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_hwpmc_hooks.h"
41 #include "opt_no_adaptive_sx.h"
43 #include <sys/cdefs.h>
44 __FBSDID("$FreeBSD$");
46 #include <sys/param.h>
47 #include <sys/systm.h>
51 #include <sys/mutex.h>
53 #include <sys/sched.h>
54 #include <sys/sleepqueue.h>
56 #include <sys/sysctl.h>
58 #if defined(SMP) && !defined(NO_ADAPTIVE_SX)
59 #include <machine/cpu.h>
66 #if defined(SMP) && !defined(NO_ADAPTIVE_SX)
70 CTASSERT((SX_NOADAPTIVE & LO_CLASSFLAGS) == SX_NOADAPTIVE);
73 #include <sys/pmckern.h>
74 PMC_SOFT_DECLARE( , , lock, failed);
77 /* Handy macros for sleep queues. */
78 #define SQ_EXCLUSIVE_QUEUE 0
79 #define SQ_SHARED_QUEUE 1
82 * Variations on DROP_GIANT()/PICKUP_GIANT() for use in this file. We
83 * drop Giant anytime we have to sleep or if we adaptively spin.
85 #define GIANT_DECLARE \
87 WITNESS_SAVE_DECL(Giant) \
89 #define GIANT_SAVE() do { \
90 if (mtx_owned(&Giant)) { \
91 WITNESS_SAVE(&Giant.lock_object, Giant); \
92 while (mtx_owned(&Giant)) { \
99 #define GIANT_RESTORE() do { \
100 if (_giantcnt > 0) { \
101 mtx_assert(&Giant, MA_NOTOWNED); \
102 while (_giantcnt--) \
104 WITNESS_RESTORE(&Giant.lock_object, Giant); \
109 * Returns true if an exclusive lock is recursed. It assumes
110 * curthread currently has an exclusive lock.
112 #define sx_recursed(sx) ((sx)->sx_recurse != 0)
114 static void assert_sx(const struct lock_object *lock, int what);
116 static void db_show_sx(const struct lock_object *lock);
118 static void lock_sx(struct lock_object *lock, uintptr_t how);
120 static int owner_sx(const struct lock_object *lock, struct thread **owner);
122 static uintptr_t unlock_sx(struct lock_object *lock);
124 struct lock_class lock_class_sx = {
126 .lc_flags = LC_SLEEPLOCK | LC_SLEEPABLE | LC_RECURSABLE | LC_UPGRADABLE,
127 .lc_assert = assert_sx,
129 .lc_ddb_show = db_show_sx,
132 .lc_unlock = unlock_sx,
134 .lc_owner = owner_sx,
139 #define _sx_assert(sx, what, file, line)
143 static u_int asx_retries = 10;
144 static u_int asx_loops = 10000;
145 static SYSCTL_NODE(_debug, OID_AUTO, sx, CTLFLAG_RD, NULL, "sxlock debugging");
146 SYSCTL_UINT(_debug_sx, OID_AUTO, retries, CTLFLAG_RW, &asx_retries, 0, "");
147 SYSCTL_UINT(_debug_sx, OID_AUTO, loops, CTLFLAG_RW, &asx_loops, 0, "");
151 assert_sx(const struct lock_object *lock, int what)
154 sx_assert((const struct sx *)lock, what);
158 lock_sx(struct lock_object *lock, uintptr_t how)
162 sx = (struct sx *)lock;
170 unlock_sx(struct lock_object *lock)
174 sx = (struct sx *)lock;
175 sx_assert(sx, SA_LOCKED | SA_NOTRECURSED);
176 if (sx_xlocked(sx)) {
187 owner_sx(const struct lock_object *lock, struct thread **owner)
189 const struct sx *sx = (const struct sx *)lock;
190 uintptr_t x = sx->sx_lock;
192 *owner = (struct thread *)SX_OWNER(x);
193 return ((x & SX_LOCK_SHARED) != 0 ? (SX_SHARERS(x) != 0) :
199 sx_sysinit(void *arg)
201 struct sx_args *sargs = arg;
203 sx_init_flags(sargs->sa_sx, sargs->sa_desc, sargs->sa_flags);
207 sx_init_flags(struct sx *sx, const char *description, int opts)
211 MPASS((opts & ~(SX_QUIET | SX_RECURSE | SX_NOWITNESS | SX_DUPOK |
212 SX_NOPROFILE | SX_NOADAPTIVE | SX_NEW)) == 0);
213 ASSERT_ATOMIC_LOAD_PTR(sx->sx_lock,
214 ("%s: sx_lock not aligned for %s: %p", __func__, description,
217 flags = LO_SLEEPABLE | LO_UPGRADABLE;
220 if (opts & SX_NOPROFILE)
221 flags |= LO_NOPROFILE;
222 if (!(opts & SX_NOWITNESS))
224 if (opts & SX_RECURSE)
225 flags |= LO_RECURSABLE;
231 flags |= opts & SX_NOADAPTIVE;
232 lock_init(&sx->lock_object, &lock_class_sx, description, NULL, flags);
233 sx->sx_lock = SX_LOCK_UNLOCKED;
238 sx_destroy(struct sx *sx)
241 KASSERT(sx->sx_lock == SX_LOCK_UNLOCKED, ("sx lock still held"));
242 KASSERT(sx->sx_recurse == 0, ("sx lock still recursed"));
243 sx->sx_lock = SX_LOCK_DESTROYED;
244 lock_destroy(&sx->lock_object);
248 _sx_slock(struct sx *sx, int opts, const char *file, int line)
252 if (SCHEDULER_STOPPED())
254 KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
255 ("sx_slock() by idle thread %p on sx %s @ %s:%d",
256 curthread, sx->lock_object.lo_name, file, line));
257 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
258 ("sx_slock() of destroyed sx @ %s:%d", file, line));
259 WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER, file, line, NULL);
260 error = __sx_slock(sx, opts, file, line);
262 LOCK_LOG_LOCK("SLOCK", &sx->lock_object, 0, 0, file, line);
263 WITNESS_LOCK(&sx->lock_object, 0, file, line);
264 curthread->td_locks++;
271 sx_try_slock_(struct sx *sx, const char *file, int line)
275 if (SCHEDULER_STOPPED())
278 KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
279 ("sx_try_slock() by idle thread %p on sx %s @ %s:%d",
280 curthread, sx->lock_object.lo_name, file, line));
284 KASSERT(x != SX_LOCK_DESTROYED,
285 ("sx_try_slock() of destroyed sx @ %s:%d", file, line));
286 if (!(x & SX_LOCK_SHARED))
288 if (atomic_cmpset_acq_ptr(&sx->sx_lock, x, x + SX_ONE_SHARER)) {
289 LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 1, file, line);
290 WITNESS_LOCK(&sx->lock_object, LOP_TRYLOCK, file, line);
291 curthread->td_locks++;
296 LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 0, file, line);
301 _sx_xlock(struct sx *sx, int opts, const char *file, int line)
305 if (SCHEDULER_STOPPED())
307 KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
308 ("sx_xlock() by idle thread %p on sx %s @ %s:%d",
309 curthread, sx->lock_object.lo_name, file, line));
310 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
311 ("sx_xlock() of destroyed sx @ %s:%d", file, line));
312 WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER | LOP_EXCLUSIVE, file,
314 error = __sx_xlock(sx, curthread, opts, file, line);
316 LOCK_LOG_LOCK("XLOCK", &sx->lock_object, 0, sx->sx_recurse,
318 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line);
319 curthread->td_locks++;
326 sx_try_xlock_(struct sx *sx, const char *file, int line)
330 if (SCHEDULER_STOPPED())
333 KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
334 ("sx_try_xlock() by idle thread %p on sx %s @ %s:%d",
335 curthread, sx->lock_object.lo_name, file, line));
336 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
337 ("sx_try_xlock() of destroyed sx @ %s:%d", file, line));
339 if (sx_xlocked(sx) &&
340 (sx->lock_object.lo_flags & LO_RECURSABLE) != 0) {
342 atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
345 rval = atomic_cmpset_acq_ptr(&sx->sx_lock, SX_LOCK_UNLOCKED,
346 (uintptr_t)curthread);
347 LOCK_LOG_TRY("XLOCK", &sx->lock_object, 0, rval, file, line);
349 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
351 curthread->td_locks++;
358 _sx_sunlock(struct sx *sx, const char *file, int line)
361 if (SCHEDULER_STOPPED())
363 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
364 ("sx_sunlock() of destroyed sx @ %s:%d", file, line));
365 _sx_assert(sx, SA_SLOCKED, file, line);
366 WITNESS_UNLOCK(&sx->lock_object, 0, file, line);
367 LOCK_LOG_LOCK("SUNLOCK", &sx->lock_object, 0, 0, file, line);
368 __sx_sunlock(sx, file, line);
369 curthread->td_locks--;
373 _sx_xunlock(struct sx *sx, const char *file, int line)
376 if (SCHEDULER_STOPPED())
378 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
379 ("sx_xunlock() of destroyed sx @ %s:%d", file, line));
380 _sx_assert(sx, SA_XLOCKED, file, line);
381 WITNESS_UNLOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line);
382 LOCK_LOG_LOCK("XUNLOCK", &sx->lock_object, 0, sx->sx_recurse, file,
384 __sx_xunlock(sx, curthread, file, line);
385 curthread->td_locks--;
389 * Try to do a non-blocking upgrade from a shared lock to an exclusive lock.
390 * This will only succeed if this thread holds a single shared lock.
391 * Return 1 if if the upgrade succeed, 0 otherwise.
394 sx_try_upgrade_(struct sx *sx, const char *file, int line)
399 if (SCHEDULER_STOPPED())
402 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
403 ("sx_try_upgrade() of destroyed sx @ %s:%d", file, line));
404 _sx_assert(sx, SA_SLOCKED, file, line);
407 * Try to switch from one shared lock to an exclusive lock. We need
408 * to maintain the SX_LOCK_EXCLUSIVE_WAITERS flag if set so that
409 * we will wake up the exclusive waiters when we drop the lock.
411 x = sx->sx_lock & SX_LOCK_EXCLUSIVE_WAITERS;
412 success = atomic_cmpset_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1) | x,
413 (uintptr_t)curthread | x);
414 LOCK_LOG_TRY("XUPGRADE", &sx->lock_object, 0, success, file, line);
416 WITNESS_UPGRADE(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
418 LOCKSTAT_RECORD0(LS_SX_TRYUPGRADE_UPGRADE, sx);
424 * Downgrade an unrecursed exclusive lock into a single shared lock.
427 sx_downgrade_(struct sx *sx, const char *file, int line)
432 if (SCHEDULER_STOPPED())
435 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
436 ("sx_downgrade() of destroyed sx @ %s:%d", file, line));
437 _sx_assert(sx, SA_XLOCKED | SA_NOTRECURSED, file, line);
440 panic("downgrade of a recursed lock");
443 WITNESS_DOWNGRADE(&sx->lock_object, 0, file, line);
446 * Try to switch from an exclusive lock with no shared waiters
447 * to one sharer with no shared waiters. If there are
448 * exclusive waiters, we don't need to lock the sleep queue so
449 * long as we preserve the flag. We do one quick try and if
450 * that fails we grab the sleepq lock to keep the flags from
451 * changing and do it the slow way.
453 * We have to lock the sleep queue if there are shared waiters
454 * so we can wake them up.
457 if (!(x & SX_LOCK_SHARED_WAITERS) &&
458 atomic_cmpset_rel_ptr(&sx->sx_lock, x, SX_SHARERS_LOCK(1) |
459 (x & SX_LOCK_EXCLUSIVE_WAITERS))) {
460 LOCK_LOG_LOCK("XDOWNGRADE", &sx->lock_object, 0, 0, file, line);
465 * Lock the sleep queue so we can read the waiters bits
466 * without any races and wakeup any shared waiters.
468 sleepq_lock(&sx->lock_object);
471 * Preserve SX_LOCK_EXCLUSIVE_WAITERS while downgraded to a single
472 * shared lock. If there are any shared waiters, wake them up.
476 atomic_store_rel_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1) |
477 (x & SX_LOCK_EXCLUSIVE_WAITERS));
478 if (x & SX_LOCK_SHARED_WAITERS)
479 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX,
481 sleepq_release(&sx->lock_object);
483 LOCK_LOG_LOCK("XDOWNGRADE", &sx->lock_object, 0, 0, file, line);
484 LOCKSTAT_RECORD0(LS_SX_DOWNGRADE_DOWNGRADE, sx);
491 * This function represents the so-called 'hard case' for sx_xlock
492 * operation. All 'easy case' failures are redirected to this. Note
493 * that ideally this would be a static function, but it needs to be
494 * accessible from at least sx.h.
497 _sx_xlock_hard(struct sx *sx, uintptr_t tid, int opts, const char *file,
502 volatile struct thread *owner;
503 u_int i, spintries = 0;
506 #ifdef LOCK_PROFILING
507 uint64_t waittime = 0;
512 uint64_t spin_cnt = 0;
513 uint64_t sleep_cnt = 0;
514 int64_t sleep_time = 0;
517 if (SCHEDULER_STOPPED())
520 /* If we already hold an exclusive lock, then recurse. */
521 if (sx_xlocked(sx)) {
522 KASSERT((sx->lock_object.lo_flags & LO_RECURSABLE) != 0,
523 ("_sx_xlock_hard: recursed on non-recursive sx %s @ %s:%d\n",
524 sx->lock_object.lo_name, file, line));
526 atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
527 if (LOCK_LOG_TEST(&sx->lock_object, 0))
528 CTR2(KTR_LOCK, "%s: %p recursing", __func__, sx);
532 if (LOCK_LOG_TEST(&sx->lock_object, 0))
533 CTR5(KTR_LOCK, "%s: %s contested (lock=%p) at %s:%d", __func__,
534 sx->lock_object.lo_name, (void *)sx->sx_lock, file, line);
536 while (!atomic_cmpset_acq_ptr(&sx->sx_lock, SX_LOCK_UNLOCKED, tid)) {
541 PMC_SOFT_CALL( , , lock, failed);
543 lock_profile_obtain_lock_failed(&sx->lock_object, &contested,
547 * If the lock is write locked and the owner is
548 * running on another CPU, spin until the owner stops
549 * running or the state of the lock changes.
552 if ((sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) {
553 if ((x & SX_LOCK_SHARED) == 0) {
555 owner = (struct thread *)x;
556 if (TD_IS_RUNNING(owner)) {
557 if (LOCK_LOG_TEST(&sx->lock_object, 0))
559 "%s: spinning on %p held by %p",
560 __func__, sx, owner);
561 KTR_STATE1(KTR_SCHED, "thread",
562 sched_tdname(curthread), "spinning",
564 sx->lock_object.lo_name);
566 while (SX_OWNER(sx->sx_lock) == x &&
567 TD_IS_RUNNING(owner)) {
573 KTR_STATE0(KTR_SCHED, "thread",
574 sched_tdname(curthread), "running");
577 } else if (SX_SHARERS(x) && spintries < asx_retries) {
578 KTR_STATE1(KTR_SCHED, "thread",
579 sched_tdname(curthread), "spinning",
580 "lockname:\"%s\"", sx->lock_object.lo_name);
583 for (i = 0; i < asx_loops; i++) {
584 if (LOCK_LOG_TEST(&sx->lock_object, 0))
586 "%s: shared spinning on %p with %u and %u",
587 __func__, sx, spintries, i);
589 if ((x & SX_LOCK_SHARED) == 0 ||
597 KTR_STATE0(KTR_SCHED, "thread",
598 sched_tdname(curthread), "running");
605 sleepq_lock(&sx->lock_object);
609 * If the lock was released while spinning on the
610 * sleep queue chain lock, try again.
612 if (x == SX_LOCK_UNLOCKED) {
613 sleepq_release(&sx->lock_object);
619 * The current lock owner might have started executing
620 * on another CPU (or the lock could have changed
621 * owners) while we were waiting on the sleep queue
622 * chain lock. If so, drop the sleep queue lock and try
625 if (!(x & SX_LOCK_SHARED) &&
626 (sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) {
627 owner = (struct thread *)SX_OWNER(x);
628 if (TD_IS_RUNNING(owner)) {
629 sleepq_release(&sx->lock_object);
636 * If an exclusive lock was released with both shared
637 * and exclusive waiters and a shared waiter hasn't
638 * woken up and acquired the lock yet, sx_lock will be
639 * set to SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS.
640 * If we see that value, try to acquire it once. Note
641 * that we have to preserve SX_LOCK_EXCLUSIVE_WAITERS
642 * as there are other exclusive waiters still. If we
643 * fail, restart the loop.
645 if (x == (SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS)) {
646 if (atomic_cmpset_acq_ptr(&sx->sx_lock,
647 SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS,
648 tid | SX_LOCK_EXCLUSIVE_WAITERS)) {
649 sleepq_release(&sx->lock_object);
650 CTR2(KTR_LOCK, "%s: %p claimed by new writer",
654 sleepq_release(&sx->lock_object);
659 * Try to set the SX_LOCK_EXCLUSIVE_WAITERS. If we fail,
660 * than loop back and retry.
662 if (!(x & SX_LOCK_EXCLUSIVE_WAITERS)) {
663 if (!atomic_cmpset_ptr(&sx->sx_lock, x,
664 x | SX_LOCK_EXCLUSIVE_WAITERS)) {
665 sleepq_release(&sx->lock_object);
668 if (LOCK_LOG_TEST(&sx->lock_object, 0))
669 CTR2(KTR_LOCK, "%s: %p set excl waiters flag",
674 * Since we have been unable to acquire the exclusive
675 * lock and the exclusive waiters flag is set, we have
678 if (LOCK_LOG_TEST(&sx->lock_object, 0))
679 CTR2(KTR_LOCK, "%s: %p blocking on sleep queue",
683 sleep_time -= lockstat_nsecs();
686 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name,
687 SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ?
688 SLEEPQ_INTERRUPTIBLE : 0), SQ_EXCLUSIVE_QUEUE);
689 if (!(opts & SX_INTERRUPTIBLE))
690 sleepq_wait(&sx->lock_object, 0);
692 error = sleepq_wait_sig(&sx->lock_object, 0);
694 sleep_time += lockstat_nsecs();
698 if (LOCK_LOG_TEST(&sx->lock_object, 0))
700 "%s: interruptible sleep by %p suspended by signal",
704 if (LOCK_LOG_TEST(&sx->lock_object, 0))
705 CTR2(KTR_LOCK, "%s: %p resuming from sleep queue",
711 LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_SX_XLOCK_ACQUIRE, sx,
712 contested, waittime, file, line);
715 LOCKSTAT_RECORD1(LS_SX_XLOCK_BLOCK, sx, sleep_time);
716 if (spin_cnt > sleep_cnt)
717 LOCKSTAT_RECORD1(LS_SX_XLOCK_SPIN, sx, (spin_cnt - sleep_cnt));
723 * This function represents the so-called 'hard case' for sx_xunlock
724 * operation. All 'easy case' failures are redirected to this. Note
725 * that ideally this would be a static function, but it needs to be
726 * accessible from at least sx.h.
729 _sx_xunlock_hard(struct sx *sx, uintptr_t tid, const char *file, int line)
732 int queue, wakeup_swapper;
734 if (SCHEDULER_STOPPED())
737 MPASS(!(sx->sx_lock & SX_LOCK_SHARED));
739 /* If the lock is recursed, then unrecurse one level. */
740 if (sx_xlocked(sx) && sx_recursed(sx)) {
741 if ((--sx->sx_recurse) == 0)
742 atomic_clear_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
743 if (LOCK_LOG_TEST(&sx->lock_object, 0))
744 CTR2(KTR_LOCK, "%s: %p unrecursing", __func__, sx);
747 MPASS(sx->sx_lock & (SX_LOCK_SHARED_WAITERS |
748 SX_LOCK_EXCLUSIVE_WAITERS));
749 if (LOCK_LOG_TEST(&sx->lock_object, 0))
750 CTR2(KTR_LOCK, "%s: %p contested", __func__, sx);
752 sleepq_lock(&sx->lock_object);
753 x = SX_LOCK_UNLOCKED;
756 * The wake up algorithm here is quite simple and probably not
757 * ideal. It gives precedence to shared waiters if they are
758 * present. For this condition, we have to preserve the
759 * state of the exclusive waiters flag.
760 * If interruptible sleeps left the shared queue empty avoid a
761 * starvation for the threads sleeping on the exclusive queue by giving
762 * them precedence and cleaning up the shared waiters bit anyway.
764 if ((sx->sx_lock & SX_LOCK_SHARED_WAITERS) != 0 &&
765 sleepq_sleepcnt(&sx->lock_object, SQ_SHARED_QUEUE) != 0) {
766 queue = SQ_SHARED_QUEUE;
767 x |= (sx->sx_lock & SX_LOCK_EXCLUSIVE_WAITERS);
769 queue = SQ_EXCLUSIVE_QUEUE;
771 /* Wake up all the waiters for the specific queue. */
772 if (LOCK_LOG_TEST(&sx->lock_object, 0))
773 CTR3(KTR_LOCK, "%s: %p waking up all threads on %s queue",
774 __func__, sx, queue == SQ_SHARED_QUEUE ? "shared" :
776 atomic_store_rel_ptr(&sx->sx_lock, x);
777 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, 0,
779 sleepq_release(&sx->lock_object);
785 * This function represents the so-called 'hard case' for sx_slock
786 * operation. All 'easy case' failures are redirected to this. Note
787 * that ideally this would be a static function, but it needs to be
788 * accessible from at least sx.h.
791 _sx_slock_hard(struct sx *sx, int opts, const char *file, int line)
795 volatile struct thread *owner;
797 #ifdef LOCK_PROFILING
798 uint64_t waittime = 0;
804 uint64_t spin_cnt = 0;
805 uint64_t sleep_cnt = 0;
806 int64_t sleep_time = 0;
809 if (SCHEDULER_STOPPED())
813 * As with rwlocks, we don't make any attempt to try to block
814 * shared locks once there is an exclusive waiter.
823 * If no other thread has an exclusive lock then try to bump up
824 * the count of sharers. Since we have to preserve the state
825 * of SX_LOCK_EXCLUSIVE_WAITERS, if we fail to acquire the
826 * shared lock loop back and retry.
828 if (x & SX_LOCK_SHARED) {
829 MPASS(!(x & SX_LOCK_SHARED_WAITERS));
830 if (atomic_cmpset_acq_ptr(&sx->sx_lock, x,
831 x + SX_ONE_SHARER)) {
832 if (LOCK_LOG_TEST(&sx->lock_object, 0))
834 "%s: %p succeed %p -> %p", __func__,
836 (void *)(x + SX_ONE_SHARER));
842 PMC_SOFT_CALL( , , lock, failed);
844 lock_profile_obtain_lock_failed(&sx->lock_object, &contested,
849 * If the owner is running on another CPU, spin until
850 * the owner stops running or the state of the lock
853 if ((sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) {
855 owner = (struct thread *)x;
856 if (TD_IS_RUNNING(owner)) {
857 if (LOCK_LOG_TEST(&sx->lock_object, 0))
859 "%s: spinning on %p held by %p",
860 __func__, sx, owner);
861 KTR_STATE1(KTR_SCHED, "thread",
862 sched_tdname(curthread), "spinning",
863 "lockname:\"%s\"", sx->lock_object.lo_name);
865 while (SX_OWNER(sx->sx_lock) == x &&
866 TD_IS_RUNNING(owner)) {
872 KTR_STATE0(KTR_SCHED, "thread",
873 sched_tdname(curthread), "running");
880 * Some other thread already has an exclusive lock, so
881 * start the process of blocking.
883 sleepq_lock(&sx->lock_object);
887 * The lock could have been released while we spun.
888 * In this case loop back and retry.
890 if (x & SX_LOCK_SHARED) {
891 sleepq_release(&sx->lock_object);
897 * If the owner is running on another CPU, spin until
898 * the owner stops running or the state of the lock
901 if (!(x & SX_LOCK_SHARED) &&
902 (sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) {
903 owner = (struct thread *)SX_OWNER(x);
904 if (TD_IS_RUNNING(owner)) {
905 sleepq_release(&sx->lock_object);
912 * Try to set the SX_LOCK_SHARED_WAITERS flag. If we
913 * fail to set it drop the sleep queue lock and loop
916 if (!(x & SX_LOCK_SHARED_WAITERS)) {
917 if (!atomic_cmpset_ptr(&sx->sx_lock, x,
918 x | SX_LOCK_SHARED_WAITERS)) {
919 sleepq_release(&sx->lock_object);
922 if (LOCK_LOG_TEST(&sx->lock_object, 0))
923 CTR2(KTR_LOCK, "%s: %p set shared waiters flag",
928 * Since we have been unable to acquire the shared lock,
931 if (LOCK_LOG_TEST(&sx->lock_object, 0))
932 CTR2(KTR_LOCK, "%s: %p blocking on sleep queue",
936 sleep_time -= lockstat_nsecs();
939 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name,
940 SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ?
941 SLEEPQ_INTERRUPTIBLE : 0), SQ_SHARED_QUEUE);
942 if (!(opts & SX_INTERRUPTIBLE))
943 sleepq_wait(&sx->lock_object, 0);
945 error = sleepq_wait_sig(&sx->lock_object, 0);
947 sleep_time += lockstat_nsecs();
951 if (LOCK_LOG_TEST(&sx->lock_object, 0))
953 "%s: interruptible sleep by %p suspended by signal",
957 if (LOCK_LOG_TEST(&sx->lock_object, 0))
958 CTR2(KTR_LOCK, "%s: %p resuming from sleep queue",
962 LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_SX_SLOCK_ACQUIRE, sx,
963 contested, waittime, file, line);
966 LOCKSTAT_RECORD1(LS_SX_XLOCK_BLOCK, sx, sleep_time);
967 if (spin_cnt > sleep_cnt)
968 LOCKSTAT_RECORD1(LS_SX_XLOCK_SPIN, sx, (spin_cnt - sleep_cnt));
975 * This function represents the so-called 'hard case' for sx_sunlock
976 * operation. All 'easy case' failures are redirected to this. Note
977 * that ideally this would be a static function, but it needs to be
978 * accessible from at least sx.h.
981 _sx_sunlock_hard(struct sx *sx, const char *file, int line)
986 if (SCHEDULER_STOPPED())
993 * We should never have sharers while at least one thread
994 * holds a shared lock.
996 KASSERT(!(x & SX_LOCK_SHARED_WAITERS),
997 ("%s: waiting sharers", __func__));
1000 * See if there is more than one shared lock held. If
1001 * so, just drop one and return.
1003 if (SX_SHARERS(x) > 1) {
1004 if (atomic_cmpset_rel_ptr(&sx->sx_lock, x,
1005 x - SX_ONE_SHARER)) {
1006 if (LOCK_LOG_TEST(&sx->lock_object, 0))
1008 "%s: %p succeeded %p -> %p",
1009 __func__, sx, (void *)x,
1010 (void *)(x - SX_ONE_SHARER));
1017 * If there aren't any waiters for an exclusive lock,
1018 * then try to drop it quickly.
1020 if (!(x & SX_LOCK_EXCLUSIVE_WAITERS)) {
1021 MPASS(x == SX_SHARERS_LOCK(1));
1022 if (atomic_cmpset_rel_ptr(&sx->sx_lock,
1023 SX_SHARERS_LOCK(1), SX_LOCK_UNLOCKED)) {
1024 if (LOCK_LOG_TEST(&sx->lock_object, 0))
1025 CTR2(KTR_LOCK, "%s: %p last succeeded",
1033 * At this point, there should just be one sharer with
1034 * exclusive waiters.
1036 MPASS(x == (SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS));
1038 sleepq_lock(&sx->lock_object);
1041 * Wake up semantic here is quite simple:
1042 * Just wake up all the exclusive waiters.
1043 * Note that the state of the lock could have changed,
1044 * so if it fails loop back and retry.
1046 if (!atomic_cmpset_rel_ptr(&sx->sx_lock,
1047 SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS,
1048 SX_LOCK_UNLOCKED)) {
1049 sleepq_release(&sx->lock_object);
1052 if (LOCK_LOG_TEST(&sx->lock_object, 0))
1053 CTR2(KTR_LOCK, "%s: %p waking up all thread on"
1054 "exclusive queue", __func__, sx);
1055 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX,
1056 0, SQ_EXCLUSIVE_QUEUE);
1057 sleepq_release(&sx->lock_object);
1064 #ifdef INVARIANT_SUPPORT
1070 * In the non-WITNESS case, sx_assert() can only detect that at least
1071 * *some* thread owns an slock, but it cannot guarantee that *this*
1072 * thread owns an slock.
1075 _sx_assert(const struct sx *sx, int what, const char *file, int line)
1081 if (panicstr != NULL)
1085 case SA_SLOCKED | SA_NOTRECURSED:
1086 case SA_SLOCKED | SA_RECURSED:
1092 case SA_LOCKED | SA_NOTRECURSED:
1093 case SA_LOCKED | SA_RECURSED:
1095 witness_assert(&sx->lock_object, what, file, line);
1098 * If some other thread has an exclusive lock or we
1099 * have one and are asserting a shared lock, fail.
1100 * Also, if no one has a lock at all, fail.
1102 if (sx->sx_lock == SX_LOCK_UNLOCKED ||
1103 (!(sx->sx_lock & SX_LOCK_SHARED) && (slocked ||
1104 sx_xholder(sx) != curthread)))
1105 panic("Lock %s not %slocked @ %s:%d\n",
1106 sx->lock_object.lo_name, slocked ? "share " : "",
1109 if (!(sx->sx_lock & SX_LOCK_SHARED)) {
1110 if (sx_recursed(sx)) {
1111 if (what & SA_NOTRECURSED)
1112 panic("Lock %s recursed @ %s:%d\n",
1113 sx->lock_object.lo_name, file,
1115 } else if (what & SA_RECURSED)
1116 panic("Lock %s not recursed @ %s:%d\n",
1117 sx->lock_object.lo_name, file, line);
1122 case SA_XLOCKED | SA_NOTRECURSED:
1123 case SA_XLOCKED | SA_RECURSED:
1124 if (sx_xholder(sx) != curthread)
1125 panic("Lock %s not exclusively locked @ %s:%d\n",
1126 sx->lock_object.lo_name, file, line);
1127 if (sx_recursed(sx)) {
1128 if (what & SA_NOTRECURSED)
1129 panic("Lock %s recursed @ %s:%d\n",
1130 sx->lock_object.lo_name, file, line);
1131 } else if (what & SA_RECURSED)
1132 panic("Lock %s not recursed @ %s:%d\n",
1133 sx->lock_object.lo_name, file, line);
1137 witness_assert(&sx->lock_object, what, file, line);
1140 * If we hold an exclusve lock fail. We can't
1141 * reliably check to see if we hold a shared lock or
1144 if (sx_xholder(sx) == curthread)
1145 panic("Lock %s exclusively locked @ %s:%d\n",
1146 sx->lock_object.lo_name, file, line);
1150 panic("Unknown sx lock assertion: %d @ %s:%d", what, file,
1154 #endif /* INVARIANT_SUPPORT */
1158 db_show_sx(const struct lock_object *lock)
1161 const struct sx *sx;
1163 sx = (const struct sx *)lock;
1165 db_printf(" state: ");
1166 if (sx->sx_lock == SX_LOCK_UNLOCKED)
1167 db_printf("UNLOCKED\n");
1168 else if (sx->sx_lock == SX_LOCK_DESTROYED) {
1169 db_printf("DESTROYED\n");
1171 } else if (sx->sx_lock & SX_LOCK_SHARED)
1172 db_printf("SLOCK: %ju\n", (uintmax_t)SX_SHARERS(sx->sx_lock));
1174 td = sx_xholder(sx);
1175 db_printf("XLOCK: %p (tid %d, pid %d, \"%s\")\n", td,
1176 td->td_tid, td->td_proc->p_pid, td->td_name);
1177 if (sx_recursed(sx))
1178 db_printf(" recursed: %d\n", sx->sx_recurse);
1181 db_printf(" waiters: ");
1182 switch(sx->sx_lock &
1183 (SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS)) {
1184 case SX_LOCK_SHARED_WAITERS:
1185 db_printf("shared\n");
1187 case SX_LOCK_EXCLUSIVE_WAITERS:
1188 db_printf("exclusive\n");
1190 case SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS:
1191 db_printf("exclusive and shared\n");
1194 db_printf("none\n");
1199 * Check to see if a thread that is blocked on a sleep queue is actually
1200 * blocked on an sx lock. If so, output some details and return true.
1201 * If the lock has an exclusive owner, return that in *ownerp.
1204 sx_chain(struct thread *td, struct thread **ownerp)
1209 * Check to see if this thread is blocked on an sx lock.
1210 * First, we check the lock class. If that is ok, then we
1211 * compare the lock name against the wait message.
1214 if (LOCK_CLASS(&sx->lock_object) != &lock_class_sx ||
1215 sx->lock_object.lo_name != td->td_wmesg)
1218 /* We think we have an sx lock, so output some details. */
1219 db_printf("blocked on sx \"%s\" ", td->td_wmesg);
1220 *ownerp = sx_xholder(sx);
1221 if (sx->sx_lock & SX_LOCK_SHARED)
1222 db_printf("SLOCK (count %ju)\n",
1223 (uintmax_t)SX_SHARERS(sx->sx_lock));
1225 db_printf("XLOCK\n");