xref: /freebsd/sys/kern/kern_lock.c (revision c66ec88fed842fbaad62c30d510644ceb7bd2d71)
1 /*-
2  * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
3  *
4  * Copyright (c) 2008 Attilio Rao <attilio@FreeBSD.org>
5  * All rights reserved.
6  *
7  * Redistribution and use in source and binary forms, with or without
8  * modification, are permitted provided that the following conditions
9  * are met:
10  * 1. Redistributions of source code must retain the above copyright
11  *    notice(s), this list of conditions and the following disclaimer as
12  *    the first lines of this file unmodified other than the possible
13  *    addition of one or more copyright notices.
14  * 2. Redistributions in binary form must reproduce the above copyright
15  *    notice(s), this list of conditions and the following disclaimer in the
16  *    documentation and/or other materials provided with the distribution.
17  *
18  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY
19  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
20  * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
21  * DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE LIABLE FOR ANY
22  * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
23  * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
24  * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
25  * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
26  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
27  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH
28  * DAMAGE.
29  */
30 
31 #include "opt_ddb.h"
32 #include "opt_hwpmc_hooks.h"
33 
34 #include <sys/cdefs.h>
35 __FBSDID("$FreeBSD$");
36 
37 #include <sys/param.h>
38 #include <sys/kdb.h>
39 #include <sys/ktr.h>
40 #include <sys/lock.h>
41 #include <sys/lock_profile.h>
42 #include <sys/lockmgr.h>
43 #include <sys/lockstat.h>
44 #include <sys/mutex.h>
45 #include <sys/proc.h>
46 #include <sys/sleepqueue.h>
47 #ifdef DEBUG_LOCKS
48 #include <sys/stack.h>
49 #endif
50 #include <sys/sysctl.h>
51 #include <sys/systm.h>
52 
53 #include <machine/cpu.h>
54 
55 #ifdef DDB
56 #include <ddb/ddb.h>
57 #endif
58 
59 #ifdef HWPMC_HOOKS
60 #include <sys/pmckern.h>
61 PMC_SOFT_DECLARE( , , lock, failed);
62 #endif
63 
64 CTASSERT(LK_UNLOCKED == (LK_UNLOCKED &
65     ~(LK_ALL_WAITERS | LK_EXCLUSIVE_SPINNERS)));
66 
67 #define	SQ_EXCLUSIVE_QUEUE	0
68 #define	SQ_SHARED_QUEUE		1
69 
70 #ifndef INVARIANTS
71 #define	_lockmgr_assert(lk, what, file, line)
72 #endif
73 
74 #define	TD_SLOCKS_INC(td)	((td)->td_lk_slocks++)
75 #define	TD_SLOCKS_DEC(td)	((td)->td_lk_slocks--)
76 
77 #ifndef DEBUG_LOCKS
78 #define	STACK_PRINT(lk)
79 #define	STACK_SAVE(lk)
80 #define	STACK_ZERO(lk)
81 #else
82 #define	STACK_PRINT(lk)	stack_print_ddb(&(lk)->lk_stack)
83 #define	STACK_SAVE(lk)	stack_save(&(lk)->lk_stack)
84 #define	STACK_ZERO(lk)	stack_zero(&(lk)->lk_stack)
85 #endif
86 
87 #define	LOCK_LOG2(lk, string, arg1, arg2)				\
88 	if (LOCK_LOG_TEST(&(lk)->lock_object, 0))			\
89 		CTR2(KTR_LOCK, (string), (arg1), (arg2))
90 #define	LOCK_LOG3(lk, string, arg1, arg2, arg3)				\
91 	if (LOCK_LOG_TEST(&(lk)->lock_object, 0))			\
92 		CTR3(KTR_LOCK, (string), (arg1), (arg2), (arg3))
93 
94 #define	GIANT_DECLARE							\
95 	int _i = 0;							\
96 	WITNESS_SAVE_DECL(Giant)
97 #define	GIANT_RESTORE() do {						\
98 	if (__predict_false(_i > 0)) {					\
99 		while (_i--)						\
100 			mtx_lock(&Giant);				\
101 		WITNESS_RESTORE(&Giant.lock_object, Giant);		\
102 	}								\
103 } while (0)
104 #define	GIANT_SAVE() do {						\
105 	if (__predict_false(mtx_owned(&Giant))) {			\
106 		WITNESS_SAVE(&Giant.lock_object, Giant);		\
107 		while (mtx_owned(&Giant)) {				\
108 			_i++;						\
109 			mtx_unlock(&Giant);				\
110 		}							\
111 	}								\
112 } while (0)
113 
114 static bool __always_inline
115 LK_CAN_SHARE(uintptr_t x, int flags, bool fp)
116 {
117 
118 	if ((x & (LK_SHARE | LK_EXCLUSIVE_WAITERS | LK_EXCLUSIVE_SPINNERS)) ==
119 	    LK_SHARE)
120 		return (true);
121 	if (fp || (!(x & LK_SHARE)))
122 		return (false);
123 	if ((curthread->td_lk_slocks != 0 && !(flags & LK_NODDLKTREAT)) ||
124 	    (curthread->td_pflags & TDP_DEADLKTREAT))
125 		return (true);
126 	return (false);
127 }
128 
129 #define	LK_TRYOP(x)							\
130 	((x) & LK_NOWAIT)
131 
132 #define	LK_CAN_WITNESS(x)						\
133 	(((x) & LK_NOWITNESS) == 0 && !LK_TRYOP(x))
134 #define	LK_TRYWIT(x)							\
135 	(LK_TRYOP(x) ? LOP_TRYLOCK : 0)
136 
137 #define	lockmgr_disowned(lk)						\
138 	(((lk)->lk_lock & ~(LK_FLAGMASK & ~LK_SHARE)) == LK_KERNPROC)
139 
140 #define	lockmgr_xlocked_v(v)						\
141 	(((v) & ~(LK_FLAGMASK & ~LK_SHARE)) == (uintptr_t)curthread)
142 
143 #define	lockmgr_xlocked(lk) lockmgr_xlocked_v(lockmgr_read_value(lk))
144 
145 static void	assert_lockmgr(const struct lock_object *lock, int how);
146 #ifdef DDB
147 static void	db_show_lockmgr(const struct lock_object *lock);
148 #endif
149 static void	lock_lockmgr(struct lock_object *lock, uintptr_t how);
150 #ifdef KDTRACE_HOOKS
151 static int	owner_lockmgr(const struct lock_object *lock,
152 		    struct thread **owner);
153 #endif
154 static uintptr_t unlock_lockmgr(struct lock_object *lock);
155 
156 struct lock_class lock_class_lockmgr = {
157 	.lc_name = "lockmgr",
158 	.lc_flags = LC_RECURSABLE | LC_SLEEPABLE | LC_SLEEPLOCK | LC_UPGRADABLE,
159 	.lc_assert = assert_lockmgr,
160 #ifdef DDB
161 	.lc_ddb_show = db_show_lockmgr,
162 #endif
163 	.lc_lock = lock_lockmgr,
164 	.lc_unlock = unlock_lockmgr,
165 #ifdef KDTRACE_HOOKS
166 	.lc_owner = owner_lockmgr,
167 #endif
168 };
169 
170 static __read_mostly bool lk_adaptive = true;
171 static SYSCTL_NODE(_debug, OID_AUTO, lockmgr, CTLFLAG_RD, NULL, "lockmgr debugging");
172 SYSCTL_BOOL(_debug_lockmgr, OID_AUTO, adaptive_spinning, CTLFLAG_RW, &lk_adaptive,
173     0, "");
174 #define lockmgr_delay  locks_delay
175 
176 struct lockmgr_wait {
177 	const char *iwmesg;
178 	int ipri;
179 	int itimo;
180 };
181 
182 static bool __always_inline lockmgr_slock_try(struct lock *lk, uintptr_t *xp,
183     int flags, bool fp);
184 static bool __always_inline lockmgr_sunlock_try(struct lock *lk, uintptr_t *xp);
185 
186 static void
187 lockmgr_exit(u_int flags, struct lock_object *ilk, int wakeup_swapper)
188 {
189 	struct lock_class *class;
190 
191 	if (flags & LK_INTERLOCK) {
192 		class = LOCK_CLASS(ilk);
193 		class->lc_unlock(ilk);
194 	}
195 
196 	if (__predict_false(wakeup_swapper))
197 		kick_proc0();
198 }
199 
200 static void
201 lockmgr_note_shared_acquire(struct lock *lk, int contested,
202     uint64_t waittime, const char *file, int line, int flags)
203 {
204 
205 	LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(lockmgr__acquire, lk, contested,
206 	    waittime, file, line, LOCKSTAT_READER);
207 	LOCK_LOG_LOCK("SLOCK", &lk->lock_object, 0, 0, file, line);
208 	WITNESS_LOCK(&lk->lock_object, LK_TRYWIT(flags), file, line);
209 	TD_LOCKS_INC(curthread);
210 	TD_SLOCKS_INC(curthread);
211 	STACK_SAVE(lk);
212 }
213 
214 static void
215 lockmgr_note_shared_release(struct lock *lk, const char *file, int line)
216 {
217 
218 	WITNESS_UNLOCK(&lk->lock_object, 0, file, line);
219 	LOCK_LOG_LOCK("SUNLOCK", &lk->lock_object, 0, 0, file, line);
220 	TD_LOCKS_DEC(curthread);
221 	TD_SLOCKS_DEC(curthread);
222 }
223 
224 static void
225 lockmgr_note_exclusive_acquire(struct lock *lk, int contested,
226     uint64_t waittime, const char *file, int line, int flags)
227 {
228 
229 	LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(lockmgr__acquire, lk, contested,
230 	    waittime, file, line, LOCKSTAT_WRITER);
231 	LOCK_LOG_LOCK("XLOCK", &lk->lock_object, 0, lk->lk_recurse, file, line);
232 	WITNESS_LOCK(&lk->lock_object, LOP_EXCLUSIVE | LK_TRYWIT(flags), file,
233 	    line);
234 	TD_LOCKS_INC(curthread);
235 	STACK_SAVE(lk);
236 }
237 
238 static void
239 lockmgr_note_exclusive_release(struct lock *lk, const char *file, int line)
240 {
241 
242 	if (LK_HOLDER(lockmgr_read_value(lk)) != LK_KERNPROC) {
243 		WITNESS_UNLOCK(&lk->lock_object, LOP_EXCLUSIVE, file, line);
244 		TD_LOCKS_DEC(curthread);
245 	}
246 	LOCK_LOG_LOCK("XUNLOCK", &lk->lock_object, 0, lk->lk_recurse, file,
247 	    line);
248 }
249 
250 static __inline struct thread *
251 lockmgr_xholder(const struct lock *lk)
252 {
253 	uintptr_t x;
254 
255 	x = lockmgr_read_value(lk);
256 	return ((x & LK_SHARE) ? NULL : (struct thread *)LK_HOLDER(x));
257 }
258 
259 /*
260  * It assumes sleepq_lock held and returns with this one unheld.
261  * It also assumes the generic interlock is sane and previously checked.
262  * If LK_INTERLOCK is specified the interlock is not reacquired after the
263  * sleep.
264  */
265 static __inline int
266 sleeplk(struct lock *lk, u_int flags, struct lock_object *ilk,
267     const char *wmesg, int pri, int timo, int queue)
268 {
269 	GIANT_DECLARE;
270 	struct lock_class *class;
271 	int catch, error;
272 
273 	class = (flags & LK_INTERLOCK) ? LOCK_CLASS(ilk) : NULL;
274 	catch = pri & PCATCH;
275 	pri &= PRIMASK;
276 	error = 0;
277 
278 	LOCK_LOG3(lk, "%s: %p blocking on the %s sleepqueue", __func__, lk,
279 	    (queue == SQ_EXCLUSIVE_QUEUE) ? "exclusive" : "shared");
280 
281 	if (flags & LK_INTERLOCK)
282 		class->lc_unlock(ilk);
283 	if (queue == SQ_EXCLUSIVE_QUEUE && (flags & LK_SLEEPFAIL) != 0)
284 		lk->lk_exslpfail++;
285 	GIANT_SAVE();
286 	sleepq_add(&lk->lock_object, NULL, wmesg, SLEEPQ_LK | (catch ?
287 	    SLEEPQ_INTERRUPTIBLE : 0), queue);
288 	if ((flags & LK_TIMELOCK) && timo)
289 		sleepq_set_timeout(&lk->lock_object, timo);
290 
291 	/*
292 	 * Decisional switch for real sleeping.
293 	 */
294 	if ((flags & LK_TIMELOCK) && timo && catch)
295 		error = sleepq_timedwait_sig(&lk->lock_object, pri);
296 	else if ((flags & LK_TIMELOCK) && timo)
297 		error = sleepq_timedwait(&lk->lock_object, pri);
298 	else if (catch)
299 		error = sleepq_wait_sig(&lk->lock_object, pri);
300 	else
301 		sleepq_wait(&lk->lock_object, pri);
302 	GIANT_RESTORE();
303 	if ((flags & LK_SLEEPFAIL) && error == 0)
304 		error = ENOLCK;
305 
306 	return (error);
307 }
308 
309 static __inline int
310 wakeupshlk(struct lock *lk, const char *file, int line)
311 {
312 	uintptr_t v, x, orig_x;
313 	u_int realexslp;
314 	int queue, wakeup_swapper;
315 
316 	wakeup_swapper = 0;
317 	for (;;) {
318 		x = lockmgr_read_value(lk);
319 		if (lockmgr_sunlock_try(lk, &x))
320 			break;
321 
322 		/*
323 		 * We should have a sharer with waiters, so enter the hard
324 		 * path in order to handle wakeups correctly.
325 		 */
326 		sleepq_lock(&lk->lock_object);
327 		orig_x = lockmgr_read_value(lk);
328 retry_sleepq:
329 		x = orig_x & (LK_ALL_WAITERS | LK_EXCLUSIVE_SPINNERS);
330 		v = LK_UNLOCKED;
331 
332 		/*
333 		 * If the lock has exclusive waiters, give them preference in
334 		 * order to avoid deadlock with shared runners up.
335 		 * If interruptible sleeps left the exclusive queue empty
336 		 * avoid a starvation for the threads sleeping on the shared
337 		 * queue by giving them precedence and cleaning up the
338 		 * exclusive waiters bit anyway.
339 		 * Please note that lk_exslpfail count may be lying about
340 		 * the real number of waiters with the LK_SLEEPFAIL flag on
341 		 * because they may be used in conjunction with interruptible
342 		 * sleeps so lk_exslpfail might be considered an 'upper limit'
343 		 * bound, including the edge cases.
344 		 */
345 		realexslp = sleepq_sleepcnt(&lk->lock_object,
346 		    SQ_EXCLUSIVE_QUEUE);
347 		if ((x & LK_EXCLUSIVE_WAITERS) != 0 && realexslp != 0) {
348 			if (lk->lk_exslpfail < realexslp) {
349 				lk->lk_exslpfail = 0;
350 				queue = SQ_EXCLUSIVE_QUEUE;
351 				v |= (x & LK_SHARED_WAITERS);
352 			} else {
353 				lk->lk_exslpfail = 0;
354 				LOCK_LOG2(lk,
355 				    "%s: %p has only LK_SLEEPFAIL sleepers",
356 				    __func__, lk);
357 				LOCK_LOG2(lk,
358 			    "%s: %p waking up threads on the exclusive queue",
359 				    __func__, lk);
360 				wakeup_swapper =
361 				    sleepq_broadcast(&lk->lock_object,
362 				    SLEEPQ_LK, 0, SQ_EXCLUSIVE_QUEUE);
363 				queue = SQ_SHARED_QUEUE;
364 			}
365 
366 		} else {
367 			/*
368 			 * Exclusive waiters sleeping with LK_SLEEPFAIL on
369 			 * and using interruptible sleeps/timeout may have
370 			 * left spourious lk_exslpfail counts on, so clean
371 			 * it up anyway.
372 			 */
373 			lk->lk_exslpfail = 0;
374 			queue = SQ_SHARED_QUEUE;
375 		}
376 
377 		if (lockmgr_sunlock_try(lk, &orig_x)) {
378 			sleepq_release(&lk->lock_object);
379 			break;
380 		}
381 
382 		x |= LK_SHARERS_LOCK(1);
383 		if (!atomic_fcmpset_rel_ptr(&lk->lk_lock, &x, v)) {
384 			orig_x = x;
385 			goto retry_sleepq;
386 		}
387 		LOCK_LOG3(lk, "%s: %p waking up threads on the %s queue",
388 		    __func__, lk, queue == SQ_SHARED_QUEUE ? "shared" :
389 		    "exclusive");
390 		wakeup_swapper |= sleepq_broadcast(&lk->lock_object, SLEEPQ_LK,
391 		    0, queue);
392 		sleepq_release(&lk->lock_object);
393 		break;
394 	}
395 
396 	LOCKSTAT_PROFILE_RELEASE_RWLOCK(lockmgr__release, lk, LOCKSTAT_READER);
397 	return (wakeup_swapper);
398 }
399 
400 static void
401 assert_lockmgr(const struct lock_object *lock, int what)
402 {
403 
404 	panic("lockmgr locks do not support assertions");
405 }
406 
407 static void
408 lock_lockmgr(struct lock_object *lock, uintptr_t how)
409 {
410 
411 	panic("lockmgr locks do not support sleep interlocking");
412 }
413 
414 static uintptr_t
415 unlock_lockmgr(struct lock_object *lock)
416 {
417 
418 	panic("lockmgr locks do not support sleep interlocking");
419 }
420 
421 #ifdef KDTRACE_HOOKS
422 static int
423 owner_lockmgr(const struct lock_object *lock, struct thread **owner)
424 {
425 
426 	panic("lockmgr locks do not support owner inquiring");
427 }
428 #endif
429 
430 void
431 lockinit(struct lock *lk, int pri, const char *wmesg, int timo, int flags)
432 {
433 	int iflags;
434 
435 	MPASS((flags & ~LK_INIT_MASK) == 0);
436 	ASSERT_ATOMIC_LOAD_PTR(lk->lk_lock,
437             ("%s: lockmgr not aligned for %s: %p", __func__, wmesg,
438             &lk->lk_lock));
439 
440 	iflags = LO_SLEEPABLE | LO_UPGRADABLE;
441 	if (flags & LK_CANRECURSE)
442 		iflags |= LO_RECURSABLE;
443 	if ((flags & LK_NODUP) == 0)
444 		iflags |= LO_DUPOK;
445 	if (flags & LK_NOPROFILE)
446 		iflags |= LO_NOPROFILE;
447 	if ((flags & LK_NOWITNESS) == 0)
448 		iflags |= LO_WITNESS;
449 	if (flags & LK_QUIET)
450 		iflags |= LO_QUIET;
451 	if (flags & LK_IS_VNODE)
452 		iflags |= LO_IS_VNODE;
453 	if (flags & LK_NEW)
454 		iflags |= LO_NEW;
455 	iflags |= flags & LK_NOSHARE;
456 
457 	lock_init(&lk->lock_object, &lock_class_lockmgr, wmesg, NULL, iflags);
458 	lk->lk_lock = LK_UNLOCKED;
459 	lk->lk_recurse = 0;
460 	lk->lk_exslpfail = 0;
461 	lk->lk_timo = timo;
462 	lk->lk_pri = pri;
463 	STACK_ZERO(lk);
464 }
465 
466 /*
467  * XXX: Gross hacks to manipulate external lock flags after
468  * initialization.  Used for certain vnode and buf locks.
469  */
470 void
471 lockallowshare(struct lock *lk)
472 {
473 
474 	lockmgr_assert(lk, KA_XLOCKED);
475 	lk->lock_object.lo_flags &= ~LK_NOSHARE;
476 }
477 
478 void
479 lockdisableshare(struct lock *lk)
480 {
481 
482 	lockmgr_assert(lk, KA_XLOCKED);
483 	lk->lock_object.lo_flags |= LK_NOSHARE;
484 }
485 
486 void
487 lockallowrecurse(struct lock *lk)
488 {
489 
490 	lockmgr_assert(lk, KA_XLOCKED);
491 	lk->lock_object.lo_flags |= LO_RECURSABLE;
492 }
493 
494 void
495 lockdisablerecurse(struct lock *lk)
496 {
497 
498 	lockmgr_assert(lk, KA_XLOCKED);
499 	lk->lock_object.lo_flags &= ~LO_RECURSABLE;
500 }
501 
502 void
503 lockdestroy(struct lock *lk)
504 {
505 
506 	KASSERT(lk->lk_lock == LK_UNLOCKED, ("lockmgr still held"));
507 	KASSERT(lk->lk_recurse == 0, ("lockmgr still recursed"));
508 	KASSERT(lk->lk_exslpfail == 0, ("lockmgr still exclusive waiters"));
509 	lock_destroy(&lk->lock_object);
510 }
511 
512 static bool __always_inline
513 lockmgr_slock_try(struct lock *lk, uintptr_t *xp, int flags, bool fp)
514 {
515 
516 	/*
517 	 * If no other thread has an exclusive lock, or
518 	 * no exclusive waiter is present, bump the count of
519 	 * sharers.  Since we have to preserve the state of
520 	 * waiters, if we fail to acquire the shared lock
521 	 * loop back and retry.
522 	 */
523 	while (LK_CAN_SHARE(*xp, flags, fp)) {
524 		if (atomic_fcmpset_acq_ptr(&lk->lk_lock, xp,
525 		    *xp + LK_ONE_SHARER)) {
526 			return (true);
527 		}
528 	}
529 	return (false);
530 }
531 
532 static bool __always_inline
533 lockmgr_sunlock_try(struct lock *lk, uintptr_t *xp)
534 {
535 
536 	for (;;) {
537 		if (LK_SHARERS(*xp) > 1 || !(*xp & LK_ALL_WAITERS)) {
538 			if (atomic_fcmpset_rel_ptr(&lk->lk_lock, xp,
539 			    *xp - LK_ONE_SHARER))
540 				return (true);
541 			continue;
542 		}
543 		break;
544 	}
545 	return (false);
546 }
547 
548 static bool
549 lockmgr_slock_adaptive(struct lock_delay_arg *lda, struct lock *lk, uintptr_t *xp,
550     int flags)
551 {
552 	struct thread *owner;
553 	uintptr_t x;
554 
555 	x = *xp;
556 	MPASS(x != LK_UNLOCKED);
557 	owner = (struct thread *)LK_HOLDER(x);
558 	for (;;) {
559 		MPASS(owner != curthread);
560 		if (owner == (struct thread *)LK_KERNPROC)
561 			return (false);
562 		if ((x & LK_SHARE) && LK_SHARERS(x) > 0)
563 			return (false);
564 		if (owner == NULL)
565 			return (false);
566 		if (!TD_IS_RUNNING(owner))
567 			return (false);
568 		if ((x & LK_ALL_WAITERS) != 0)
569 			return (false);
570 		lock_delay(lda);
571 		x = lockmgr_read_value(lk);
572 		if (LK_CAN_SHARE(x, flags, false)) {
573 			*xp = x;
574 			return (true);
575 		}
576 		owner = (struct thread *)LK_HOLDER(x);
577 	}
578 }
579 
580 static __noinline int
581 lockmgr_slock_hard(struct lock *lk, u_int flags, struct lock_object *ilk,
582     const char *file, int line, struct lockmgr_wait *lwa)
583 {
584 	uintptr_t tid, x;
585 	int error = 0;
586 	const char *iwmesg;
587 	int ipri, itimo;
588 
589 #ifdef KDTRACE_HOOKS
590 	uint64_t sleep_time = 0;
591 #endif
592 #ifdef LOCK_PROFILING
593 	uint64_t waittime = 0;
594 	int contested = 0;
595 #endif
596 	struct lock_delay_arg lda;
597 
598 	if (KERNEL_PANICKED())
599 		goto out;
600 
601 	tid = (uintptr_t)curthread;
602 
603 	if (LK_CAN_WITNESS(flags))
604 		WITNESS_CHECKORDER(&lk->lock_object, LOP_NEWORDER,
605 		    file, line, flags & LK_INTERLOCK ? ilk : NULL);
606 	x = lockmgr_read_value(lk);
607 	lock_delay_arg_init(&lda, &lockmgr_delay);
608 	if (!lk_adaptive)
609 		flags &= ~LK_ADAPTIVE;
610 	/*
611 	 * The lock may already be locked exclusive by curthread,
612 	 * avoid deadlock.
613 	 */
614 	if (LK_HOLDER(x) == tid) {
615 		LOCK_LOG2(lk,
616 		    "%s: %p already held in exclusive mode",
617 		    __func__, lk);
618 		error = EDEADLK;
619 		goto out;
620 	}
621 
622 	for (;;) {
623 		if (lockmgr_slock_try(lk, &x, flags, false))
624 			break;
625 
626 		if ((flags & (LK_ADAPTIVE | LK_INTERLOCK)) == LK_ADAPTIVE) {
627 			if (lockmgr_slock_adaptive(&lda, lk, &x, flags))
628 				continue;
629 		}
630 
631 #ifdef HWPMC_HOOKS
632 		PMC_SOFT_CALL( , , lock, failed);
633 #endif
634 		lock_profile_obtain_lock_failed(&lk->lock_object,
635 		    &contested, &waittime);
636 
637 		/*
638 		 * If the lock is expected to not sleep just give up
639 		 * and return.
640 		 */
641 		if (LK_TRYOP(flags)) {
642 			LOCK_LOG2(lk, "%s: %p fails the try operation",
643 			    __func__, lk);
644 			error = EBUSY;
645 			break;
646 		}
647 
648 		/*
649 		 * Acquire the sleepqueue chain lock because we
650 		 * probabilly will need to manipulate waiters flags.
651 		 */
652 		sleepq_lock(&lk->lock_object);
653 		x = lockmgr_read_value(lk);
654 retry_sleepq:
655 
656 		/*
657 		 * if the lock can be acquired in shared mode, try
658 		 * again.
659 		 */
660 		if (LK_CAN_SHARE(x, flags, false)) {
661 			sleepq_release(&lk->lock_object);
662 			continue;
663 		}
664 
665 		/*
666 		 * Try to set the LK_SHARED_WAITERS flag.  If we fail,
667 		 * loop back and retry.
668 		 */
669 		if ((x & LK_SHARED_WAITERS) == 0) {
670 			if (!atomic_fcmpset_acq_ptr(&lk->lk_lock, &x,
671 			    x | LK_SHARED_WAITERS)) {
672 				goto retry_sleepq;
673 			}
674 			LOCK_LOG2(lk, "%s: %p set shared waiters flag",
675 			    __func__, lk);
676 		}
677 
678 		if (lwa == NULL) {
679 			iwmesg = lk->lock_object.lo_name;
680 			ipri = lk->lk_pri;
681 			itimo = lk->lk_timo;
682 		} else {
683 			iwmesg = lwa->iwmesg;
684 			ipri = lwa->ipri;
685 			itimo = lwa->itimo;
686 		}
687 
688 		/*
689 		 * As far as we have been unable to acquire the
690 		 * shared lock and the shared waiters flag is set,
691 		 * we will sleep.
692 		 */
693 #ifdef KDTRACE_HOOKS
694 		sleep_time -= lockstat_nsecs(&lk->lock_object);
695 #endif
696 		error = sleeplk(lk, flags, ilk, iwmesg, ipri, itimo,
697 		    SQ_SHARED_QUEUE);
698 #ifdef KDTRACE_HOOKS
699 		sleep_time += lockstat_nsecs(&lk->lock_object);
700 #endif
701 		flags &= ~LK_INTERLOCK;
702 		if (error) {
703 			LOCK_LOG3(lk,
704 			    "%s: interrupted sleep for %p with %d",
705 			    __func__, lk, error);
706 			break;
707 		}
708 		LOCK_LOG2(lk, "%s: %p resuming from the sleep queue",
709 		    __func__, lk);
710 		x = lockmgr_read_value(lk);
711 	}
712 	if (error == 0) {
713 #ifdef KDTRACE_HOOKS
714 		if (sleep_time != 0)
715 			LOCKSTAT_RECORD4(lockmgr__block, lk, sleep_time,
716 			    LOCKSTAT_READER, (x & LK_SHARE) == 0,
717 			    (x & LK_SHARE) == 0 ? 0 : LK_SHARERS(x));
718 #endif
719 #ifdef LOCK_PROFILING
720 		lockmgr_note_shared_acquire(lk, contested, waittime,
721 		    file, line, flags);
722 #else
723 		lockmgr_note_shared_acquire(lk, 0, 0, file, line,
724 		    flags);
725 #endif
726 	}
727 
728 out:
729 	lockmgr_exit(flags, ilk, 0);
730 	return (error);
731 }
732 
733 static bool
734 lockmgr_xlock_adaptive(struct lock_delay_arg *lda, struct lock *lk, uintptr_t *xp)
735 {
736 	struct thread *owner;
737 	uintptr_t x;
738 
739 	x = *xp;
740 	MPASS(x != LK_UNLOCKED);
741 	owner = (struct thread *)LK_HOLDER(x);
742 	for (;;) {
743 		MPASS(owner != curthread);
744 		if (owner == NULL)
745 			return (false);
746 		if ((x & LK_SHARE) && LK_SHARERS(x) > 0)
747 			return (false);
748 		if (owner == (struct thread *)LK_KERNPROC)
749 			return (false);
750 		if (!TD_IS_RUNNING(owner))
751 			return (false);
752 		if ((x & LK_ALL_WAITERS) != 0)
753 			return (false);
754 		lock_delay(lda);
755 		x = lockmgr_read_value(lk);
756 		if (x == LK_UNLOCKED) {
757 			*xp = x;
758 			return (true);
759 		}
760 		owner = (struct thread *)LK_HOLDER(x);
761 	}
762 }
763 
764 static __noinline int
765 lockmgr_xlock_hard(struct lock *lk, u_int flags, struct lock_object *ilk,
766     const char *file, int line, struct lockmgr_wait *lwa)
767 {
768 	struct lock_class *class;
769 	uintptr_t tid, x, v;
770 	int error = 0;
771 	const char *iwmesg;
772 	int ipri, itimo;
773 
774 #ifdef KDTRACE_HOOKS
775 	uint64_t sleep_time = 0;
776 #endif
777 #ifdef LOCK_PROFILING
778 	uint64_t waittime = 0;
779 	int contested = 0;
780 #endif
781 	struct lock_delay_arg lda;
782 
783 	if (KERNEL_PANICKED())
784 		goto out;
785 
786 	tid = (uintptr_t)curthread;
787 
788 	if (LK_CAN_WITNESS(flags))
789 		WITNESS_CHECKORDER(&lk->lock_object, LOP_NEWORDER |
790 		    LOP_EXCLUSIVE, file, line, flags & LK_INTERLOCK ?
791 		    ilk : NULL);
792 
793 	/*
794 	 * If curthread already holds the lock and this one is
795 	 * allowed to recurse, simply recurse on it.
796 	 */
797 	if (lockmgr_xlocked(lk)) {
798 		if ((flags & LK_CANRECURSE) == 0 &&
799 		    (lk->lock_object.lo_flags & LO_RECURSABLE) == 0) {
800 			/*
801 			 * If the lock is expected to not panic just
802 			 * give up and return.
803 			 */
804 			if (LK_TRYOP(flags)) {
805 				LOCK_LOG2(lk,
806 				    "%s: %p fails the try operation",
807 				    __func__, lk);
808 				error = EBUSY;
809 				goto out;
810 			}
811 			if (flags & LK_INTERLOCK) {
812 				class = LOCK_CLASS(ilk);
813 				class->lc_unlock(ilk);
814 			}
815 			STACK_PRINT(lk);
816 			panic("%s: recursing on non recursive lockmgr %p "
817 			    "@ %s:%d\n", __func__, lk, file, line);
818 		}
819 		atomic_set_ptr(&lk->lk_lock, LK_WRITER_RECURSED);
820 		lk->lk_recurse++;
821 		LOCK_LOG2(lk, "%s: %p recursing", __func__, lk);
822 		LOCK_LOG_LOCK("XLOCK", &lk->lock_object, 0,
823 		    lk->lk_recurse, file, line);
824 		WITNESS_LOCK(&lk->lock_object, LOP_EXCLUSIVE |
825 		    LK_TRYWIT(flags), file, line);
826 		TD_LOCKS_INC(curthread);
827 		goto out;
828 	}
829 
830 	x = LK_UNLOCKED;
831 	lock_delay_arg_init(&lda, &lockmgr_delay);
832 	if (!lk_adaptive)
833 		flags &= ~LK_ADAPTIVE;
834 	for (;;) {
835 		if (x == LK_UNLOCKED) {
836 			if (atomic_fcmpset_acq_ptr(&lk->lk_lock, &x, tid))
837 				break;
838 			continue;
839 		}
840 		if ((flags & (LK_ADAPTIVE | LK_INTERLOCK)) == LK_ADAPTIVE) {
841 			if (lockmgr_xlock_adaptive(&lda, lk, &x))
842 				continue;
843 		}
844 #ifdef HWPMC_HOOKS
845 		PMC_SOFT_CALL( , , lock, failed);
846 #endif
847 		lock_profile_obtain_lock_failed(&lk->lock_object,
848 		    &contested, &waittime);
849 
850 		/*
851 		 * If the lock is expected to not sleep just give up
852 		 * and return.
853 		 */
854 		if (LK_TRYOP(flags)) {
855 			LOCK_LOG2(lk, "%s: %p fails the try operation",
856 			    __func__, lk);
857 			error = EBUSY;
858 			break;
859 		}
860 
861 		/*
862 		 * Acquire the sleepqueue chain lock because we
863 		 * probabilly will need to manipulate waiters flags.
864 		 */
865 		sleepq_lock(&lk->lock_object);
866 		x = lockmgr_read_value(lk);
867 retry_sleepq:
868 
869 		/*
870 		 * if the lock has been released while we spun on
871 		 * the sleepqueue chain lock just try again.
872 		 */
873 		if (x == LK_UNLOCKED) {
874 			sleepq_release(&lk->lock_object);
875 			continue;
876 		}
877 
878 		/*
879 		 * The lock can be in the state where there is a
880 		 * pending queue of waiters, but still no owner.
881 		 * This happens when the lock is contested and an
882 		 * owner is going to claim the lock.
883 		 * If curthread is the one successfully acquiring it
884 		 * claim lock ownership and return, preserving waiters
885 		 * flags.
886 		 */
887 		v = x & (LK_ALL_WAITERS | LK_EXCLUSIVE_SPINNERS);
888 		if ((x & ~v) == LK_UNLOCKED) {
889 			v &= ~LK_EXCLUSIVE_SPINNERS;
890 			if (atomic_fcmpset_acq_ptr(&lk->lk_lock, &x,
891 			    tid | v)) {
892 				sleepq_release(&lk->lock_object);
893 				LOCK_LOG2(lk,
894 				    "%s: %p claimed by a new writer",
895 				    __func__, lk);
896 				break;
897 			}
898 			goto retry_sleepq;
899 		}
900 
901 		/*
902 		 * Try to set the LK_EXCLUSIVE_WAITERS flag.  If we
903 		 * fail, loop back and retry.
904 		 */
905 		if ((x & LK_EXCLUSIVE_WAITERS) == 0) {
906 			if (!atomic_fcmpset_ptr(&lk->lk_lock, &x,
907 			    x | LK_EXCLUSIVE_WAITERS)) {
908 				goto retry_sleepq;
909 			}
910 			LOCK_LOG2(lk, "%s: %p set excl waiters flag",
911 			    __func__, lk);
912 		}
913 
914 		if (lwa == NULL) {
915 			iwmesg = lk->lock_object.lo_name;
916 			ipri = lk->lk_pri;
917 			itimo = lk->lk_timo;
918 		} else {
919 			iwmesg = lwa->iwmesg;
920 			ipri = lwa->ipri;
921 			itimo = lwa->itimo;
922 		}
923 
924 		/*
925 		 * As far as we have been unable to acquire the
926 		 * exclusive lock and the exclusive waiters flag
927 		 * is set, we will sleep.
928 		 */
929 #ifdef KDTRACE_HOOKS
930 		sleep_time -= lockstat_nsecs(&lk->lock_object);
931 #endif
932 		error = sleeplk(lk, flags, ilk, iwmesg, ipri, itimo,
933 		    SQ_EXCLUSIVE_QUEUE);
934 #ifdef KDTRACE_HOOKS
935 		sleep_time += lockstat_nsecs(&lk->lock_object);
936 #endif
937 		flags &= ~LK_INTERLOCK;
938 		if (error) {
939 			LOCK_LOG3(lk,
940 			    "%s: interrupted sleep for %p with %d",
941 			    __func__, lk, error);
942 			break;
943 		}
944 		LOCK_LOG2(lk, "%s: %p resuming from the sleep queue",
945 		    __func__, lk);
946 		x = lockmgr_read_value(lk);
947 	}
948 	if (error == 0) {
949 #ifdef KDTRACE_HOOKS
950 		if (sleep_time != 0)
951 			LOCKSTAT_RECORD4(lockmgr__block, lk, sleep_time,
952 			    LOCKSTAT_WRITER, (x & LK_SHARE) == 0,
953 			    (x & LK_SHARE) == 0 ? 0 : LK_SHARERS(x));
954 #endif
955 #ifdef LOCK_PROFILING
956 		lockmgr_note_exclusive_acquire(lk, contested, waittime,
957 		    file, line, flags);
958 #else
959 		lockmgr_note_exclusive_acquire(lk, 0, 0, file, line,
960 		    flags);
961 #endif
962 	}
963 
964 out:
965 	lockmgr_exit(flags, ilk, 0);
966 	return (error);
967 }
968 
969 static __noinline int
970 lockmgr_upgrade(struct lock *lk, u_int flags, struct lock_object *ilk,
971     const char *file, int line, struct lockmgr_wait *lwa)
972 {
973 	uintptr_t tid, v, setv;
974 	int error = 0;
975 	int op;
976 
977 	if (KERNEL_PANICKED())
978 		goto out;
979 
980 	tid = (uintptr_t)curthread;
981 
982 	_lockmgr_assert(lk, KA_SLOCKED, file, line);
983 
984 	op = flags & LK_TYPE_MASK;
985 	v = lockmgr_read_value(lk);
986 	for (;;) {
987 		if (LK_SHARERS_LOCK(v) > 1) {
988 			if (op == LK_TRYUPGRADE) {
989 				LOCK_LOG2(lk, "%s: %p failed the nowait upgrade",
990 				    __func__, lk);
991 				error = EBUSY;
992 				goto out;
993 			}
994 			if (lockmgr_sunlock_try(lk, &v)) {
995 				lockmgr_note_shared_release(lk, file, line);
996 				goto out_xlock;
997 			}
998 		}
999 		MPASS((v & ~LK_ALL_WAITERS) == LK_SHARERS_LOCK(1));
1000 
1001 		setv = tid;
1002 		setv |= (v & LK_ALL_WAITERS);
1003 
1004 		/*
1005 		 * Try to switch from one shared lock to an exclusive one.
1006 		 * We need to preserve waiters flags during the operation.
1007 		 */
1008 		if (atomic_fcmpset_ptr(&lk->lk_lock, &v, setv)) {
1009 			LOCK_LOG_LOCK("XUPGRADE", &lk->lock_object, 0, 0, file,
1010 			    line);
1011 			WITNESS_UPGRADE(&lk->lock_object, LOP_EXCLUSIVE |
1012 			    LK_TRYWIT(flags), file, line);
1013 			LOCKSTAT_RECORD0(lockmgr__upgrade, lk);
1014 			TD_SLOCKS_DEC(curthread);
1015 			goto out;
1016 		}
1017 	}
1018 
1019 out_xlock:
1020 	error = lockmgr_xlock_hard(lk, flags, ilk, file, line, lwa);
1021 	flags &= ~LK_INTERLOCK;
1022 out:
1023 	lockmgr_exit(flags, ilk, 0);
1024 	return (error);
1025 }
1026 
1027 int
1028 lockmgr_lock_flags(struct lock *lk, u_int flags, struct lock_object *ilk,
1029     const char *file, int line)
1030 {
1031 	struct lock_class *class;
1032 	uintptr_t x, tid;
1033 	u_int op;
1034 	bool locked;
1035 
1036 	if (KERNEL_PANICKED())
1037 		return (0);
1038 
1039 	op = flags & LK_TYPE_MASK;
1040 	locked = false;
1041 	switch (op) {
1042 	case LK_SHARED:
1043 		if (LK_CAN_WITNESS(flags))
1044 			WITNESS_CHECKORDER(&lk->lock_object, LOP_NEWORDER,
1045 			    file, line, flags & LK_INTERLOCK ? ilk : NULL);
1046 		if (__predict_false(lk->lock_object.lo_flags & LK_NOSHARE))
1047 			break;
1048 		x = lockmgr_read_value(lk);
1049 		if (lockmgr_slock_try(lk, &x, flags, true)) {
1050 			lockmgr_note_shared_acquire(lk, 0, 0,
1051 			    file, line, flags);
1052 			locked = true;
1053 		} else {
1054 			return (lockmgr_slock_hard(lk, flags, ilk, file, line,
1055 			    NULL));
1056 		}
1057 		break;
1058 	case LK_EXCLUSIVE:
1059 		if (LK_CAN_WITNESS(flags))
1060 			WITNESS_CHECKORDER(&lk->lock_object, LOP_NEWORDER |
1061 			    LOP_EXCLUSIVE, file, line, flags & LK_INTERLOCK ?
1062 			    ilk : NULL);
1063 		tid = (uintptr_t)curthread;
1064 		if (lockmgr_read_value(lk) == LK_UNLOCKED &&
1065 		    atomic_cmpset_acq_ptr(&lk->lk_lock, LK_UNLOCKED, tid)) {
1066 			lockmgr_note_exclusive_acquire(lk, 0, 0, file, line,
1067 			    flags);
1068 			locked = true;
1069 		} else {
1070 			return (lockmgr_xlock_hard(lk, flags, ilk, file, line,
1071 			    NULL));
1072 		}
1073 		break;
1074 	case LK_UPGRADE:
1075 	case LK_TRYUPGRADE:
1076 		return (lockmgr_upgrade(lk, flags, ilk, file, line, NULL));
1077 	default:
1078 		break;
1079 	}
1080 	if (__predict_true(locked)) {
1081 		if (__predict_false(flags & LK_INTERLOCK)) {
1082 			class = LOCK_CLASS(ilk);
1083 			class->lc_unlock(ilk);
1084 		}
1085 		return (0);
1086 	} else {
1087 		return (__lockmgr_args(lk, flags, ilk, LK_WMESG_DEFAULT,
1088 		    LK_PRIO_DEFAULT, LK_TIMO_DEFAULT, file, line));
1089 	}
1090 }
1091 
1092 static __noinline int
1093 lockmgr_sunlock_hard(struct lock *lk, uintptr_t x, u_int flags, struct lock_object *ilk,
1094     const char *file, int line)
1095 
1096 {
1097 	int wakeup_swapper = 0;
1098 
1099 	if (KERNEL_PANICKED())
1100 		goto out;
1101 
1102 	wakeup_swapper = wakeupshlk(lk, file, line);
1103 
1104 out:
1105 	lockmgr_exit(flags, ilk, wakeup_swapper);
1106 	return (0);
1107 }
1108 
1109 static __noinline int
1110 lockmgr_xunlock_hard(struct lock *lk, uintptr_t x, u_int flags, struct lock_object *ilk,
1111     const char *file, int line)
1112 {
1113 	uintptr_t tid, v;
1114 	int wakeup_swapper = 0;
1115 	u_int realexslp;
1116 	int queue;
1117 
1118 	if (KERNEL_PANICKED())
1119 		goto out;
1120 
1121 	tid = (uintptr_t)curthread;
1122 
1123 	/*
1124 	 * As first option, treact the lock as if it has not
1125 	 * any waiter.
1126 	 * Fix-up the tid var if the lock has been disowned.
1127 	 */
1128 	if (LK_HOLDER(x) == LK_KERNPROC)
1129 		tid = LK_KERNPROC;
1130 
1131 	/*
1132 	 * The lock is held in exclusive mode.
1133 	 * If the lock is recursed also, then unrecurse it.
1134 	 */
1135 	if (lockmgr_recursed_v(x)) {
1136 		LOCK_LOG2(lk, "%s: %p unrecursing", __func__, lk);
1137 		lk->lk_recurse--;
1138 		if (lk->lk_recurse == 0)
1139 			atomic_clear_ptr(&lk->lk_lock, LK_WRITER_RECURSED);
1140 		goto out;
1141 	}
1142 	if (tid != LK_KERNPROC)
1143 		LOCKSTAT_PROFILE_RELEASE_RWLOCK(lockmgr__release, lk,
1144 		    LOCKSTAT_WRITER);
1145 
1146 	if (x == tid && atomic_cmpset_rel_ptr(&lk->lk_lock, tid, LK_UNLOCKED))
1147 		goto out;
1148 
1149 	sleepq_lock(&lk->lock_object);
1150 	x = lockmgr_read_value(lk);
1151 	v = LK_UNLOCKED;
1152 
1153 	/*
1154 	 * If the lock has exclusive waiters, give them
1155 	 * preference in order to avoid deadlock with
1156 	 * shared runners up.
1157 	 * If interruptible sleeps left the exclusive queue
1158 	 * empty avoid a starvation for the threads sleeping
1159 	 * on the shared queue by giving them precedence
1160 	 * and cleaning up the exclusive waiters bit anyway.
1161 	 * Please note that lk_exslpfail count may be lying
1162 	 * about the real number of waiters with the
1163 	 * LK_SLEEPFAIL flag on because they may be used in
1164 	 * conjunction with interruptible sleeps so
1165 	 * lk_exslpfail might be considered an 'upper limit'
1166 	 * bound, including the edge cases.
1167 	 */
1168 	MPASS((x & LK_EXCLUSIVE_SPINNERS) == 0);
1169 	realexslp = sleepq_sleepcnt(&lk->lock_object, SQ_EXCLUSIVE_QUEUE);
1170 	if ((x & LK_EXCLUSIVE_WAITERS) != 0 && realexslp != 0) {
1171 		if (lk->lk_exslpfail < realexslp) {
1172 			lk->lk_exslpfail = 0;
1173 			queue = SQ_EXCLUSIVE_QUEUE;
1174 			v |= (x & LK_SHARED_WAITERS);
1175 		} else {
1176 			lk->lk_exslpfail = 0;
1177 			LOCK_LOG2(lk,
1178 			    "%s: %p has only LK_SLEEPFAIL sleepers",
1179 			    __func__, lk);
1180 			LOCK_LOG2(lk,
1181 			    "%s: %p waking up threads on the exclusive queue",
1182 			    __func__, lk);
1183 			wakeup_swapper = sleepq_broadcast(&lk->lock_object,
1184 			    SLEEPQ_LK, 0, SQ_EXCLUSIVE_QUEUE);
1185 			queue = SQ_SHARED_QUEUE;
1186 		}
1187 	} else {
1188 		/*
1189 		 * Exclusive waiters sleeping with LK_SLEEPFAIL
1190 		 * on and using interruptible sleeps/timeout
1191 		 * may have left spourious lk_exslpfail counts
1192 		 * on, so clean it up anyway.
1193 		 */
1194 		lk->lk_exslpfail = 0;
1195 		queue = SQ_SHARED_QUEUE;
1196 	}
1197 
1198 	LOCK_LOG3(lk, "%s: %p waking up threads on the %s queue",
1199 	    __func__, lk, queue == SQ_SHARED_QUEUE ? "shared" :
1200 	    "exclusive");
1201 	atomic_store_rel_ptr(&lk->lk_lock, v);
1202 	wakeup_swapper |= sleepq_broadcast(&lk->lock_object, SLEEPQ_LK, 0, queue);
1203 	sleepq_release(&lk->lock_object);
1204 
1205 out:
1206 	lockmgr_exit(flags, ilk, wakeup_swapper);
1207 	return (0);
1208 }
1209 
1210 /*
1211  * Lightweight entry points for common operations.
1212  *
1213  * Functionality is similar to sx locks, in that none of the additional lockmgr
1214  * features are supported. To be clear, these are NOT supported:
1215  * 1. shared locking disablement
1216  * 2. returning with an error after sleep
1217  * 3. unlocking the interlock
1218  *
1219  * If in doubt, use lockmgr_lock_flags.
1220  */
1221 int
1222 lockmgr_slock(struct lock *lk, u_int flags, const char *file, int line)
1223 {
1224 	uintptr_t x;
1225 
1226 	MPASS((flags & LK_TYPE_MASK) == LK_SHARED);
1227 	MPASS((flags & LK_INTERLOCK) == 0);
1228 	MPASS((lk->lock_object.lo_flags & LK_NOSHARE) == 0);
1229 
1230 	if (LK_CAN_WITNESS(flags))
1231 		WITNESS_CHECKORDER(&lk->lock_object, LOP_NEWORDER,
1232 		    file, line, NULL);
1233 	x = lockmgr_read_value(lk);
1234 	if (__predict_true(lockmgr_slock_try(lk, &x, flags, true))) {
1235 		lockmgr_note_shared_acquire(lk, 0, 0, file, line, flags);
1236 		return (0);
1237 	}
1238 
1239 	return (lockmgr_slock_hard(lk, flags | LK_ADAPTIVE, NULL, file, line, NULL));
1240 }
1241 
1242 int
1243 lockmgr_xlock(struct lock *lk, u_int flags, const char *file, int line)
1244 {
1245 	uintptr_t tid;
1246 
1247 	MPASS((flags & LK_TYPE_MASK) == LK_EXCLUSIVE);
1248 	MPASS((flags & LK_INTERLOCK) == 0);
1249 
1250 	if (LK_CAN_WITNESS(flags))
1251 		WITNESS_CHECKORDER(&lk->lock_object, LOP_NEWORDER |
1252 		    LOP_EXCLUSIVE, file, line, NULL);
1253 	tid = (uintptr_t)curthread;
1254 	if (atomic_cmpset_acq_ptr(&lk->lk_lock, LK_UNLOCKED, tid)) {
1255 		lockmgr_note_exclusive_acquire(lk, 0, 0, file, line,
1256 		    flags);
1257 		return (0);
1258 	}
1259 
1260 	return (lockmgr_xlock_hard(lk, flags | LK_ADAPTIVE, NULL, file, line, NULL));
1261 }
1262 
1263 int
1264 lockmgr_unlock(struct lock *lk)
1265 {
1266 	uintptr_t x, tid;
1267 	const char *file;
1268 	int line;
1269 
1270 	file = __FILE__;
1271 	line = __LINE__;
1272 
1273 	_lockmgr_assert(lk, KA_LOCKED, file, line);
1274 	x = lockmgr_read_value(lk);
1275 	if (__predict_true(x & LK_SHARE) != 0) {
1276 		lockmgr_note_shared_release(lk, file, line);
1277 		if (lockmgr_sunlock_try(lk, &x)) {
1278 			LOCKSTAT_PROFILE_RELEASE_RWLOCK(lockmgr__release, lk, LOCKSTAT_READER);
1279 		} else {
1280 			return (lockmgr_sunlock_hard(lk, x, LK_RELEASE, NULL, file, line));
1281 		}
1282 	} else {
1283 		tid = (uintptr_t)curthread;
1284 		lockmgr_note_exclusive_release(lk, file, line);
1285 		if (x == tid && atomic_cmpset_rel_ptr(&lk->lk_lock, tid, LK_UNLOCKED)) {
1286 			LOCKSTAT_PROFILE_RELEASE_RWLOCK(lockmgr__release, lk,LOCKSTAT_WRITER);
1287 		} else {
1288 			return (lockmgr_xunlock_hard(lk, x, LK_RELEASE, NULL, file, line));
1289 		}
1290 	}
1291 	return (0);
1292 }
1293 
1294 int
1295 __lockmgr_args(struct lock *lk, u_int flags, struct lock_object *ilk,
1296     const char *wmesg, int pri, int timo, const char *file, int line)
1297 {
1298 	GIANT_DECLARE;
1299 	struct lockmgr_wait lwa;
1300 	struct lock_class *class;
1301 	const char *iwmesg;
1302 	uintptr_t tid, v, x;
1303 	u_int op, realexslp;
1304 	int error, ipri, itimo, queue, wakeup_swapper;
1305 #ifdef LOCK_PROFILING
1306 	uint64_t waittime = 0;
1307 	int contested = 0;
1308 #endif
1309 
1310 	if (KERNEL_PANICKED())
1311 		return (0);
1312 
1313 	error = 0;
1314 	tid = (uintptr_t)curthread;
1315 	op = (flags & LK_TYPE_MASK);
1316 	iwmesg = (wmesg == LK_WMESG_DEFAULT) ? lk->lock_object.lo_name : wmesg;
1317 	ipri = (pri == LK_PRIO_DEFAULT) ? lk->lk_pri : pri;
1318 	itimo = (timo == LK_TIMO_DEFAULT) ? lk->lk_timo : timo;
1319 
1320 	lwa.iwmesg = iwmesg;
1321 	lwa.ipri = ipri;
1322 	lwa.itimo = itimo;
1323 
1324 	MPASS((flags & ~LK_TOTAL_MASK) == 0);
1325 	KASSERT((op & (op - 1)) == 0,
1326 	    ("%s: Invalid requested operation @ %s:%d", __func__, file, line));
1327 	KASSERT((flags & (LK_NOWAIT | LK_SLEEPFAIL)) == 0 ||
1328 	    (op != LK_DOWNGRADE && op != LK_RELEASE),
1329 	    ("%s: Invalid flags in regard of the operation desired @ %s:%d",
1330 	    __func__, file, line));
1331 	KASSERT((flags & LK_INTERLOCK) == 0 || ilk != NULL,
1332 	    ("%s: LK_INTERLOCK passed without valid interlock @ %s:%d",
1333 	    __func__, file, line));
1334 	KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
1335 	    ("%s: idle thread %p on lockmgr %s @ %s:%d", __func__, curthread,
1336 	    lk->lock_object.lo_name, file, line));
1337 
1338 	class = (flags & LK_INTERLOCK) ? LOCK_CLASS(ilk) : NULL;
1339 
1340 	if (lk->lock_object.lo_flags & LK_NOSHARE) {
1341 		switch (op) {
1342 		case LK_SHARED:
1343 			op = LK_EXCLUSIVE;
1344 			break;
1345 		case LK_UPGRADE:
1346 		case LK_TRYUPGRADE:
1347 		case LK_DOWNGRADE:
1348 			_lockmgr_assert(lk, KA_XLOCKED | KA_NOTRECURSED,
1349 			    file, line);
1350 			if (flags & LK_INTERLOCK)
1351 				class->lc_unlock(ilk);
1352 			return (0);
1353 		}
1354 	}
1355 
1356 	wakeup_swapper = 0;
1357 	switch (op) {
1358 	case LK_SHARED:
1359 		return (lockmgr_slock_hard(lk, flags, ilk, file, line, &lwa));
1360 		break;
1361 	case LK_UPGRADE:
1362 	case LK_TRYUPGRADE:
1363 		return (lockmgr_upgrade(lk, flags, ilk, file, line, &lwa));
1364 		break;
1365 	case LK_EXCLUSIVE:
1366 		return (lockmgr_xlock_hard(lk, flags, ilk, file, line, &lwa));
1367 		break;
1368 	case LK_DOWNGRADE:
1369 		_lockmgr_assert(lk, KA_XLOCKED, file, line);
1370 		WITNESS_DOWNGRADE(&lk->lock_object, 0, file, line);
1371 
1372 		/*
1373 		 * Panic if the lock is recursed.
1374 		 */
1375 		if (lockmgr_xlocked(lk) && lockmgr_recursed(lk)) {
1376 			if (flags & LK_INTERLOCK)
1377 				class->lc_unlock(ilk);
1378 			panic("%s: downgrade a recursed lockmgr %s @ %s:%d\n",
1379 			    __func__, iwmesg, file, line);
1380 		}
1381 		TD_SLOCKS_INC(curthread);
1382 
1383 		/*
1384 		 * In order to preserve waiters flags, just spin.
1385 		 */
1386 		for (;;) {
1387 			x = lockmgr_read_value(lk);
1388 			MPASS((x & LK_EXCLUSIVE_SPINNERS) == 0);
1389 			x &= LK_ALL_WAITERS;
1390 			if (atomic_cmpset_rel_ptr(&lk->lk_lock, tid | x,
1391 			    LK_SHARERS_LOCK(1) | x))
1392 				break;
1393 			cpu_spinwait();
1394 		}
1395 		LOCK_LOG_LOCK("XDOWNGRADE", &lk->lock_object, 0, 0, file, line);
1396 		LOCKSTAT_RECORD0(lockmgr__downgrade, lk);
1397 		break;
1398 	case LK_RELEASE:
1399 		_lockmgr_assert(lk, KA_LOCKED, file, line);
1400 		x = lockmgr_read_value(lk);
1401 
1402 		if (__predict_true(x & LK_SHARE) != 0) {
1403 			lockmgr_note_shared_release(lk, file, line);
1404 			return (lockmgr_sunlock_hard(lk, x, flags, ilk, file, line));
1405 		} else {
1406 			lockmgr_note_exclusive_release(lk, file, line);
1407 			return (lockmgr_xunlock_hard(lk, x, flags, ilk, file, line));
1408 		}
1409 		break;
1410 	case LK_DRAIN:
1411 		if (LK_CAN_WITNESS(flags))
1412 			WITNESS_CHECKORDER(&lk->lock_object, LOP_NEWORDER |
1413 			    LOP_EXCLUSIVE, file, line, flags & LK_INTERLOCK ?
1414 			    ilk : NULL);
1415 
1416 		/*
1417 		 * Trying to drain a lock we already own will result in a
1418 		 * deadlock.
1419 		 */
1420 		if (lockmgr_xlocked(lk)) {
1421 			if (flags & LK_INTERLOCK)
1422 				class->lc_unlock(ilk);
1423 			panic("%s: draining %s with the lock held @ %s:%d\n",
1424 			    __func__, iwmesg, file, line);
1425 		}
1426 
1427 		for (;;) {
1428 			if (lk->lk_lock == LK_UNLOCKED &&
1429 			    atomic_cmpset_acq_ptr(&lk->lk_lock, LK_UNLOCKED, tid))
1430 				break;
1431 
1432 #ifdef HWPMC_HOOKS
1433 			PMC_SOFT_CALL( , , lock, failed);
1434 #endif
1435 			lock_profile_obtain_lock_failed(&lk->lock_object,
1436 			    &contested, &waittime);
1437 
1438 			/*
1439 			 * If the lock is expected to not sleep just give up
1440 			 * and return.
1441 			 */
1442 			if (LK_TRYOP(flags)) {
1443 				LOCK_LOG2(lk, "%s: %p fails the try operation",
1444 				    __func__, lk);
1445 				error = EBUSY;
1446 				break;
1447 			}
1448 
1449 			/*
1450 			 * Acquire the sleepqueue chain lock because we
1451 			 * probabilly will need to manipulate waiters flags.
1452 			 */
1453 			sleepq_lock(&lk->lock_object);
1454 			x = lockmgr_read_value(lk);
1455 
1456 			/*
1457 			 * if the lock has been released while we spun on
1458 			 * the sleepqueue chain lock just try again.
1459 			 */
1460 			if (x == LK_UNLOCKED) {
1461 				sleepq_release(&lk->lock_object);
1462 				continue;
1463 			}
1464 
1465 			v = x & (LK_ALL_WAITERS | LK_EXCLUSIVE_SPINNERS);
1466 			if ((x & ~v) == LK_UNLOCKED) {
1467 				v = (x & ~LK_EXCLUSIVE_SPINNERS);
1468 
1469 				/*
1470 				 * If interruptible sleeps left the exclusive
1471 				 * queue empty avoid a starvation for the
1472 				 * threads sleeping on the shared queue by
1473 				 * giving them precedence and cleaning up the
1474 				 * exclusive waiters bit anyway.
1475 				 * Please note that lk_exslpfail count may be
1476 				 * lying about the real number of waiters with
1477 				 * the LK_SLEEPFAIL flag on because they may
1478 				 * be used in conjunction with interruptible
1479 				 * sleeps so lk_exslpfail might be considered
1480 				 * an 'upper limit' bound, including the edge
1481 				 * cases.
1482 				 */
1483 				if (v & LK_EXCLUSIVE_WAITERS) {
1484 					queue = SQ_EXCLUSIVE_QUEUE;
1485 					v &= ~LK_EXCLUSIVE_WAITERS;
1486 				} else {
1487 					/*
1488 					 * Exclusive waiters sleeping with
1489 					 * LK_SLEEPFAIL on and using
1490 					 * interruptible sleeps/timeout may
1491 					 * have left spourious lk_exslpfail
1492 					 * counts on, so clean it up anyway.
1493 					 */
1494 					MPASS(v & LK_SHARED_WAITERS);
1495 					lk->lk_exslpfail = 0;
1496 					queue = SQ_SHARED_QUEUE;
1497 					v &= ~LK_SHARED_WAITERS;
1498 				}
1499 				if (queue == SQ_EXCLUSIVE_QUEUE) {
1500 					realexslp =
1501 					    sleepq_sleepcnt(&lk->lock_object,
1502 					    SQ_EXCLUSIVE_QUEUE);
1503 					if (lk->lk_exslpfail >= realexslp) {
1504 						lk->lk_exslpfail = 0;
1505 						queue = SQ_SHARED_QUEUE;
1506 						v &= ~LK_SHARED_WAITERS;
1507 						if (realexslp != 0) {
1508 							LOCK_LOG2(lk,
1509 					"%s: %p has only LK_SLEEPFAIL sleepers",
1510 							    __func__, lk);
1511 							LOCK_LOG2(lk,
1512 			"%s: %p waking up threads on the exclusive queue",
1513 							    __func__, lk);
1514 							wakeup_swapper =
1515 							    sleepq_broadcast(
1516 							    &lk->lock_object,
1517 							    SLEEPQ_LK, 0,
1518 							    SQ_EXCLUSIVE_QUEUE);
1519 						}
1520 					} else
1521 						lk->lk_exslpfail = 0;
1522 				}
1523 				if (!atomic_cmpset_ptr(&lk->lk_lock, x, v)) {
1524 					sleepq_release(&lk->lock_object);
1525 					continue;
1526 				}
1527 				LOCK_LOG3(lk,
1528 				"%s: %p waking up all threads on the %s queue",
1529 				    __func__, lk, queue == SQ_SHARED_QUEUE ?
1530 				    "shared" : "exclusive");
1531 				wakeup_swapper |= sleepq_broadcast(
1532 				    &lk->lock_object, SLEEPQ_LK, 0, queue);
1533 
1534 				/*
1535 				 * If shared waiters have been woken up we need
1536 				 * to wait for one of them to acquire the lock
1537 				 * before to set the exclusive waiters in
1538 				 * order to avoid a deadlock.
1539 				 */
1540 				if (queue == SQ_SHARED_QUEUE) {
1541 					for (v = lk->lk_lock;
1542 					    (v & LK_SHARE) && !LK_SHARERS(v);
1543 					    v = lk->lk_lock)
1544 						cpu_spinwait();
1545 				}
1546 			}
1547 
1548 			/*
1549 			 * Try to set the LK_EXCLUSIVE_WAITERS flag.  If we
1550 			 * fail, loop back and retry.
1551 			 */
1552 			if ((x & LK_EXCLUSIVE_WAITERS) == 0) {
1553 				if (!atomic_cmpset_ptr(&lk->lk_lock, x,
1554 				    x | LK_EXCLUSIVE_WAITERS)) {
1555 					sleepq_release(&lk->lock_object);
1556 					continue;
1557 				}
1558 				LOCK_LOG2(lk, "%s: %p set drain waiters flag",
1559 				    __func__, lk);
1560 			}
1561 
1562 			/*
1563 			 * As far as we have been unable to acquire the
1564 			 * exclusive lock and the exclusive waiters flag
1565 			 * is set, we will sleep.
1566 			 */
1567 			if (flags & LK_INTERLOCK) {
1568 				class->lc_unlock(ilk);
1569 				flags &= ~LK_INTERLOCK;
1570 			}
1571 			GIANT_SAVE();
1572 			sleepq_add(&lk->lock_object, NULL, iwmesg, SLEEPQ_LK,
1573 			    SQ_EXCLUSIVE_QUEUE);
1574 			sleepq_wait(&lk->lock_object, ipri & PRIMASK);
1575 			GIANT_RESTORE();
1576 			LOCK_LOG2(lk, "%s: %p resuming from the sleep queue",
1577 			    __func__, lk);
1578 		}
1579 
1580 		if (error == 0) {
1581 			lock_profile_obtain_lock_success(&lk->lock_object,
1582 			    contested, waittime, file, line);
1583 			LOCK_LOG_LOCK("DRAIN", &lk->lock_object, 0,
1584 			    lk->lk_recurse, file, line);
1585 			WITNESS_LOCK(&lk->lock_object, LOP_EXCLUSIVE |
1586 			    LK_TRYWIT(flags), file, line);
1587 			TD_LOCKS_INC(curthread);
1588 			STACK_SAVE(lk);
1589 		}
1590 		break;
1591 	default:
1592 		if (flags & LK_INTERLOCK)
1593 			class->lc_unlock(ilk);
1594 		panic("%s: unknown lockmgr request 0x%x\n", __func__, op);
1595 	}
1596 
1597 	if (flags & LK_INTERLOCK)
1598 		class->lc_unlock(ilk);
1599 	if (wakeup_swapper)
1600 		kick_proc0();
1601 
1602 	return (error);
1603 }
1604 
1605 void
1606 _lockmgr_disown(struct lock *lk, const char *file, int line)
1607 {
1608 	uintptr_t tid, x;
1609 
1610 	if (SCHEDULER_STOPPED())
1611 		return;
1612 
1613 	tid = (uintptr_t)curthread;
1614 	_lockmgr_assert(lk, KA_XLOCKED, file, line);
1615 
1616 	/*
1617 	 * Panic if the lock is recursed.
1618 	 */
1619 	if (lockmgr_xlocked(lk) && lockmgr_recursed(lk))
1620 		panic("%s: disown a recursed lockmgr @ %s:%d\n",
1621 		    __func__,  file, line);
1622 
1623 	/*
1624 	 * If the owner is already LK_KERNPROC just skip the whole operation.
1625 	 */
1626 	if (LK_HOLDER(lk->lk_lock) != tid)
1627 		return;
1628 	lock_profile_release_lock(&lk->lock_object);
1629 	LOCKSTAT_RECORD1(lockmgr__disown, lk, LOCKSTAT_WRITER);
1630 	LOCK_LOG_LOCK("XDISOWN", &lk->lock_object, 0, 0, file, line);
1631 	WITNESS_UNLOCK(&lk->lock_object, LOP_EXCLUSIVE, file, line);
1632 	TD_LOCKS_DEC(curthread);
1633 	STACK_SAVE(lk);
1634 
1635 	/*
1636 	 * In order to preserve waiters flags, just spin.
1637 	 */
1638 	for (;;) {
1639 		x = lockmgr_read_value(lk);
1640 		MPASS((x & LK_EXCLUSIVE_SPINNERS) == 0);
1641 		x &= LK_ALL_WAITERS;
1642 		if (atomic_cmpset_rel_ptr(&lk->lk_lock, tid | x,
1643 		    LK_KERNPROC | x))
1644 			return;
1645 		cpu_spinwait();
1646 	}
1647 }
1648 
1649 void
1650 lockmgr_printinfo(const struct lock *lk)
1651 {
1652 	struct thread *td;
1653 	uintptr_t x;
1654 
1655 	if (lk->lk_lock == LK_UNLOCKED)
1656 		printf("lock type %s: UNLOCKED\n", lk->lock_object.lo_name);
1657 	else if (lk->lk_lock & LK_SHARE)
1658 		printf("lock type %s: SHARED (count %ju)\n",
1659 		    lk->lock_object.lo_name,
1660 		    (uintmax_t)LK_SHARERS(lk->lk_lock));
1661 	else {
1662 		td = lockmgr_xholder(lk);
1663 		if (td == (struct thread *)LK_KERNPROC)
1664 			printf("lock type %s: EXCL by KERNPROC\n",
1665 			    lk->lock_object.lo_name);
1666 		else
1667 			printf("lock type %s: EXCL by thread %p "
1668 			    "(pid %d, %s, tid %d)\n", lk->lock_object.lo_name,
1669 			    td, td->td_proc->p_pid, td->td_proc->p_comm,
1670 			    td->td_tid);
1671 	}
1672 
1673 	x = lk->lk_lock;
1674 	if (x & LK_EXCLUSIVE_WAITERS)
1675 		printf(" with exclusive waiters pending\n");
1676 	if (x & LK_SHARED_WAITERS)
1677 		printf(" with shared waiters pending\n");
1678 	if (x & LK_EXCLUSIVE_SPINNERS)
1679 		printf(" with exclusive spinners pending\n");
1680 
1681 	STACK_PRINT(lk);
1682 }
1683 
1684 int
1685 lockstatus(const struct lock *lk)
1686 {
1687 	uintptr_t v, x;
1688 	int ret;
1689 
1690 	ret = LK_SHARED;
1691 	x = lockmgr_read_value(lk);
1692 	v = LK_HOLDER(x);
1693 
1694 	if ((x & LK_SHARE) == 0) {
1695 		if (v == (uintptr_t)curthread || v == LK_KERNPROC)
1696 			ret = LK_EXCLUSIVE;
1697 		else
1698 			ret = LK_EXCLOTHER;
1699 	} else if (x == LK_UNLOCKED)
1700 		ret = 0;
1701 
1702 	return (ret);
1703 }
1704 
1705 #ifdef INVARIANT_SUPPORT
1706 
1707 FEATURE(invariant_support,
1708     "Support for modules compiled with INVARIANTS option");
1709 
1710 #ifndef INVARIANTS
1711 #undef	_lockmgr_assert
1712 #endif
1713 
1714 void
1715 _lockmgr_assert(const struct lock *lk, int what, const char *file, int line)
1716 {
1717 	int slocked = 0;
1718 
1719 	if (KERNEL_PANICKED())
1720 		return;
1721 	switch (what) {
1722 	case KA_SLOCKED:
1723 	case KA_SLOCKED | KA_NOTRECURSED:
1724 	case KA_SLOCKED | KA_RECURSED:
1725 		slocked = 1;
1726 	case KA_LOCKED:
1727 	case KA_LOCKED | KA_NOTRECURSED:
1728 	case KA_LOCKED | KA_RECURSED:
1729 #ifdef WITNESS
1730 
1731 		/*
1732 		 * We cannot trust WITNESS if the lock is held in exclusive
1733 		 * mode and a call to lockmgr_disown() happened.
1734 		 * Workaround this skipping the check if the lock is held in
1735 		 * exclusive mode even for the KA_LOCKED case.
1736 		 */
1737 		if (slocked || (lk->lk_lock & LK_SHARE)) {
1738 			witness_assert(&lk->lock_object, what, file, line);
1739 			break;
1740 		}
1741 #endif
1742 		if (lk->lk_lock == LK_UNLOCKED ||
1743 		    ((lk->lk_lock & LK_SHARE) == 0 && (slocked ||
1744 		    (!lockmgr_xlocked(lk) && !lockmgr_disowned(lk)))))
1745 			panic("Lock %s not %slocked @ %s:%d\n",
1746 			    lk->lock_object.lo_name, slocked ? "share" : "",
1747 			    file, line);
1748 
1749 		if ((lk->lk_lock & LK_SHARE) == 0) {
1750 			if (lockmgr_recursed(lk)) {
1751 				if (what & KA_NOTRECURSED)
1752 					panic("Lock %s recursed @ %s:%d\n",
1753 					    lk->lock_object.lo_name, file,
1754 					    line);
1755 			} else if (what & KA_RECURSED)
1756 				panic("Lock %s not recursed @ %s:%d\n",
1757 				    lk->lock_object.lo_name, file, line);
1758 		}
1759 		break;
1760 	case KA_XLOCKED:
1761 	case KA_XLOCKED | KA_NOTRECURSED:
1762 	case KA_XLOCKED | KA_RECURSED:
1763 		if (!lockmgr_xlocked(lk) && !lockmgr_disowned(lk))
1764 			panic("Lock %s not exclusively locked @ %s:%d\n",
1765 			    lk->lock_object.lo_name, file, line);
1766 		if (lockmgr_recursed(lk)) {
1767 			if (what & KA_NOTRECURSED)
1768 				panic("Lock %s recursed @ %s:%d\n",
1769 				    lk->lock_object.lo_name, file, line);
1770 		} else if (what & KA_RECURSED)
1771 			panic("Lock %s not recursed @ %s:%d\n",
1772 			    lk->lock_object.lo_name, file, line);
1773 		break;
1774 	case KA_UNLOCKED:
1775 		if (lockmgr_xlocked(lk) || lockmgr_disowned(lk))
1776 			panic("Lock %s exclusively locked @ %s:%d\n",
1777 			    lk->lock_object.lo_name, file, line);
1778 		break;
1779 	default:
1780 		panic("Unknown lockmgr assertion: %d @ %s:%d\n", what, file,
1781 		    line);
1782 	}
1783 }
1784 #endif
1785 
1786 #ifdef DDB
1787 int
1788 lockmgr_chain(struct thread *td, struct thread **ownerp)
1789 {
1790 	const struct lock *lk;
1791 
1792 	lk = td->td_wchan;
1793 
1794 	if (LOCK_CLASS(&lk->lock_object) != &lock_class_lockmgr)
1795 		return (0);
1796 	db_printf("blocked on lockmgr %s", lk->lock_object.lo_name);
1797 	if (lk->lk_lock & LK_SHARE)
1798 		db_printf("SHARED (count %ju)\n",
1799 		    (uintmax_t)LK_SHARERS(lk->lk_lock));
1800 	else
1801 		db_printf("EXCL\n");
1802 	*ownerp = lockmgr_xholder(lk);
1803 
1804 	return (1);
1805 }
1806 
1807 static void
1808 db_show_lockmgr(const struct lock_object *lock)
1809 {
1810 	struct thread *td;
1811 	const struct lock *lk;
1812 
1813 	lk = (const struct lock *)lock;
1814 
1815 	db_printf(" state: ");
1816 	if (lk->lk_lock == LK_UNLOCKED)
1817 		db_printf("UNLOCKED\n");
1818 	else if (lk->lk_lock & LK_SHARE)
1819 		db_printf("SLOCK: %ju\n", (uintmax_t)LK_SHARERS(lk->lk_lock));
1820 	else {
1821 		td = lockmgr_xholder(lk);
1822 		if (td == (struct thread *)LK_KERNPROC)
1823 			db_printf("XLOCK: LK_KERNPROC\n");
1824 		else
1825 			db_printf("XLOCK: %p (tid %d, pid %d, \"%s\")\n", td,
1826 			    td->td_tid, td->td_proc->p_pid,
1827 			    td->td_proc->p_comm);
1828 		if (lockmgr_recursed(lk))
1829 			db_printf(" recursed: %d\n", lk->lk_recurse);
1830 	}
1831 	db_printf(" waiters: ");
1832 	switch (lk->lk_lock & LK_ALL_WAITERS) {
1833 	case LK_SHARED_WAITERS:
1834 		db_printf("shared\n");
1835 		break;
1836 	case LK_EXCLUSIVE_WAITERS:
1837 		db_printf("exclusive\n");
1838 		break;
1839 	case LK_ALL_WAITERS:
1840 		db_printf("shared and exclusive\n");
1841 		break;
1842 	default:
1843 		db_printf("none\n");
1844 	}
1845 	db_printf(" spinners: ");
1846 	if (lk->lk_lock & LK_EXCLUSIVE_SPINNERS)
1847 		db_printf("exclusive\n");
1848 	else
1849 		db_printf("none\n");
1850 }
1851 #endif
1852