2 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
4 * Copyright (c) 2007 Attilio Rao <attilio@freebsd.org>
5 * Copyright (c) 2001 Jason Evans <jasone@freebsd.org>
8 * Redistribution and use in source and binary forms, with or without
9 * modification, are permitted provided that the following conditions
11 * 1. Redistributions of source code must retain the above copyright
12 * notice(s), this list of conditions and the following disclaimer as
13 * the first lines of this file unmodified other than the possible
14 * addition of one or more copyright notices.
15 * 2. Redistributions in binary form must reproduce the above copyright
16 * notice(s), this list of conditions and the following disclaimer in the
17 * documentation and/or other materials provided with the distribution.
19 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY
20 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
21 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
22 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE LIABLE FOR ANY
23 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
24 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
25 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
26 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
27 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
28 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH
33 * Shared/exclusive locks. This implementation attempts to ensure
34 * deterministic lock granting behavior, so that slocks and xlocks are
37 * Priority propagation will not generally raise the priority of lock holders,
38 * so should not be relied upon in combination with sx locks.
42 #include "opt_hwpmc_hooks.h"
43 #include "opt_no_adaptive_sx.h"
45 #include <sys/cdefs.h>
46 __FBSDID("$FreeBSD$");
48 #include <sys/param.h>
49 #include <sys/systm.h>
51 #include <sys/kernel.h>
54 #include <sys/mutex.h>
56 #include <sys/sched.h>
57 #include <sys/sleepqueue.h>
60 #include <sys/sysctl.h>
62 #if defined(SMP) && !defined(NO_ADAPTIVE_SX)
63 #include <machine/cpu.h>
70 #if defined(SMP) && !defined(NO_ADAPTIVE_SX)
74 CTASSERT((SX_NOADAPTIVE & LO_CLASSFLAGS) == SX_NOADAPTIVE);
77 #include <sys/pmckern.h>
78 PMC_SOFT_DECLARE( , , lock, failed);
81 /* Handy macros for sleep queues. */
82 #define SQ_EXCLUSIVE_QUEUE 0
83 #define SQ_SHARED_QUEUE 1
86 * Variations on DROP_GIANT()/PICKUP_GIANT() for use in this file. We
87 * drop Giant anytime we have to sleep or if we adaptively spin.
89 #define GIANT_DECLARE \
91 WITNESS_SAVE_DECL(Giant) \
93 #define GIANT_SAVE(work) do { \
94 if (__predict_false(mtx_owned(&Giant))) { \
96 WITNESS_SAVE(&Giant.lock_object, Giant); \
97 while (mtx_owned(&Giant)) { \
104 #define GIANT_RESTORE() do { \
105 if (_giantcnt > 0) { \
106 mtx_assert(&Giant, MA_NOTOWNED); \
107 while (_giantcnt--) \
109 WITNESS_RESTORE(&Giant.lock_object, Giant); \
114 * Returns true if an exclusive lock is recursed. It assumes
115 * curthread currently has an exclusive lock.
117 #define sx_recursed(sx) ((sx)->sx_recurse != 0)
119 static void assert_sx(const struct lock_object *lock, int what);
121 static void db_show_sx(const struct lock_object *lock);
123 static void lock_sx(struct lock_object *lock, uintptr_t how);
125 static int owner_sx(const struct lock_object *lock, struct thread **owner);
127 static uintptr_t unlock_sx(struct lock_object *lock);
129 struct lock_class lock_class_sx = {
131 .lc_flags = LC_SLEEPLOCK | LC_SLEEPABLE | LC_RECURSABLE | LC_UPGRADABLE,
132 .lc_assert = assert_sx,
134 .lc_ddb_show = db_show_sx,
137 .lc_unlock = unlock_sx,
139 .lc_owner = owner_sx,
144 #define _sx_assert(sx, what, file, line)
148 static __read_frequently u_int asx_retries = 10;
149 static __read_frequently u_int asx_loops = 10000;
150 static SYSCTL_NODE(_debug, OID_AUTO, sx, CTLFLAG_RD, NULL, "sxlock debugging");
151 SYSCTL_UINT(_debug_sx, OID_AUTO, retries, CTLFLAG_RW, &asx_retries, 0, "");
152 SYSCTL_UINT(_debug_sx, OID_AUTO, loops, CTLFLAG_RW, &asx_loops, 0, "");
154 static struct lock_delay_config __read_frequently sx_delay;
156 SYSCTL_INT(_debug_sx, OID_AUTO, delay_base, CTLFLAG_RW, &sx_delay.base,
158 SYSCTL_INT(_debug_sx, OID_AUTO, delay_max, CTLFLAG_RW, &sx_delay.max,
161 LOCK_DELAY_SYSINIT_DEFAULT(sx_delay);
165 assert_sx(const struct lock_object *lock, int what)
168 sx_assert((const struct sx *)lock, what);
172 lock_sx(struct lock_object *lock, uintptr_t how)
176 sx = (struct sx *)lock;
184 unlock_sx(struct lock_object *lock)
188 sx = (struct sx *)lock;
189 sx_assert(sx, SA_LOCKED | SA_NOTRECURSED);
190 if (sx_xlocked(sx)) {
201 owner_sx(const struct lock_object *lock, struct thread **owner)
206 sx = (const struct sx *)lock;
209 return ((x & SX_LOCK_SHARED) != 0 ? (SX_SHARERS(x) != 0) :
210 ((*owner = (struct thread *)SX_OWNER(x)) != NULL));
215 sx_sysinit(void *arg)
217 struct sx_args *sargs = arg;
219 sx_init_flags(sargs->sa_sx, sargs->sa_desc, sargs->sa_flags);
223 sx_init_flags(struct sx *sx, const char *description, int opts)
227 MPASS((opts & ~(SX_QUIET | SX_RECURSE | SX_NOWITNESS | SX_DUPOK |
228 SX_NOPROFILE | SX_NOADAPTIVE | SX_NEW)) == 0);
229 ASSERT_ATOMIC_LOAD_PTR(sx->sx_lock,
230 ("%s: sx_lock not aligned for %s: %p", __func__, description,
233 flags = LO_SLEEPABLE | LO_UPGRADABLE;
236 if (opts & SX_NOPROFILE)
237 flags |= LO_NOPROFILE;
238 if (!(opts & SX_NOWITNESS))
240 if (opts & SX_RECURSE)
241 flags |= LO_RECURSABLE;
247 flags |= opts & SX_NOADAPTIVE;
248 lock_init(&sx->lock_object, &lock_class_sx, description, NULL, flags);
249 sx->sx_lock = SX_LOCK_UNLOCKED;
254 sx_destroy(struct sx *sx)
257 KASSERT(sx->sx_lock == SX_LOCK_UNLOCKED, ("sx lock still held"));
258 KASSERT(sx->sx_recurse == 0, ("sx lock still recursed"));
259 sx->sx_lock = SX_LOCK_DESTROYED;
260 lock_destroy(&sx->lock_object);
264 sx_try_slock_int(struct sx *sx LOCK_FILE_LINE_ARG_DEF)
268 if (SCHEDULER_STOPPED())
271 KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
272 ("sx_try_slock() by idle thread %p on sx %s @ %s:%d",
273 curthread, sx->lock_object.lo_name, file, line));
277 KASSERT(x != SX_LOCK_DESTROYED,
278 ("sx_try_slock() of destroyed sx @ %s:%d", file, line));
279 if (!(x & SX_LOCK_SHARED))
281 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, x + SX_ONE_SHARER)) {
282 LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 1, file, line);
283 WITNESS_LOCK(&sx->lock_object, LOP_TRYLOCK, file, line);
284 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire,
285 sx, 0, 0, file, line, LOCKSTAT_READER);
286 TD_LOCKS_INC(curthread);
291 LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 0, file, line);
296 sx_try_slock_(struct sx *sx, const char *file, int line)
299 return (sx_try_slock_int(sx LOCK_FILE_LINE_ARG));
303 _sx_xlock(struct sx *sx, int opts, const char *file, int line)
308 KASSERT(kdb_active != 0 || SCHEDULER_STOPPED() ||
309 !TD_IS_IDLETHREAD(curthread),
310 ("sx_xlock() by idle thread %p on sx %s @ %s:%d",
311 curthread, sx->lock_object.lo_name, file, line));
312 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
313 ("sx_xlock() of destroyed sx @ %s:%d", file, line));
314 WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER | LOP_EXCLUSIVE, file,
316 tid = (uintptr_t)curthread;
317 x = SX_LOCK_UNLOCKED;
318 if (!atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, tid))
319 error = _sx_xlock_hard(sx, x, opts LOCK_FILE_LINE_ARG);
321 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire, sx,
322 0, 0, file, line, LOCKSTAT_WRITER);
324 LOCK_LOG_LOCK("XLOCK", &sx->lock_object, 0, sx->sx_recurse,
326 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line);
327 TD_LOCKS_INC(curthread);
334 sx_try_xlock_int(struct sx *sx LOCK_FILE_LINE_ARG_DEF)
343 if (SCHEDULER_STOPPED_TD(td))
346 KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(td),
347 ("sx_try_xlock() by idle thread %p on sx %s @ %s:%d",
348 curthread, sx->lock_object.lo_name, file, line));
349 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
350 ("sx_try_xlock() of destroyed sx @ %s:%d", file, line));
354 x = SX_LOCK_UNLOCKED;
356 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, tid))
358 if (x == SX_LOCK_UNLOCKED)
360 if (x == tid && (sx->lock_object.lo_flags & LO_RECURSABLE)) {
362 atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
369 LOCK_LOG_TRY("XLOCK", &sx->lock_object, 0, rval, file, line);
371 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
374 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire,
375 sx, 0, 0, file, line, LOCKSTAT_WRITER);
376 TD_LOCKS_INC(curthread);
383 sx_try_xlock_(struct sx *sx, const char *file, int line)
386 return (sx_try_xlock_int(sx LOCK_FILE_LINE_ARG));
390 _sx_xunlock(struct sx *sx, const char *file, int line)
393 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
394 ("sx_xunlock() of destroyed sx @ %s:%d", file, line));
395 _sx_assert(sx, SA_XLOCKED, file, line);
396 WITNESS_UNLOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line);
397 LOCK_LOG_LOCK("XUNLOCK", &sx->lock_object, 0, sx->sx_recurse, file,
400 _sx_xunlock_hard(sx, (uintptr_t)curthread, file, line);
402 __sx_xunlock(sx, curthread, file, line);
404 TD_LOCKS_DEC(curthread);
408 * Try to do a non-blocking upgrade from a shared lock to an exclusive lock.
409 * This will only succeed if this thread holds a single shared lock.
410 * Return 1 if if the upgrade succeed, 0 otherwise.
413 sx_try_upgrade_int(struct sx *sx LOCK_FILE_LINE_ARG_DEF)
418 if (SCHEDULER_STOPPED())
421 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
422 ("sx_try_upgrade() of destroyed sx @ %s:%d", file, line));
423 _sx_assert(sx, SA_SLOCKED, file, line);
426 * Try to switch from one shared lock to an exclusive lock. We need
427 * to maintain the SX_LOCK_EXCLUSIVE_WAITERS flag if set so that
428 * we will wake up the exclusive waiters when we drop the lock.
430 x = sx->sx_lock & SX_LOCK_EXCLUSIVE_WAITERS;
431 success = atomic_cmpset_acq_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1) | x,
432 (uintptr_t)curthread | x);
433 LOCK_LOG_TRY("XUPGRADE", &sx->lock_object, 0, success, file, line);
435 WITNESS_UPGRADE(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
437 LOCKSTAT_RECORD0(sx__upgrade, sx);
443 sx_try_upgrade_(struct sx *sx, const char *file, int line)
446 return (sx_try_upgrade_int(sx LOCK_FILE_LINE_ARG));
450 * Downgrade an unrecursed exclusive lock into a single shared lock.
453 sx_downgrade_int(struct sx *sx LOCK_FILE_LINE_ARG_DEF)
458 if (SCHEDULER_STOPPED())
461 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
462 ("sx_downgrade() of destroyed sx @ %s:%d", file, line));
463 _sx_assert(sx, SA_XLOCKED | SA_NOTRECURSED, file, line);
466 panic("downgrade of a recursed lock");
469 WITNESS_DOWNGRADE(&sx->lock_object, 0, file, line);
472 * Try to switch from an exclusive lock with no shared waiters
473 * to one sharer with no shared waiters. If there are
474 * exclusive waiters, we don't need to lock the sleep queue so
475 * long as we preserve the flag. We do one quick try and if
476 * that fails we grab the sleepq lock to keep the flags from
477 * changing and do it the slow way.
479 * We have to lock the sleep queue if there are shared waiters
480 * so we can wake them up.
483 if (!(x & SX_LOCK_SHARED_WAITERS) &&
484 atomic_cmpset_rel_ptr(&sx->sx_lock, x, SX_SHARERS_LOCK(1) |
485 (x & SX_LOCK_EXCLUSIVE_WAITERS)))
489 * Lock the sleep queue so we can read the waiters bits
490 * without any races and wakeup any shared waiters.
492 sleepq_lock(&sx->lock_object);
495 * Preserve SX_LOCK_EXCLUSIVE_WAITERS while downgraded to a single
496 * shared lock. If there are any shared waiters, wake them up.
500 atomic_store_rel_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1) |
501 (x & SX_LOCK_EXCLUSIVE_WAITERS));
502 if (x & SX_LOCK_SHARED_WAITERS)
503 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX,
505 sleepq_release(&sx->lock_object);
511 LOCK_LOG_LOCK("XDOWNGRADE", &sx->lock_object, 0, 0, file, line);
512 LOCKSTAT_RECORD0(sx__downgrade, sx);
516 sx_downgrade_(struct sx *sx, const char *file, int line)
519 sx_downgrade_int(sx LOCK_FILE_LINE_ARG);
523 * This function represents the so-called 'hard case' for sx_xlock
524 * operation. All 'easy case' failures are redirected to this. Note
525 * that ideally this would be a static function, but it needs to be
526 * accessible from at least sx.h.
529 _sx_xlock_hard(struct sx *sx, uintptr_t x, int opts LOCK_FILE_LINE_ARG_DEF)
534 volatile struct thread *owner;
535 u_int i, n, spintries = 0;
537 int sleep_reason = 0;
539 #ifdef LOCK_PROFILING
540 uint64_t waittime = 0;
544 #if defined(ADAPTIVE_SX) || defined(KDTRACE_HOOKS)
545 struct lock_delay_arg lda;
549 int64_t sleep_time = 0;
550 int64_t all_time = 0;
552 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING)
557 tid = (uintptr_t)curthread;
558 if (SCHEDULER_STOPPED())
561 #if defined(ADAPTIVE_SX)
562 lock_delay_arg_init(&lda, &sx_delay);
563 #elif defined(KDTRACE_HOOKS)
564 lock_delay_arg_init(&lda, NULL);
567 if (__predict_false(x == SX_LOCK_UNLOCKED))
568 x = SX_READ_VALUE(sx);
570 /* If we already hold an exclusive lock, then recurse. */
571 if (__predict_false(lv_sx_owner(x) == (struct thread *)tid)) {
572 KASSERT((sx->lock_object.lo_flags & LO_RECURSABLE) != 0,
573 ("_sx_xlock_hard: recursed on non-recursive sx %s @ %s:%d\n",
574 sx->lock_object.lo_name, file, line));
576 atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
577 if (LOCK_LOG_TEST(&sx->lock_object, 0))
578 CTR2(KTR_LOCK, "%s: %p recursing", __func__, sx);
582 if (LOCK_LOG_TEST(&sx->lock_object, 0))
583 CTR5(KTR_LOCK, "%s: %s contested (lock=%p) at %s:%d", __func__,
584 sx->lock_object.lo_name, (void *)sx->sx_lock, file, line);
587 adaptive = ((sx->lock_object.lo_flags & SX_NOADAPTIVE) != 0);
591 PMC_SOFT_CALL( , , lock, failed);
593 lock_profile_obtain_lock_failed(&sx->lock_object, &contested,
596 #ifdef LOCK_PROFILING
599 #elif defined(KDTRACE_HOOKS)
600 extra_work = lockstat_enabled;
601 if (__predict_false(extra_work)) {
602 all_time -= lockstat_nsecs(&sx->lock_object);
607 GIANT_SAVE(extra_work);
611 if (x == SX_LOCK_UNLOCKED) {
612 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, tid))
617 GIANT_SAVE(extra_work);
623 if (__predict_false(!adaptive))
626 * If the lock is write locked and the owner is
627 * running on another CPU, spin until the owner stops
628 * running or the state of the lock changes.
630 if ((x & SX_LOCK_SHARED) == 0) {
631 owner = lv_sx_owner(x);
632 if (TD_IS_RUNNING(owner)) {
633 if (LOCK_LOG_TEST(&sx->lock_object, 0))
635 "%s: spinning on %p held by %p",
636 __func__, sx, owner);
637 KTR_STATE1(KTR_SCHED, "thread",
638 sched_tdname(curthread), "spinning",
640 sx->lock_object.lo_name);
643 x = SX_READ_VALUE(sx);
644 owner = lv_sx_owner(x);
645 } while (owner != NULL &&
646 TD_IS_RUNNING(owner));
647 KTR_STATE0(KTR_SCHED, "thread",
648 sched_tdname(curthread), "running");
652 } else if (SX_SHARERS(x) && spintries < asx_retries) {
653 KTR_STATE1(KTR_SCHED, "thread",
654 sched_tdname(curthread), "spinning",
655 "lockname:\"%s\"", sx->lock_object.lo_name);
657 for (i = 0; i < asx_loops; i += n) {
658 if (LOCK_LOG_TEST(&sx->lock_object, 0))
660 "%s: shared spinning on %p with %u and %u",
661 __func__, sx, spintries, i);
664 x = SX_READ_VALUE(sx);
665 if ((x & SX_LOCK_SHARED) == 0 ||
672 KTR_STATE0(KTR_SCHED, "thread",
673 sched_tdname(curthread), "running");
680 sleepq_lock(&sx->lock_object);
681 x = SX_READ_VALUE(sx);
685 * If the lock was released while spinning on the
686 * sleep queue chain lock, try again.
688 if (x == SX_LOCK_UNLOCKED) {
689 sleepq_release(&sx->lock_object);
695 * The current lock owner might have started executing
696 * on another CPU (or the lock could have changed
697 * owners) while we were waiting on the sleep queue
698 * chain lock. If so, drop the sleep queue lock and try
702 if (!(x & SX_LOCK_SHARED)) {
703 owner = (struct thread *)SX_OWNER(x);
704 if (TD_IS_RUNNING(owner)) {
705 sleepq_release(&sx->lock_object);
708 } else if (SX_SHARERS(x) > 0 && sleep_reason == 1) {
709 sleepq_release(&sx->lock_object);
716 * If an exclusive lock was released with both shared
717 * and exclusive waiters and a shared waiter hasn't
718 * woken up and acquired the lock yet, sx_lock will be
719 * set to SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS.
720 * If we see that value, try to acquire it once. Note
721 * that we have to preserve SX_LOCK_EXCLUSIVE_WAITERS
722 * as there are other exclusive waiters still. If we
723 * fail, restart the loop.
725 if (x == (SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS)) {
726 if (!atomic_fcmpset_acq_ptr(&sx->sx_lock, &x,
727 tid | SX_LOCK_EXCLUSIVE_WAITERS))
729 sleepq_release(&sx->lock_object);
730 CTR2(KTR_LOCK, "%s: %p claimed by new writer",
736 * Try to set the SX_LOCK_EXCLUSIVE_WAITERS. If we fail,
737 * than loop back and retry.
739 if (!(x & SX_LOCK_EXCLUSIVE_WAITERS)) {
740 if (!atomic_fcmpset_ptr(&sx->sx_lock, &x,
741 x | SX_LOCK_EXCLUSIVE_WAITERS)) {
744 if (LOCK_LOG_TEST(&sx->lock_object, 0))
745 CTR2(KTR_LOCK, "%s: %p set excl waiters flag",
750 * Since we have been unable to acquire the exclusive
751 * lock and the exclusive waiters flag is set, we have
754 if (LOCK_LOG_TEST(&sx->lock_object, 0))
755 CTR2(KTR_LOCK, "%s: %p blocking on sleep queue",
759 sleep_time -= lockstat_nsecs(&sx->lock_object);
761 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name,
762 SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ?
763 SLEEPQ_INTERRUPTIBLE : 0), SQ_EXCLUSIVE_QUEUE);
764 if (!(opts & SX_INTERRUPTIBLE))
765 sleepq_wait(&sx->lock_object, 0);
767 error = sleepq_wait_sig(&sx->lock_object, 0);
769 sleep_time += lockstat_nsecs(&sx->lock_object);
773 if (LOCK_LOG_TEST(&sx->lock_object, 0))
775 "%s: interruptible sleep by %p suspended by signal",
779 if (LOCK_LOG_TEST(&sx->lock_object, 0))
780 CTR2(KTR_LOCK, "%s: %p resuming from sleep queue",
782 x = SX_READ_VALUE(sx);
784 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING)
785 if (__predict_true(!extra_work))
789 all_time += lockstat_nsecs(&sx->lock_object);
791 LOCKSTAT_RECORD4(sx__block, sx, sleep_time,
792 LOCKSTAT_WRITER, (state & SX_LOCK_SHARED) == 0,
793 (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state));
794 if (lda.spin_cnt > sleep_cnt)
795 LOCKSTAT_RECORD4(sx__spin, sx, all_time - sleep_time,
796 LOCKSTAT_WRITER, (state & SX_LOCK_SHARED) == 0,
797 (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state));
800 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire, sx,
801 contested, waittime, file, line, LOCKSTAT_WRITER);
807 * This function represents the so-called 'hard case' for sx_xunlock
808 * operation. All 'easy case' failures are redirected to this. Note
809 * that ideally this would be a static function, but it needs to be
810 * accessible from at least sx.h.
813 _sx_xunlock_hard(struct sx *sx, uintptr_t x LOCK_FILE_LINE_ARG_DEF)
816 int queue, wakeup_swapper;
818 if (SCHEDULER_STOPPED())
821 tid = (uintptr_t)curthread;
823 if (__predict_false(x == tid))
824 x = SX_READ_VALUE(sx);
826 MPASS(!(x & SX_LOCK_SHARED));
828 if (__predict_false(x & SX_LOCK_RECURSED)) {
829 /* The lock is recursed, unrecurse one level. */
830 if ((--sx->sx_recurse) == 0)
831 atomic_clear_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
832 if (LOCK_LOG_TEST(&sx->lock_object, 0))
833 CTR2(KTR_LOCK, "%s: %p unrecursing", __func__, sx);
837 LOCKSTAT_PROFILE_RELEASE_RWLOCK(sx__release, sx, LOCKSTAT_WRITER);
839 atomic_cmpset_rel_ptr(&sx->sx_lock, tid, SX_LOCK_UNLOCKED))
842 if (LOCK_LOG_TEST(&sx->lock_object, 0))
843 CTR2(KTR_LOCK, "%s: %p contested", __func__, sx);
845 sleepq_lock(&sx->lock_object);
846 x = SX_READ_VALUE(sx);
847 MPASS(x & (SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS));
850 * The wake up algorithm here is quite simple and probably not
851 * ideal. It gives precedence to shared waiters if they are
852 * present. For this condition, we have to preserve the
853 * state of the exclusive waiters flag.
854 * If interruptible sleeps left the shared queue empty avoid a
855 * starvation for the threads sleeping on the exclusive queue by giving
856 * them precedence and cleaning up the shared waiters bit anyway.
858 setx = SX_LOCK_UNLOCKED;
859 queue = SQ_EXCLUSIVE_QUEUE;
860 if ((x & SX_LOCK_SHARED_WAITERS) != 0 &&
861 sleepq_sleepcnt(&sx->lock_object, SQ_SHARED_QUEUE) != 0) {
862 queue = SQ_SHARED_QUEUE;
863 setx |= (x & SX_LOCK_EXCLUSIVE_WAITERS);
865 atomic_store_rel_ptr(&sx->sx_lock, setx);
867 /* Wake up all the waiters for the specific queue. */
868 if (LOCK_LOG_TEST(&sx->lock_object, 0))
869 CTR3(KTR_LOCK, "%s: %p waking up all threads on %s queue",
870 __func__, sx, queue == SQ_SHARED_QUEUE ? "shared" :
873 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, 0,
875 sleepq_release(&sx->lock_object);
880 static bool __always_inline
881 __sx_slock_try(struct sx *sx, uintptr_t *xp LOCK_FILE_LINE_ARG_DEF)
885 * If no other thread has an exclusive lock then try to bump up
886 * the count of sharers. Since we have to preserve the state
887 * of SX_LOCK_EXCLUSIVE_WAITERS, if we fail to acquire the
888 * shared lock loop back and retry.
890 while (*xp & SX_LOCK_SHARED) {
891 MPASS(!(*xp & SX_LOCK_SHARED_WAITERS));
892 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, xp,
893 *xp + SX_ONE_SHARER)) {
894 if (LOCK_LOG_TEST(&sx->lock_object, 0))
895 CTR4(KTR_LOCK, "%s: %p succeed %p -> %p",
896 __func__, sx, (void *)*xp,
897 (void *)(*xp + SX_ONE_SHARER));
904 static int __noinline
905 _sx_slock_hard(struct sx *sx, int opts, uintptr_t x LOCK_FILE_LINE_ARG_DEF)
909 volatile struct thread *owner;
912 #ifdef LOCK_PROFILING
913 uint64_t waittime = 0;
917 #if defined(ADAPTIVE_SX) || defined(KDTRACE_HOOKS)
918 struct lock_delay_arg lda;
922 int64_t sleep_time = 0;
923 int64_t all_time = 0;
925 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING)
930 if (SCHEDULER_STOPPED())
933 #if defined(ADAPTIVE_SX)
934 lock_delay_arg_init(&lda, &sx_delay);
935 #elif defined(KDTRACE_HOOKS)
936 lock_delay_arg_init(&lda, NULL);
940 adaptive = ((sx->lock_object.lo_flags & SX_NOADAPTIVE) != 0);
944 PMC_SOFT_CALL( , , lock, failed);
946 lock_profile_obtain_lock_failed(&sx->lock_object, &contested,
949 #ifdef LOCK_PROFILING
952 #elif defined(KDTRACE_HOOKS)
953 extra_work = lockstat_enabled;
954 if (__predict_false(extra_work)) {
955 all_time -= lockstat_nsecs(&sx->lock_object);
960 GIANT_SAVE(extra_work);
964 * As with rwlocks, we don't make any attempt to try to block
965 * shared locks once there is an exclusive waiter.
968 if (__sx_slock_try(sx, &x LOCK_FILE_LINE_ARG))
971 GIANT_SAVE(extra_work);
978 if (__predict_false(!adaptive))
981 * If the owner is running on another CPU, spin until
982 * the owner stops running or the state of the lock
985 owner = lv_sx_owner(x);
986 if (TD_IS_RUNNING(owner)) {
987 if (LOCK_LOG_TEST(&sx->lock_object, 0))
989 "%s: spinning on %p held by %p",
990 __func__, sx, owner);
991 KTR_STATE1(KTR_SCHED, "thread",
992 sched_tdname(curthread), "spinning",
993 "lockname:\"%s\"", sx->lock_object.lo_name);
996 x = SX_READ_VALUE(sx);
997 owner = lv_sx_owner(x);
998 } while (owner != NULL && TD_IS_RUNNING(owner));
999 KTR_STATE0(KTR_SCHED, "thread",
1000 sched_tdname(curthread), "running");
1007 * Some other thread already has an exclusive lock, so
1008 * start the process of blocking.
1010 sleepq_lock(&sx->lock_object);
1011 x = SX_READ_VALUE(sx);
1014 * The lock could have been released while we spun.
1015 * In this case loop back and retry.
1017 if (x & SX_LOCK_SHARED) {
1018 sleepq_release(&sx->lock_object);
1024 * If the owner is running on another CPU, spin until
1025 * the owner stops running or the state of the lock
1028 if (!(x & SX_LOCK_SHARED) && adaptive) {
1029 owner = (struct thread *)SX_OWNER(x);
1030 if (TD_IS_RUNNING(owner)) {
1031 sleepq_release(&sx->lock_object);
1032 x = SX_READ_VALUE(sx);
1039 * Try to set the SX_LOCK_SHARED_WAITERS flag. If we
1040 * fail to set it drop the sleep queue lock and loop
1043 if (!(x & SX_LOCK_SHARED_WAITERS)) {
1044 if (!atomic_fcmpset_ptr(&sx->sx_lock, &x,
1045 x | SX_LOCK_SHARED_WAITERS))
1047 if (LOCK_LOG_TEST(&sx->lock_object, 0))
1048 CTR2(KTR_LOCK, "%s: %p set shared waiters flag",
1053 * Since we have been unable to acquire the shared lock,
1056 if (LOCK_LOG_TEST(&sx->lock_object, 0))
1057 CTR2(KTR_LOCK, "%s: %p blocking on sleep queue",
1060 #ifdef KDTRACE_HOOKS
1061 sleep_time -= lockstat_nsecs(&sx->lock_object);
1063 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name,
1064 SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ?
1065 SLEEPQ_INTERRUPTIBLE : 0), SQ_SHARED_QUEUE);
1066 if (!(opts & SX_INTERRUPTIBLE))
1067 sleepq_wait(&sx->lock_object, 0);
1069 error = sleepq_wait_sig(&sx->lock_object, 0);
1070 #ifdef KDTRACE_HOOKS
1071 sleep_time += lockstat_nsecs(&sx->lock_object);
1075 if (LOCK_LOG_TEST(&sx->lock_object, 0))
1077 "%s: interruptible sleep by %p suspended by signal",
1081 if (LOCK_LOG_TEST(&sx->lock_object, 0))
1082 CTR2(KTR_LOCK, "%s: %p resuming from sleep queue",
1084 x = SX_READ_VALUE(sx);
1086 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING)
1087 if (__predict_true(!extra_work))
1090 #ifdef KDTRACE_HOOKS
1091 all_time += lockstat_nsecs(&sx->lock_object);
1093 LOCKSTAT_RECORD4(sx__block, sx, sleep_time,
1094 LOCKSTAT_READER, (state & SX_LOCK_SHARED) == 0,
1095 (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state));
1096 if (lda.spin_cnt > sleep_cnt)
1097 LOCKSTAT_RECORD4(sx__spin, sx, all_time - sleep_time,
1098 LOCKSTAT_READER, (state & SX_LOCK_SHARED) == 0,
1099 (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state));
1102 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire, sx,
1103 contested, waittime, file, line, LOCKSTAT_READER);
1110 _sx_slock_int(struct sx *sx, int opts LOCK_FILE_LINE_ARG_DEF)
1115 KASSERT(kdb_active != 0 || SCHEDULER_STOPPED() ||
1116 !TD_IS_IDLETHREAD(curthread),
1117 ("sx_slock() by idle thread %p on sx %s @ %s:%d",
1118 curthread, sx->lock_object.lo_name, file, line));
1119 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
1120 ("sx_slock() of destroyed sx @ %s:%d", file, line));
1121 WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER, file, line, NULL);
1124 x = SX_READ_VALUE(sx);
1125 if (__predict_false(LOCKSTAT_PROFILE_ENABLED(sx__acquire) ||
1126 !__sx_slock_try(sx, &x LOCK_FILE_LINE_ARG)))
1127 error = _sx_slock_hard(sx, opts, x LOCK_FILE_LINE_ARG);
1129 lock_profile_obtain_lock_success(&sx->lock_object, 0, 0,
1132 LOCK_LOG_LOCK("SLOCK", &sx->lock_object, 0, 0, file, line);
1133 WITNESS_LOCK(&sx->lock_object, 0, file, line);
1134 TD_LOCKS_INC(curthread);
1140 _sx_slock(struct sx *sx, int opts, const char *file, int line)
1143 return (_sx_slock_int(sx, opts LOCK_FILE_LINE_ARG));
1146 static bool __always_inline
1147 _sx_sunlock_try(struct sx *sx, uintptr_t *xp)
1152 * We should never have sharers while at least one thread
1153 * holds a shared lock.
1155 KASSERT(!(*xp & SX_LOCK_SHARED_WAITERS),
1156 ("%s: waiting sharers", __func__));
1159 * See if there is more than one shared lock held. If
1160 * so, just drop one and return.
1162 if (SX_SHARERS(*xp) > 1) {
1163 if (atomic_fcmpset_rel_ptr(&sx->sx_lock, xp,
1164 *xp - SX_ONE_SHARER)) {
1165 if (LOCK_LOG_TEST(&sx->lock_object, 0))
1167 "%s: %p succeeded %p -> %p",
1168 __func__, sx, (void *)*xp,
1169 (void *)(*xp - SX_ONE_SHARER));
1176 * If there aren't any waiters for an exclusive lock,
1177 * then try to drop it quickly.
1179 if (!(*xp & SX_LOCK_EXCLUSIVE_WAITERS)) {
1180 MPASS(*xp == SX_SHARERS_LOCK(1));
1181 *xp = SX_SHARERS_LOCK(1);
1182 if (atomic_fcmpset_rel_ptr(&sx->sx_lock,
1183 xp, SX_LOCK_UNLOCKED)) {
1184 if (LOCK_LOG_TEST(&sx->lock_object, 0))
1185 CTR2(KTR_LOCK, "%s: %p last succeeded",
1196 static void __noinline
1197 _sx_sunlock_hard(struct sx *sx, uintptr_t x LOCK_FILE_LINE_ARG_DEF)
1199 int wakeup_swapper = 0;
1202 if (SCHEDULER_STOPPED())
1205 if (_sx_sunlock_try(sx, &x))
1209 * At this point, there should just be one sharer with
1210 * exclusive waiters.
1212 MPASS(x == (SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS));
1214 sleepq_lock(&sx->lock_object);
1215 x = SX_READ_VALUE(sx);
1217 MPASS(x & SX_LOCK_EXCLUSIVE_WAITERS);
1218 MPASS(!(x & SX_LOCK_SHARED_WAITERS));
1219 if (_sx_sunlock_try(sx, &x))
1223 * Wake up semantic here is quite simple:
1224 * Just wake up all the exclusive waiters.
1225 * Note that the state of the lock could have changed,
1226 * so if it fails loop back and retry.
1228 setx = x - SX_ONE_SHARER;
1229 setx &= ~SX_LOCK_EXCLUSIVE_WAITERS;
1230 if (!atomic_fcmpset_rel_ptr(&sx->sx_lock, &x, setx))
1232 if (LOCK_LOG_TEST(&sx->lock_object, 0))
1233 CTR2(KTR_LOCK, "%s: %p waking up all thread on"
1234 "exclusive queue", __func__, sx);
1235 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX,
1236 0, SQ_EXCLUSIVE_QUEUE);
1239 sleepq_release(&sx->lock_object);
1243 LOCKSTAT_PROFILE_RELEASE_RWLOCK(sx__release, sx, LOCKSTAT_READER);
1247 _sx_sunlock_int(struct sx *sx LOCK_FILE_LINE_ARG_DEF)
1251 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
1252 ("sx_sunlock() of destroyed sx @ %s:%d", file, line));
1253 _sx_assert(sx, SA_SLOCKED, file, line);
1254 WITNESS_UNLOCK(&sx->lock_object, 0, file, line);
1255 LOCK_LOG_LOCK("SUNLOCK", &sx->lock_object, 0, 0, file, line);
1257 x = SX_READ_VALUE(sx);
1258 if (__predict_false(LOCKSTAT_PROFILE_ENABLED(sx__release) ||
1259 !_sx_sunlock_try(sx, &x)))
1260 _sx_sunlock_hard(sx, x LOCK_FILE_LINE_ARG);
1262 lock_profile_release_lock(&sx->lock_object);
1264 TD_LOCKS_DEC(curthread);
1268 _sx_sunlock(struct sx *sx, const char *file, int line)
1271 _sx_sunlock_int(sx LOCK_FILE_LINE_ARG);
1274 #ifdef INVARIANT_SUPPORT
1280 * In the non-WITNESS case, sx_assert() can only detect that at least
1281 * *some* thread owns an slock, but it cannot guarantee that *this*
1282 * thread owns an slock.
1285 _sx_assert(const struct sx *sx, int what, const char *file, int line)
1291 if (panicstr != NULL)
1295 case SA_SLOCKED | SA_NOTRECURSED:
1296 case SA_SLOCKED | SA_RECURSED:
1302 case SA_LOCKED | SA_NOTRECURSED:
1303 case SA_LOCKED | SA_RECURSED:
1305 witness_assert(&sx->lock_object, what, file, line);
1308 * If some other thread has an exclusive lock or we
1309 * have one and are asserting a shared lock, fail.
1310 * Also, if no one has a lock at all, fail.
1312 if (sx->sx_lock == SX_LOCK_UNLOCKED ||
1313 (!(sx->sx_lock & SX_LOCK_SHARED) && (slocked ||
1314 sx_xholder(sx) != curthread)))
1315 panic("Lock %s not %slocked @ %s:%d\n",
1316 sx->lock_object.lo_name, slocked ? "share " : "",
1319 if (!(sx->sx_lock & SX_LOCK_SHARED)) {
1320 if (sx_recursed(sx)) {
1321 if (what & SA_NOTRECURSED)
1322 panic("Lock %s recursed @ %s:%d\n",
1323 sx->lock_object.lo_name, file,
1325 } else if (what & SA_RECURSED)
1326 panic("Lock %s not recursed @ %s:%d\n",
1327 sx->lock_object.lo_name, file, line);
1332 case SA_XLOCKED | SA_NOTRECURSED:
1333 case SA_XLOCKED | SA_RECURSED:
1334 if (sx_xholder(sx) != curthread)
1335 panic("Lock %s not exclusively locked @ %s:%d\n",
1336 sx->lock_object.lo_name, file, line);
1337 if (sx_recursed(sx)) {
1338 if (what & SA_NOTRECURSED)
1339 panic("Lock %s recursed @ %s:%d\n",
1340 sx->lock_object.lo_name, file, line);
1341 } else if (what & SA_RECURSED)
1342 panic("Lock %s not recursed @ %s:%d\n",
1343 sx->lock_object.lo_name, file, line);
1347 witness_assert(&sx->lock_object, what, file, line);
1350 * If we hold an exclusve lock fail. We can't
1351 * reliably check to see if we hold a shared lock or
1354 if (sx_xholder(sx) == curthread)
1355 panic("Lock %s exclusively locked @ %s:%d\n",
1356 sx->lock_object.lo_name, file, line);
1360 panic("Unknown sx lock assertion: %d @ %s:%d", what, file,
1364 #endif /* INVARIANT_SUPPORT */
1368 db_show_sx(const struct lock_object *lock)
1371 const struct sx *sx;
1373 sx = (const struct sx *)lock;
1375 db_printf(" state: ");
1376 if (sx->sx_lock == SX_LOCK_UNLOCKED)
1377 db_printf("UNLOCKED\n");
1378 else if (sx->sx_lock == SX_LOCK_DESTROYED) {
1379 db_printf("DESTROYED\n");
1381 } else if (sx->sx_lock & SX_LOCK_SHARED)
1382 db_printf("SLOCK: %ju\n", (uintmax_t)SX_SHARERS(sx->sx_lock));
1384 td = sx_xholder(sx);
1385 db_printf("XLOCK: %p (tid %d, pid %d, \"%s\")\n", td,
1386 td->td_tid, td->td_proc->p_pid, td->td_name);
1387 if (sx_recursed(sx))
1388 db_printf(" recursed: %d\n", sx->sx_recurse);
1391 db_printf(" waiters: ");
1392 switch(sx->sx_lock &
1393 (SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS)) {
1394 case SX_LOCK_SHARED_WAITERS:
1395 db_printf("shared\n");
1397 case SX_LOCK_EXCLUSIVE_WAITERS:
1398 db_printf("exclusive\n");
1400 case SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS:
1401 db_printf("exclusive and shared\n");
1404 db_printf("none\n");
1409 * Check to see if a thread that is blocked on a sleep queue is actually
1410 * blocked on an sx lock. If so, output some details and return true.
1411 * If the lock has an exclusive owner, return that in *ownerp.
1414 sx_chain(struct thread *td, struct thread **ownerp)
1419 * Check to see if this thread is blocked on an sx lock.
1420 * First, we check the lock class. If that is ok, then we
1421 * compare the lock name against the wait message.
1424 if (LOCK_CLASS(&sx->lock_object) != &lock_class_sx ||
1425 sx->lock_object.lo_name != td->td_wmesg)
1428 /* We think we have an sx lock, so output some details. */
1429 db_printf("blocked on sx \"%s\" ", td->td_wmesg);
1430 *ownerp = sx_xholder(sx);
1431 if (sx->sx_lock & SX_LOCK_SHARED)
1432 db_printf("SLOCK (count %ju)\n",
1433 (uintmax_t)SX_SHARERS(sx->sx_lock));
1435 db_printf("XLOCK\n");