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>
48 #include <sys/linker_set.h>
50 #include <sys/mutex.h>
52 #include <sys/sleepqueue.h>
54 #include <sys/sysctl.h>
55 #include <sys/systm.h>
57 #if defined(SMP) && !defined(NO_ADAPTIVE_SX)
58 #include <machine/cpu.h>
65 #if defined(SMP) && !defined(NO_ADAPTIVE_SX)
69 CTASSERT((SX_NOADAPTIVE & LO_CLASSFLAGS) == SX_NOADAPTIVE);
71 /* Handy macros for sleep queues. */
72 #define SQ_EXCLUSIVE_QUEUE 0
73 #define SQ_SHARED_QUEUE 1
76 * Variations on DROP_GIANT()/PICKUP_GIANT() for use in this file. We
77 * drop Giant anytime we have to sleep or if we adaptively spin.
79 #define GIANT_DECLARE \
81 WITNESS_SAVE_DECL(Giant) \
83 #define GIANT_SAVE() do { \
84 if (mtx_owned(&Giant)) { \
85 WITNESS_SAVE(&Giant.lock_object, Giant); \
86 while (mtx_owned(&Giant)) { \
93 #define GIANT_RESTORE() do { \
94 if (_giantcnt > 0) { \
95 mtx_assert(&Giant, MA_NOTOWNED); \
98 WITNESS_RESTORE(&Giant.lock_object, Giant); \
103 * Returns true if an exclusive lock is recursed. It assumes
104 * curthread currently has an exclusive lock.
106 #define sx_recurse lock_object.lo_data
107 #define sx_recursed(sx) ((sx)->sx_recurse != 0)
109 static void assert_sx(struct lock_object *lock, int what);
111 static void db_show_sx(struct lock_object *lock);
113 static void lock_sx(struct lock_object *lock, int how);
115 static int owner_sx(struct lock_object *lock, struct thread **owner);
117 static int unlock_sx(struct lock_object *lock);
119 struct lock_class lock_class_sx = {
121 .lc_flags = LC_SLEEPLOCK | LC_SLEEPABLE | LC_RECURSABLE | LC_UPGRADABLE,
122 .lc_assert = assert_sx,
124 .lc_ddb_show = db_show_sx,
127 .lc_unlock = unlock_sx,
129 .lc_owner = owner_sx,
134 #define _sx_assert(sx, what, file, line)
138 static u_int asx_retries = 10;
139 static u_int asx_loops = 10000;
140 SYSCTL_NODE(_debug, OID_AUTO, sx, CTLFLAG_RD, NULL, "sxlock debugging");
141 SYSCTL_INT(_debug_sx, OID_AUTO, retries, CTLFLAG_RW, &asx_retries, 0, "");
142 SYSCTL_INT(_debug_sx, OID_AUTO, loops, CTLFLAG_RW, &asx_loops, 0, "");
146 assert_sx(struct lock_object *lock, int what)
149 sx_assert((struct sx *)lock, what);
153 lock_sx(struct lock_object *lock, int how)
157 sx = (struct sx *)lock;
165 unlock_sx(struct lock_object *lock)
169 sx = (struct sx *)lock;
170 sx_assert(sx, SA_LOCKED | SA_NOTRECURSED);
171 if (sx_xlocked(sx)) {
182 owner_sx(struct lock_object *lock, struct thread **owner)
184 struct sx *sx = (struct sx *)lock;
185 uintptr_t x = sx->sx_lock;
187 *owner = (struct thread *)SX_OWNER(x);
188 return ((x & SX_LOCK_SHARED) != 0 ? (SX_SHARERS(x) != 0) :
194 sx_sysinit(void *arg)
196 struct sx_args *sargs = arg;
198 sx_init(sargs->sa_sx, sargs->sa_desc);
202 sx_init_flags(struct sx *sx, const char *description, int opts)
206 MPASS((opts & ~(SX_QUIET | SX_RECURSE | SX_NOWITNESS | SX_DUPOK |
207 SX_NOPROFILE | SX_NOADAPTIVE)) == 0);
208 ASSERT_ATOMIC_LOAD_PTR(sx->sx_lock,
209 ("%s: sx_lock not aligned for %s: %p", __func__, description,
212 flags = LO_SLEEPABLE | LO_UPGRADABLE;
215 if (opts & SX_NOPROFILE)
216 flags |= LO_NOPROFILE;
217 if (!(opts & SX_NOWITNESS))
219 if (opts & SX_RECURSE)
220 flags |= LO_RECURSABLE;
224 flags |= opts & SX_NOADAPTIVE;
225 sx->sx_lock = SX_LOCK_UNLOCKED;
227 lock_init(&sx->lock_object, &lock_class_sx, description, NULL, flags);
231 sx_destroy(struct sx *sx)
234 KASSERT(sx->sx_lock == SX_LOCK_UNLOCKED, ("sx lock still held"));
235 KASSERT(sx->sx_recurse == 0, ("sx lock still recursed"));
236 sx->sx_lock = SX_LOCK_DESTROYED;
237 lock_destroy(&sx->lock_object);
241 _sx_slock(struct sx *sx, int opts, const char *file, int line)
245 MPASS(curthread != NULL);
246 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
247 ("sx_slock() of destroyed sx @ %s:%d", file, line));
248 WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER, file, line, NULL);
249 error = __sx_slock(sx, opts, file, line);
251 LOCK_LOG_LOCK("SLOCK", &sx->lock_object, 0, 0, file, line);
252 WITNESS_LOCK(&sx->lock_object, 0, file, line);
253 curthread->td_locks++;
260 _sx_try_slock(struct sx *sx, const char *file, int line)
266 KASSERT(x != SX_LOCK_DESTROYED,
267 ("sx_try_slock() of destroyed sx @ %s:%d", file, line));
268 if (!(x & SX_LOCK_SHARED))
270 if (atomic_cmpset_acq_ptr(&sx->sx_lock, x, x + SX_ONE_SHARER)) {
271 LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 1, file, line);
272 WITNESS_LOCK(&sx->lock_object, LOP_TRYLOCK, file, line);
273 curthread->td_locks++;
278 LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 0, file, line);
283 _sx_xlock(struct sx *sx, int opts, const char *file, int line)
287 MPASS(curthread != NULL);
288 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
289 ("sx_xlock() of destroyed sx @ %s:%d", file, line));
290 WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER | LOP_EXCLUSIVE, file,
292 error = __sx_xlock(sx, curthread, opts, file, line);
294 LOCK_LOG_LOCK("XLOCK", &sx->lock_object, 0, sx->sx_recurse,
296 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line);
297 curthread->td_locks++;
304 _sx_try_xlock(struct sx *sx, const char *file, int line)
308 MPASS(curthread != NULL);
309 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
310 ("sx_try_xlock() of destroyed sx @ %s:%d", file, line));
312 if (sx_xlocked(sx) &&
313 (sx->lock_object.lo_flags & LO_RECURSABLE) != 0) {
315 atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
318 rval = atomic_cmpset_acq_ptr(&sx->sx_lock, SX_LOCK_UNLOCKED,
319 (uintptr_t)curthread);
320 LOCK_LOG_TRY("XLOCK", &sx->lock_object, 0, rval, file, line);
322 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
324 curthread->td_locks++;
331 _sx_sunlock(struct sx *sx, const char *file, int line)
334 MPASS(curthread != NULL);
335 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
336 ("sx_sunlock() of destroyed sx @ %s:%d", file, line));
337 _sx_assert(sx, SA_SLOCKED, file, line);
338 curthread->td_locks--;
339 WITNESS_UNLOCK(&sx->lock_object, 0, file, line);
340 LOCK_LOG_LOCK("SUNLOCK", &sx->lock_object, 0, 0, file, line);
341 __sx_sunlock(sx, file, line);
342 LOCKSTAT_PROFILE_RELEASE_LOCK(LS_SX_SUNLOCK_RELEASE, sx);
346 _sx_xunlock(struct sx *sx, const char *file, int line)
349 MPASS(curthread != NULL);
350 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
351 ("sx_xunlock() of destroyed sx @ %s:%d", file, line));
352 _sx_assert(sx, SA_XLOCKED, file, line);
353 curthread->td_locks--;
354 WITNESS_UNLOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line);
355 LOCK_LOG_LOCK("XUNLOCK", &sx->lock_object, 0, sx->sx_recurse, file,
357 if (!sx_recursed(sx))
358 LOCKSTAT_PROFILE_RELEASE_LOCK(LS_SX_XUNLOCK_RELEASE, sx);
359 __sx_xunlock(sx, curthread, file, line);
363 * Try to do a non-blocking upgrade from a shared lock to an exclusive lock.
364 * This will only succeed if this thread holds a single shared lock.
365 * Return 1 if if the upgrade succeed, 0 otherwise.
368 _sx_try_upgrade(struct sx *sx, const char *file, int line)
373 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
374 ("sx_try_upgrade() of destroyed sx @ %s:%d", file, line));
375 _sx_assert(sx, SA_SLOCKED, file, line);
378 * Try to switch from one shared lock to an exclusive lock. We need
379 * to maintain the SX_LOCK_EXCLUSIVE_WAITERS flag if set so that
380 * we will wake up the exclusive waiters when we drop the lock.
382 x = sx->sx_lock & SX_LOCK_EXCLUSIVE_WAITERS;
383 success = atomic_cmpset_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1) | x,
384 (uintptr_t)curthread | x);
385 LOCK_LOG_TRY("XUPGRADE", &sx->lock_object, 0, success, file, line);
387 WITNESS_UPGRADE(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
389 LOCKSTAT_RECORD0(LS_SX_TRYUPGRADE_UPGRADE, sx);
395 * Downgrade an unrecursed exclusive lock into a single shared lock.
398 _sx_downgrade(struct sx *sx, const char *file, int line)
403 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
404 ("sx_downgrade() of destroyed sx @ %s:%d", file, line));
405 _sx_assert(sx, SA_XLOCKED | SA_NOTRECURSED, file, line);
408 panic("downgrade of a recursed lock");
411 WITNESS_DOWNGRADE(&sx->lock_object, 0, file, line);
414 * Try to switch from an exclusive lock with no shared waiters
415 * to one sharer with no shared waiters. If there are
416 * exclusive waiters, we don't need to lock the sleep queue so
417 * long as we preserve the flag. We do one quick try and if
418 * that fails we grab the sleepq lock to keep the flags from
419 * changing and do it the slow way.
421 * We have to lock the sleep queue if there are shared waiters
422 * so we can wake them up.
425 if (!(x & SX_LOCK_SHARED_WAITERS) &&
426 atomic_cmpset_rel_ptr(&sx->sx_lock, x, SX_SHARERS_LOCK(1) |
427 (x & SX_LOCK_EXCLUSIVE_WAITERS))) {
428 LOCK_LOG_LOCK("XDOWNGRADE", &sx->lock_object, 0, 0, file, line);
433 * Lock the sleep queue so we can read the waiters bits
434 * without any races and wakeup any shared waiters.
436 sleepq_lock(&sx->lock_object);
439 * Preserve SX_LOCK_EXCLUSIVE_WAITERS while downgraded to a single
440 * shared lock. If there are any shared waiters, wake them up.
444 atomic_store_rel_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1) |
445 (x & SX_LOCK_EXCLUSIVE_WAITERS));
446 if (x & SX_LOCK_SHARED_WAITERS)
447 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX,
449 sleepq_release(&sx->lock_object);
451 LOCK_LOG_LOCK("XDOWNGRADE", &sx->lock_object, 0, 0, file, line);
452 LOCKSTAT_RECORD0(LS_SX_DOWNGRADE_DOWNGRADE, sx);
459 * This function represents the so-called 'hard case' for sx_xlock
460 * operation. All 'easy case' failures are redirected to this. Note
461 * that ideally this would be a static function, but it needs to be
462 * accessible from at least sx.h.
465 _sx_xlock_hard(struct sx *sx, uintptr_t tid, int opts, const char *file,
470 volatile struct thread *owner;
471 u_int i, spintries = 0;
474 #ifdef LOCK_PROFILING
475 uint64_t waittime = 0;
480 uint64_t spin_cnt = 0;
481 uint64_t sleep_cnt = 0;
482 int64_t sleep_time = 0;
485 /* If we already hold an exclusive lock, then recurse. */
486 if (sx_xlocked(sx)) {
487 KASSERT((sx->lock_object.lo_flags & LO_RECURSABLE) != 0,
488 ("_sx_xlock_hard: recursed on non-recursive sx %s @ %s:%d\n",
489 sx->lock_object.lo_name, file, line));
491 atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
492 if (LOCK_LOG_TEST(&sx->lock_object, 0))
493 CTR2(KTR_LOCK, "%s: %p recursing", __func__, sx);
497 if (LOCK_LOG_TEST(&sx->lock_object, 0))
498 CTR5(KTR_LOCK, "%s: %s contested (lock=%p) at %s:%d", __func__,
499 sx->lock_object.lo_name, (void *)sx->sx_lock, file, line);
501 while (!atomic_cmpset_acq_ptr(&sx->sx_lock, SX_LOCK_UNLOCKED, tid)) {
505 lock_profile_obtain_lock_failed(&sx->lock_object, &contested,
509 * If the lock is write locked and the owner is
510 * running on another CPU, spin until the owner stops
511 * running or the state of the lock changes.
514 if ((sx->lock_object.lo_flags & SX_NOADAPTIVE) != 0) {
515 if ((x & SX_LOCK_SHARED) == 0) {
517 owner = (struct thread *)x;
518 if (TD_IS_RUNNING(owner)) {
519 if (LOCK_LOG_TEST(&sx->lock_object, 0))
521 "%s: spinning on %p held by %p",
522 __func__, sx, owner);
524 while (SX_OWNER(sx->sx_lock) == x &&
525 TD_IS_RUNNING(owner)) {
533 } else if (SX_SHARERS(x) && spintries < asx_retries) {
536 for (i = 0; i < asx_loops; i++) {
537 if (LOCK_LOG_TEST(&sx->lock_object, 0))
539 "%s: shared spinning on %p with %u and %u",
540 __func__, sx, spintries, i);
542 if ((x & SX_LOCK_SHARED) == 0 ||
556 sleepq_lock(&sx->lock_object);
560 * If the lock was released while spinning on the
561 * sleep queue chain lock, try again.
563 if (x == SX_LOCK_UNLOCKED) {
564 sleepq_release(&sx->lock_object);
570 * The current lock owner might have started executing
571 * on another CPU (or the lock could have changed
572 * owners) while we were waiting on the sleep queue
573 * chain lock. If so, drop the sleep queue lock and try
576 if (!(x & SX_LOCK_SHARED) &&
577 (sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) {
578 owner = (struct thread *)SX_OWNER(x);
579 if (TD_IS_RUNNING(owner)) {
580 sleepq_release(&sx->lock_object);
587 * If an exclusive lock was released with both shared
588 * and exclusive waiters and a shared waiter hasn't
589 * woken up and acquired the lock yet, sx_lock will be
590 * set to SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS.
591 * If we see that value, try to acquire it once. Note
592 * that we have to preserve SX_LOCK_EXCLUSIVE_WAITERS
593 * as there are other exclusive waiters still. If we
594 * fail, restart the loop.
596 if (x == (SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS)) {
597 if (atomic_cmpset_acq_ptr(&sx->sx_lock,
598 SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS,
599 tid | SX_LOCK_EXCLUSIVE_WAITERS)) {
600 sleepq_release(&sx->lock_object);
601 CTR2(KTR_LOCK, "%s: %p claimed by new writer",
605 sleepq_release(&sx->lock_object);
610 * Try to set the SX_LOCK_EXCLUSIVE_WAITERS. If we fail,
611 * than loop back and retry.
613 if (!(x & SX_LOCK_EXCLUSIVE_WAITERS)) {
614 if (!atomic_cmpset_ptr(&sx->sx_lock, x,
615 x | SX_LOCK_EXCLUSIVE_WAITERS)) {
616 sleepq_release(&sx->lock_object);
619 if (LOCK_LOG_TEST(&sx->lock_object, 0))
620 CTR2(KTR_LOCK, "%s: %p set excl waiters flag",
625 * Since we have been unable to acquire the exclusive
626 * lock and the exclusive waiters flag is set, we have
629 if (LOCK_LOG_TEST(&sx->lock_object, 0))
630 CTR2(KTR_LOCK, "%s: %p blocking on sleep queue",
634 sleep_time -= lockstat_nsecs();
637 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name,
638 SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ?
639 SLEEPQ_INTERRUPTIBLE : 0), SQ_EXCLUSIVE_QUEUE);
640 if (!(opts & SX_INTERRUPTIBLE))
641 sleepq_wait(&sx->lock_object, 0);
643 error = sleepq_wait_sig(&sx->lock_object, 0);
645 sleep_time += lockstat_nsecs();
649 if (LOCK_LOG_TEST(&sx->lock_object, 0))
651 "%s: interruptible sleep by %p suspended by signal",
655 if (LOCK_LOG_TEST(&sx->lock_object, 0))
656 CTR2(KTR_LOCK, "%s: %p resuming from sleep queue",
662 LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_SX_XLOCK_ACQUIRE, sx,
663 contested, waittime, file, line);
666 LOCKSTAT_RECORD1(LS_SX_XLOCK_BLOCK, sx, sleep_time);
667 if (spin_cnt > sleep_cnt)
668 LOCKSTAT_RECORD1(LS_SX_XLOCK_SPIN, sx, (spin_cnt - sleep_cnt));
674 * This function represents the so-called 'hard case' for sx_xunlock
675 * operation. All 'easy case' failures are redirected to this. Note
676 * that ideally this would be a static function, but it needs to be
677 * accessible from at least sx.h.
680 _sx_xunlock_hard(struct sx *sx, uintptr_t tid, const char *file, int line)
683 int queue, wakeup_swapper;
685 MPASS(!(sx->sx_lock & SX_LOCK_SHARED));
687 /* If the lock is recursed, then unrecurse one level. */
688 if (sx_xlocked(sx) && sx_recursed(sx)) {
689 if ((--sx->sx_recurse) == 0)
690 atomic_clear_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
691 if (LOCK_LOG_TEST(&sx->lock_object, 0))
692 CTR2(KTR_LOCK, "%s: %p unrecursing", __func__, sx);
695 MPASS(sx->sx_lock & (SX_LOCK_SHARED_WAITERS |
696 SX_LOCK_EXCLUSIVE_WAITERS));
697 if (LOCK_LOG_TEST(&sx->lock_object, 0))
698 CTR2(KTR_LOCK, "%s: %p contested", __func__, sx);
700 sleepq_lock(&sx->lock_object);
701 x = SX_LOCK_UNLOCKED;
704 * The wake up algorithm here is quite simple and probably not
705 * ideal. It gives precedence to shared waiters if they are
706 * present. For this condition, we have to preserve the
707 * state of the exclusive waiters flag.
709 if (sx->sx_lock & SX_LOCK_SHARED_WAITERS) {
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_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_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1),
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_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");