1 // SPDX-License-Identifier: GPL-2.0
2 /* kernel/rwsem.c: R/W semaphores, public implementation
4 * Written by David Howells (dhowells@redhat.com).
5 * Derived from asm-i386/semaphore.h
7 * Writer lock-stealing by Alex Shi <alex.shi@intel.com>
8 * and Michel Lespinasse <walken@google.com>
10 * Optimistic spinning by Tim Chen <tim.c.chen@intel.com>
11 * and Davidlohr Bueso <davidlohr@hp.com>. Based on mutexes.
13 * Rwsem count bit fields re-definition and rwsem rearchitecture by
14 * Waiman Long <longman@redhat.com> and
15 * Peter Zijlstra <peterz@infradead.org>.
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>
31 #ifndef CONFIG_PREEMPT_RT
32 #include "lock_events.h"
35 * The least significant 2 bits of the owner value has the following
37 * - Bit 0: RWSEM_READER_OWNED - The rwsem is owned by readers
38 * - Bit 1: RWSEM_NONSPINNABLE - Cannot spin on a reader-owned lock
40 * When the rwsem is reader-owned and a spinning writer has timed out,
41 * the nonspinnable bit will be set to disable optimistic spinning.
43 * When a writer acquires a rwsem, it puts its task_struct pointer
44 * into the owner field. It is cleared after an unlock.
46 * When a reader acquires a rwsem, it will also puts its task_struct
47 * pointer into the owner field with the RWSEM_READER_OWNED bit set.
48 * On unlock, the owner field will largely be left untouched. So
49 * for a free or reader-owned rwsem, the owner value may contain
50 * information about the last reader that acquires the rwsem.
52 * That information may be helpful in debugging cases where the system
53 * seems to hang on a reader owned rwsem especially if only one reader
54 * is involved. Ideally we would like to track all the readers that own
55 * a rwsem, but the overhead is simply too big.
57 * A fast path reader optimistic lock stealing is supported when the rwsem
58 * is previously owned by a writer and the following conditions are met:
59 * - rwsem is not currently writer owned
60 * - the handoff isn't set.
62 #define RWSEM_READER_OWNED (1UL << 0)
63 #define RWSEM_NONSPINNABLE (1UL << 1)
64 #define RWSEM_OWNER_FLAGS_MASK (RWSEM_READER_OWNED | RWSEM_NONSPINNABLE)
66 #ifdef CONFIG_DEBUG_RWSEMS
67 # define DEBUG_RWSEMS_WARN_ON(c, sem) do { \
68 if (!debug_locks_silent && \
69 WARN_ONCE(c, "DEBUG_RWSEMS_WARN_ON(%s): count = 0x%lx, magic = 0x%lx, owner = 0x%lx, curr 0x%lx, list %sempty\n",\
70 #c, atomic_long_read(&(sem)->count), \
71 (unsigned long) sem->magic, \
72 atomic_long_read(&(sem)->owner), (long)current, \
73 list_empty(&(sem)->wait_list) ? "" : "not ")) \
77 # define DEBUG_RWSEMS_WARN_ON(c, sem)
81 * On 64-bit architectures, the bit definitions of the count are:
83 * Bit 0 - writer locked bit
84 * Bit 1 - waiters present bit
85 * Bit 2 - lock handoff bit
87 * Bits 8-62 - 55-bit reader count
88 * Bit 63 - read fail bit
90 * On 32-bit architectures, the bit definitions of the count are:
92 * Bit 0 - writer locked bit
93 * Bit 1 - waiters present bit
94 * Bit 2 - lock handoff bit
96 * Bits 8-30 - 23-bit reader count
97 * Bit 31 - read fail bit
99 * It is not likely that the most significant bit (read fail bit) will ever
100 * be set. This guard bit is still checked anyway in the down_read() fastpath
101 * just in case we need to use up more of the reader bits for other purpose
104 * atomic_long_fetch_add() is used to obtain reader lock, whereas
105 * atomic_long_cmpxchg() will be used to obtain writer lock.
107 * There are three places where the lock handoff bit may be set or cleared.
108 * 1) rwsem_mark_wake() for readers -- set, clear
109 * 2) rwsem_try_write_lock() for writers -- set, clear
110 * 3) rwsem_del_waiter() -- clear
112 * For all the above cases, wait_lock will be held. A writer must also
113 * be the first one in the wait_list to be eligible for setting the handoff
114 * bit. So concurrent setting/clearing of handoff bit is not possible.
116 #define RWSEM_WRITER_LOCKED (1UL << 0)
117 #define RWSEM_FLAG_WAITERS (1UL << 1)
118 #define RWSEM_FLAG_HANDOFF (1UL << 2)
119 #define RWSEM_FLAG_READFAIL (1UL << (BITS_PER_LONG - 1))
121 #define RWSEM_READER_SHIFT 8
122 #define RWSEM_READER_BIAS (1UL << RWSEM_READER_SHIFT)
123 #define RWSEM_READER_MASK (~(RWSEM_READER_BIAS - 1))
124 #define RWSEM_WRITER_MASK RWSEM_WRITER_LOCKED
125 #define RWSEM_LOCK_MASK (RWSEM_WRITER_MASK|RWSEM_READER_MASK)
126 #define RWSEM_READ_FAILED_MASK (RWSEM_WRITER_MASK|RWSEM_FLAG_WAITERS|\
127 RWSEM_FLAG_HANDOFF|RWSEM_FLAG_READFAIL)
130 * All writes to owner are protected by WRITE_ONCE() to make sure that
131 * store tearing can't happen as optimistic spinners may read and use
132 * the owner value concurrently without lock. Read from owner, however,
133 * may not need READ_ONCE() as long as the pointer value is only used
134 * for comparison and isn't being dereferenced.
136 static inline void rwsem_set_owner(struct rw_semaphore *sem)
138 atomic_long_set(&sem->owner, (long)current);
141 static inline void rwsem_clear_owner(struct rw_semaphore *sem)
143 atomic_long_set(&sem->owner, 0);
147 * Test the flags in the owner field.
149 static inline bool rwsem_test_oflags(struct rw_semaphore *sem, long flags)
151 return atomic_long_read(&sem->owner) & flags;
155 * The task_struct pointer of the last owning reader will be left in
158 * Note that the owner value just indicates the task has owned the rwsem
159 * previously, it may not be the real owner or one of the real owners
160 * anymore when that field is examined, so take it with a grain of salt.
162 * The reader non-spinnable bit is preserved.
164 static inline void __rwsem_set_reader_owned(struct rw_semaphore *sem,
165 struct task_struct *owner)
167 unsigned long val = (unsigned long)owner | RWSEM_READER_OWNED |
168 (atomic_long_read(&sem->owner) & RWSEM_NONSPINNABLE);
170 atomic_long_set(&sem->owner, val);
173 static inline void rwsem_set_reader_owned(struct rw_semaphore *sem)
175 __rwsem_set_reader_owned(sem, current);
179 * Return true if the rwsem is owned by a reader.
181 static inline bool is_rwsem_reader_owned(struct rw_semaphore *sem)
183 #ifdef CONFIG_DEBUG_RWSEMS
185 * Check the count to see if it is write-locked.
187 long count = atomic_long_read(&sem->count);
189 if (count & RWSEM_WRITER_MASK)
192 return rwsem_test_oflags(sem, RWSEM_READER_OWNED);
195 #ifdef CONFIG_DEBUG_RWSEMS
197 * With CONFIG_DEBUG_RWSEMS configured, it will make sure that if there
198 * is a task pointer in owner of a reader-owned rwsem, it will be the
199 * real owner or one of the real owners. The only exception is when the
200 * unlock is done by up_read_non_owner().
202 static inline void rwsem_clear_reader_owned(struct rw_semaphore *sem)
204 unsigned long val = atomic_long_read(&sem->owner);
206 while ((val & ~RWSEM_OWNER_FLAGS_MASK) == (unsigned long)current) {
207 if (atomic_long_try_cmpxchg(&sem->owner, &val,
208 val & RWSEM_OWNER_FLAGS_MASK))
213 static inline void rwsem_clear_reader_owned(struct rw_semaphore *sem)
219 * Set the RWSEM_NONSPINNABLE bits if the RWSEM_READER_OWNED flag
220 * remains set. Otherwise, the operation will be aborted.
222 static inline void rwsem_set_nonspinnable(struct rw_semaphore *sem)
224 unsigned long owner = atomic_long_read(&sem->owner);
227 if (!(owner & RWSEM_READER_OWNED))
229 if (owner & RWSEM_NONSPINNABLE)
231 } while (!atomic_long_try_cmpxchg(&sem->owner, &owner,
232 owner | RWSEM_NONSPINNABLE));
235 static inline bool rwsem_read_trylock(struct rw_semaphore *sem, long *cntp)
237 *cntp = atomic_long_add_return_acquire(RWSEM_READER_BIAS, &sem->count);
239 if (WARN_ON_ONCE(*cntp < 0))
240 rwsem_set_nonspinnable(sem);
242 if (!(*cntp & RWSEM_READ_FAILED_MASK)) {
243 rwsem_set_reader_owned(sem);
250 static inline bool rwsem_write_trylock(struct rw_semaphore *sem)
252 long tmp = RWSEM_UNLOCKED_VALUE;
254 if (atomic_long_try_cmpxchg_acquire(&sem->count, &tmp, RWSEM_WRITER_LOCKED)) {
255 rwsem_set_owner(sem);
263 * Return just the real task structure pointer of the owner
265 static inline struct task_struct *rwsem_owner(struct rw_semaphore *sem)
267 return (struct task_struct *)
268 (atomic_long_read(&sem->owner) & ~RWSEM_OWNER_FLAGS_MASK);
272 * Return the real task structure pointer of the owner and the embedded
273 * flags in the owner. pflags must be non-NULL.
275 static inline struct task_struct *
276 rwsem_owner_flags(struct rw_semaphore *sem, unsigned long *pflags)
278 unsigned long owner = atomic_long_read(&sem->owner);
280 *pflags = owner & RWSEM_OWNER_FLAGS_MASK;
281 return (struct task_struct *)(owner & ~RWSEM_OWNER_FLAGS_MASK);
285 * Guide to the rw_semaphore's count field.
287 * When the RWSEM_WRITER_LOCKED bit in count is set, the lock is owned
290 * The lock is owned by readers when
291 * (1) the RWSEM_WRITER_LOCKED isn't set in count,
292 * (2) some of the reader bits are set in count, and
293 * (3) the owner field has RWSEM_READ_OWNED bit set.
295 * Having some reader bits set is not enough to guarantee a readers owned
296 * lock as the readers may be in the process of backing out from the count
297 * and a writer has just released the lock. So another writer may steal
298 * the lock immediately after that.
302 * Initialize an rwsem:
304 void __init_rwsem(struct rw_semaphore *sem, const char *name,
305 struct lock_class_key *key)
307 #ifdef CONFIG_DEBUG_LOCK_ALLOC
309 * Make sure we are not reinitializing a held semaphore:
311 debug_check_no_locks_freed((void *)sem, sizeof(*sem));
312 lockdep_init_map_wait(&sem->dep_map, name, key, 0, LD_WAIT_SLEEP);
314 #ifdef CONFIG_DEBUG_RWSEMS
317 atomic_long_set(&sem->count, RWSEM_UNLOCKED_VALUE);
318 raw_spin_lock_init(&sem->wait_lock);
319 INIT_LIST_HEAD(&sem->wait_list);
320 atomic_long_set(&sem->owner, 0L);
321 #ifdef CONFIG_RWSEM_SPIN_ON_OWNER
322 osq_lock_init(&sem->osq);
325 EXPORT_SYMBOL(__init_rwsem);
327 enum rwsem_waiter_type {
328 RWSEM_WAITING_FOR_WRITE,
329 RWSEM_WAITING_FOR_READ
332 struct rwsem_waiter {
333 struct list_head list;
334 struct task_struct *task;
335 enum rwsem_waiter_type type;
336 unsigned long timeout;
338 /* Writer only, not initialized in reader */
341 #define rwsem_first_waiter(sem) \
342 list_first_entry(&sem->wait_list, struct rwsem_waiter, list)
344 enum rwsem_wake_type {
345 RWSEM_WAKE_ANY, /* Wake whatever's at head of wait list */
346 RWSEM_WAKE_READERS, /* Wake readers only */
347 RWSEM_WAKE_READ_OWNED /* Waker thread holds the read lock */
351 * The typical HZ value is either 250 or 1000. So set the minimum waiting
352 * time to at least 4ms or 1 jiffy (if it is higher than 4ms) in the wait
353 * queue before initiating the handoff protocol.
355 #define RWSEM_WAIT_TIMEOUT DIV_ROUND_UP(HZ, 250)
358 * Magic number to batch-wakeup waiting readers, even when writers are
359 * also present in the queue. This both limits the amount of work the
360 * waking thread must do and also prevents any potential counter overflow,
363 #define MAX_READERS_WAKEUP 0x100
366 rwsem_add_waiter(struct rw_semaphore *sem, struct rwsem_waiter *waiter)
368 lockdep_assert_held(&sem->wait_lock);
369 list_add_tail(&waiter->list, &sem->wait_list);
370 /* caller will set RWSEM_FLAG_WAITERS */
374 * Remove a waiter from the wait_list and clear flags.
376 * Both rwsem_mark_wake() and rwsem_try_write_lock() contain a full 'copy' of
377 * this function. Modify with care.
380 rwsem_del_waiter(struct rw_semaphore *sem, struct rwsem_waiter *waiter)
382 lockdep_assert_held(&sem->wait_lock);
383 list_del(&waiter->list);
384 if (likely(!list_empty(&sem->wait_list)))
387 atomic_long_andnot(RWSEM_FLAG_HANDOFF | RWSEM_FLAG_WAITERS, &sem->count);
391 * handle the lock release when processes blocked on it that can now run
392 * - if we come here from up_xxxx(), then the RWSEM_FLAG_WAITERS bit must
394 * - there must be someone on the queue
395 * - the wait_lock must be held by the caller
396 * - tasks are marked for wakeup, the caller must later invoke wake_up_q()
397 * to actually wakeup the blocked task(s) and drop the reference count,
398 * preferably when the wait_lock is released
399 * - woken process blocks are discarded from the list after having task zeroed
400 * - writers are only marked woken if downgrading is false
402 * Implies rwsem_del_waiter() for all woken readers.
404 static void rwsem_mark_wake(struct rw_semaphore *sem,
405 enum rwsem_wake_type wake_type,
406 struct wake_q_head *wake_q)
408 struct rwsem_waiter *waiter, *tmp;
409 long oldcount, woken = 0, adjustment = 0;
410 struct list_head wlist;
412 lockdep_assert_held(&sem->wait_lock);
415 * Take a peek at the queue head waiter such that we can determine
416 * the wakeup(s) to perform.
418 waiter = rwsem_first_waiter(sem);
420 if (waiter->type == RWSEM_WAITING_FOR_WRITE) {
421 if (wake_type == RWSEM_WAKE_ANY) {
423 * Mark writer at the front of the queue for wakeup.
424 * Until the task is actually later awoken later by
425 * the caller, other writers are able to steal it.
426 * Readers, on the other hand, will block as they
427 * will notice the queued writer.
429 wake_q_add(wake_q, waiter->task);
430 lockevent_inc(rwsem_wake_writer);
437 * No reader wakeup if there are too many of them already.
439 if (unlikely(atomic_long_read(&sem->count) < 0))
443 * Writers might steal the lock before we grant it to the next reader.
444 * We prefer to do the first reader grant before counting readers
445 * so we can bail out early if a writer stole the lock.
447 if (wake_type != RWSEM_WAKE_READ_OWNED) {
448 struct task_struct *owner;
450 adjustment = RWSEM_READER_BIAS;
451 oldcount = atomic_long_fetch_add(adjustment, &sem->count);
452 if (unlikely(oldcount & RWSEM_WRITER_MASK)) {
454 * When we've been waiting "too" long (for writers
455 * to give up the lock), request a HANDOFF to
458 if (!(oldcount & RWSEM_FLAG_HANDOFF) &&
459 time_after(jiffies, waiter->timeout)) {
460 adjustment -= RWSEM_FLAG_HANDOFF;
461 lockevent_inc(rwsem_rlock_handoff);
464 atomic_long_add(-adjustment, &sem->count);
468 * Set it to reader-owned to give spinners an early
469 * indication that readers now have the lock.
470 * The reader nonspinnable bit seen at slowpath entry of
471 * the reader is copied over.
473 owner = waiter->task;
474 __rwsem_set_reader_owned(sem, owner);
478 * Grant up to MAX_READERS_WAKEUP read locks to all the readers in the
479 * queue. We know that the woken will be at least 1 as we accounted
480 * for above. Note we increment the 'active part' of the count by the
481 * number of readers before waking any processes up.
483 * This is an adaptation of the phase-fair R/W locks where at the
484 * reader phase (first waiter is a reader), all readers are eligible
485 * to acquire the lock at the same time irrespective of their order
486 * in the queue. The writers acquire the lock according to their
487 * order in the queue.
489 * We have to do wakeup in 2 passes to prevent the possibility that
490 * the reader count may be decremented before it is incremented. It
491 * is because the to-be-woken waiter may not have slept yet. So it
492 * may see waiter->task got cleared, finish its critical section and
493 * do an unlock before the reader count increment.
495 * 1) Collect the read-waiters in a separate list, count them and
496 * fully increment the reader count in rwsem.
497 * 2) For each waiters in the new list, clear waiter->task and
498 * put them into wake_q to be woken up later.
500 INIT_LIST_HEAD(&wlist);
501 list_for_each_entry_safe(waiter, tmp, &sem->wait_list, list) {
502 if (waiter->type == RWSEM_WAITING_FOR_WRITE)
506 list_move_tail(&waiter->list, &wlist);
509 * Limit # of readers that can be woken up per wakeup call.
511 if (unlikely(woken >= MAX_READERS_WAKEUP))
515 adjustment = woken * RWSEM_READER_BIAS - adjustment;
516 lockevent_cond_inc(rwsem_wake_reader, woken);
518 oldcount = atomic_long_read(&sem->count);
519 if (list_empty(&sem->wait_list)) {
521 * Combined with list_move_tail() above, this implies
522 * rwsem_del_waiter().
524 adjustment -= RWSEM_FLAG_WAITERS;
525 if (oldcount & RWSEM_FLAG_HANDOFF)
526 adjustment -= RWSEM_FLAG_HANDOFF;
529 * When we've woken a reader, we no longer need to force
530 * writers to give up the lock and we can clear HANDOFF.
532 if (oldcount & RWSEM_FLAG_HANDOFF)
533 adjustment -= RWSEM_FLAG_HANDOFF;
537 atomic_long_add(adjustment, &sem->count);
540 list_for_each_entry_safe(waiter, tmp, &wlist, list) {
541 struct task_struct *tsk;
544 get_task_struct(tsk);
547 * Ensure calling get_task_struct() before setting the reader
548 * waiter to nil such that rwsem_down_read_slowpath() cannot
549 * race with do_exit() by always holding a reference count
550 * to the task to wakeup.
552 smp_store_release(&waiter->task, NULL);
554 * Ensure issuing the wakeup (either by us or someone else)
555 * after setting the reader waiter to nil.
557 wake_q_add_safe(wake_q, tsk);
562 * This function must be called with the sem->wait_lock held to prevent
563 * race conditions between checking the rwsem wait list and setting the
564 * sem->count accordingly.
566 * Implies rwsem_del_waiter() on success.
568 static inline bool rwsem_try_write_lock(struct rw_semaphore *sem,
569 struct rwsem_waiter *waiter)
571 bool first = rwsem_first_waiter(sem) == waiter;
574 lockdep_assert_held(&sem->wait_lock);
576 count = atomic_long_read(&sem->count);
578 bool has_handoff = !!(count & RWSEM_FLAG_HANDOFF);
584 /* First waiter inherits a previously set handoff bit */
585 waiter->handoff_set = true;
590 if (count & RWSEM_LOCK_MASK) {
591 if (has_handoff || (!rt_task(waiter->task) &&
592 !time_after(jiffies, waiter->timeout)))
595 new |= RWSEM_FLAG_HANDOFF;
597 new |= RWSEM_WRITER_LOCKED;
598 new &= ~RWSEM_FLAG_HANDOFF;
600 if (list_is_singular(&sem->wait_list))
601 new &= ~RWSEM_FLAG_WAITERS;
603 } while (!atomic_long_try_cmpxchg_acquire(&sem->count, &count, new));
606 * We have either acquired the lock with handoff bit cleared or
607 * set the handoff bit.
609 if (new & RWSEM_FLAG_HANDOFF) {
610 waiter->handoff_set = true;
611 lockevent_inc(rwsem_wlock_handoff);
616 * Have rwsem_try_write_lock() fully imply rwsem_del_waiter() on
619 list_del(&waiter->list);
620 rwsem_set_owner(sem);
625 * The rwsem_spin_on_owner() function returns the following 4 values
626 * depending on the lock owner state.
627 * OWNER_NULL : owner is currently NULL
628 * OWNER_WRITER: when owner changes and is a writer
629 * OWNER_READER: when owner changes and the new owner may be a reader.
630 * OWNER_NONSPINNABLE:
631 * when optimistic spinning has to stop because either the
632 * owner stops running, is unknown, or its timeslice has
637 OWNER_WRITER = 1 << 1,
638 OWNER_READER = 1 << 2,
639 OWNER_NONSPINNABLE = 1 << 3,
642 #ifdef CONFIG_RWSEM_SPIN_ON_OWNER
644 * Try to acquire write lock before the writer has been put on wait queue.
646 static inline bool rwsem_try_write_lock_unqueued(struct rw_semaphore *sem)
648 long count = atomic_long_read(&sem->count);
650 while (!(count & (RWSEM_LOCK_MASK|RWSEM_FLAG_HANDOFF))) {
651 if (atomic_long_try_cmpxchg_acquire(&sem->count, &count,
652 count | RWSEM_WRITER_LOCKED)) {
653 rwsem_set_owner(sem);
654 lockevent_inc(rwsem_opt_lock);
661 static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem)
663 struct task_struct *owner;
667 if (need_resched()) {
668 lockevent_inc(rwsem_opt_fail);
674 * Disable preemption is equal to the RCU read-side crital section,
675 * thus the task_strcut structure won't go away.
677 owner = rwsem_owner_flags(sem, &flags);
679 * Don't check the read-owner as the entry may be stale.
681 if ((flags & RWSEM_NONSPINNABLE) ||
682 (owner && !(flags & RWSEM_READER_OWNED) && !owner_on_cpu(owner)))
686 lockevent_cond_inc(rwsem_opt_fail, !ret);
690 #define OWNER_SPINNABLE (OWNER_NULL | OWNER_WRITER | OWNER_READER)
692 static inline enum owner_state
693 rwsem_owner_state(struct task_struct *owner, unsigned long flags)
695 if (flags & RWSEM_NONSPINNABLE)
696 return OWNER_NONSPINNABLE;
698 if (flags & RWSEM_READER_OWNED)
701 return owner ? OWNER_WRITER : OWNER_NULL;
704 static noinline enum owner_state
705 rwsem_spin_on_owner(struct rw_semaphore *sem)
707 struct task_struct *new, *owner;
708 unsigned long flags, new_flags;
709 enum owner_state state;
711 lockdep_assert_preemption_disabled();
713 owner = rwsem_owner_flags(sem, &flags);
714 state = rwsem_owner_state(owner, flags);
715 if (state != OWNER_WRITER)
720 * When a waiting writer set the handoff flag, it may spin
721 * on the owner as well. Once that writer acquires the lock,
722 * we can spin on it. So we don't need to quit even when the
723 * handoff bit is set.
725 new = rwsem_owner_flags(sem, &new_flags);
726 if ((new != owner) || (new_flags != flags)) {
727 state = rwsem_owner_state(new, new_flags);
732 * Ensure we emit the owner->on_cpu, dereference _after_
733 * checking sem->owner still matches owner, if that fails,
734 * owner might point to free()d memory, if it still matches,
735 * our spinning context already disabled preemption which is
736 * equal to RCU read-side crital section ensures the memory
741 if (need_resched() || !owner_on_cpu(owner)) {
742 state = OWNER_NONSPINNABLE;
753 * Calculate reader-owned rwsem spinning threshold for writer
755 * The more readers own the rwsem, the longer it will take for them to
756 * wind down and free the rwsem. So the empirical formula used to
757 * determine the actual spinning time limit here is:
759 * Spinning threshold = (10 + nr_readers/2)us
761 * The limit is capped to a maximum of 25us (30 readers). This is just
762 * a heuristic and is subjected to change in the future.
764 static inline u64 rwsem_rspin_threshold(struct rw_semaphore *sem)
766 long count = atomic_long_read(&sem->count);
767 int readers = count >> RWSEM_READER_SHIFT;
772 delta = (20 + readers) * NSEC_PER_USEC / 2;
774 return sched_clock() + delta;
777 static bool rwsem_optimistic_spin(struct rw_semaphore *sem)
780 int prev_owner_state = OWNER_NULL;
782 u64 rspin_threshold = 0;
786 /* sem->wait_lock should not be held when doing optimistic spinning */
787 if (!osq_lock(&sem->osq))
791 * Optimistically spin on the owner field and attempt to acquire the
792 * lock whenever the owner changes. Spinning will be stopped when:
793 * 1) the owning writer isn't running; or
794 * 2) readers own the lock and spinning time has exceeded limit.
797 enum owner_state owner_state;
799 owner_state = rwsem_spin_on_owner(sem);
800 if (!(owner_state & OWNER_SPINNABLE))
804 * Try to acquire the lock
806 taken = rwsem_try_write_lock_unqueued(sem);
812 * Time-based reader-owned rwsem optimistic spinning
814 if (owner_state == OWNER_READER) {
816 * Re-initialize rspin_threshold every time when
817 * the owner state changes from non-reader to reader.
818 * This allows a writer to steal the lock in between
819 * 2 reader phases and have the threshold reset at
820 * the beginning of the 2nd reader phase.
822 if (prev_owner_state != OWNER_READER) {
823 if (rwsem_test_oflags(sem, RWSEM_NONSPINNABLE))
825 rspin_threshold = rwsem_rspin_threshold(sem);
830 * Check time threshold once every 16 iterations to
831 * avoid calling sched_clock() too frequently so
832 * as to reduce the average latency between the times
833 * when the lock becomes free and when the spinner
834 * is ready to do a trylock.
836 else if (!(++loop & 0xf) && (sched_clock() > rspin_threshold)) {
837 rwsem_set_nonspinnable(sem);
838 lockevent_inc(rwsem_opt_nospin);
844 * An RT task cannot do optimistic spinning if it cannot
845 * be sure the lock holder is running or live-lock may
846 * happen if the current task and the lock holder happen
847 * to run in the same CPU. However, aborting optimistic
848 * spinning while a NULL owner is detected may miss some
849 * opportunity where spinning can continue without causing
852 * There are 2 possible cases where an RT task may be able
853 * to continue spinning.
855 * 1) The lock owner is in the process of releasing the
856 * lock, sem->owner is cleared but the lock has not
858 * 2) The lock was free and owner cleared, but another
859 * task just comes in and acquire the lock before
860 * we try to get it. The new owner may be a spinnable
863 * To take advantage of two scenarios listed above, the RT
864 * task is made to retry one more time to see if it can
865 * acquire the lock or continue spinning on the new owning
866 * writer. Of course, if the time lag is long enough or the
867 * new owner is not a writer or spinnable, the RT task will
870 * If the owner is a writer, the need_resched() check is
871 * done inside rwsem_spin_on_owner(). If the owner is not
872 * a writer, need_resched() check needs to be done here.
874 if (owner_state != OWNER_WRITER) {
877 if (rt_task(current) &&
878 (prev_owner_state != OWNER_WRITER))
881 prev_owner_state = owner_state;
884 * The cpu_relax() call is a compiler barrier which forces
885 * everything in this loop to be re-loaded. We don't need
886 * memory barriers as we'll eventually observe the right
887 * values at the cost of a few extra spins.
891 osq_unlock(&sem->osq);
894 lockevent_cond_inc(rwsem_opt_fail, !taken);
899 * Clear the owner's RWSEM_NONSPINNABLE bit if it is set. This should
900 * only be called when the reader count reaches 0.
902 static inline void clear_nonspinnable(struct rw_semaphore *sem)
904 if (rwsem_test_oflags(sem, RWSEM_NONSPINNABLE))
905 atomic_long_andnot(RWSEM_NONSPINNABLE, &sem->owner);
909 static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem)
914 static inline bool rwsem_optimistic_spin(struct rw_semaphore *sem)
919 static inline void clear_nonspinnable(struct rw_semaphore *sem) { }
921 static inline enum owner_state
922 rwsem_spin_on_owner(struct rw_semaphore *sem)
924 return OWNER_NONSPINNABLE;
929 * Wait for the read lock to be granted
931 static struct rw_semaphore __sched *
932 rwsem_down_read_slowpath(struct rw_semaphore *sem, long count, unsigned int state)
934 long adjustment = -RWSEM_READER_BIAS;
935 long rcnt = (count >> RWSEM_READER_SHIFT);
936 struct rwsem_waiter waiter;
937 DEFINE_WAKE_Q(wake_q);
941 * To prevent a constant stream of readers from starving a sleeping
942 * waiter, don't attempt optimistic lock stealing if the lock is
943 * currently owned by readers.
945 if ((atomic_long_read(&sem->owner) & RWSEM_READER_OWNED) &&
946 (rcnt > 1) && !(count & RWSEM_WRITER_LOCKED))
950 * Reader optimistic lock stealing.
952 if (!(count & (RWSEM_WRITER_LOCKED | RWSEM_FLAG_HANDOFF))) {
953 rwsem_set_reader_owned(sem);
954 lockevent_inc(rwsem_rlock_steal);
957 * Wake up other readers in the wait queue if it is
960 if ((rcnt == 1) && (count & RWSEM_FLAG_WAITERS)) {
961 raw_spin_lock_irq(&sem->wait_lock);
962 if (!list_empty(&sem->wait_list))
963 rwsem_mark_wake(sem, RWSEM_WAKE_READ_OWNED,
965 raw_spin_unlock_irq(&sem->wait_lock);
972 waiter.task = current;
973 waiter.type = RWSEM_WAITING_FOR_READ;
974 waiter.timeout = jiffies + RWSEM_WAIT_TIMEOUT;
976 raw_spin_lock_irq(&sem->wait_lock);
977 if (list_empty(&sem->wait_list)) {
979 * In case the wait queue is empty and the lock isn't owned
980 * by a writer or has the handoff bit set, this reader can
981 * exit the slowpath and return immediately as its
982 * RWSEM_READER_BIAS has already been set in the count.
984 if (!(atomic_long_read(&sem->count) &
985 (RWSEM_WRITER_MASK | RWSEM_FLAG_HANDOFF))) {
986 /* Provide lock ACQUIRE */
987 smp_acquire__after_ctrl_dep();
988 raw_spin_unlock_irq(&sem->wait_lock);
989 rwsem_set_reader_owned(sem);
990 lockevent_inc(rwsem_rlock_fast);
993 adjustment += RWSEM_FLAG_WAITERS;
995 rwsem_add_waiter(sem, &waiter);
997 /* we're now waiting on the lock, but no longer actively locking */
998 count = atomic_long_add_return(adjustment, &sem->count);
1001 * If there are no active locks, wake the front queued process(es).
1003 * If there are no writers and we are first in the queue,
1004 * wake our own waiter to join the existing active readers !
1006 if (!(count & RWSEM_LOCK_MASK)) {
1007 clear_nonspinnable(sem);
1010 if (wake || (!(count & RWSEM_WRITER_MASK) &&
1011 (adjustment & RWSEM_FLAG_WAITERS)))
1012 rwsem_mark_wake(sem, RWSEM_WAKE_ANY, &wake_q);
1014 raw_spin_unlock_irq(&sem->wait_lock);
1017 /* wait to be given the lock */
1019 set_current_state(state);
1020 if (!smp_load_acquire(&waiter.task)) {
1021 /* Matches rwsem_mark_wake()'s smp_store_release(). */
1024 if (signal_pending_state(state, current)) {
1025 raw_spin_lock_irq(&sem->wait_lock);
1028 raw_spin_unlock_irq(&sem->wait_lock);
1029 /* Ordered by sem->wait_lock against rwsem_mark_wake(). */
1033 lockevent_inc(rwsem_sleep_reader);
1036 __set_current_state(TASK_RUNNING);
1037 lockevent_inc(rwsem_rlock);
1041 rwsem_del_waiter(sem, &waiter);
1042 raw_spin_unlock_irq(&sem->wait_lock);
1043 __set_current_state(TASK_RUNNING);
1044 lockevent_inc(rwsem_rlock_fail);
1045 return ERR_PTR(-EINTR);
1049 * Wait until we successfully acquire the write lock
1051 static struct rw_semaphore __sched *
1052 rwsem_down_write_slowpath(struct rw_semaphore *sem, int state)
1055 struct rwsem_waiter waiter;
1056 DEFINE_WAKE_Q(wake_q);
1058 /* do optimistic spinning and steal lock if possible */
1059 if (rwsem_can_spin_on_owner(sem) && rwsem_optimistic_spin(sem)) {
1060 /* rwsem_optimistic_spin() implies ACQUIRE on success */
1065 * Optimistic spinning failed, proceed to the slowpath
1066 * and block until we can acquire the sem.
1068 waiter.task = current;
1069 waiter.type = RWSEM_WAITING_FOR_WRITE;
1070 waiter.timeout = jiffies + RWSEM_WAIT_TIMEOUT;
1071 waiter.handoff_set = false;
1073 raw_spin_lock_irq(&sem->wait_lock);
1074 rwsem_add_waiter(sem, &waiter);
1076 /* we're now waiting on the lock */
1077 if (rwsem_first_waiter(sem) != &waiter) {
1078 count = atomic_long_read(&sem->count);
1081 * If there were already threads queued before us and:
1082 * 1) there are no active locks, wake the front
1083 * queued process(es) as the handoff bit might be set.
1084 * 2) there are no active writers and some readers, the lock
1085 * must be read owned; so we try to wake any read lock
1086 * waiters that were queued ahead of us.
1088 if (count & RWSEM_WRITER_MASK)
1091 rwsem_mark_wake(sem, (count & RWSEM_READER_MASK)
1092 ? RWSEM_WAKE_READERS
1093 : RWSEM_WAKE_ANY, &wake_q);
1095 if (!wake_q_empty(&wake_q)) {
1097 * We want to minimize wait_lock hold time especially
1098 * when a large number of readers are to be woken up.
1100 raw_spin_unlock_irq(&sem->wait_lock);
1102 wake_q_init(&wake_q); /* Used again, reinit */
1103 raw_spin_lock_irq(&sem->wait_lock);
1106 atomic_long_or(RWSEM_FLAG_WAITERS, &sem->count);
1110 /* wait until we successfully acquire the lock */
1111 set_current_state(state);
1113 if (rwsem_try_write_lock(sem, &waiter)) {
1114 /* rwsem_try_write_lock() implies ACQUIRE on success */
1118 raw_spin_unlock_irq(&sem->wait_lock);
1120 if (signal_pending_state(state, current))
1124 * After setting the handoff bit and failing to acquire
1125 * the lock, attempt to spin on owner to accelerate lock
1126 * transfer. If the previous owner is a on-cpu writer and it
1127 * has just released the lock, OWNER_NULL will be returned.
1128 * In this case, we attempt to acquire the lock again
1131 if (waiter.handoff_set) {
1132 enum owner_state owner_state;
1135 owner_state = rwsem_spin_on_owner(sem);
1138 if (owner_state == OWNER_NULL)
1143 lockevent_inc(rwsem_sleep_writer);
1144 set_current_state(state);
1146 raw_spin_lock_irq(&sem->wait_lock);
1148 __set_current_state(TASK_RUNNING);
1149 raw_spin_unlock_irq(&sem->wait_lock);
1150 lockevent_inc(rwsem_wlock);
1154 __set_current_state(TASK_RUNNING);
1155 raw_spin_lock_irq(&sem->wait_lock);
1156 rwsem_del_waiter(sem, &waiter);
1157 if (!list_empty(&sem->wait_list))
1158 rwsem_mark_wake(sem, RWSEM_WAKE_ANY, &wake_q);
1159 raw_spin_unlock_irq(&sem->wait_lock);
1161 lockevent_inc(rwsem_wlock_fail);
1162 return ERR_PTR(-EINTR);
1166 * handle waking up a waiter on the semaphore
1167 * - up_read/up_write has decremented the active part of count if we come here
1169 static struct rw_semaphore *rwsem_wake(struct rw_semaphore *sem)
1171 unsigned long flags;
1172 DEFINE_WAKE_Q(wake_q);
1174 raw_spin_lock_irqsave(&sem->wait_lock, flags);
1176 if (!list_empty(&sem->wait_list))
1177 rwsem_mark_wake(sem, RWSEM_WAKE_ANY, &wake_q);
1179 raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
1186 * downgrade a write lock into a read lock
1187 * - caller incremented waiting part of count and discovered it still negative
1188 * - just wake up any readers at the front of the queue
1190 static struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem)
1192 unsigned long flags;
1193 DEFINE_WAKE_Q(wake_q);
1195 raw_spin_lock_irqsave(&sem->wait_lock, flags);
1197 if (!list_empty(&sem->wait_list))
1198 rwsem_mark_wake(sem, RWSEM_WAKE_READ_OWNED, &wake_q);
1200 raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
1209 static inline int __down_read_common(struct rw_semaphore *sem, int state)
1213 if (!rwsem_read_trylock(sem, &count)) {
1214 if (IS_ERR(rwsem_down_read_slowpath(sem, count, state)))
1216 DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);
1221 static inline void __down_read(struct rw_semaphore *sem)
1223 __down_read_common(sem, TASK_UNINTERRUPTIBLE);
1226 static inline int __down_read_interruptible(struct rw_semaphore *sem)
1228 return __down_read_common(sem, TASK_INTERRUPTIBLE);
1231 static inline int __down_read_killable(struct rw_semaphore *sem)
1233 return __down_read_common(sem, TASK_KILLABLE);
1236 static inline int __down_read_trylock(struct rw_semaphore *sem)
1240 DEBUG_RWSEMS_WARN_ON(sem->magic != sem, sem);
1242 tmp = atomic_long_read(&sem->count);
1243 while (!(tmp & RWSEM_READ_FAILED_MASK)) {
1244 if (atomic_long_try_cmpxchg_acquire(&sem->count, &tmp,
1245 tmp + RWSEM_READER_BIAS)) {
1246 rwsem_set_reader_owned(sem);
1256 static inline int __down_write_common(struct rw_semaphore *sem, int state)
1258 if (unlikely(!rwsem_write_trylock(sem))) {
1259 if (IS_ERR(rwsem_down_write_slowpath(sem, state)))
1266 static inline void __down_write(struct rw_semaphore *sem)
1268 __down_write_common(sem, TASK_UNINTERRUPTIBLE);
1271 static inline int __down_write_killable(struct rw_semaphore *sem)
1273 return __down_write_common(sem, TASK_KILLABLE);
1276 static inline int __down_write_trylock(struct rw_semaphore *sem)
1278 DEBUG_RWSEMS_WARN_ON(sem->magic != sem, sem);
1279 return rwsem_write_trylock(sem);
1283 * unlock after reading
1285 static inline void __up_read(struct rw_semaphore *sem)
1289 DEBUG_RWSEMS_WARN_ON(sem->magic != sem, sem);
1290 DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);
1292 rwsem_clear_reader_owned(sem);
1293 tmp = atomic_long_add_return_release(-RWSEM_READER_BIAS, &sem->count);
1294 DEBUG_RWSEMS_WARN_ON(tmp < 0, sem);
1295 if (unlikely((tmp & (RWSEM_LOCK_MASK|RWSEM_FLAG_WAITERS)) ==
1296 RWSEM_FLAG_WAITERS)) {
1297 clear_nonspinnable(sem);
1303 * unlock after writing
1305 static inline void __up_write(struct rw_semaphore *sem)
1309 DEBUG_RWSEMS_WARN_ON(sem->magic != sem, sem);
1311 * sem->owner may differ from current if the ownership is transferred
1312 * to an anonymous writer by setting the RWSEM_NONSPINNABLE bits.
1314 DEBUG_RWSEMS_WARN_ON((rwsem_owner(sem) != current) &&
1315 !rwsem_test_oflags(sem, RWSEM_NONSPINNABLE), sem);
1317 rwsem_clear_owner(sem);
1318 tmp = atomic_long_fetch_add_release(-RWSEM_WRITER_LOCKED, &sem->count);
1319 if (unlikely(tmp & RWSEM_FLAG_WAITERS))
1324 * downgrade write lock to read lock
1326 static inline void __downgrade_write(struct rw_semaphore *sem)
1331 * When downgrading from exclusive to shared ownership,
1332 * anything inside the write-locked region cannot leak
1333 * into the read side. In contrast, anything in the
1334 * read-locked region is ok to be re-ordered into the
1335 * write side. As such, rely on RELEASE semantics.
1337 DEBUG_RWSEMS_WARN_ON(rwsem_owner(sem) != current, sem);
1338 tmp = atomic_long_fetch_add_release(
1339 -RWSEM_WRITER_LOCKED+RWSEM_READER_BIAS, &sem->count);
1340 rwsem_set_reader_owned(sem);
1341 if (tmp & RWSEM_FLAG_WAITERS)
1342 rwsem_downgrade_wake(sem);
1345 #else /* !CONFIG_PREEMPT_RT */
1347 #define RT_MUTEX_BUILD_MUTEX
1348 #include "rtmutex.c"
1350 #define rwbase_set_and_save_current_state(state) \
1351 set_current_state(state)
1353 #define rwbase_restore_current_state() \
1354 __set_current_state(TASK_RUNNING)
1356 #define rwbase_rtmutex_lock_state(rtm, state) \
1357 __rt_mutex_lock(rtm, state)
1359 #define rwbase_rtmutex_slowlock_locked(rtm, state) \
1360 __rt_mutex_slowlock_locked(rtm, NULL, state)
1362 #define rwbase_rtmutex_unlock(rtm) \
1363 __rt_mutex_unlock(rtm)
1365 #define rwbase_rtmutex_trylock(rtm) \
1366 __rt_mutex_trylock(rtm)
1368 #define rwbase_signal_pending_state(state, current) \
1369 signal_pending_state(state, current)
1371 #define rwbase_schedule() \
1374 #include "rwbase_rt.c"
1376 void __init_rwsem(struct rw_semaphore *sem, const char *name,
1377 struct lock_class_key *key)
1379 init_rwbase_rt(&(sem)->rwbase);
1381 #ifdef CONFIG_DEBUG_LOCK_ALLOC
1382 debug_check_no_locks_freed((void *)sem, sizeof(*sem));
1383 lockdep_init_map_wait(&sem->dep_map, name, key, 0, LD_WAIT_SLEEP);
1386 EXPORT_SYMBOL(__init_rwsem);
1388 static inline void __down_read(struct rw_semaphore *sem)
1390 rwbase_read_lock(&sem->rwbase, TASK_UNINTERRUPTIBLE);
1393 static inline int __down_read_interruptible(struct rw_semaphore *sem)
1395 return rwbase_read_lock(&sem->rwbase, TASK_INTERRUPTIBLE);
1398 static inline int __down_read_killable(struct rw_semaphore *sem)
1400 return rwbase_read_lock(&sem->rwbase, TASK_KILLABLE);
1403 static inline int __down_read_trylock(struct rw_semaphore *sem)
1405 return rwbase_read_trylock(&sem->rwbase);
1408 static inline void __up_read(struct rw_semaphore *sem)
1410 rwbase_read_unlock(&sem->rwbase, TASK_NORMAL);
1413 static inline void __sched __down_write(struct rw_semaphore *sem)
1415 rwbase_write_lock(&sem->rwbase, TASK_UNINTERRUPTIBLE);
1418 static inline int __sched __down_write_killable(struct rw_semaphore *sem)
1420 return rwbase_write_lock(&sem->rwbase, TASK_KILLABLE);
1423 static inline int __down_write_trylock(struct rw_semaphore *sem)
1425 return rwbase_write_trylock(&sem->rwbase);
1428 static inline void __up_write(struct rw_semaphore *sem)
1430 rwbase_write_unlock(&sem->rwbase);
1433 static inline void __downgrade_write(struct rw_semaphore *sem)
1435 rwbase_write_downgrade(&sem->rwbase);
1438 /* Debug stubs for the common API */
1439 #define DEBUG_RWSEMS_WARN_ON(c, sem)
1441 static inline void __rwsem_set_reader_owned(struct rw_semaphore *sem,
1442 struct task_struct *owner)
1446 static inline bool is_rwsem_reader_owned(struct rw_semaphore *sem)
1448 int count = atomic_read(&sem->rwbase.readers);
1450 return count < 0 && count != READER_BIAS;
1453 #endif /* CONFIG_PREEMPT_RT */
1458 void __sched down_read(struct rw_semaphore *sem)
1461 rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_);
1463 LOCK_CONTENDED(sem, __down_read_trylock, __down_read);
1465 EXPORT_SYMBOL(down_read);
1467 int __sched down_read_interruptible(struct rw_semaphore *sem)
1470 rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_);
1472 if (LOCK_CONTENDED_RETURN(sem, __down_read_trylock, __down_read_interruptible)) {
1473 rwsem_release(&sem->dep_map, _RET_IP_);
1479 EXPORT_SYMBOL(down_read_interruptible);
1481 int __sched down_read_killable(struct rw_semaphore *sem)
1484 rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_);
1486 if (LOCK_CONTENDED_RETURN(sem, __down_read_trylock, __down_read_killable)) {
1487 rwsem_release(&sem->dep_map, _RET_IP_);
1493 EXPORT_SYMBOL(down_read_killable);
1496 * trylock for reading -- returns 1 if successful, 0 if contention
1498 int down_read_trylock(struct rw_semaphore *sem)
1500 int ret = __down_read_trylock(sem);
1503 rwsem_acquire_read(&sem->dep_map, 0, 1, _RET_IP_);
1506 EXPORT_SYMBOL(down_read_trylock);
1511 void __sched down_write(struct rw_semaphore *sem)
1514 rwsem_acquire(&sem->dep_map, 0, 0, _RET_IP_);
1515 LOCK_CONTENDED(sem, __down_write_trylock, __down_write);
1517 EXPORT_SYMBOL(down_write);
1522 int __sched down_write_killable(struct rw_semaphore *sem)
1525 rwsem_acquire(&sem->dep_map, 0, 0, _RET_IP_);
1527 if (LOCK_CONTENDED_RETURN(sem, __down_write_trylock,
1528 __down_write_killable)) {
1529 rwsem_release(&sem->dep_map, _RET_IP_);
1535 EXPORT_SYMBOL(down_write_killable);
1538 * trylock for writing -- returns 1 if successful, 0 if contention
1540 int down_write_trylock(struct rw_semaphore *sem)
1542 int ret = __down_write_trylock(sem);
1545 rwsem_acquire(&sem->dep_map, 0, 1, _RET_IP_);
1549 EXPORT_SYMBOL(down_write_trylock);
1552 * release a read lock
1554 void up_read(struct rw_semaphore *sem)
1556 rwsem_release(&sem->dep_map, _RET_IP_);
1559 EXPORT_SYMBOL(up_read);
1562 * release a write lock
1564 void up_write(struct rw_semaphore *sem)
1566 rwsem_release(&sem->dep_map, _RET_IP_);
1569 EXPORT_SYMBOL(up_write);
1572 * downgrade write lock to read lock
1574 void downgrade_write(struct rw_semaphore *sem)
1576 lock_downgrade(&sem->dep_map, _RET_IP_);
1577 __downgrade_write(sem);
1579 EXPORT_SYMBOL(downgrade_write);
1581 #ifdef CONFIG_DEBUG_LOCK_ALLOC
1583 void down_read_nested(struct rw_semaphore *sem, int subclass)
1586 rwsem_acquire_read(&sem->dep_map, subclass, 0, _RET_IP_);
1587 LOCK_CONTENDED(sem, __down_read_trylock, __down_read);
1589 EXPORT_SYMBOL(down_read_nested);
1591 int down_read_killable_nested(struct rw_semaphore *sem, int subclass)
1594 rwsem_acquire_read(&sem->dep_map, subclass, 0, _RET_IP_);
1596 if (LOCK_CONTENDED_RETURN(sem, __down_read_trylock, __down_read_killable)) {
1597 rwsem_release(&sem->dep_map, _RET_IP_);
1603 EXPORT_SYMBOL(down_read_killable_nested);
1605 void _down_write_nest_lock(struct rw_semaphore *sem, struct lockdep_map *nest)
1608 rwsem_acquire_nest(&sem->dep_map, 0, 0, nest, _RET_IP_);
1609 LOCK_CONTENDED(sem, __down_write_trylock, __down_write);
1611 EXPORT_SYMBOL(_down_write_nest_lock);
1613 void down_read_non_owner(struct rw_semaphore *sem)
1617 __rwsem_set_reader_owned(sem, NULL);
1619 EXPORT_SYMBOL(down_read_non_owner);
1621 void down_write_nested(struct rw_semaphore *sem, int subclass)
1624 rwsem_acquire(&sem->dep_map, subclass, 0, _RET_IP_);
1625 LOCK_CONTENDED(sem, __down_write_trylock, __down_write);
1627 EXPORT_SYMBOL(down_write_nested);
1629 int __sched down_write_killable_nested(struct rw_semaphore *sem, int subclass)
1632 rwsem_acquire(&sem->dep_map, subclass, 0, _RET_IP_);
1634 if (LOCK_CONTENDED_RETURN(sem, __down_write_trylock,
1635 __down_write_killable)) {
1636 rwsem_release(&sem->dep_map, _RET_IP_);
1642 EXPORT_SYMBOL(down_write_killable_nested);
1644 void up_read_non_owner(struct rw_semaphore *sem)
1646 DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);
1649 EXPORT_SYMBOL(up_read_non_owner);