owner | RWSEM_RD_NONSPINNABLE);
469 lockevent_inc(rwsem_opt_norspin);
470 }
471 __rwsem_set_reader_owned(sem, owner);
472 }
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496
497 INIT_LIST_HEAD(&wlist);
498 list_for_each_entry_safe(waiter, tmp, &sem->wait_list, list) {
499 if (waiter->type == RWSEM_WAITING_FOR_WRITE)
500 continue;
501
502 woken++;
503 list_move_tail(&waiter->list, &wlist);
504
505
506
507
508 if (woken >= MAX_READERS_WAKEUP)
509 break;
510 }
511
512 adjustment = woken * RWSEM_READER_BIAS - adjustment;
513 lockevent_cond_inc(rwsem_wake_reader, woken);
514 if (list_empty(&sem->wait_list)) {
515
516 adjustment -= RWSEM_FLAG_WAITERS;
517 }
518
519
520
521
522
523 if (woken && (atomic_long_read(&sem->count) & RWSEM_FLAG_HANDOFF))
524 adjustment -= RWSEM_FLAG_HANDOFF;
525
526 if (adjustment)
527 atomic_long_add(adjustment, &sem->count);
528
529
530 list_for_each_entry_safe(waiter, tmp, &wlist, list) {
531 struct task_struct *tsk;
532
533 tsk = waiter->task;
534 get_task_struct(tsk);
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542 smp_store_release(&waiter->task, NULL);
543
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547 wake_q_add_safe(wake_q, tsk);
548 }
549}
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558
559static inline bool rwsem_try_write_lock(struct rw_semaphore *sem,
560 enum writer_wait_state wstate)
561{
562 long count, new;
563
564 lockdep_assert_held(&sem->wait_lock);
565
566 count = atomic_long_read(&sem->count);
567 do {
568 bool has_handoff = !!(count & RWSEM_FLAG_HANDOFF);
569
570 if (has_handoff && wstate == WRITER_NOT_FIRST)
571 return false;
572
573 new = count;
574
575 if (count & RWSEM_LOCK_MASK) {
576 if (has_handoff || (wstate != WRITER_HANDOFF))
577 return false;
578
579 new |= RWSEM_FLAG_HANDOFF;
580 } else {
581 new |= RWSEM_WRITER_LOCKED;
582 new &= ~RWSEM_FLAG_HANDOFF;
583
584 if (list_is_singular(&sem->wait_list))
585 new &= ~RWSEM_FLAG_WAITERS;
586 }
587 } while (!atomic_long_try_cmpxchg_acquire(&sem->count, &count, new));
588
589
590
591
592
593 if (new & RWSEM_FLAG_HANDOFF)
594 return false;
595
596 rwsem_set_owner(sem);
597 return true;
598}
599
600#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
601
602
603
604
605
606static inline bool rwsem_try_read_lock_unqueued(struct rw_semaphore *sem)
607{
608 long count = atomic_long_read(&sem->count);
609
610 if (count & (RWSEM_WRITER_MASK | RWSEM_FLAG_HANDOFF))
611 return false;
612
613 count = atomic_long_fetch_add_acquire(RWSEM_READER_BIAS, &sem->count);
614 if (!(count & (RWSEM_WRITER_MASK | RWSEM_FLAG_HANDOFF))) {
615 rwsem_set_reader_owned(sem);
616 lockevent_inc(rwsem_opt_rlock);
617 return true;
618 }
619
620
621 atomic_long_add(-RWSEM_READER_BIAS, &sem->count);
622 return false;
623}
624
625
626
627
628static inline bool rwsem_try_write_lock_unqueued(struct rw_semaphore *sem)
629{
630 long count = atomic_long_read(&sem->count);
631
632 while (!(count & (RWSEM_LOCK_MASK|RWSEM_FLAG_HANDOFF))) {
633 if (atomic_long_try_cmpxchg_acquire(&sem->count, &count,
634 count | RWSEM_WRITER_LOCKED)) {
635 rwsem_set_owner(sem);
636 lockevent_inc(rwsem_opt_wlock);
637 return true;
638 }
639 }
640 return false;
641}
642
643static inline bool owner_on_cpu(struct task_struct *owner)
644{
645
646
647
648
649 return owner->on_cpu && !vcpu_is_preempted(task_cpu(owner));
650}
651
652static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem,
653 unsigned long nonspinnable)
654{
655 struct task_struct *owner;
656 unsigned long flags;
657 bool ret = true;
658
659 BUILD_BUG_ON(!(RWSEM_OWNER_UNKNOWN & RWSEM_NONSPINNABLE));
660
661 if (need_resched()) {
662 lockevent_inc(rwsem_opt_fail);
663 return false;
664 }
665
666 preempt_disable();
667 rcu_read_lock();
668 owner = rwsem_owner_flags(sem, &flags);
669
670
671
672 if ((flags & nonspinnable) ||
673 (owner && !(flags & RWSEM_READER_OWNED) && !owner_on_cpu(owner)))
674 ret = false;
675 rcu_read_unlock();
676 preempt_enable();
677
678 lockevent_cond_inc(rwsem_opt_fail, !ret);
679 return ret;
680}
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693enum owner_state {
694 OWNER_NULL = 1 << 0,
695 OWNER_WRITER = 1 << 1,
696 OWNER_READER = 1 << 2,
697 OWNER_NONSPINNABLE = 1 << 3,
698};
699#define OWNER_SPINNABLE (OWNER_NULL | OWNER_WRITER | OWNER_READER)
700
701static inline enum owner_state
702rwsem_owner_state(struct task_struct *owner, unsigned long flags, unsigned long nonspinnable)
703{
704 if (flags & nonspinnable)
705 return OWNER_NONSPINNABLE;
706
707 if (flags & RWSEM_READER_OWNED)
708 return OWNER_READER;
709
710 return owner ? OWNER_WRITER : OWNER_NULL;
711}
712
713static noinline enum owner_state
714rwsem_spin_on_owner(struct rw_semaphore *sem, unsigned long nonspinnable)
715{
716 struct task_struct *new, *owner;
717 unsigned long flags, new_flags;
718 enum owner_state state;
719
720 owner = rwsem_owner_flags(sem, &flags);
721 state = rwsem_owner_state(owner, flags, nonspinnable);
722 if (state != OWNER_WRITER)
723 return state;
724
725 rcu_read_lock();
726 for (;;) {
727 if (atomic_long_read(&sem->count) & RWSEM_FLAG_HANDOFF) {
728 state = OWNER_NONSPINNABLE;
729 break;
730 }
731
732 new = rwsem_owner_flags(sem, &new_flags);
733 if ((new != owner) || (new_flags != flags)) {
734 state = rwsem_owner_state(new, new_flags, nonspinnable);
735 break;
736 }
737
738
739
740
741
742
743
744 barrier();
745
746 if (need_resched() || !owner_on_cpu(owner)) {
747 state = OWNER_NONSPINNABLE;
748 break;
749 }
750
751 cpu_relax();
752 }
753 rcu_read_unlock();
754
755 return state;
756}
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769
770static inline u64 rwsem_rspin_threshold(struct rw_semaphore *sem)
771{
772 long count = atomic_long_read(&sem->count);
773 int readers = count >> RWSEM_READER_SHIFT;
774 u64 delta;
775
776 if (readers > 30)
777 readers = 30;
778 delta = (20 + readers) * NSEC_PER_USEC / 2;
779
780 return sched_clock() + delta;
781}
782
783static bool rwsem_optimistic_spin(struct rw_semaphore *sem, bool wlock)
784{
785 bool taken = false;
786 int prev_owner_state = OWNER_NULL;
787 int loop = 0;
788 u64 rspin_threshold = 0;
789 unsigned long nonspinnable = wlock ? RWSEM_WR_NONSPINNABLE
790 : RWSEM_RD_NONSPINNABLE;
791
792 preempt_disable();
793
794
795 if (!osq_lock(&sem->osq))
796 goto done;
797
798
799
800
801
802
803
804 for (;;) {
805 enum owner_state owner_state;
806
807 owner_state = rwsem_spin_on_owner(sem, nonspinnable);
808 if (!(owner_state & OWNER_SPINNABLE))
809 break;
810
811
812
813
814 taken = wlock ? rwsem_try_write_lock_unqueued(sem)
815 : rwsem_try_read_lock_unqueued(sem);
816
817 if (taken)
818 break;
819
820
821
822
823 if (wlock && (owner_state == OWNER_READER)) {
824
825
826
827
828
829
830
831 if (prev_owner_state != OWNER_READER) {
832 if (rwsem_test_oflags(sem, nonspinnable))
833 break;
834 rspin_threshold = rwsem_rspin_threshold(sem);
835 loop = 0;
836 }
837
838
839
840
841
842
843
844
845 else if (!(++loop & 0xf) && (sched_clock() > rspin_threshold)) {
846 rwsem_set_nonspinnable(sem);
847 lockevent_inc(rwsem_opt_nospin);
848 break;
849 }
850 }
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883 if (owner_state != OWNER_WRITER) {
884 if (need_resched())
885 break;
886 if (rt_task(current) &&
887 (prev_owner_state != OWNER_WRITER))
888 break;
889 }
890 prev_owner_state = owner_state;
891
892
893
894
895
896
897
898 cpu_relax();
899 }
900 osq_unlock(&sem->osq);
901done:
902 preempt_enable();
903 lockevent_cond_inc(rwsem_opt_fail, !taken);
904 return taken;
905}
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916
917static inline void clear_wr_nonspinnable(struct rw_semaphore *sem)
918{
919 if (rwsem_test_oflags(sem, RWSEM_WR_NONSPINNABLE))
920 atomic_long_andnot(RWSEM_WR_NONSPINNABLE, &sem->owner);
921}
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941
942static inline bool rwsem_reader_phase_trylock(struct rw_semaphore *sem,
943 unsigned long last_rowner)
944{
945 unsigned long owner = atomic_long_read(&sem->owner);
946
947 if (!(owner & RWSEM_READER_OWNED))
948 return false;
949
950 if (((owner ^ last_rowner) & ~RWSEM_OWNER_FLAGS_MASK) &&
951 rwsem_try_read_lock_unqueued(sem)) {
952 lockevent_inc(rwsem_opt_rlock2);
953 lockevent_add(rwsem_opt_fail, -1);
954 return true;
955 }
956 return false;
957}
958#else
959static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem,
960 unsigned long nonspinnable)
961{
962 return false;
963}
964
965static inline bool rwsem_optimistic_spin(struct rw_semaphore *sem, bool wlock)
966{
967 return false;
968}
969
970static inline void clear_wr_nonspinnable(struct rw_semaphore *sem) { }
971
972static inline bool rwsem_reader_phase_trylock(struct rw_semaphore *sem,
973 unsigned long last_rowner)
974{
975 return false;
976}
977#endif
978
979
980
981
982static struct rw_semaphore __sched *
983rwsem_down_read_slowpath(struct rw_semaphore *sem, int state)
984{
985 long count, adjustment = -RWSEM_READER_BIAS;
986 struct rwsem_waiter waiter;
987 DEFINE_WAKE_Q(wake_q);
988 bool wake = false;
989
990
991
992
993
994 waiter.last_rowner = atomic_long_read(&sem->owner);
995 if (!(waiter.last_rowner & RWSEM_READER_OWNED))
996 waiter.last_rowner &= RWSEM_RD_NONSPINNABLE;
997
998 if (!rwsem_can_spin_on_owner(sem, RWSEM_RD_NONSPINNABLE))
999 goto queue;
1000
1001
1002
1003
1004 atomic_long_add(-RWSEM_READER_BIAS, &sem->count);
1005 adjustment = 0;
1006 if (rwsem_optimistic_spin(sem, false)) {
1007
1008
1009
1010
1011
1012 if ((atomic_long_read(&sem->count) & RWSEM_FLAG_WAITERS)) {
1013 raw_spin_lock_irq(&sem->wait_lock);
1014 if (!list_empty(&sem->wait_list))
1015 rwsem_mark_wake(sem, RWSEM_WAKE_READ_OWNED,
1016 &wake_q);
1017 raw_spin_unlock_irq(&sem->wait_lock);
1018 wake_up_q(&wake_q);
1019 }
1020 return sem;
1021 } else if (rwsem_reader_phase_trylock(sem, waiter.last_rowner)) {
1022
1023 return sem;
1024 }
1025
1026queue:
1027 waiter.task = current;
1028 waiter.type = RWSEM_WAITING_FOR_READ;
1029 waiter.timeout = jiffies + RWSEM_WAIT_TIMEOUT;
1030
1031 raw_spin_lock_irq(&sem->wait_lock);
1032 if (list_empty(&sem->wait_list)) {
1033
1034
1035
1036
1037
1038
1039 if (adjustment && !(atomic_long_read(&sem->count) &
1040 (RWSEM_WRITER_MASK | RWSEM_FLAG_HANDOFF))) {
1041
1042 smp_acquire__after_ctrl_dep();
1043 raw_spin_unlock_irq(&sem->wait_lock);
1044 rwsem_set_reader_owned(sem);
1045 lockevent_inc(rwsem_rlock_fast);
1046 return sem;
1047 }
1048 adjustment += RWSEM_FLAG_WAITERS;
1049 }
1050 list_add_tail(&waiter.list, &sem->wait_list);
1051
1052
1053 if (adjustment)
1054 count = atomic_long_add_return(adjustment, &sem->count);
1055 else
1056 count = atomic_long_read(&sem->count);
1057
1058
1059
1060
1061
1062
1063
1064 if (!(count & RWSEM_LOCK_MASK)) {
1065 clear_wr_nonspinnable(sem);
1066 wake = true;
1067 }
1068 if (wake || (!(count & RWSEM_WRITER_MASK) &&
1069 (adjustment & RWSEM_FLAG_WAITERS)))
1070 rwsem_mark_wake(sem, RWSEM_WAKE_ANY, &wake_q);
1071
1072 raw_spin_unlock_irq(&sem->wait_lock);
1073 wake_up_q(&wake_q);
1074
1075
1076 for (;;) {
1077 set_current_state(state);
1078 if (!smp_load_acquire(&waiter.task)) {
1079
1080 break;
1081 }
1082 if (signal_pending_state(state, current)) {
1083 raw_spin_lock_irq(&sem->wait_lock);
1084 if (waiter.task)
1085 goto out_nolock;
1086 raw_spin_unlock_irq(&sem->wait_lock);
1087
1088 break;
1089 }
1090 schedule();
1091 lockevent_inc(rwsem_sleep_reader);
1092 }
1093
1094 __set_current_state(TASK_RUNNING);
1095 lockevent_inc(rwsem_rlock);
1096 return sem;
1097
1098out_nolock:
1099 list_del(&waiter.list);
1100 if (list_empty(&sem->wait_list)) {
1101 atomic_long_andnot(RWSEM_FLAG_WAITERS|RWSEM_FLAG_HANDOFF,
1102 &sem->count);
1103 }
1104 raw_spin_unlock_irq(&sem->wait_lock);
1105 __set_current_state(TASK_RUNNING);
1106 lockevent_inc(rwsem_rlock_fail);
1107 return ERR_PTR(-EINTR);
1108}
1109
1110
1111
1112
1113
1114static inline void rwsem_disable_reader_optspin(struct rw_semaphore *sem,
1115 bool disable)
1116{
1117 if (unlikely(disable)) {
1118 atomic_long_or(RWSEM_RD_NONSPINNABLE, &sem->owner);
1119 lockevent_inc(rwsem_opt_norspin);
1120 }
1121}
1122
1123
1124
1125
1126static struct rw_semaphore *
1127rwsem_down_write_slowpath(struct rw_semaphore *sem, int state)
1128{
1129 long count;
1130 bool disable_rspin;
1131 enum writer_wait_state wstate;
1132 struct rwsem_waiter waiter;
1133 struct rw_semaphore *ret = sem;
1134 DEFINE_WAKE_Q(wake_q);
1135
1136
1137 if (rwsem_can_spin_on_owner(sem, RWSEM_WR_NONSPINNABLE) &&
1138 rwsem_optimistic_spin(sem, true)) {
1139
1140 return sem;
1141 }
1142
1143
1144
1145
1146
1147
1148 disable_rspin = atomic_long_read(&sem->owner) & RWSEM_NONSPINNABLE;
1149
1150
1151
1152
1153
1154 waiter.task = current;
1155 waiter.type = RWSEM_WAITING_FOR_WRITE;
1156 waiter.timeout = jiffies + RWSEM_WAIT_TIMEOUT;
1157
1158 raw_spin_lock_irq(&sem->wait_lock);
1159
1160
1161 wstate = list_empty(&sem->wait_list) ? WRITER_FIRST : WRITER_NOT_FIRST;
1162
1163 list_add_tail(&waiter.list, &sem->wait_list);
1164
1165
1166 if (wstate == WRITER_NOT_FIRST) {
1167 count = atomic_long_read(&sem->count);
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177 if (count & RWSEM_WRITER_MASK)
1178 goto wait;
1179
1180 rwsem_mark_wake(sem, (count & RWSEM_READER_MASK)
1181 ? RWSEM_WAKE_READERS
1182 : RWSEM_WAKE_ANY, &wake_q);
1183
1184 if (!wake_q_empty(&wake_q)) {
1185
1186
1187
1188
1189 raw_spin_unlock_irq(&sem->wait_lock);
1190 wake_up_q(&wake_q);
1191 wake_q_init(&wake_q);
1192 raw_spin_lock_irq(&sem->wait_lock);
1193 }
1194 } else {
1195 atomic_long_or(RWSEM_FLAG_WAITERS, &sem->count);
1196 }
1197
1198wait:
1199
1200 set_current_state(state);
1201 for (;;) {
1202 if (rwsem_try_write_lock(sem, wstate)) {
1203
1204 break;
1205 }
1206
1207 raw_spin_unlock_irq(&sem->wait_lock);
1208
1209
1210 for (;;) {
1211 if (signal_pending_state(state, current))
1212 goto out_nolock;
1213
1214 schedule();
1215 lockevent_inc(rwsem_sleep_writer);
1216 set_current_state(state);
1217
1218
1219
1220
1221 if (wstate == WRITER_HANDOFF)
1222 break;
1223
1224 if ((wstate == WRITER_NOT_FIRST) &&
1225 (rwsem_first_waiter(sem) == &waiter))
1226 wstate = WRITER_FIRST;
1227
1228 count = atomic_long_read(&sem->count);
1229 if (!(count & RWSEM_LOCK_MASK))
1230 break;
1231
1232
1233
1234
1235
1236 if ((wstate == WRITER_FIRST) && (rt_task(current) ||
1237 time_after(jiffies, waiter.timeout))) {
1238 wstate = WRITER_HANDOFF;
1239 lockevent_inc(rwsem_wlock_handoff);
1240 break;
1241 }
1242 }
1243
1244 raw_spin_lock_irq(&sem->wait_lock);
1245 }
1246 __set_current_state(TASK_RUNNING);
1247 list_del(&waiter.list);
1248 rwsem_disable_reader_optspin(sem, disable_rspin);
1249 raw_spin_unlock_irq(&sem->wait_lock);
1250 lockevent_inc(rwsem_wlock);
1251
1252 return ret;
1253
1254out_nolock:
1255 __set_current_state(TASK_RUNNING);
1256 raw_spin_lock_irq(&sem->wait_lock);
1257 list_del(&waiter.list);
1258
1259 if (unlikely(wstate == WRITER_HANDOFF))
1260 atomic_long_add(-RWSEM_FLAG_HANDOFF, &sem->count);
1261
1262 if (list_empty(&sem->wait_list))
1263 atomic_long_andnot(RWSEM_FLAG_WAITERS, &sem->count);
1264 else
1265 rwsem_mark_wake(sem, RWSEM_WAKE_ANY, &wake_q);
1266 raw_spin_unlock_irq(&sem->wait_lock);
1267 wake_up_q(&wake_q);
1268 lockevent_inc(rwsem_wlock_fail);
1269
1270 return ERR_PTR(-EINTR);
1271}
1272
1273
1274
1275
1276
1277static struct rw_semaphore *rwsem_wake(struct rw_semaphore *sem, long count)
1278{
1279 unsigned long flags;
1280 DEFINE_WAKE_Q(wake_q);
1281
1282 raw_spin_lock_irqsave(&sem->wait_lock, flags);
1283
1284 if (!list_empty(&sem->wait_list))
1285 rwsem_mark_wake(sem, RWSEM_WAKE_ANY, &wake_q);
1286
1287 raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
1288 wake_up_q(&wake_q);
1289
1290 return sem;
1291}
1292
1293
1294
1295
1296
1297
1298static struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem)
1299{
1300 unsigned long flags;
1301 DEFINE_WAKE_Q(wake_q);
1302
1303 raw_spin_lock_irqsave(&sem->wait_lock, flags);
1304
1305 if (!list_empty(&sem->wait_list))
1306 rwsem_mark_wake(sem, RWSEM_WAKE_READ_OWNED, &wake_q);
1307
1308 raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
1309 wake_up_q(&wake_q);
1310
1311 return sem;
1312}
1313
1314
1315
1316
1317inline void __down_read(struct rw_semaphore *sem)
1318{
1319 if (!rwsem_read_trylock(sem)) {
1320 rwsem_down_read_slowpath(sem, TASK_UNINTERRUPTIBLE);
1321 DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);
1322 } else {
1323 rwsem_set_reader_owned(sem);
1324 }
1325}
1326
1327static inline int __down_read_killable(struct rw_semaphore *sem)
1328{
1329 if (!rwsem_read_trylock(sem)) {
1330 if (IS_ERR(rwsem_down_read_slowpath(sem, TASK_KILLABLE)))
1331 return -EINTR;
1332 DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);
1333 } else {
1334 rwsem_set_reader_owned(sem);
1335 }
1336 return 0;
1337}
1338
1339static inline int __down_read_trylock(struct rw_semaphore *sem)
1340{
1341
1342
1343
1344 long tmp = RWSEM_UNLOCKED_VALUE;
1345
1346 do {
1347 if (atomic_long_try_cmpxchg_acquire(&sem->count, &tmp,
1348 tmp + RWSEM_READER_BIAS)) {
1349 rwsem_set_reader_owned(sem);
1350 return 1;
1351 }
1352 } while (!(tmp & RWSEM_READ_FAILED_MASK));
1353 return 0;
1354}
1355
1356
1357
1358
1359static inline void __down_write(struct rw_semaphore *sem)
1360{
1361 long tmp = RWSEM_UNLOCKED_VALUE;
1362
1363 if (unlikely(!atomic_long_try_cmpxchg_acquire(&sem->count, &tmp,
1364 RWSEM_WRITER_LOCKED)))
1365 rwsem_down_write_slowpath(sem, TASK_UNINTERRUPTIBLE);
1366 else
1367 rwsem_set_owner(sem);
1368}
1369
1370static inline int __down_write_killable(struct rw_semaphore *sem)
1371{
1372 long tmp = RWSEM_UNLOCKED_VALUE;
1373
1374 if (unlikely(!atomic_long_try_cmpxchg_acquire(&sem->count, &tmp,
1375 RWSEM_WRITER_LOCKED))) {
1376 if (IS_ERR(rwsem_down_write_slowpath(sem, TASK_KILLABLE)))
1377 return -EINTR;
1378 } else {
1379 rwsem_set_owner(sem);
1380 }
1381 return 0;
1382}
1383
1384static inline int __down_write_trylock(struct rw_semaphore *sem)
1385{
1386 long tmp = RWSEM_UNLOCKED_VALUE;
1387
1388 if (atomic_long_try_cmpxchg_acquire(&sem->count, &tmp,
1389 RWSEM_WRITER_LOCKED)) {
1390 rwsem_set_owner(sem);
1391 return true;
1392 }
1393 return false;
1394}
1395
1396
1397
1398
1399inline void __up_read(struct rw_semaphore *sem)
1400{
1401 long tmp;
1402
1403 DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);
1404 rwsem_clear_reader_owned(sem);
1405 tmp = atomic_long_add_return_release(-RWSEM_READER_BIAS, &sem->count);
1406 DEBUG_RWSEMS_WARN_ON(tmp < 0, sem);
1407 if (unlikely((tmp & (RWSEM_LOCK_MASK|RWSEM_FLAG_WAITERS)) ==
1408 RWSEM_FLAG_WAITERS)) {
1409 clear_wr_nonspinnable(sem);
1410 rwsem_wake(sem, tmp);
1411 }
1412}
1413
1414
1415
1416
1417static inline void __up_write(struct rw_semaphore *sem)
1418{
1419 long tmp;
1420
1421
1422
1423
1424
1425 DEBUG_RWSEMS_WARN_ON((rwsem_owner(sem) != current) &&
1426 !rwsem_test_oflags(sem, RWSEM_NONSPINNABLE), sem);
1427 rwsem_clear_owner(sem);
1428 tmp = atomic_long_fetch_add_release(-RWSEM_WRITER_LOCKED, &sem->count);
1429 if (unlikely(tmp & RWSEM_FLAG_WAITERS))
1430 rwsem_wake(sem, tmp);
1431}
1432
1433
1434
1435
1436static inline void __downgrade_write(struct rw_semaphore *sem)
1437{
1438 long tmp;
1439
1440
1441
1442
1443
1444
1445
1446
1447 DEBUG_RWSEMS_WARN_ON(rwsem_owner(sem) != current, sem);
1448 tmp = atomic_long_fetch_add_release(
1449 -RWSEM_WRITER_LOCKED+RWSEM_READER_BIAS, &sem->count);
1450 rwsem_set_reader_owned(sem);
1451 if (tmp & RWSEM_FLAG_WAITERS)
1452 rwsem_downgrade_wake(sem);
1453}
1454
1455
1456
1457
1458void __sched down_read(struct rw_semaphore *sem)
1459{
1460 might_sleep();
1461 rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_);
1462
1463 LOCK_CONTENDED(sem, __down_read_trylock, __down_read);
1464}
1465EXPORT_SYMBOL(down_read);
1466
1467int __sched down_read_killable(struct rw_semaphore *sem)
1468{
1469 might_sleep();
1470 rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_);
1471
1472 if (LOCK_CONTENDED_RETURN(sem, __down_read_trylock, __down_read_killable)) {
1473 rwsem_release(&sem->dep_map, 1, _RET_IP_);
1474 return -EINTR;
1475 }
1476
1477 return 0;
1478}
1479EXPORT_SYMBOL(down_read_killable);
1480
1481
1482
1483
1484int down_read_trylock(struct rw_semaphore *sem)
1485{
1486 int ret = __down_read_trylock(sem);
1487
1488 if (ret == 1)
1489 rwsem_acquire_read(&sem->dep_map, 0, 1, _RET_IP_);
1490 return ret;
1491}
1492EXPORT_SYMBOL(down_read_trylock);
1493
1494
1495
1496
1497void __sched down_write(struct rw_semaphore *sem)
1498{
1499 might_sleep();
1500 rwsem_acquire(&sem->dep_map, 0, 0, _RET_IP_);
1501 LOCK_CONTENDED(sem, __down_write_trylock, __down_write);
1502}
1503EXPORT_SYMBOL(down_write);
1504
1505
1506
1507
1508int __sched down_write_killable(struct rw_semaphore *sem)
1509{
1510 might_sleep();
1511 rwsem_acquire(&sem->dep_map, 0, 0, _RET_IP_);
1512
1513 if (LOCK_CONTENDED_RETURN(sem, __down_write_trylock,
1514 __down_write_killable)) {
1515 rwsem_release(&sem->dep_map, 1, _RET_IP_);
1516 return -EINTR;
1517 }
1518
1519 return 0;
1520}
1521EXPORT_SYMBOL(down_write_killable);
1522
1523
1524
1525
1526int down_write_trylock(struct rw_semaphore *sem)
1527{
1528 int ret = __down_write_trylock(sem);
1529
1530 if (ret == 1)
1531 rwsem_acquire(&sem->dep_map, 0, 1, _RET_IP_);
1532
1533 return ret;
1534}
1535EXPORT_SYMBOL(down_write_trylock);
1536
1537
1538
1539
1540void up_read(struct rw_semaphore *sem)
1541{
1542 rwsem_release(&sem->dep_map, 1, _RET_IP_);
1543 __up_read(sem);
1544}
1545EXPORT_SYMBOL(up_read);
1546
1547
1548
1549
1550void up_write(struct rw_semaphore *sem)
1551{
1552 rwsem_release(&sem->dep_map, 1, _RET_IP_);
1553 __up_write(sem);
1554}
1555EXPORT_SYMBOL(up_write);
1556
1557
1558
1559
1560void downgrade_write(struct rw_semaphore *sem)
1561{
1562 lock_downgrade(&sem->dep_map, _RET_IP_);
1563 __downgrade_write(sem);
1564}
1565EXPORT_SYMBOL(downgrade_write);
1566
1567#ifdef CONFIG_DEBUG_LOCK_ALLOC
1568
1569void down_read_nested(struct rw_semaphore *sem, int subclass)
1570{
1571 might_sleep();
1572 rwsem_acquire_read(&sem->dep_map, subclass, 0, _RET_IP_);
1573 LOCK_CONTENDED(sem, __down_read_trylock, __down_read);
1574}
1575EXPORT_SYMBOL(down_read_nested);
1576
1577void _down_write_nest_lock(struct rw_semaphore *sem, struct lockdep_map *nest)
1578{
1579 might_sleep();
1580 rwsem_acquire_nest(&sem->dep_map, 0, 0, nest, _RET_IP_);
1581 LOCK_CONTENDED(sem, __down_write_trylock, __down_write);
1582}
1583EXPORT_SYMBOL(_down_write_nest_lock);
1584
1585void down_read_non_owner(struct rw_semaphore *sem)
1586{
1587 might_sleep();
1588 __down_read(sem);
1589 __rwsem_set_reader_owned(sem, NULL);
1590}
1591EXPORT_SYMBOL(down_read_non_owner);
1592
1593void down_write_nested(struct rw_semaphore *sem, int subclass)
1594{
1595 might_sleep();
1596 rwsem_acquire(&sem->dep_map, subclass, 0, _RET_IP_);
1597 LOCK_CONTENDED(sem, __down_write_trylock, __down_write);
1598}
1599EXPORT_SYMBOL(down_write_nested);
1600
1601int __sched down_write_killable_nested(struct rw_semaphore *sem, int subclass)
1602{
1603 might_sleep();
1604 rwsem_acquire(&sem->dep_map, subclass, 0, _RET_IP_);
1605
1606 if (LOCK_CONTENDED_RETURN(sem, __down_write_trylock,
1607 __down_write_killable)) {
1608 rwsem_release(&sem->dep_map, 1, _RET_IP_);
1609 return -EINTR;
1610 }
1611
1612 return 0;
1613}
1614EXPORT_SYMBOL(down_write_killable_nested);
1615
1616void up_read_non_owner(struct rw_semaphore *sem)
1617{
1618 DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);
1619 __up_read(sem);
1620}
1621EXPORT_SYMBOL(up_read_non_owner);
1622
1623#endif
1624