2 * Copyright (c) 2007 Attilio Rao <attilio@freebsd.org>
3 * Copyright (c) 2001 Jason Evans <jasone@freebsd.org>
6 * Redistribution and use in source and binary forms, with or without
7 * modification, are permitted provided that the following conditions
9 * 1. Redistributions of source code must retain the above copyright
10 * notice(s), this list of conditions and the following disclaimer as
11 * the first lines of this file unmodified other than the possible
12 * addition of one or more copyright notices.
13 * 2. Redistributions in binary form must reproduce the above copyright
14 * notice(s), this list of conditions and the following disclaimer in the
15 * documentation and/or other materials provided with the distribution.
17 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY
18 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
19 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
20 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE LIABLE FOR ANY
21 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
22 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
23 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
24 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
25 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
26 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH
31 * Shared/exclusive locks. This implementation attempts to ensure
32 * deterministic lock granting behavior, so that slocks and xlocks are
35 * Priority propagation will not generally raise the priority of lock holders,
36 * so should not be relied upon in combination with sx locks.
40 #include "opt_kdtrace.h"
41 #include "opt_no_adaptive_sx.h"
43 #include <sys/cdefs.h>
44 __FBSDID("$FreeBSD$");
46 #include <sys/param.h>
49 #include <sys/mutex.h>
51 #include <sys/sleepqueue.h>
53 #include <sys/sysctl.h>
54 #include <sys/systm.h>
56 #if defined(SMP) && !defined(NO_ADAPTIVE_SX)
57 #include <machine/cpu.h>
64 #if defined(SMP) && !defined(NO_ADAPTIVE_SX)
68 CTASSERT((SX_NOADAPTIVE & LO_CLASSFLAGS) == SX_NOADAPTIVE);
70 /* Handy macros for sleep queues. */
71 #define SQ_EXCLUSIVE_QUEUE 0
72 #define SQ_SHARED_QUEUE 1
75 #define ASX_RETRIES 10
76 #define ASX_LOOPS 10000
80 * Variations on DROP_GIANT()/PICKUP_GIANT() for use in this file. We
81 * drop Giant anytime we have to sleep or if we adaptively spin.
83 #define GIANT_DECLARE \
85 WITNESS_SAVE_DECL(Giant) \
87 #define GIANT_SAVE() do { \
88 if (mtx_owned(&Giant)) { \
89 WITNESS_SAVE(&Giant.lock_object, Giant); \
90 while (mtx_owned(&Giant)) { \
97 #define GIANT_RESTORE() do { \
98 if (_giantcnt > 0) { \
99 mtx_assert(&Giant, MA_NOTOWNED); \
100 while (_giantcnt--) \
102 WITNESS_RESTORE(&Giant.lock_object, Giant); \
107 * Returns true if an exclusive lock is recursed. It assumes
108 * curthread currently has an exclusive lock.
110 #define sx_recurse lock_object.lo_data
111 #define sx_recursed(sx) ((sx)->sx_recurse != 0)
113 static void assert_sx(struct lock_object *lock, int what);
115 static void db_show_sx(struct lock_object *lock);
117 static void lock_sx(struct lock_object *lock, int how);
119 static int owner_sx(struct lock_object *lock, struct thread **owner);
121 static int unlock_sx(struct lock_object *lock);
123 struct lock_class lock_class_sx = {
125 .lc_flags = LC_SLEEPLOCK | LC_SLEEPABLE | LC_RECURSABLE | LC_UPGRADABLE,
126 .lc_assert = assert_sx,
128 .lc_ddb_show = db_show_sx,
131 .lc_unlock = unlock_sx,
133 .lc_owner = owner_sx,
138 #define _sx_assert(sx, what, file, line)
142 assert_sx(struct lock_object *lock, int what)
145 sx_assert((struct sx *)lock, what);
149 lock_sx(struct lock_object *lock, int how)
153 sx = (struct sx *)lock;
161 unlock_sx(struct lock_object *lock)
165 sx = (struct sx *)lock;
166 sx_assert(sx, SA_LOCKED | SA_NOTRECURSED);
167 if (sx_xlocked(sx)) {
178 owner_sx(struct lock_object *lock, struct thread **owner)
180 struct sx *sx = (struct sx *)lock;
181 uintptr_t x = sx->sx_lock;
183 *owner = (struct thread *)SX_OWNER(x);
184 return ((x & SX_LOCK_SHARED) != 0 ? (SX_SHARERS(x) != 0) :
190 sx_sysinit(void *arg)
192 struct sx_args *sargs = arg;
194 sx_init_flags(sargs->sa_sx, sargs->sa_desc, sargs->sa_flags);
198 sx_init_flags(struct sx *sx, const char *description, int opts)
202 MPASS((opts & ~(SX_QUIET | SX_RECURSE | SX_NOWITNESS | SX_DUPOK |
203 SX_NOPROFILE | SX_NOADAPTIVE)) == 0);
204 ASSERT_ATOMIC_LOAD_PTR(sx->sx_lock,
205 ("%s: sx_lock not aligned for %s: %p", __func__, description,
208 flags = LO_SLEEPABLE | LO_UPGRADABLE;
211 if (opts & SX_NOPROFILE)
212 flags |= LO_NOPROFILE;
213 if (!(opts & SX_NOWITNESS))
215 if (opts & SX_RECURSE)
216 flags |= LO_RECURSABLE;
220 flags |= opts & SX_NOADAPTIVE;
221 sx->sx_lock = SX_LOCK_UNLOCKED;
223 lock_init(&sx->lock_object, &lock_class_sx, description, NULL, flags);
227 sx_destroy(struct sx *sx)
230 KASSERT(sx->sx_lock == SX_LOCK_UNLOCKED, ("sx lock still held"));
231 KASSERT(sx->sx_recurse == 0, ("sx lock still recursed"));
232 sx->sx_lock = SX_LOCK_DESTROYED;
233 lock_destroy(&sx->lock_object);
237 _sx_slock(struct sx *sx, int opts, const char *file, int line)
241 MPASS(curthread != NULL);
242 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
243 ("sx_slock() of destroyed sx @ %s:%d", file, line));
244 WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER, file, line, NULL);
245 error = __sx_slock(sx, opts, file, line);
247 LOCK_LOG_LOCK("SLOCK", &sx->lock_object, 0, 0, file, line);
248 WITNESS_LOCK(&sx->lock_object, 0, file, line);
249 curthread->td_locks++;
256 _sx_try_slock(struct sx *sx, const char *file, int line)
262 KASSERT(x != SX_LOCK_DESTROYED,
263 ("sx_try_slock() of destroyed sx @ %s:%d", file, line));
264 if (!(x & SX_LOCK_SHARED))
266 if (atomic_cmpset_acq_ptr(&sx->sx_lock, x, x + SX_ONE_SHARER)) {
267 LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 1, file, line);
268 WITNESS_LOCK(&sx->lock_object, LOP_TRYLOCK, file, line);
269 curthread->td_locks++;
274 LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 0, file, line);
279 _sx_xlock(struct sx *sx, int opts, const char *file, int line)
283 MPASS(curthread != NULL);
284 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
285 ("sx_xlock() of destroyed sx @ %s:%d", file, line));
286 WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER | LOP_EXCLUSIVE, file,
288 error = __sx_xlock(sx, curthread, opts, file, line);
290 LOCK_LOG_LOCK("XLOCK", &sx->lock_object, 0, sx->sx_recurse,
292 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line);
293 curthread->td_locks++;
300 _sx_try_xlock(struct sx *sx, const char *file, int line)
304 MPASS(curthread != NULL);
305 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
306 ("sx_try_xlock() of destroyed sx @ %s:%d", file, line));
308 if (sx_xlocked(sx) &&
309 (sx->lock_object.lo_flags & LO_RECURSABLE) != 0) {
311 atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
314 rval = atomic_cmpset_acq_ptr(&sx->sx_lock, SX_LOCK_UNLOCKED,
315 (uintptr_t)curthread);
316 LOCK_LOG_TRY("XLOCK", &sx->lock_object, 0, rval, file, line);
318 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
320 curthread->td_locks++;
327 _sx_sunlock(struct sx *sx, const char *file, int line)
330 MPASS(curthread != NULL);
331 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
332 ("sx_sunlock() of destroyed sx @ %s:%d", file, line));
333 _sx_assert(sx, SA_SLOCKED, file, line);
334 curthread->td_locks--;
335 WITNESS_UNLOCK(&sx->lock_object, 0, file, line);
336 LOCK_LOG_LOCK("SUNLOCK", &sx->lock_object, 0, 0, file, line);
337 __sx_sunlock(sx, file, line);
338 LOCKSTAT_PROFILE_RELEASE_LOCK(LS_SX_SUNLOCK_RELEASE, sx);
342 _sx_xunlock(struct sx *sx, const char *file, int line)
345 MPASS(curthread != NULL);
346 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
347 ("sx_xunlock() of destroyed sx @ %s:%d", file, line));
348 _sx_assert(sx, SA_XLOCKED, file, line);
349 curthread->td_locks--;
350 WITNESS_UNLOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line);
351 LOCK_LOG_LOCK("XUNLOCK", &sx->lock_object, 0, sx->sx_recurse, file,
353 if (!sx_recursed(sx))
354 LOCKSTAT_PROFILE_RELEASE_LOCK(LS_SX_XUNLOCK_RELEASE, sx);
355 __sx_xunlock(sx, curthread, file, line);
359 * Try to do a non-blocking upgrade from a shared lock to an exclusive lock.
360 * This will only succeed if this thread holds a single shared lock.
361 * Return 1 if if the upgrade succeed, 0 otherwise.
364 _sx_try_upgrade(struct sx *sx, const char *file, int line)
369 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
370 ("sx_try_upgrade() of destroyed sx @ %s:%d", file, line));
371 _sx_assert(sx, SA_SLOCKED, file, line);
374 * Try to switch from one shared lock to an exclusive lock. We need
375 * to maintain the SX_LOCK_EXCLUSIVE_WAITERS flag if set so that
376 * we will wake up the exclusive waiters when we drop the lock.
378 x = sx->sx_lock & SX_LOCK_EXCLUSIVE_WAITERS;
379 success = atomic_cmpset_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1) | x,
380 (uintptr_t)curthread | x);
381 LOCK_LOG_TRY("XUPGRADE", &sx->lock_object, 0, success, file, line);
383 WITNESS_UPGRADE(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
385 LOCKSTAT_RECORD0(LS_SX_TRYUPGRADE_UPGRADE, sx);
391 * Downgrade an unrecursed exclusive lock into a single shared lock.
394 _sx_downgrade(struct sx *sx, const char *file, int line)
399 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
400 ("sx_downgrade() of destroyed sx @ %s:%d", file, line));
401 _sx_assert(sx, SA_XLOCKED | SA_NOTRECURSED, file, line);
404 panic("downgrade of a recursed lock");
407 WITNESS_DOWNGRADE(&sx->lock_object, 0, file, line);
410 * Try to switch from an exclusive lock with no shared waiters
411 * to one sharer with no shared waiters. If there are
412 * exclusive waiters, we don't need to lock the sleep queue so
413 * long as we preserve the flag. We do one quick try and if
414 * that fails we grab the sleepq lock to keep the flags from
415 * changing and do it the slow way.
417 * We have to lock the sleep queue if there are shared waiters
418 * so we can wake them up.
421 if (!(x & SX_LOCK_SHARED_WAITERS) &&
422 atomic_cmpset_rel_ptr(&sx->sx_lock, x, SX_SHARERS_LOCK(1) |
423 (x & SX_LOCK_EXCLUSIVE_WAITERS))) {
424 LOCK_LOG_LOCK("XDOWNGRADE", &sx->lock_object, 0, 0, file, line);
429 * Lock the sleep queue so we can read the waiters bits
430 * without any races and wakeup any shared waiters.
432 sleepq_lock(&sx->lock_object);
435 * Preserve SX_LOCK_EXCLUSIVE_WAITERS while downgraded to a single
436 * shared lock. If there are any shared waiters, wake them up.
440 atomic_store_rel_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1) |
441 (x & SX_LOCK_EXCLUSIVE_WAITERS));
442 if (x & SX_LOCK_SHARED_WAITERS)
443 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX,
445 sleepq_release(&sx->lock_object);
447 LOCK_LOG_LOCK("XDOWNGRADE", &sx->lock_object, 0, 0, file, line);
448 LOCKSTAT_RECORD0(LS_SX_DOWNGRADE_DOWNGRADE, sx);
455 * This function represents the so-called 'hard case' for sx_xlock
456 * operation. All 'easy case' failures are redirected to this. Note
457 * that ideally this would be a static function, but it needs to be
458 * accessible from at least sx.h.
461 _sx_xlock_hard(struct sx *sx, uintptr_t tid, int opts, const char *file,
466 volatile struct thread *owner;
467 u_int i, spintries = 0;
470 #ifdef LOCK_PROFILING
471 uint64_t waittime = 0;
476 uint64_t spin_cnt = 0;
477 uint64_t sleep_cnt = 0;
478 int64_t sleep_time = 0;
481 /* If we already hold an exclusive lock, then recurse. */
482 if (sx_xlocked(sx)) {
483 KASSERT((sx->lock_object.lo_flags & LO_RECURSABLE) != 0,
484 ("_sx_xlock_hard: recursed on non-recursive sx %s @ %s:%d\n",
485 sx->lock_object.lo_name, file, line));
487 atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
488 if (LOCK_LOG_TEST(&sx->lock_object, 0))
489 CTR2(KTR_LOCK, "%s: %p recursing", __func__, sx);
493 if (LOCK_LOG_TEST(&sx->lock_object, 0))
494 CTR5(KTR_LOCK, "%s: %s contested (lock=%p) at %s:%d", __func__,
495 sx->lock_object.lo_name, (void *)sx->sx_lock, file, line);
497 while (!atomic_cmpset_acq_ptr(&sx->sx_lock, SX_LOCK_UNLOCKED, tid)) {
501 lock_profile_obtain_lock_failed(&sx->lock_object, &contested,
505 * If the lock is write locked and the owner is
506 * running on another CPU, spin until the owner stops
507 * running or the state of the lock changes.
510 if ((sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) {
511 if ((x & SX_LOCK_SHARED) == 0) {
513 owner = (struct thread *)x;
514 if (TD_IS_RUNNING(owner)) {
515 if (LOCK_LOG_TEST(&sx->lock_object, 0))
517 "%s: spinning on %p held by %p",
518 __func__, sx, owner);
520 while (SX_OWNER(sx->sx_lock) == x &&
521 TD_IS_RUNNING(owner)) {
529 } else if (SX_SHARERS(x) && spintries < ASX_RETRIES) {
532 for (i = 0; i < ASX_LOOPS; i++) {
533 if (LOCK_LOG_TEST(&sx->lock_object, 0))
535 "%s: shared spinning on %p with %u and %u",
536 __func__, sx, spintries, i);
538 if ((x & SX_LOCK_SHARED) == 0 ||
552 sleepq_lock(&sx->lock_object);
556 * If the lock was released while spinning on the
557 * sleep queue chain lock, try again.
559 if (x == SX_LOCK_UNLOCKED) {
560 sleepq_release(&sx->lock_object);
566 * The current lock owner might have started executing
567 * on another CPU (or the lock could have changed
568 * owners) while we were waiting on the sleep queue
569 * chain lock. If so, drop the sleep queue lock and try
572 if (!(x & SX_LOCK_SHARED) &&
573 (sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) {
574 owner = (struct thread *)SX_OWNER(x);
575 if (TD_IS_RUNNING(owner)) {
576 sleepq_release(&sx->lock_object);
583 * If an exclusive lock was released with both shared
584 * and exclusive waiters and a shared waiter hasn't
585 * woken up and acquired the lock yet, sx_lock will be
586 * set to SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS.
587 * If we see that value, try to acquire it once. Note
588 * that we have to preserve SX_LOCK_EXCLUSIVE_WAITERS
589 * as there are other exclusive waiters still. If we
590 * fail, restart the loop.
592 if (x == (SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS)) {
593 if (atomic_cmpset_acq_ptr(&sx->sx_lock,
594 SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS,
595 tid | SX_LOCK_EXCLUSIVE_WAITERS)) {
596 sleepq_release(&sx->lock_object);
597 CTR2(KTR_LOCK, "%s: %p claimed by new writer",
601 sleepq_release(&sx->lock_object);
606 * Try to set the SX_LOCK_EXCLUSIVE_WAITERS. If we fail,
607 * than loop back and retry.
609 if (!(x & SX_LOCK_EXCLUSIVE_WAITERS)) {
610 if (!atomic_cmpset_ptr(&sx->sx_lock, x,
611 x | SX_LOCK_EXCLUSIVE_WAITERS)) {
612 sleepq_release(&sx->lock_object);
615 if (LOCK_LOG_TEST(&sx->lock_object, 0))
616 CTR2(KTR_LOCK, "%s: %p set excl waiters flag",
621 * Since we have been unable to acquire the exclusive
622 * lock and the exclusive waiters flag is set, we have
625 if (LOCK_LOG_TEST(&sx->lock_object, 0))
626 CTR2(KTR_LOCK, "%s: %p blocking on sleep queue",
630 sleep_time -= lockstat_nsecs();
633 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name,
634 SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ?
635 SLEEPQ_INTERRUPTIBLE : 0), SQ_EXCLUSIVE_QUEUE);
636 if (!(opts & SX_INTERRUPTIBLE))
637 sleepq_wait(&sx->lock_object, 0);
639 error = sleepq_wait_sig(&sx->lock_object, 0);
641 sleep_time += lockstat_nsecs();
645 if (LOCK_LOG_TEST(&sx->lock_object, 0))
647 "%s: interruptible sleep by %p suspended by signal",
651 if (LOCK_LOG_TEST(&sx->lock_object, 0))
652 CTR2(KTR_LOCK, "%s: %p resuming from sleep queue",
658 LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_SX_XLOCK_ACQUIRE, sx,
659 contested, waittime, file, line);
662 LOCKSTAT_RECORD1(LS_SX_XLOCK_BLOCK, sx, sleep_time);
663 if (spin_cnt > sleep_cnt)
664 LOCKSTAT_RECORD1(LS_SX_XLOCK_SPIN, sx, (spin_cnt - sleep_cnt));
670 * This function represents the so-called 'hard case' for sx_xunlock
671 * operation. All 'easy case' failures are redirected to this. Note
672 * that ideally this would be a static function, but it needs to be
673 * accessible from at least sx.h.
676 _sx_xunlock_hard(struct sx *sx, uintptr_t tid, const char *file, int line)
679 int queue, wakeup_swapper;
681 MPASS(!(sx->sx_lock & SX_LOCK_SHARED));
683 /* If the lock is recursed, then unrecurse one level. */
684 if (sx_xlocked(sx) && sx_recursed(sx)) {
685 if ((--sx->sx_recurse) == 0)
686 atomic_clear_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
687 if (LOCK_LOG_TEST(&sx->lock_object, 0))
688 CTR2(KTR_LOCK, "%s: %p unrecursing", __func__, sx);
691 MPASS(sx->sx_lock & (SX_LOCK_SHARED_WAITERS |
692 SX_LOCK_EXCLUSIVE_WAITERS));
693 if (LOCK_LOG_TEST(&sx->lock_object, 0))
694 CTR2(KTR_LOCK, "%s: %p contested", __func__, sx);
696 sleepq_lock(&sx->lock_object);
697 x = SX_LOCK_UNLOCKED;
700 * The wake up algorithm here is quite simple and probably not
701 * ideal. It gives precedence to shared waiters if they are
702 * present. For this condition, we have to preserve the
703 * state of the exclusive waiters flag.
704 * If interruptible sleeps left the shared queue empty avoid a
705 * starvation for the threads sleeping on the exclusive queue by giving
706 * them precedence and cleaning up the shared waiters bit anyway.
708 if ((sx->sx_lock & SX_LOCK_SHARED_WAITERS) != 0 &&
709 sleepq_sleepcnt(&sx->lock_object, SQ_SHARED_QUEUE) != 0) {
710 queue = SQ_SHARED_QUEUE;
711 x |= (sx->sx_lock & SX_LOCK_EXCLUSIVE_WAITERS);
713 queue = SQ_EXCLUSIVE_QUEUE;
715 /* Wake up all the waiters for the specific queue. */
716 if (LOCK_LOG_TEST(&sx->lock_object, 0))
717 CTR3(KTR_LOCK, "%s: %p waking up all threads on %s queue",
718 __func__, sx, queue == SQ_SHARED_QUEUE ? "shared" :
720 atomic_store_rel_ptr(&sx->sx_lock, x);
721 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, 0,
723 sleepq_release(&sx->lock_object);
729 * This function represents the so-called 'hard case' for sx_slock
730 * operation. All 'easy case' failures are redirected to this. Note
731 * that ideally this would be a static function, but it needs to be
732 * accessible from at least sx.h.
735 _sx_slock_hard(struct sx *sx, int opts, const char *file, int line)
739 volatile struct thread *owner;
741 #ifdef LOCK_PROFILING
742 uint64_t waittime = 0;
748 uint64_t spin_cnt = 0;
749 uint64_t sleep_cnt = 0;
750 int64_t sleep_time = 0;
754 * As with rwlocks, we don't make any attempt to try to block
755 * shared locks once there is an exclusive waiter.
764 * If no other thread has an exclusive lock then try to bump up
765 * the count of sharers. Since we have to preserve the state
766 * of SX_LOCK_EXCLUSIVE_WAITERS, if we fail to acquire the
767 * shared lock loop back and retry.
769 if (x & SX_LOCK_SHARED) {
770 MPASS(!(x & SX_LOCK_SHARED_WAITERS));
771 if (atomic_cmpset_acq_ptr(&sx->sx_lock, x,
772 x + SX_ONE_SHARER)) {
773 if (LOCK_LOG_TEST(&sx->lock_object, 0))
775 "%s: %p succeed %p -> %p", __func__,
777 (void *)(x + SX_ONE_SHARER));
782 lock_profile_obtain_lock_failed(&sx->lock_object, &contested,
787 * If the owner is running on another CPU, spin until
788 * the owner stops running or the state of the lock
791 if ((sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) {
793 owner = (struct thread *)x;
794 if (TD_IS_RUNNING(owner)) {
795 if (LOCK_LOG_TEST(&sx->lock_object, 0))
797 "%s: spinning on %p held by %p",
798 __func__, sx, owner);
800 while (SX_OWNER(sx->sx_lock) == x &&
801 TD_IS_RUNNING(owner)) {
813 * Some other thread already has an exclusive lock, so
814 * start the process of blocking.
816 sleepq_lock(&sx->lock_object);
820 * The lock could have been released while we spun.
821 * In this case loop back and retry.
823 if (x & SX_LOCK_SHARED) {
824 sleepq_release(&sx->lock_object);
830 * If the owner is running on another CPU, spin until
831 * the owner stops running or the state of the lock
834 if (!(x & SX_LOCK_SHARED) &&
835 (sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) {
836 owner = (struct thread *)SX_OWNER(x);
837 if (TD_IS_RUNNING(owner)) {
838 sleepq_release(&sx->lock_object);
845 * Try to set the SX_LOCK_SHARED_WAITERS flag. If we
846 * fail to set it drop the sleep queue lock and loop
849 if (!(x & SX_LOCK_SHARED_WAITERS)) {
850 if (!atomic_cmpset_ptr(&sx->sx_lock, x,
851 x | SX_LOCK_SHARED_WAITERS)) {
852 sleepq_release(&sx->lock_object);
855 if (LOCK_LOG_TEST(&sx->lock_object, 0))
856 CTR2(KTR_LOCK, "%s: %p set shared waiters flag",
861 * Since we have been unable to acquire the shared lock,
864 if (LOCK_LOG_TEST(&sx->lock_object, 0))
865 CTR2(KTR_LOCK, "%s: %p blocking on sleep queue",
869 sleep_time -= lockstat_nsecs();
872 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name,
873 SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ?
874 SLEEPQ_INTERRUPTIBLE : 0), SQ_SHARED_QUEUE);
875 if (!(opts & SX_INTERRUPTIBLE))
876 sleepq_wait(&sx->lock_object, 0);
878 error = sleepq_wait_sig(&sx->lock_object, 0);
880 sleep_time += lockstat_nsecs();
884 if (LOCK_LOG_TEST(&sx->lock_object, 0))
886 "%s: interruptible sleep by %p suspended by signal",
890 if (LOCK_LOG_TEST(&sx->lock_object, 0))
891 CTR2(KTR_LOCK, "%s: %p resuming from sleep queue",
895 LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_SX_SLOCK_ACQUIRE, sx,
896 contested, waittime, file, line);
899 LOCKSTAT_RECORD1(LS_SX_XLOCK_BLOCK, sx, sleep_time);
900 if (spin_cnt > sleep_cnt)
901 LOCKSTAT_RECORD1(LS_SX_XLOCK_SPIN, sx, (spin_cnt - sleep_cnt));
908 * This function represents the so-called 'hard case' for sx_sunlock
909 * operation. All 'easy case' failures are redirected to this. Note
910 * that ideally this would be a static function, but it needs to be
911 * accessible from at least sx.h.
914 _sx_sunlock_hard(struct sx *sx, const char *file, int line)
923 * We should never have sharers while at least one thread
924 * holds a shared lock.
926 KASSERT(!(x & SX_LOCK_SHARED_WAITERS),
927 ("%s: waiting sharers", __func__));
930 * See if there is more than one shared lock held. If
931 * so, just drop one and return.
933 if (SX_SHARERS(x) > 1) {
934 if (atomic_cmpset_rel_ptr(&sx->sx_lock, x,
935 x - SX_ONE_SHARER)) {
936 if (LOCK_LOG_TEST(&sx->lock_object, 0))
938 "%s: %p succeeded %p -> %p",
939 __func__, sx, (void *)x,
940 (void *)(x - SX_ONE_SHARER));
947 * If there aren't any waiters for an exclusive lock,
948 * then try to drop it quickly.
950 if (!(x & SX_LOCK_EXCLUSIVE_WAITERS)) {
951 MPASS(x == SX_SHARERS_LOCK(1));
952 if (atomic_cmpset_rel_ptr(&sx->sx_lock,
953 SX_SHARERS_LOCK(1), SX_LOCK_UNLOCKED)) {
954 if (LOCK_LOG_TEST(&sx->lock_object, 0))
955 CTR2(KTR_LOCK, "%s: %p last succeeded",
963 * At this point, there should just be one sharer with
966 MPASS(x == (SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS));
968 sleepq_lock(&sx->lock_object);
971 * Wake up semantic here is quite simple:
972 * Just wake up all the exclusive waiters.
973 * Note that the state of the lock could have changed,
974 * so if it fails loop back and retry.
976 if (!atomic_cmpset_rel_ptr(&sx->sx_lock,
977 SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS,
979 sleepq_release(&sx->lock_object);
982 if (LOCK_LOG_TEST(&sx->lock_object, 0))
983 CTR2(KTR_LOCK, "%s: %p waking up all thread on"
984 "exclusive queue", __func__, sx);
985 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX,
986 0, SQ_EXCLUSIVE_QUEUE);
987 sleepq_release(&sx->lock_object);
994 #ifdef INVARIANT_SUPPORT
1000 * In the non-WITNESS case, sx_assert() can only detect that at least
1001 * *some* thread owns an slock, but it cannot guarantee that *this*
1002 * thread owns an slock.
1005 _sx_assert(struct sx *sx, int what, const char *file, int line)
1011 if (panicstr != NULL)
1015 case SA_SLOCKED | SA_NOTRECURSED:
1016 case SA_SLOCKED | SA_RECURSED:
1022 case SA_LOCKED | SA_NOTRECURSED:
1023 case SA_LOCKED | SA_RECURSED:
1025 witness_assert(&sx->lock_object, what, file, line);
1028 * If some other thread has an exclusive lock or we
1029 * have one and are asserting a shared lock, fail.
1030 * Also, if no one has a lock at all, fail.
1032 if (sx->sx_lock == SX_LOCK_UNLOCKED ||
1033 (!(sx->sx_lock & SX_LOCK_SHARED) && (slocked ||
1034 sx_xholder(sx) != curthread)))
1035 panic("Lock %s not %slocked @ %s:%d\n",
1036 sx->lock_object.lo_name, slocked ? "share " : "",
1039 if (!(sx->sx_lock & SX_LOCK_SHARED)) {
1040 if (sx_recursed(sx)) {
1041 if (what & SA_NOTRECURSED)
1042 panic("Lock %s recursed @ %s:%d\n",
1043 sx->lock_object.lo_name, file,
1045 } else if (what & SA_RECURSED)
1046 panic("Lock %s not recursed @ %s:%d\n",
1047 sx->lock_object.lo_name, file, line);
1052 case SA_XLOCKED | SA_NOTRECURSED:
1053 case SA_XLOCKED | SA_RECURSED:
1054 if (sx_xholder(sx) != curthread)
1055 panic("Lock %s not exclusively locked @ %s:%d\n",
1056 sx->lock_object.lo_name, file, line);
1057 if (sx_recursed(sx)) {
1058 if (what & SA_NOTRECURSED)
1059 panic("Lock %s recursed @ %s:%d\n",
1060 sx->lock_object.lo_name, file, line);
1061 } else if (what & SA_RECURSED)
1062 panic("Lock %s not recursed @ %s:%d\n",
1063 sx->lock_object.lo_name, file, line);
1067 witness_assert(&sx->lock_object, what, file, line);
1070 * If we hold an exclusve lock fail. We can't
1071 * reliably check to see if we hold a shared lock or
1074 if (sx_xholder(sx) == curthread)
1075 panic("Lock %s exclusively locked @ %s:%d\n",
1076 sx->lock_object.lo_name, file, line);
1080 panic("Unknown sx lock assertion: %d @ %s:%d", what, file,
1084 #endif /* INVARIANT_SUPPORT */
1088 db_show_sx(struct lock_object *lock)
1093 sx = (struct sx *)lock;
1095 db_printf(" state: ");
1096 if (sx->sx_lock == SX_LOCK_UNLOCKED)
1097 db_printf("UNLOCKED\n");
1098 else if (sx->sx_lock == SX_LOCK_DESTROYED) {
1099 db_printf("DESTROYED\n");
1101 } else if (sx->sx_lock & SX_LOCK_SHARED)
1102 db_printf("SLOCK: %ju\n", (uintmax_t)SX_SHARERS(sx->sx_lock));
1104 td = sx_xholder(sx);
1105 db_printf("XLOCK: %p (tid %d, pid %d, \"%s\")\n", td,
1106 td->td_tid, td->td_proc->p_pid, td->td_name);
1107 if (sx_recursed(sx))
1108 db_printf(" recursed: %d\n", sx->sx_recurse);
1111 db_printf(" waiters: ");
1112 switch(sx->sx_lock &
1113 (SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS)) {
1114 case SX_LOCK_SHARED_WAITERS:
1115 db_printf("shared\n");
1117 case SX_LOCK_EXCLUSIVE_WAITERS:
1118 db_printf("exclusive\n");
1120 case SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS:
1121 db_printf("exclusive and shared\n");
1124 db_printf("none\n");
1129 * Check to see if a thread that is blocked on a sleep queue is actually
1130 * blocked on an sx lock. If so, output some details and return true.
1131 * If the lock has an exclusive owner, return that in *ownerp.
1134 sx_chain(struct thread *td, struct thread **ownerp)
1139 * Check to see if this thread is blocked on an sx lock.
1140 * First, we check the lock class. If that is ok, then we
1141 * compare the lock name against the wait message.
1144 if (LOCK_CLASS(&sx->lock_object) != &lock_class_sx ||
1145 sx->lock_object.lo_name != td->td_wmesg)
1148 /* We think we have an sx lock, so output some details. */
1149 db_printf("blocked on sx \"%s\" ", td->td_wmesg);
1150 *ownerp = sx_xholder(sx);
1151 if (sx->sx_lock & SX_LOCK_SHARED)
1152 db_printf("SLOCK (count %ju)\n",
1153 (uintmax_t)SX_SHARERS(sx->sx_lock));
1155 db_printf("XLOCK\n");