1 /*-
2 * SPDX-License-Identifier: BSD-2-Clause
3 *
4 * Copyright (c) 2007 Attilio Rao <[email protected]>
5 * Copyright (c) 2001 Jason Evans <[email protected]>
6 * All rights reserved.
7 *
8 * Redistribution and use in source and binary forms, with or without
9 * modification, are permitted provided that the following conditions
10 * are met:
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.
18 *
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
29 * DAMAGE.
30 */
31
32 /*
33 * Shared/exclusive locks. This implementation attempts to ensure
34 * deterministic lock granting behavior, so that slocks and xlocks are
35 * interleaved.
36 *
37 * Priority propagation will not generally raise the priority of lock holders,
38 * so should not be relied upon in combination with sx locks.
39 */
40
41 #include "opt_ddb.h"
42 #include "opt_hwpmc_hooks.h"
43 #include "opt_no_adaptive_sx.h"
44
45 #include <sys/cdefs.h>
46 #include <sys/param.h>
47 #include <sys/systm.h>
48 #include <sys/kdb.h>
49 #include <sys/kernel.h>
50 #include <sys/ktr.h>
51 #include <sys/lock.h>
52 #include <sys/mutex.h>
53 #include <sys/proc.h>
54 #include <sys/sched.h>
55 #include <sys/sleepqueue.h>
56 #include <sys/sx.h>
57 #include <sys/smp.h>
58 #include <sys/sysctl.h>
59
60 #if defined(SMP) && !defined(NO_ADAPTIVE_SX)
61 #include <machine/cpu.h>
62 #endif
63
64 #ifdef DDB
65 #include <ddb/ddb.h>
66 #endif
67
68 #if defined(SMP) && !defined(NO_ADAPTIVE_SX)
69 #define ADAPTIVE_SX
70 #endif
71
72 #ifdef HWPMC_HOOKS
73 #include <sys/pmckern.h>
74 PMC_SOFT_DECLARE( , , lock, failed);
75 #endif
76
77 /* Handy macros for sleep queues. */
78 #define SQ_EXCLUSIVE_QUEUE 0
79 #define SQ_SHARED_QUEUE 1
80
81 /*
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.
84 */
85 #define GIANT_DECLARE \
86 int _giantcnt = 0; \
87 WITNESS_SAVE_DECL(Giant) \
88
89 #define GIANT_SAVE(work) do { \
90 if (__predict_false(mtx_owned(&Giant))) { \
91 work++; \
92 WITNESS_SAVE(&Giant.lock_object, Giant); \
93 while (mtx_owned(&Giant)) { \
94 _giantcnt++; \
95 mtx_unlock(&Giant); \
96 } \
97 } \
98 } while (0)
99
100 #define GIANT_RESTORE() do { \
101 if (_giantcnt > 0) { \
102 mtx_assert(&Giant, MA_NOTOWNED); \
103 while (_giantcnt--) \
104 mtx_lock(&Giant); \
105 WITNESS_RESTORE(&Giant.lock_object, Giant); \
106 } \
107 } while (0)
108
109 /*
110 * Returns true if an exclusive lock is recursed. It assumes
111 * curthread currently has an exclusive lock.
112 */
113 #define sx_recursed(sx) ((sx)->sx_recurse != 0)
114
115 static void assert_sx(const struct lock_object *lock, int what);
116 #ifdef DDB
117 static void db_show_sx(const struct lock_object *lock);
118 #endif
119 static void lock_sx(struct lock_object *lock, uintptr_t how);
120 #ifdef KDTRACE_HOOKS
121 static int owner_sx(const struct lock_object *lock, struct thread **owner);
122 #endif
123 static uintptr_t unlock_sx(struct lock_object *lock);
124
125 struct lock_class lock_class_sx = {
126 .lc_name = "sx",
127 .lc_flags = LC_SLEEPLOCK | LC_SLEEPABLE | LC_RECURSABLE | LC_UPGRADABLE,
128 .lc_assert = assert_sx,
129 #ifdef DDB
130 .lc_ddb_show = db_show_sx,
131 #endif
132 .lc_lock = lock_sx,
133 .lc_unlock = unlock_sx,
134 #ifdef KDTRACE_HOOKS
135 .lc_owner = owner_sx,
136 #endif
137 };
138
139 #ifndef INVARIANTS
140 #define _sx_assert(sx, what, file, line)
141 #endif
142
143 #ifdef ADAPTIVE_SX
144 #ifdef SX_CUSTOM_BACKOFF
145 static u_short __read_frequently asx_retries;
146 static u_short __read_frequently asx_loops;
147 static SYSCTL_NODE(_debug, OID_AUTO, sx, CTLFLAG_RD | CTLFLAG_MPSAFE, NULL,
148 "sxlock debugging");
149 SYSCTL_U16(_debug_sx, OID_AUTO, retries, CTLFLAG_RW, &asx_retries, 0, "");
150 SYSCTL_U16(_debug_sx, OID_AUTO, loops, CTLFLAG_RW, &asx_loops, 0, "");
151
152 static struct lock_delay_config __read_frequently sx_delay;
153
154 SYSCTL_U16(_debug_sx, OID_AUTO, delay_base, CTLFLAG_RW, &sx_delay.base,
155 0, "");
156 SYSCTL_U16(_debug_sx, OID_AUTO, delay_max, CTLFLAG_RW, &sx_delay.max,
157 0, "");
158
159 static void
sx_lock_delay_init(void * arg __unused)160 sx_lock_delay_init(void *arg __unused)
161 {
162
163 lock_delay_default_init(&sx_delay);
164 asx_retries = 10;
165 asx_loops = max(10000, sx_delay.max);
166 }
167 LOCK_DELAY_SYSINIT(sx_lock_delay_init);
168 #else
169 #define sx_delay locks_delay
170 #define asx_retries locks_delay_retries
171 #define asx_loops locks_delay_loops
172 #endif
173 #endif
174
175 void
assert_sx(const struct lock_object * lock,int what)176 assert_sx(const struct lock_object *lock, int what)
177 {
178
179 sx_assert((const struct sx *)lock, what);
180 }
181
182 void
lock_sx(struct lock_object * lock,uintptr_t how)183 lock_sx(struct lock_object *lock, uintptr_t how)
184 {
185 struct sx *sx;
186
187 sx = (struct sx *)lock;
188 if (how)
189 sx_slock(sx);
190 else
191 sx_xlock(sx);
192 }
193
194 uintptr_t
unlock_sx(struct lock_object * lock)195 unlock_sx(struct lock_object *lock)
196 {
197 struct sx *sx;
198
199 sx = (struct sx *)lock;
200 sx_assert(sx, SA_LOCKED | SA_NOTRECURSED);
201 if (sx_xlocked(sx)) {
202 sx_xunlock(sx);
203 return (0);
204 } else {
205 sx_sunlock(sx);
206 return (1);
207 }
208 }
209
210 #ifdef KDTRACE_HOOKS
211 int
owner_sx(const struct lock_object * lock,struct thread ** owner)212 owner_sx(const struct lock_object *lock, struct thread **owner)
213 {
214 const struct sx *sx;
215 uintptr_t x;
216
217 sx = (const struct sx *)lock;
218 x = sx->sx_lock;
219 *owner = NULL;
220 return ((x & SX_LOCK_SHARED) != 0 ? (SX_SHARERS(x) != 0) :
221 ((*owner = (struct thread *)SX_OWNER(x)) != NULL));
222 }
223 #endif
224
225 void
sx_sysinit(void * arg)226 sx_sysinit(void *arg)
227 {
228 struct sx_args *sargs = arg;
229
230 sx_init_flags(sargs->sa_sx, sargs->sa_desc, sargs->sa_flags);
231 }
232
233 void
sx_init_flags(struct sx * sx,const char * description,int opts)234 sx_init_flags(struct sx *sx, const char *description, int opts)
235 {
236 int flags;
237
238 MPASS((opts & ~(SX_QUIET | SX_RECURSE | SX_NOWITNESS | SX_DUPOK |
239 SX_NOPROFILE | SX_NEW)) == 0);
240 ASSERT_ATOMIC_LOAD_PTR(sx->sx_lock,
241 ("%s: sx_lock not aligned for %s: %p", __func__, description,
242 &sx->sx_lock));
243
244 flags = LO_SLEEPABLE | LO_UPGRADABLE;
245 if (opts & SX_DUPOK)
246 flags |= LO_DUPOK;
247 if (opts & SX_NOPROFILE)
248 flags |= LO_NOPROFILE;
249 if (!(opts & SX_NOWITNESS))
250 flags |= LO_WITNESS;
251 if (opts & SX_RECURSE)
252 flags |= LO_RECURSABLE;
253 if (opts & SX_QUIET)
254 flags |= LO_QUIET;
255 if (opts & SX_NEW)
256 flags |= LO_NEW;
257
258 lock_init(&sx->lock_object, &lock_class_sx, description, NULL, flags);
259 sx->sx_lock = SX_LOCK_UNLOCKED;
260 sx->sx_recurse = 0;
261 }
262
263 void
sx_destroy(struct sx * sx)264 sx_destroy(struct sx *sx)
265 {
266
267 KASSERT(sx->sx_lock == SX_LOCK_UNLOCKED, ("sx lock still held"));
268 KASSERT(sx->sx_recurse == 0, ("sx lock still recursed"));
269 sx->sx_lock = SX_LOCK_DESTROYED;
270 lock_destroy(&sx->lock_object);
271 }
272
273 int
sx_try_slock_int(struct sx * sx LOCK_FILE_LINE_ARG_DEF)274 sx_try_slock_int(struct sx *sx LOCK_FILE_LINE_ARG_DEF)
275 {
276 uintptr_t x;
277
278 if (SCHEDULER_STOPPED())
279 return (1);
280
281 KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
282 ("sx_try_slock() by idle thread %p on sx %s @ %s:%d",
283 curthread, sx->lock_object.lo_name, file, line));
284
285 x = sx->sx_lock;
286 for (;;) {
287 KASSERT(x != SX_LOCK_DESTROYED,
288 ("sx_try_slock() of destroyed sx @ %s:%d", file, line));
289 if (!(x & SX_LOCK_SHARED))
290 break;
291 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, x + SX_ONE_SHARER)) {
292 LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 1, file, line);
293 WITNESS_LOCK(&sx->lock_object, LOP_TRYLOCK, file, line);
294 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire,
295 sx, 0, 0, file, line, LOCKSTAT_READER);
296 TD_LOCKS_INC(curthread);
297 curthread->td_sx_slocks++;
298 return (1);
299 }
300 }
301
302 LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 0, file, line);
303 return (0);
304 }
305
306 int
sx_try_slock_(struct sx * sx,const char * file,int line)307 sx_try_slock_(struct sx *sx, const char *file, int line)
308 {
309
310 return (sx_try_slock_int(sx LOCK_FILE_LINE_ARG));
311 }
312
313 int
_sx_xlock(struct sx * sx,int opts,const char * file,int line)314 _sx_xlock(struct sx *sx, int opts, const char *file, int line)
315 {
316 uintptr_t tid, x;
317 int error = 0;
318
319 KASSERT(kdb_active != 0 || SCHEDULER_STOPPED() ||
320 !TD_IS_IDLETHREAD(curthread),
321 ("sx_xlock() by idle thread %p on sx %s @ %s:%d",
322 curthread, sx->lock_object.lo_name, file, line));
323 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
324 ("sx_xlock() of destroyed sx @ %s:%d", file, line));
325 WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER | LOP_EXCLUSIVE, file,
326 line, NULL);
327 tid = (uintptr_t)curthread;
328 x = SX_LOCK_UNLOCKED;
329 if (!atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, tid))
330 error = _sx_xlock_hard(sx, x, opts LOCK_FILE_LINE_ARG);
331 else
332 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire, sx,
333 0, 0, file, line, LOCKSTAT_WRITER);
334 if (!error) {
335 LOCK_LOG_LOCK("XLOCK", &sx->lock_object, 0, sx->sx_recurse,
336 file, line);
337 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line);
338 TD_LOCKS_INC(curthread);
339 }
340
341 return (error);
342 }
343
344 int
sx_try_xlock_int(struct sx * sx LOCK_FILE_LINE_ARG_DEF)345 sx_try_xlock_int(struct sx *sx LOCK_FILE_LINE_ARG_DEF)
346 {
347 struct thread *td;
348 uintptr_t tid, x;
349 int rval;
350 bool recursed;
351
352 td = curthread;
353 tid = (uintptr_t)td;
354 if (SCHEDULER_STOPPED_TD(td))
355 return (1);
356
357 KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(td),
358 ("sx_try_xlock() by idle thread %p on sx %s @ %s:%d",
359 curthread, sx->lock_object.lo_name, file, line));
360 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
361 ("sx_try_xlock() of destroyed sx @ %s:%d", file, line));
362
363 rval = 1;
364 recursed = false;
365 x = SX_LOCK_UNLOCKED;
366 for (;;) {
367 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, tid))
368 break;
369 if (x == SX_LOCK_UNLOCKED)
370 continue;
371 if (x == tid && (sx->lock_object.lo_flags & LO_RECURSABLE)) {
372 sx->sx_recurse++;
373 atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
374 break;
375 }
376 rval = 0;
377 break;
378 }
379
380 LOCK_LOG_TRY("XLOCK", &sx->lock_object, 0, rval, file, line);
381 if (rval) {
382 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
383 file, line);
384 if (!recursed)
385 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire,
386 sx, 0, 0, file, line, LOCKSTAT_WRITER);
387 TD_LOCKS_INC(curthread);
388 }
389
390 return (rval);
391 }
392
393 int
sx_try_xlock_(struct sx * sx,const char * file,int line)394 sx_try_xlock_(struct sx *sx, const char *file, int line)
395 {
396
397 return (sx_try_xlock_int(sx LOCK_FILE_LINE_ARG));
398 }
399
400 void
_sx_xunlock(struct sx * sx,const char * file,int line)401 _sx_xunlock(struct sx *sx, const char *file, int line)
402 {
403
404 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
405 ("sx_xunlock() of destroyed sx @ %s:%d", file, line));
406 _sx_assert(sx, SA_XLOCKED, file, line);
407 WITNESS_UNLOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line);
408 LOCK_LOG_LOCK("XUNLOCK", &sx->lock_object, 0, sx->sx_recurse, file,
409 line);
410 #if LOCK_DEBUG > 0
411 _sx_xunlock_hard(sx, (uintptr_t)curthread, file, line);
412 #else
413 __sx_xunlock(sx, curthread, file, line);
414 #endif
415 TD_LOCKS_DEC(curthread);
416 }
417
418 /*
419 * Try to do a non-blocking upgrade from a shared lock to an exclusive lock.
420 * This will only succeed if this thread holds a single shared lock.
421 * Return 1 if if the upgrade succeed, 0 otherwise.
422 */
423 int
sx_try_upgrade_int(struct sx * sx LOCK_FILE_LINE_ARG_DEF)424 sx_try_upgrade_int(struct sx *sx LOCK_FILE_LINE_ARG_DEF)
425 {
426 uintptr_t x;
427 uintptr_t waiters;
428 int success;
429
430 if (SCHEDULER_STOPPED())
431 return (1);
432
433 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
434 ("sx_try_upgrade() of destroyed sx @ %s:%d", file, line));
435 _sx_assert(sx, SA_SLOCKED, file, line);
436
437 /*
438 * Try to switch from one shared lock to an exclusive lock. We need
439 * to maintain the SX_LOCK_EXCLUSIVE_WAITERS flag if set so that
440 * we will wake up the exclusive waiters when we drop the lock.
441 */
442 success = 0;
443 x = SX_READ_VALUE(sx);
444 for (;;) {
445 if (SX_SHARERS(x) > 1)
446 break;
447 waiters = (x & SX_LOCK_WAITERS);
448 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x,
449 (uintptr_t)curthread | waiters)) {
450 success = 1;
451 break;
452 }
453 }
454 LOCK_LOG_TRY("XUPGRADE", &sx->lock_object, 0, success, file, line);
455 if (success) {
456 curthread->td_sx_slocks--;
457 WITNESS_UPGRADE(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
458 file, line);
459 LOCKSTAT_RECORD0(sx__upgrade, sx);
460 }
461 return (success);
462 }
463
464 int
sx_try_upgrade_(struct sx * sx,const char * file,int line)465 sx_try_upgrade_(struct sx *sx, const char *file, int line)
466 {
467
468 return (sx_try_upgrade_int(sx LOCK_FILE_LINE_ARG));
469 }
470
471 /*
472 * Downgrade an unrecursed exclusive lock into a single shared lock.
473 */
474 void
sx_downgrade_int(struct sx * sx LOCK_FILE_LINE_ARG_DEF)475 sx_downgrade_int(struct sx *sx LOCK_FILE_LINE_ARG_DEF)
476 {
477 uintptr_t x;
478 int wakeup_swapper;
479
480 if (SCHEDULER_STOPPED())
481 return;
482
483 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
484 ("sx_downgrade() of destroyed sx @ %s:%d", file, line));
485 _sx_assert(sx, SA_XLOCKED | SA_NOTRECURSED, file, line);
486 #ifndef INVARIANTS
487 if (sx_recursed(sx))
488 panic("downgrade of a recursed lock");
489 #endif
490
491 WITNESS_DOWNGRADE(&sx->lock_object, 0, file, line);
492
493 /*
494 * Try to switch from an exclusive lock with no shared waiters
495 * to one sharer with no shared waiters. If there are
496 * exclusive waiters, we don't need to lock the sleep queue so
497 * long as we preserve the flag. We do one quick try and if
498 * that fails we grab the sleepq lock to keep the flags from
499 * changing and do it the slow way.
500 *
501 * We have to lock the sleep queue if there are shared waiters
502 * so we can wake them up.
503 */
504 x = sx->sx_lock;
505 if (!(x & SX_LOCK_SHARED_WAITERS) &&
506 atomic_cmpset_rel_ptr(&sx->sx_lock, x, SX_SHARERS_LOCK(1) |
507 (x & SX_LOCK_EXCLUSIVE_WAITERS)))
508 goto out;
509
510 /*
511 * Lock the sleep queue so we can read the waiters bits
512 * without any races and wakeup any shared waiters.
513 */
514 sleepq_lock(&sx->lock_object);
515
516 /*
517 * Preserve SX_LOCK_EXCLUSIVE_WAITERS while downgraded to a single
518 * shared lock. If there are any shared waiters, wake them up.
519 */
520 wakeup_swapper = 0;
521 x = sx->sx_lock;
522 atomic_store_rel_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1) |
523 (x & SX_LOCK_EXCLUSIVE_WAITERS));
524 if (x & SX_LOCK_SHARED_WAITERS)
525 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX,
526 0, SQ_SHARED_QUEUE);
527 sleepq_release(&sx->lock_object);
528
529 if (wakeup_swapper)
530 kick_proc0();
531
532 out:
533 curthread->td_sx_slocks++;
534 LOCK_LOG_LOCK("XDOWNGRADE", &sx->lock_object, 0, 0, file, line);
535 LOCKSTAT_RECORD0(sx__downgrade, sx);
536 }
537
538 void
sx_downgrade_(struct sx * sx,const char * file,int line)539 sx_downgrade_(struct sx *sx, const char *file, int line)
540 {
541
542 sx_downgrade_int(sx LOCK_FILE_LINE_ARG);
543 }
544
545 #ifdef ADAPTIVE_SX
546 static inline void
sx_drop_critical(uintptr_t x,bool * in_critical,int * extra_work)547 sx_drop_critical(uintptr_t x, bool *in_critical, int *extra_work)
548 {
549
550 if (x & SX_LOCK_WRITE_SPINNER)
551 return;
552 if (*in_critical) {
553 critical_exit();
554 *in_critical = false;
555 (*extra_work)--;
556 }
557 }
558 #else
559 #define sx_drop_critical(x, in_critical, extra_work) do { } while (0)
560 #endif
561
562 /*
563 * This function represents the so-called 'hard case' for sx_xlock
564 * operation. All 'easy case' failures are redirected to this. Note
565 * that ideally this would be a static function, but it needs to be
566 * accessible from at least sx.h.
567 */
568 int
_sx_xlock_hard(struct sx * sx,uintptr_t x,int opts LOCK_FILE_LINE_ARG_DEF)569 _sx_xlock_hard(struct sx *sx, uintptr_t x, int opts LOCK_FILE_LINE_ARG_DEF)
570 {
571 GIANT_DECLARE;
572 uintptr_t tid, setx;
573 #ifdef ADAPTIVE_SX
574 struct thread *owner;
575 u_int i, n, spintries = 0;
576 enum { READERS, WRITER } sleep_reason = READERS;
577 bool in_critical = false;
578 #endif
579 #ifdef LOCK_PROFILING
580 uint64_t waittime = 0;
581 int contested = 0;
582 #endif
583 int error = 0;
584 #if defined(ADAPTIVE_SX) || defined(KDTRACE_HOOKS)
585 struct lock_delay_arg lda;
586 #endif
587 #ifdef KDTRACE_HOOKS
588 u_int sleep_cnt = 0;
589 int64_t sleep_time = 0;
590 int64_t all_time = 0;
591 #endif
592 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING)
593 uintptr_t state = 0;
594 int doing_lockprof = 0;
595 #endif
596 int extra_work = 0;
597
598 tid = (uintptr_t)curthread;
599
600 #ifdef KDTRACE_HOOKS
601 if (LOCKSTAT_PROFILE_ENABLED(sx__acquire)) {
602 while (x == SX_LOCK_UNLOCKED) {
603 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, tid))
604 goto out_lockstat;
605 }
606 extra_work = 1;
607 doing_lockprof = 1;
608 all_time -= lockstat_nsecs(&sx->lock_object);
609 state = x;
610 }
611 #endif
612 #ifdef LOCK_PROFILING
613 extra_work = 1;
614 doing_lockprof = 1;
615 state = x;
616 #endif
617
618 if (SCHEDULER_STOPPED())
619 return (0);
620
621 if (__predict_false(x == SX_LOCK_UNLOCKED))
622 x = SX_READ_VALUE(sx);
623
624 /* If we already hold an exclusive lock, then recurse. */
625 if (__predict_false(lv_sx_owner(x) == (struct thread *)tid)) {
626 KASSERT((sx->lock_object.lo_flags & LO_RECURSABLE) != 0,
627 ("_sx_xlock_hard: recursed on non-recursive sx %s @ %s:%d\n",
628 sx->lock_object.lo_name, file, line));
629 sx->sx_recurse++;
630 atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
631 if (LOCK_LOG_TEST(&sx->lock_object, 0))
632 CTR2(KTR_LOCK, "%s: %p recursing", __func__, sx);
633 return (0);
634 }
635
636 if (LOCK_LOG_TEST(&sx->lock_object, 0))
637 CTR5(KTR_LOCK, "%s: %s contested (lock=%p) at %s:%d", __func__,
638 sx->lock_object.lo_name, (void *)sx->sx_lock, file, line);
639
640 #if defined(ADAPTIVE_SX)
641 lock_delay_arg_init(&lda, &sx_delay);
642 #elif defined(KDTRACE_HOOKS)
643 lock_delay_arg_init_noadapt(&lda);
644 #endif
645
646 #ifdef HWPMC_HOOKS
647 PMC_SOFT_CALL( , , lock, failed);
648 #endif
649 lock_profile_obtain_lock_failed(&sx->lock_object, false, &contested,
650 &waittime);
651
652 #ifndef INVARIANTS
653 GIANT_SAVE(extra_work);
654 #endif
655
656 for (;;) {
657 if (x == SX_LOCK_UNLOCKED) {
658 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, tid))
659 break;
660 continue;
661 }
662 #ifdef INVARIANTS
663 GIANT_SAVE(extra_work);
664 #endif
665 #ifdef KDTRACE_HOOKS
666 lda.spin_cnt++;
667 #endif
668 #ifdef ADAPTIVE_SX
669 if (x == (SX_LOCK_SHARED | SX_LOCK_WRITE_SPINNER)) {
670 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, tid))
671 break;
672 continue;
673 }
674
675 /*
676 * If the lock is write locked and the owner is
677 * running on another CPU, spin until the owner stops
678 * running or the state of the lock changes.
679 */
680 if ((x & SX_LOCK_SHARED) == 0) {
681 sx_drop_critical(x, &in_critical, &extra_work);
682 sleep_reason = WRITER;
683 owner = lv_sx_owner(x);
684 if (!TD_IS_RUNNING(owner))
685 goto sleepq;
686 if (LOCK_LOG_TEST(&sx->lock_object, 0))
687 CTR3(KTR_LOCK, "%s: spinning on %p held by %p",
688 __func__, sx, owner);
689 KTR_STATE1(KTR_SCHED, "thread", sched_tdname(curthread),
690 "spinning", "lockname:\"%s\"",
691 sx->lock_object.lo_name);
692 do {
693 lock_delay(&lda);
694 x = SX_READ_VALUE(sx);
695 owner = lv_sx_owner(x);
696 } while (owner != NULL && TD_IS_RUNNING(owner));
697 KTR_STATE0(KTR_SCHED, "thread", sched_tdname(curthread),
698 "running");
699 continue;
700 } else if (SX_SHARERS(x) > 0) {
701 sleep_reason = READERS;
702 if (spintries == asx_retries)
703 goto sleepq;
704 if (!(x & SX_LOCK_WRITE_SPINNER)) {
705 if (!in_critical) {
706 critical_enter();
707 in_critical = true;
708 extra_work++;
709 }
710 if (!atomic_fcmpset_ptr(&sx->sx_lock, &x,
711 x | SX_LOCK_WRITE_SPINNER)) {
712 critical_exit();
713 in_critical = false;
714 extra_work--;
715 continue;
716 }
717 }
718 spintries++;
719 KTR_STATE1(KTR_SCHED, "thread", sched_tdname(curthread),
720 "spinning", "lockname:\"%s\"",
721 sx->lock_object.lo_name);
722 n = SX_SHARERS(x);
723 for (i = 0; i < asx_loops; i += n) {
724 lock_delay_spin(n);
725 x = SX_READ_VALUE(sx);
726 if (!(x & SX_LOCK_WRITE_SPINNER))
727 break;
728 if (!(x & SX_LOCK_SHARED))
729 break;
730 n = SX_SHARERS(x);
731 if (n == 0)
732 break;
733 }
734 #ifdef KDTRACE_HOOKS
735 lda.spin_cnt += i;
736 #endif
737 KTR_STATE0(KTR_SCHED, "thread", sched_tdname(curthread),
738 "running");
739 if (i < asx_loops)
740 continue;
741 }
742 sleepq:
743 #endif
744 sleepq_lock(&sx->lock_object);
745 x = SX_READ_VALUE(sx);
746 retry_sleepq:
747
748 /*
749 * If the lock was released while spinning on the
750 * sleep queue chain lock, try again.
751 */
752 if (x == SX_LOCK_UNLOCKED) {
753 sleepq_release(&sx->lock_object);
754 sx_drop_critical(x, &in_critical, &extra_work);
755 continue;
756 }
757
758 #ifdef ADAPTIVE_SX
759 /*
760 * The current lock owner might have started executing
761 * on another CPU (or the lock could have changed
762 * owners) while we were waiting on the sleep queue
763 * chain lock. If so, drop the sleep queue lock and try
764 * again.
765 */
766 if (!(x & SX_LOCK_SHARED)) {
767 owner = (struct thread *)SX_OWNER(x);
768 if (TD_IS_RUNNING(owner)) {
769 sleepq_release(&sx->lock_object);
770 sx_drop_critical(x, &in_critical,
771 &extra_work);
772 continue;
773 }
774 } else if (SX_SHARERS(x) > 0 && sleep_reason == WRITER) {
775 sleepq_release(&sx->lock_object);
776 sx_drop_critical(x, &in_critical, &extra_work);
777 continue;
778 }
779 #endif
780
781 /*
782 * If an exclusive lock was released with both shared
783 * and exclusive waiters and a shared waiter hasn't
784 * woken up and acquired the lock yet, sx_lock will be
785 * set to SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS.
786 * If we see that value, try to acquire it once. Note
787 * that we have to preserve SX_LOCK_EXCLUSIVE_WAITERS
788 * as there are other exclusive waiters still. If we
789 * fail, restart the loop.
790 */
791 setx = x & (SX_LOCK_WAITERS | SX_LOCK_WRITE_SPINNER);
792 if ((x & ~setx) == SX_LOCK_SHARED) {
793 setx &= ~SX_LOCK_WRITE_SPINNER;
794 if (!atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, tid | setx))
795 goto retry_sleepq;
796 sleepq_release(&sx->lock_object);
797 CTR2(KTR_LOCK, "%s: %p claimed by new writer",
798 __func__, sx);
799 break;
800 }
801
802 #ifdef ADAPTIVE_SX
803 /*
804 * It is possible we set the SX_LOCK_WRITE_SPINNER bit.
805 * It is an invariant that when the bit is set, there is
806 * a writer ready to grab the lock. Thus clear the bit since
807 * we are going to sleep.
808 */
809 if (in_critical) {
810 if ((x & SX_LOCK_WRITE_SPINNER) ||
811 !((x & SX_LOCK_EXCLUSIVE_WAITERS))) {
812 setx = x & ~SX_LOCK_WRITE_SPINNER;
813 setx |= SX_LOCK_EXCLUSIVE_WAITERS;
814 if (!atomic_fcmpset_ptr(&sx->sx_lock, &x,
815 setx)) {
816 goto retry_sleepq;
817 }
818 }
819 critical_exit();
820 in_critical = false;
821 } else {
822 #endif
823 /*
824 * Try to set the SX_LOCK_EXCLUSIVE_WAITERS. If we fail,
825 * than loop back and retry.
826 */
827 if (!(x & SX_LOCK_EXCLUSIVE_WAITERS)) {
828 if (!atomic_fcmpset_ptr(&sx->sx_lock, &x,
829 x | SX_LOCK_EXCLUSIVE_WAITERS)) {
830 goto retry_sleepq;
831 }
832 if (LOCK_LOG_TEST(&sx->lock_object, 0))
833 CTR2(KTR_LOCK, "%s: %p set excl waiters flag",
834 __func__, sx);
835 }
836 #ifdef ADAPTIVE_SX
837 }
838 #endif
839
840 /*
841 * Since we have been unable to acquire the exclusive
842 * lock and the exclusive waiters flag is set, we have
843 * to sleep.
844 */
845 if (LOCK_LOG_TEST(&sx->lock_object, 0))
846 CTR2(KTR_LOCK, "%s: %p blocking on sleep queue",
847 __func__, sx);
848
849 #ifdef KDTRACE_HOOKS
850 sleep_time -= lockstat_nsecs(&sx->lock_object);
851 #endif
852 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name,
853 SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ?
854 SLEEPQ_INTERRUPTIBLE : 0), SQ_EXCLUSIVE_QUEUE);
855 if (!(opts & SX_INTERRUPTIBLE))
856 sleepq_wait(&sx->lock_object, 0);
857 else
858 error = sleepq_wait_sig(&sx->lock_object, 0);
859 #ifdef KDTRACE_HOOKS
860 sleep_time += lockstat_nsecs(&sx->lock_object);
861 sleep_cnt++;
862 #endif
863 if (error) {
864 if (LOCK_LOG_TEST(&sx->lock_object, 0))
865 CTR2(KTR_LOCK,
866 "%s: interruptible sleep by %p suspended by signal",
867 __func__, sx);
868 break;
869 }
870 if (LOCK_LOG_TEST(&sx->lock_object, 0))
871 CTR2(KTR_LOCK, "%s: %p resuming from sleep queue",
872 __func__, sx);
873 x = SX_READ_VALUE(sx);
874 }
875 if (__predict_true(!extra_work))
876 return (error);
877 #ifdef ADAPTIVE_SX
878 if (in_critical)
879 critical_exit();
880 #endif
881 GIANT_RESTORE();
882 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING)
883 if (__predict_true(!doing_lockprof))
884 return (error);
885 #endif
886 #ifdef KDTRACE_HOOKS
887 all_time += lockstat_nsecs(&sx->lock_object);
888 if (sleep_time)
889 LOCKSTAT_RECORD4(sx__block, sx, sleep_time,
890 LOCKSTAT_WRITER, (state & SX_LOCK_SHARED) == 0,
891 (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state));
892 if (lda.spin_cnt > sleep_cnt)
893 LOCKSTAT_RECORD4(sx__spin, sx, all_time - sleep_time,
894 LOCKSTAT_WRITER, (state & SX_LOCK_SHARED) == 0,
895 (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state));
896 out_lockstat:
897 #endif
898 if (!error)
899 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire, sx,
900 contested, waittime, file, line, LOCKSTAT_WRITER);
901 return (error);
902 }
903
904 /*
905 * This function represents the so-called 'hard case' for sx_xunlock
906 * operation. All 'easy case' failures are redirected to this. Note
907 * that ideally this would be a static function, but it needs to be
908 * accessible from at least sx.h.
909 */
910 void
_sx_xunlock_hard(struct sx * sx,uintptr_t x LOCK_FILE_LINE_ARG_DEF)911 _sx_xunlock_hard(struct sx *sx, uintptr_t x LOCK_FILE_LINE_ARG_DEF)
912 {
913 uintptr_t tid, setx;
914 int queue, wakeup_swapper;
915
916 if (SCHEDULER_STOPPED())
917 return;
918
919 tid = (uintptr_t)curthread;
920
921 if (__predict_false(x == tid))
922 x = SX_READ_VALUE(sx);
923
924 MPASS(!(x & SX_LOCK_SHARED));
925
926 if (__predict_false(x & SX_LOCK_RECURSED)) {
927 /* The lock is recursed, unrecurse one level. */
928 if ((--sx->sx_recurse) == 0)
929 atomic_clear_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
930 if (LOCK_LOG_TEST(&sx->lock_object, 0))
931 CTR2(KTR_LOCK, "%s: %p unrecursing", __func__, sx);
932 return;
933 }
934
935 LOCKSTAT_PROFILE_RELEASE_RWLOCK(sx__release, sx, LOCKSTAT_WRITER);
936 if (x == tid &&
937 atomic_cmpset_rel_ptr(&sx->sx_lock, tid, SX_LOCK_UNLOCKED))
938 return;
939
940 if (LOCK_LOG_TEST(&sx->lock_object, 0))
941 CTR2(KTR_LOCK, "%s: %p contested", __func__, sx);
942
943 sleepq_lock(&sx->lock_object);
944 x = SX_READ_VALUE(sx);
945 MPASS(x & (SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS));
946
947 /*
948 * The wake up algorithm here is quite simple and probably not
949 * ideal. It gives precedence to shared waiters if they are
950 * present. For this condition, we have to preserve the
951 * state of the exclusive waiters flag.
952 * If interruptible sleeps left the shared queue empty avoid a
953 * starvation for the threads sleeping on the exclusive queue by giving
954 * them precedence and cleaning up the shared waiters bit anyway.
955 */
956 setx = SX_LOCK_UNLOCKED;
957 queue = SQ_SHARED_QUEUE;
958 if ((x & SX_LOCK_EXCLUSIVE_WAITERS) != 0 &&
959 sleepq_sleepcnt(&sx->lock_object, SQ_EXCLUSIVE_QUEUE) != 0) {
960 queue = SQ_EXCLUSIVE_QUEUE;
961 setx |= (x & SX_LOCK_SHARED_WAITERS);
962 }
963 atomic_store_rel_ptr(&sx->sx_lock, setx);
964
965 /* Wake up all the waiters for the specific queue. */
966 if (LOCK_LOG_TEST(&sx->lock_object, 0))
967 CTR3(KTR_LOCK, "%s: %p waking up all threads on %s queue",
968 __func__, sx, queue == SQ_SHARED_QUEUE ? "shared" :
969 "exclusive");
970
971 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, 0,
972 queue);
973 sleepq_release(&sx->lock_object);
974 if (wakeup_swapper)
975 kick_proc0();
976 }
977
978 static bool __always_inline
__sx_can_read(struct thread * td,uintptr_t x,bool fp)979 __sx_can_read(struct thread *td, uintptr_t x, bool fp)
980 {
981
982 if ((x & (SX_LOCK_SHARED | SX_LOCK_EXCLUSIVE_WAITERS | SX_LOCK_WRITE_SPINNER))
983 == SX_LOCK_SHARED)
984 return (true);
985 if (!fp && td->td_sx_slocks && (x & SX_LOCK_SHARED))
986 return (true);
987 return (false);
988 }
989
990 static bool __always_inline
__sx_slock_try(struct sx * sx,struct thread * td,uintptr_t * xp,bool fp LOCK_FILE_LINE_ARG_DEF)991 __sx_slock_try(struct sx *sx, struct thread *td, uintptr_t *xp, bool fp
992 LOCK_FILE_LINE_ARG_DEF)
993 {
994
995 /*
996 * If no other thread has an exclusive lock then try to bump up
997 * the count of sharers. Since we have to preserve the state
998 * of SX_LOCK_EXCLUSIVE_WAITERS, if we fail to acquire the
999 * shared lock loop back and retry.
1000 */
1001 while (__sx_can_read(td, *xp, fp)) {
1002 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, xp,
1003 *xp + SX_ONE_SHARER)) {
1004 if (LOCK_LOG_TEST(&sx->lock_object, 0))
1005 CTR4(KTR_LOCK, "%s: %p succeed %p -> %p",
1006 __func__, sx, (void *)*xp,
1007 (void *)(*xp + SX_ONE_SHARER));
1008 td->td_sx_slocks++;
1009 return (true);
1010 }
1011 }
1012 return (false);
1013 }
1014
1015 static int __noinline
_sx_slock_hard(struct sx * sx,int opts,uintptr_t x LOCK_FILE_LINE_ARG_DEF)1016 _sx_slock_hard(struct sx *sx, int opts, uintptr_t x LOCK_FILE_LINE_ARG_DEF)
1017 {
1018 GIANT_DECLARE;
1019 struct thread *td;
1020 #ifdef ADAPTIVE_SX
1021 struct thread *owner;
1022 u_int i, n, spintries = 0;
1023 #endif
1024 #ifdef LOCK_PROFILING
1025 uint64_t waittime = 0;
1026 int contested = 0;
1027 #endif
1028 int error = 0;
1029 #if defined(ADAPTIVE_SX) || defined(KDTRACE_HOOKS)
1030 struct lock_delay_arg lda;
1031 #endif
1032 #ifdef KDTRACE_HOOKS
1033 u_int sleep_cnt = 0;
1034 int64_t sleep_time = 0;
1035 int64_t all_time = 0;
1036 #endif
1037 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING)
1038 uintptr_t state = 0;
1039 #endif
1040 int extra_work __sdt_used = 0;
1041
1042 td = curthread;
1043
1044 #ifdef KDTRACE_HOOKS
1045 if (LOCKSTAT_PROFILE_ENABLED(sx__acquire)) {
1046 if (__sx_slock_try(sx, td, &x, false LOCK_FILE_LINE_ARG))
1047 goto out_lockstat;
1048 extra_work = 1;
1049 all_time -= lockstat_nsecs(&sx->lock_object);
1050 state = x;
1051 }
1052 #endif
1053 #ifdef LOCK_PROFILING
1054 extra_work = 1;
1055 state = x;
1056 #endif
1057
1058 if (SCHEDULER_STOPPED())
1059 return (0);
1060
1061 #if defined(ADAPTIVE_SX)
1062 lock_delay_arg_init(&lda, &sx_delay);
1063 #elif defined(KDTRACE_HOOKS)
1064 lock_delay_arg_init_noadapt(&lda);
1065 #endif
1066
1067 #ifdef HWPMC_HOOKS
1068 PMC_SOFT_CALL( , , lock, failed);
1069 #endif
1070 lock_profile_obtain_lock_failed(&sx->lock_object, false, &contested,
1071 &waittime);
1072
1073 #ifndef INVARIANTS
1074 GIANT_SAVE(extra_work);
1075 #endif
1076
1077 /*
1078 * As with rwlocks, we don't make any attempt to try to block
1079 * shared locks once there is an exclusive waiter.
1080 */
1081 for (;;) {
1082 if (__sx_slock_try(sx, td, &x, false LOCK_FILE_LINE_ARG))
1083 break;
1084 #ifdef INVARIANTS
1085 GIANT_SAVE(extra_work);
1086 #endif
1087 #ifdef KDTRACE_HOOKS
1088 lda.spin_cnt++;
1089 #endif
1090
1091 #ifdef ADAPTIVE_SX
1092 /*
1093 * If the owner is running on another CPU, spin until
1094 * the owner stops running or the state of the lock
1095 * changes.
1096 */
1097 if ((x & SX_LOCK_SHARED) == 0) {
1098 owner = lv_sx_owner(x);
1099 if (TD_IS_RUNNING(owner)) {
1100 if (LOCK_LOG_TEST(&sx->lock_object, 0))
1101 CTR3(KTR_LOCK,
1102 "%s: spinning on %p held by %p",
1103 __func__, sx, owner);
1104 KTR_STATE1(KTR_SCHED, "thread",
1105 sched_tdname(curthread), "spinning",
1106 "lockname:\"%s\"", sx->lock_object.lo_name);
1107 do {
1108 lock_delay(&lda);
1109 x = SX_READ_VALUE(sx);
1110 owner = lv_sx_owner(x);
1111 } while (owner != NULL && TD_IS_RUNNING(owner));
1112 KTR_STATE0(KTR_SCHED, "thread",
1113 sched_tdname(curthread), "running");
1114 continue;
1115 }
1116 } else {
1117 if ((x & SX_LOCK_WRITE_SPINNER) && SX_SHARERS(x) == 0) {
1118 MPASS(!__sx_can_read(td, x, false));
1119 lock_delay_spin(2);
1120 x = SX_READ_VALUE(sx);
1121 continue;
1122 }
1123 if (spintries < asx_retries) {
1124 KTR_STATE1(KTR_SCHED, "thread", sched_tdname(curthread),
1125 "spinning", "lockname:\"%s\"",
1126 sx->lock_object.lo_name);
1127 n = SX_SHARERS(x);
1128 for (i = 0; i < asx_loops; i += n) {
1129 lock_delay_spin(n);
1130 x = SX_READ_VALUE(sx);
1131 if (!(x & SX_LOCK_SHARED))
1132 break;
1133 n = SX_SHARERS(x);
1134 if (n == 0)
1135 break;
1136 if (__sx_can_read(td, x, false))
1137 break;
1138 }
1139 #ifdef KDTRACE_HOOKS
1140 lda.spin_cnt += i;
1141 #endif
1142 KTR_STATE0(KTR_SCHED, "thread", sched_tdname(curthread),
1143 "running");
1144 if (i < asx_loops)
1145 continue;
1146 }
1147 }
1148 #endif
1149
1150 /*
1151 * Some other thread already has an exclusive lock, so
1152 * start the process of blocking.
1153 */
1154 sleepq_lock(&sx->lock_object);
1155 x = SX_READ_VALUE(sx);
1156 retry_sleepq:
1157 if (((x & SX_LOCK_WRITE_SPINNER) && SX_SHARERS(x) == 0) ||
1158 __sx_can_read(td, x, false)) {
1159 sleepq_release(&sx->lock_object);
1160 continue;
1161 }
1162
1163 #ifdef ADAPTIVE_SX
1164 /*
1165 * If the owner is running on another CPU, spin until
1166 * the owner stops running or the state of the lock
1167 * changes.
1168 */
1169 if (!(x & SX_LOCK_SHARED)) {
1170 owner = (struct thread *)SX_OWNER(x);
1171 if (TD_IS_RUNNING(owner)) {
1172 sleepq_release(&sx->lock_object);
1173 x = SX_READ_VALUE(sx);
1174 continue;
1175 }
1176 }
1177 #endif
1178
1179 /*
1180 * Try to set the SX_LOCK_SHARED_WAITERS flag. If we
1181 * fail to set it drop the sleep queue lock and loop
1182 * back.
1183 */
1184 if (!(x & SX_LOCK_SHARED_WAITERS)) {
1185 if (!atomic_fcmpset_ptr(&sx->sx_lock, &x,
1186 x | SX_LOCK_SHARED_WAITERS))
1187 goto retry_sleepq;
1188 if (LOCK_LOG_TEST(&sx->lock_object, 0))
1189 CTR2(KTR_LOCK, "%s: %p set shared waiters flag",
1190 __func__, sx);
1191 }
1192
1193 /*
1194 * Since we have been unable to acquire the shared lock,
1195 * we have to sleep.
1196 */
1197 if (LOCK_LOG_TEST(&sx->lock_object, 0))
1198 CTR2(KTR_LOCK, "%s: %p blocking on sleep queue",
1199 __func__, sx);
1200
1201 #ifdef KDTRACE_HOOKS
1202 sleep_time -= lockstat_nsecs(&sx->lock_object);
1203 #endif
1204 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name,
1205 SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ?
1206 SLEEPQ_INTERRUPTIBLE : 0), SQ_SHARED_QUEUE);
1207 if (!(opts & SX_INTERRUPTIBLE))
1208 sleepq_wait(&sx->lock_object, 0);
1209 else
1210 error = sleepq_wait_sig(&sx->lock_object, 0);
1211 #ifdef KDTRACE_HOOKS
1212 sleep_time += lockstat_nsecs(&sx->lock_object);
1213 sleep_cnt++;
1214 #endif
1215 if (error) {
1216 if (LOCK_LOG_TEST(&sx->lock_object, 0))
1217 CTR2(KTR_LOCK,
1218 "%s: interruptible sleep by %p suspended by signal",
1219 __func__, sx);
1220 break;
1221 }
1222 if (LOCK_LOG_TEST(&sx->lock_object, 0))
1223 CTR2(KTR_LOCK, "%s: %p resuming from sleep queue",
1224 __func__, sx);
1225 x = SX_READ_VALUE(sx);
1226 }
1227 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING)
1228 if (__predict_true(!extra_work))
1229 return (error);
1230 #endif
1231 #ifdef KDTRACE_HOOKS
1232 all_time += lockstat_nsecs(&sx->lock_object);
1233 if (sleep_time)
1234 LOCKSTAT_RECORD4(sx__block, sx, sleep_time,
1235 LOCKSTAT_READER, (state & SX_LOCK_SHARED) == 0,
1236 (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state));
1237 if (lda.spin_cnt > sleep_cnt)
1238 LOCKSTAT_RECORD4(sx__spin, sx, all_time - sleep_time,
1239 LOCKSTAT_READER, (state & SX_LOCK_SHARED) == 0,
1240 (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state));
1241 out_lockstat:
1242 #endif
1243 if (error == 0) {
1244 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire, sx,
1245 contested, waittime, file, line, LOCKSTAT_READER);
1246 }
1247 GIANT_RESTORE();
1248 return (error);
1249 }
1250
1251 int
_sx_slock_int(struct sx * sx,int opts LOCK_FILE_LINE_ARG_DEF)1252 _sx_slock_int(struct sx *sx, int opts LOCK_FILE_LINE_ARG_DEF)
1253 {
1254 struct thread *td;
1255 uintptr_t x;
1256 int error;
1257
1258 KASSERT(kdb_active != 0 || SCHEDULER_STOPPED() ||
1259 !TD_IS_IDLETHREAD(curthread),
1260 ("sx_slock() by idle thread %p on sx %s @ %s:%d",
1261 curthread, sx->lock_object.lo_name, file, line));
1262 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
1263 ("sx_slock() of destroyed sx @ %s:%d", file, line));
1264 WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER, file, line, NULL);
1265
1266 error = 0;
1267 td = curthread;
1268 x = SX_READ_VALUE(sx);
1269 if (__predict_false(LOCKSTAT_PROFILE_ENABLED(sx__acquire) ||
1270 !__sx_slock_try(sx, td, &x, true LOCK_FILE_LINE_ARG)))
1271 error = _sx_slock_hard(sx, opts, x LOCK_FILE_LINE_ARG);
1272 else
1273 lock_profile_obtain_lock_success(&sx->lock_object, false, 0, 0,
1274 file, line);
1275 if (error == 0) {
1276 LOCK_LOG_LOCK("SLOCK", &sx->lock_object, 0, 0, file, line);
1277 WITNESS_LOCK(&sx->lock_object, 0, file, line);
1278 TD_LOCKS_INC(curthread);
1279 }
1280 return (error);
1281 }
1282
1283 int
_sx_slock(struct sx * sx,int opts,const char * file,int line)1284 _sx_slock(struct sx *sx, int opts, const char *file, int line)
1285 {
1286
1287 return (_sx_slock_int(sx, opts LOCK_FILE_LINE_ARG));
1288 }
1289
1290 static bool __always_inline
_sx_sunlock_try(struct sx * sx,struct thread * td,uintptr_t * xp)1291 _sx_sunlock_try(struct sx *sx, struct thread *td, uintptr_t *xp)
1292 {
1293
1294 for (;;) {
1295 if (SX_SHARERS(*xp) > 1 || !(*xp & SX_LOCK_WAITERS)) {
1296 if (atomic_fcmpset_rel_ptr(&sx->sx_lock, xp,
1297 *xp - SX_ONE_SHARER)) {
1298 if (LOCK_LOG_TEST(&sx->lock_object, 0))
1299 CTR4(KTR_LOCK,
1300 "%s: %p succeeded %p -> %p",
1301 __func__, sx, (void *)*xp,
1302 (void *)(*xp - SX_ONE_SHARER));
1303 td->td_sx_slocks--;
1304 return (true);
1305 }
1306 continue;
1307 }
1308 break;
1309 }
1310 return (false);
1311 }
1312
1313 static void __noinline
_sx_sunlock_hard(struct sx * sx,struct thread * td,uintptr_t x LOCK_FILE_LINE_ARG_DEF)1314 _sx_sunlock_hard(struct sx *sx, struct thread *td, uintptr_t x
1315 LOCK_FILE_LINE_ARG_DEF)
1316 {
1317 int wakeup_swapper = 0;
1318 uintptr_t setx, queue;
1319
1320 if (SCHEDULER_STOPPED())
1321 return;
1322
1323 if (_sx_sunlock_try(sx, td, &x))
1324 goto out_lockstat;
1325
1326 sleepq_lock(&sx->lock_object);
1327 x = SX_READ_VALUE(sx);
1328 for (;;) {
1329 if (_sx_sunlock_try(sx, td, &x))
1330 break;
1331
1332 /*
1333 * Wake up semantic here is quite simple:
1334 * Just wake up all the exclusive waiters.
1335 * Note that the state of the lock could have changed,
1336 * so if it fails loop back and retry.
1337 */
1338 setx = SX_LOCK_UNLOCKED;
1339 queue = SQ_SHARED_QUEUE;
1340 if (x & SX_LOCK_EXCLUSIVE_WAITERS) {
1341 setx |= (x & SX_LOCK_SHARED_WAITERS);
1342 queue = SQ_EXCLUSIVE_QUEUE;
1343 }
1344 setx |= (x & SX_LOCK_WRITE_SPINNER);
1345 if (!atomic_fcmpset_rel_ptr(&sx->sx_lock, &x, setx))
1346 continue;
1347 if (LOCK_LOG_TEST(&sx->lock_object, 0))
1348 CTR2(KTR_LOCK, "%s: %p waking up all thread on"
1349 "exclusive queue", __func__, sx);
1350 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX,
1351 0, queue);
1352 td->td_sx_slocks--;
1353 break;
1354 }
1355 sleepq_release(&sx->lock_object);
1356 if (wakeup_swapper)
1357 kick_proc0();
1358 out_lockstat:
1359 LOCKSTAT_PROFILE_RELEASE_RWLOCK(sx__release, sx, LOCKSTAT_READER);
1360 }
1361
1362 void
_sx_sunlock_int(struct sx * sx LOCK_FILE_LINE_ARG_DEF)1363 _sx_sunlock_int(struct sx *sx LOCK_FILE_LINE_ARG_DEF)
1364 {
1365 struct thread *td;
1366 uintptr_t x;
1367
1368 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
1369 ("sx_sunlock() of destroyed sx @ %s:%d", file, line));
1370 _sx_assert(sx, SA_SLOCKED, file, line);
1371 WITNESS_UNLOCK(&sx->lock_object, 0, file, line);
1372 LOCK_LOG_LOCK("SUNLOCK", &sx->lock_object, 0, 0, file, line);
1373
1374 td = curthread;
1375 x = SX_READ_VALUE(sx);
1376 if (__predict_false(LOCKSTAT_PROFILE_ENABLED(sx__release) ||
1377 !_sx_sunlock_try(sx, td, &x)))
1378 _sx_sunlock_hard(sx, td, x LOCK_FILE_LINE_ARG);
1379 else
1380 lock_profile_release_lock(&sx->lock_object, false);
1381
1382 TD_LOCKS_DEC(curthread);
1383 }
1384
1385 void
_sx_sunlock(struct sx * sx,const char * file,int line)1386 _sx_sunlock(struct sx *sx, const char *file, int line)
1387 {
1388
1389 _sx_sunlock_int(sx LOCK_FILE_LINE_ARG);
1390 }
1391
1392 #ifdef INVARIANT_SUPPORT
1393 #ifndef INVARIANTS
1394 #undef _sx_assert
1395 #endif
1396
1397 /*
1398 * In the non-WITNESS case, sx_assert() can only detect that at least
1399 * *some* thread owns an slock, but it cannot guarantee that *this*
1400 * thread owns an slock.
1401 */
1402 void
_sx_assert(const struct sx * sx,int what,const char * file,int line)1403 _sx_assert(const struct sx *sx, int what, const char *file, int line)
1404 {
1405 #ifndef WITNESS
1406 int slocked = 0;
1407 #endif
1408
1409 if (SCHEDULER_STOPPED())
1410 return;
1411 switch (what) {
1412 case SA_SLOCKED:
1413 case SA_SLOCKED | SA_NOTRECURSED:
1414 case SA_SLOCKED | SA_RECURSED:
1415 #ifndef WITNESS
1416 slocked = 1;
1417 /* FALLTHROUGH */
1418 #endif
1419 case SA_LOCKED:
1420 case SA_LOCKED | SA_NOTRECURSED:
1421 case SA_LOCKED | SA_RECURSED:
1422 #ifdef WITNESS
1423 witness_assert(&sx->lock_object, what, file, line);
1424 #else
1425 /*
1426 * If some other thread has an exclusive lock or we
1427 * have one and are asserting a shared lock, fail.
1428 * Also, if no one has a lock at all, fail.
1429 */
1430 if (sx->sx_lock == SX_LOCK_UNLOCKED ||
1431 (!(sx->sx_lock & SX_LOCK_SHARED) && (slocked ||
1432 sx_xholder(sx) != curthread)))
1433 panic("Lock %s not %slocked @ %s:%d\n",
1434 sx->lock_object.lo_name, slocked ? "share " : "",
1435 file, line);
1436
1437 if (!(sx->sx_lock & SX_LOCK_SHARED)) {
1438 if (sx_recursed(sx)) {
1439 if (what & SA_NOTRECURSED)
1440 panic("Lock %s recursed @ %s:%d\n",
1441 sx->lock_object.lo_name, file,
1442 line);
1443 } else if (what & SA_RECURSED)
1444 panic("Lock %s not recursed @ %s:%d\n",
1445 sx->lock_object.lo_name, file, line);
1446 }
1447 #endif
1448 break;
1449 case SA_XLOCKED:
1450 case SA_XLOCKED | SA_NOTRECURSED:
1451 case SA_XLOCKED | SA_RECURSED:
1452 if (sx_xholder(sx) != curthread)
1453 panic("Lock %s not exclusively locked @ %s:%d\n",
1454 sx->lock_object.lo_name, file, line);
1455 if (sx_recursed(sx)) {
1456 if (what & SA_NOTRECURSED)
1457 panic("Lock %s recursed @ %s:%d\n",
1458 sx->lock_object.lo_name, file, line);
1459 } else if (what & SA_RECURSED)
1460 panic("Lock %s not recursed @ %s:%d\n",
1461 sx->lock_object.lo_name, file, line);
1462 break;
1463 case SA_UNLOCKED:
1464 #ifdef WITNESS
1465 witness_assert(&sx->lock_object, what, file, line);
1466 #else
1467 /*
1468 * If we hold an exclusve lock fail. We can't
1469 * reliably check to see if we hold a shared lock or
1470 * not.
1471 */
1472 if (sx_xholder(sx) == curthread)
1473 panic("Lock %s exclusively locked @ %s:%d\n",
1474 sx->lock_object.lo_name, file, line);
1475 #endif
1476 break;
1477 default:
1478 panic("Unknown sx lock assertion: %d @ %s:%d", what, file,
1479 line);
1480 }
1481 }
1482 #endif /* INVARIANT_SUPPORT */
1483
1484 #ifdef DDB
1485 static void
db_show_sx(const struct lock_object * lock)1486 db_show_sx(const struct lock_object *lock)
1487 {
1488 struct thread *td;
1489 const struct sx *sx;
1490
1491 sx = (const struct sx *)lock;
1492
1493 db_printf(" state: ");
1494 if (sx->sx_lock == SX_LOCK_UNLOCKED)
1495 db_printf("UNLOCKED\n");
1496 else if (sx->sx_lock == SX_LOCK_DESTROYED) {
1497 db_printf("DESTROYED\n");
1498 return;
1499 } else if (sx->sx_lock & SX_LOCK_SHARED)
1500 db_printf("SLOCK: %ju\n", (uintmax_t)SX_SHARERS(sx->sx_lock));
1501 else {
1502 td = sx_xholder(sx);
1503 db_printf("XLOCK: %p (tid %d, pid %d, \"%s\")\n", td,
1504 td->td_tid, td->td_proc->p_pid, td->td_name);
1505 if (sx_recursed(sx))
1506 db_printf(" recursed: %d\n", sx->sx_recurse);
1507 }
1508
1509 db_printf(" waiters: ");
1510 switch(sx->sx_lock &
1511 (SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS)) {
1512 case SX_LOCK_SHARED_WAITERS:
1513 db_printf("shared\n");
1514 break;
1515 case SX_LOCK_EXCLUSIVE_WAITERS:
1516 db_printf("exclusive\n");
1517 break;
1518 case SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS:
1519 db_printf("exclusive and shared\n");
1520 break;
1521 default:
1522 db_printf("none\n");
1523 }
1524 }
1525
1526 /*
1527 * Check to see if a thread that is blocked on a sleep queue is actually
1528 * blocked on an sx lock. If so, output some details and return true.
1529 * If the lock has an exclusive owner, return that in *ownerp.
1530 */
1531 int
sx_chain(struct thread * td,struct thread ** ownerp)1532 sx_chain(struct thread *td, struct thread **ownerp)
1533 {
1534 const struct sx *sx;
1535
1536 /*
1537 * Check to see if this thread is blocked on an sx lock.
1538 * First, we check the lock class. If that is ok, then we
1539 * compare the lock name against the wait message.
1540 */
1541 sx = td->td_wchan;
1542 if (LOCK_CLASS(&sx->lock_object) != &lock_class_sx ||
1543 sx->lock_object.lo_name != td->td_wmesg)
1544 return (0);
1545
1546 /* We think we have an sx lock, so output some details. */
1547 db_printf("blocked on sx \"%s\" ", td->td_wmesg);
1548 *ownerp = sx_xholder(sx);
1549 if (sx->sx_lock & SX_LOCK_SHARED)
1550 db_printf("SLOCK (count %ju)\n",
1551 (uintmax_t)SX_SHARERS(sx->sx_lock));
1552 else
1553 db_printf("XLOCK\n");
1554 return (1);
1555 }
1556 #endif
1557