xref: /freebsd/sys/kern/kern_lock.c (revision 1e413cf93298b5b97441a21d9a50fdcd0ee9945e)
1 /*-
2  * Copyright (c) 1995
3  *	The Regents of the University of California.  All rights reserved.
4  *
5  * Copyright (C) 1997
6  *	John S. Dyson.  All rights reserved.
7  *
8  * This code contains ideas from software contributed to Berkeley by
9  * Avadis Tevanian, Jr., Michael Wayne Young, and the Mach Operating
10  * System project at Carnegie-Mellon University.
11  *
12  * Redistribution and use in source and binary forms, with or without
13  * modification, are permitted provided that the following conditions
14  * are met:
15  * 1. Redistributions of source code must retain the above copyright
16  *    notice, this list of conditions and the following disclaimer.
17  * 2. Redistributions in binary form must reproduce the above copyright
18  *    notice, this list of conditions and the following disclaimer in the
19  *    documentation and/or other materials provided with the distribution.
20  * 3. All advertising materials mentioning features or use of this software
21  *    must display the following acknowledgement:
22  *	This product includes software developed by the University of
23  *	California, Berkeley and its contributors.
24  * 4. Neither the name of the University nor the names of its contributors
25  *    may be used to endorse or promote products derived from this software
26  *    without specific prior written permission.
27  *
28  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
29  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
30  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
31  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
32  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
33  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
34  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
35  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
36  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
37  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
38  * SUCH DAMAGE.
39  *
40  *	@(#)kern_lock.c	8.18 (Berkeley) 5/21/95
41  */
42 
43 #include <sys/cdefs.h>
44 __FBSDID("$FreeBSD$");
45 
46 #include "opt_ddb.h"
47 #include "opt_global.h"
48 
49 #include <sys/param.h>
50 #include <sys/kdb.h>
51 #include <sys/kernel.h>
52 #include <sys/ktr.h>
53 #include <sys/lock.h>
54 #include <sys/lockmgr.h>
55 #include <sys/mutex.h>
56 #include <sys/proc.h>
57 #include <sys/systm.h>
58 #include <sys/lock_profile.h>
59 #ifdef DEBUG_LOCKS
60 #include <sys/stack.h>
61 #endif
62 
63 static void	assert_lockmgr(struct lock_object *lock, int what);
64 #ifdef DDB
65 #include <ddb/ddb.h>
66 static void	db_show_lockmgr(struct lock_object *lock);
67 #endif
68 static void	lock_lockmgr(struct lock_object *lock, int how);
69 static int	unlock_lockmgr(struct lock_object *lock);
70 
71 struct lock_class lock_class_lockmgr = {
72 	.lc_name = "lockmgr",
73 	.lc_flags = LC_SLEEPLOCK | LC_SLEEPABLE | LC_RECURSABLE | LC_UPGRADABLE,
74 	.lc_assert = assert_lockmgr,
75 #ifdef DDB
76 	.lc_ddb_show = db_show_lockmgr,
77 #endif
78 	.lc_lock = lock_lockmgr,
79 	.lc_unlock = unlock_lockmgr,
80 };
81 
82 /*
83  * Locking primitives implementation.
84  * Locks provide shared/exclusive sychronization.
85  */
86 
87 void
88 assert_lockmgr(struct lock_object *lock, int what)
89 {
90 
91 	panic("lockmgr locks do not support assertions");
92 }
93 
94 void
95 lock_lockmgr(struct lock_object *lock, int how)
96 {
97 
98 	panic("lockmgr locks do not support sleep interlocking");
99 }
100 
101 int
102 unlock_lockmgr(struct lock_object *lock)
103 {
104 
105 	panic("lockmgr locks do not support sleep interlocking");
106 }
107 
108 #define	COUNT(td, x)	((td)->td_locks += (x))
109 #define LK_ALL (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | \
110 	LK_SHARE_NONZERO | LK_WAIT_NONZERO)
111 
112 static int acquire(struct lock **lkpp, int extflags, int wanted, int *contested, uint64_t *waittime);
113 static int acquiredrain(struct lock *lkp, int extflags) ;
114 
115 static __inline void
116 sharelock(struct thread *td, struct lock *lkp, int incr) {
117 	lkp->lk_flags |= LK_SHARE_NONZERO;
118 	lkp->lk_sharecount += incr;
119 	COUNT(td, incr);
120 }
121 
122 static __inline void
123 shareunlock(struct thread *td, struct lock *lkp, int decr) {
124 
125 	KASSERT(lkp->lk_sharecount >= decr, ("shareunlock: count < decr"));
126 
127 	COUNT(td, -decr);
128 	if (lkp->lk_sharecount == decr) {
129 		lkp->lk_flags &= ~LK_SHARE_NONZERO;
130 		if (lkp->lk_flags & (LK_WANT_UPGRADE | LK_WANT_EXCL)) {
131 			wakeup(lkp);
132 		}
133 		lkp->lk_sharecount = 0;
134 	} else {
135 		lkp->lk_sharecount -= decr;
136 	}
137 }
138 
139 static int
140 acquire(struct lock **lkpp, int extflags, int wanted, int *contested, uint64_t *waittime)
141 {
142 	struct lock *lkp = *lkpp;
143 	int error;
144 	CTR3(KTR_LOCK,
145 	    "acquire(): lkp == %p, extflags == 0x%x, wanted == 0x%x",
146 	    lkp, extflags, wanted);
147 
148 	if ((extflags & LK_NOWAIT) && (lkp->lk_flags & wanted))
149 		return EBUSY;
150 	error = 0;
151 	if ((lkp->lk_flags & wanted) != 0)
152 		lock_profile_obtain_lock_failed(&lkp->lk_object, contested, waittime);
153 
154 	while ((lkp->lk_flags & wanted) != 0) {
155 		CTR2(KTR_LOCK,
156 		    "acquire(): lkp == %p, lk_flags == 0x%x sleeping",
157 		    lkp, lkp->lk_flags);
158 		lkp->lk_flags |= LK_WAIT_NONZERO;
159 		lkp->lk_waitcount++;
160 		error = msleep(lkp, lkp->lk_interlock, lkp->lk_prio,
161 		    lkp->lk_wmesg,
162 		    ((extflags & LK_TIMELOCK) ? lkp->lk_timo : 0));
163 		lkp->lk_waitcount--;
164 		if (lkp->lk_waitcount == 0)
165 			lkp->lk_flags &= ~LK_WAIT_NONZERO;
166 		if (error)
167 			break;
168 		if (extflags & LK_SLEEPFAIL) {
169 			error = ENOLCK;
170 			break;
171 		}
172 		if (lkp->lk_newlock != NULL) {
173 			mtx_lock(lkp->lk_newlock->lk_interlock);
174 			mtx_unlock(lkp->lk_interlock);
175 			if (lkp->lk_waitcount == 0)
176 				wakeup((void *)(&lkp->lk_newlock));
177 			*lkpp = lkp = lkp->lk_newlock;
178 		}
179 	}
180 	mtx_assert(lkp->lk_interlock, MA_OWNED);
181 	return (error);
182 }
183 
184 /*
185  * Set, change, or release a lock.
186  *
187  * Shared requests increment the shared count. Exclusive requests set the
188  * LK_WANT_EXCL flag (preventing further shared locks), and wait for already
189  * accepted shared locks and shared-to-exclusive upgrades to go away.
190  */
191 int
192 _lockmgr(struct lock *lkp, u_int flags, struct mtx *interlkp,
193 	 struct thread *td, char *file, int line)
194 
195 {
196 	int error;
197 	int extflags, lockflags;
198 	int contested = 0;
199 	uint64_t waitstart = 0;
200 
201 	/*
202 	 * Lock owner can only be curthread in order to have a deadlock
203 	 * free implementation of the primitive.
204 	 */
205 	KASSERT(td == curthread,
206 	    ("lockmgr: owner thread (%p) cannot differ from curthread", td));
207 
208 	error = 0;
209 
210 	if ((flags & LK_INTERNAL) == 0)
211 		mtx_lock(lkp->lk_interlock);
212 	CTR6(KTR_LOCK,
213 	    "lockmgr(): lkp == %p (lk_wmesg == \"%s\"), owner == %p, exclusivecount == %d, flags == 0x%x, "
214 	    "td == %p", lkp, lkp->lk_wmesg, lkp->lk_lockholder,
215 	    lkp->lk_exclusivecount, flags, td);
216 #ifdef DEBUG_LOCKS
217 	{
218 		struct stack stack; /* XXX */
219 		stack_save(&stack);
220 		CTRSTACK(KTR_LOCK, &stack, 0, 1);
221 	}
222 #endif
223 
224 	if (flags & LK_INTERLOCK) {
225 		mtx_assert(interlkp, MA_OWNED | MA_NOTRECURSED);
226 		mtx_unlock(interlkp);
227 	}
228 
229 	if ((flags & (LK_NOWAIT|LK_RELEASE)) == 0)
230 		WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK,
231 		    &lkp->lk_interlock->lock_object,
232 		    "Acquiring lockmgr lock \"%s\"", lkp->lk_wmesg);
233 
234 	if (panicstr != NULL) {
235 		mtx_unlock(lkp->lk_interlock);
236 		return (0);
237 	}
238 	if ((lkp->lk_flags & LK_NOSHARE) &&
239 	    (flags & LK_TYPE_MASK) == LK_SHARED) {
240 		flags &= ~LK_TYPE_MASK;
241 		flags |= LK_EXCLUSIVE;
242 	}
243 	extflags = (flags | lkp->lk_flags) & LK_EXTFLG_MASK;
244 
245 	switch (flags & LK_TYPE_MASK) {
246 
247 	case LK_SHARED:
248 		/*
249 		 * If we are not the exclusive lock holder, we have to block
250 		 * while there is an exclusive lock holder or while an
251 		 * exclusive lock request or upgrade request is in progress.
252 		 *
253 		 * However, if TDP_DEADLKTREAT is set, we override exclusive
254 		 * lock requests or upgrade requests ( but not the exclusive
255 		 * lock itself ).
256 		 */
257 		if (lkp->lk_lockholder != td) {
258 			lockflags = LK_HAVE_EXCL;
259 			if (td != NULL && !(td->td_pflags & TDP_DEADLKTREAT))
260 				lockflags |= LK_WANT_EXCL | LK_WANT_UPGRADE;
261 			error = acquire(&lkp, extflags, lockflags, &contested, &waitstart);
262 			if (error)
263 				break;
264 			sharelock(td, lkp, 1);
265 			if (lkp->lk_sharecount == 1)
266 				lock_profile_obtain_lock_success(&lkp->lk_object, contested, waitstart, file, line);
267 
268 #if defined(DEBUG_LOCKS)
269 			stack_save(&lkp->lk_stack);
270 #endif
271 			break;
272 		}
273 		/*
274 		 * We hold an exclusive lock, so downgrade it to shared.
275 		 * An alternative would be to fail with EDEADLK.
276 		 */
277 		sharelock(td, lkp, 1);
278 		if (lkp->lk_sharecount == 1)
279 			lock_profile_obtain_lock_success(&lkp->lk_object, contested, waitstart, file, line);
280 		/* FALLTHROUGH downgrade */
281 
282 	case LK_DOWNGRADE:
283 		KASSERT(lkp->lk_lockholder == td && lkp->lk_exclusivecount != 0,
284 			("lockmgr: not holding exclusive lock "
285 			"(owner thread (%p) != thread (%p), exlcnt (%d) != 0",
286 			lkp->lk_lockholder, td, lkp->lk_exclusivecount));
287 		sharelock(td, lkp, lkp->lk_exclusivecount);
288 		COUNT(td, -lkp->lk_exclusivecount);
289 		lkp->lk_exclusivecount = 0;
290 		lkp->lk_flags &= ~LK_HAVE_EXCL;
291 		lkp->lk_lockholder = LK_NOPROC;
292 		if (lkp->lk_waitcount)
293 			wakeup((void *)lkp);
294 		break;
295 
296 	case LK_UPGRADE:
297 		/*
298 		 * Upgrade a shared lock to an exclusive one. If another
299 		 * shared lock has already requested an upgrade to an
300 		 * exclusive lock, our shared lock is released and an
301 		 * exclusive lock is requested (which will be granted
302 		 * after the upgrade). If we return an error, the file
303 		 * will always be unlocked.
304 		 */
305 		if (lkp->lk_lockholder == td)
306 			panic("lockmgr: upgrade exclusive lock");
307 		if (lkp->lk_sharecount <= 0)
308 			panic("lockmgr: upgrade without shared");
309 		shareunlock(td, lkp, 1);
310 		if (lkp->lk_sharecount == 0)
311 			lock_profile_release_lock(&lkp->lk_object);
312 		/*
313 		 * If we are just polling, check to see if we will block.
314 		 */
315 		if ((extflags & LK_NOWAIT) &&
316 		    ((lkp->lk_flags & LK_WANT_UPGRADE) ||
317 		     lkp->lk_sharecount > 1)) {
318 			error = EBUSY;
319 			break;
320 		}
321 		if ((lkp->lk_flags & LK_WANT_UPGRADE) == 0) {
322 			/*
323 			 * We are first shared lock to request an upgrade, so
324 			 * request upgrade and wait for the shared count to
325 			 * drop to zero, then take exclusive lock.
326 			 */
327 			lkp->lk_flags |= LK_WANT_UPGRADE;
328 			error = acquire(&lkp, extflags, LK_SHARE_NONZERO, &contested, &waitstart);
329 			lkp->lk_flags &= ~LK_WANT_UPGRADE;
330 
331 			if (error) {
332 			         if ((lkp->lk_flags & ( LK_WANT_EXCL | LK_WAIT_NONZERO)) == (LK_WANT_EXCL | LK_WAIT_NONZERO))
333 			                   wakeup((void *)lkp);
334 			         break;
335 			}
336 			if (lkp->lk_exclusivecount != 0)
337 				panic("lockmgr: non-zero exclusive count");
338 			lkp->lk_flags |= LK_HAVE_EXCL;
339 			lkp->lk_lockholder = td;
340 			lkp->lk_exclusivecount = 1;
341 			COUNT(td, 1);
342 			lock_profile_obtain_lock_success(&lkp->lk_object, contested, waitstart, file, line);
343 #if defined(DEBUG_LOCKS)
344 			stack_save(&lkp->lk_stack);
345 #endif
346 			break;
347 		}
348 		/*
349 		 * Someone else has requested upgrade. Release our shared
350 		 * lock, awaken upgrade requestor if we are the last shared
351 		 * lock, then request an exclusive lock.
352 		 */
353 		if ( (lkp->lk_flags & (LK_SHARE_NONZERO|LK_WAIT_NONZERO)) ==
354 			LK_WAIT_NONZERO)
355 			wakeup((void *)lkp);
356 		/* FALLTHROUGH exclusive request */
357 
358 	case LK_EXCLUSIVE:
359 		if (lkp->lk_lockholder == td) {
360 			/*
361 			 *	Recursive lock.
362 			 */
363 			if ((extflags & (LK_NOWAIT | LK_CANRECURSE)) == 0)
364 				panic("lockmgr: locking against myself");
365 			if ((extflags & LK_CANRECURSE) != 0) {
366 				lkp->lk_exclusivecount++;
367 				COUNT(td, 1);
368 				break;
369 			}
370 		}
371 		/*
372 		 * If we are just polling, check to see if we will sleep.
373 		 */
374 		if ((extflags & LK_NOWAIT) &&
375 		    (lkp->lk_flags & (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | LK_SHARE_NONZERO))) {
376 			error = EBUSY;
377 			break;
378 		}
379 		/*
380 		 * Try to acquire the want_exclusive flag.
381 		 */
382 		error = acquire(&lkp, extflags, (LK_HAVE_EXCL | LK_WANT_EXCL), &contested, &waitstart);
383 		if (error)
384 			break;
385 		lkp->lk_flags |= LK_WANT_EXCL;
386 		/*
387 		 * Wait for shared locks and upgrades to finish.
388 		 */
389 		error = acquire(&lkp, extflags, LK_HAVE_EXCL | LK_WANT_UPGRADE | LK_SHARE_NONZERO, &contested, &waitstart);
390 		lkp->lk_flags &= ~LK_WANT_EXCL;
391 		if (error) {
392 			if (lkp->lk_flags & LK_WAIT_NONZERO)
393 			         wakeup((void *)lkp);
394 			break;
395 		}
396 		lkp->lk_flags |= LK_HAVE_EXCL;
397 		lkp->lk_lockholder = td;
398 		if (lkp->lk_exclusivecount != 0)
399 			panic("lockmgr: non-zero exclusive count");
400 		lkp->lk_exclusivecount = 1;
401 		COUNT(td, 1);
402 		lock_profile_obtain_lock_success(&lkp->lk_object, contested, waitstart, file, line);
403 #if defined(DEBUG_LOCKS)
404 		stack_save(&lkp->lk_stack);
405 #endif
406 		break;
407 
408 	case LK_RELEASE:
409 		if (lkp->lk_exclusivecount != 0) {
410 			if (lkp->lk_lockholder != td &&
411 			    lkp->lk_lockholder != LK_KERNPROC) {
412 				panic("lockmgr: thread %p, not %s %p unlocking",
413 				    td, "exclusive lock holder",
414 				    lkp->lk_lockholder);
415 			}
416 			if (lkp->lk_lockholder != LK_KERNPROC)
417 				COUNT(td, -1);
418 			if (lkp->lk_exclusivecount == 1) {
419 				lkp->lk_flags &= ~LK_HAVE_EXCL;
420 				lkp->lk_lockholder = LK_NOPROC;
421 				lkp->lk_exclusivecount = 0;
422 				lock_profile_release_lock(&lkp->lk_object);
423 			} else {
424 				lkp->lk_exclusivecount--;
425 			}
426 		} else if (lkp->lk_flags & LK_SHARE_NONZERO)
427 			shareunlock(td, lkp, 1);
428 		else  {
429 			printf("lockmgr: thread %p unlocking unheld lock\n",
430 			    td);
431 			kdb_backtrace();
432 		}
433 
434 		if (lkp->lk_flags & LK_WAIT_NONZERO)
435 			wakeup((void *)lkp);
436 		break;
437 
438 	case LK_DRAIN:
439 		/*
440 		 * Check that we do not already hold the lock, as it can
441 		 * never drain if we do. Unfortunately, we have no way to
442 		 * check for holding a shared lock, but at least we can
443 		 * check for an exclusive one.
444 		 */
445 		if (lkp->lk_lockholder == td)
446 			panic("lockmgr: draining against myself");
447 
448 		error = acquiredrain(lkp, extflags);
449 		if (error)
450 			break;
451 		lkp->lk_flags |= LK_DRAINING | LK_HAVE_EXCL;
452 		lkp->lk_lockholder = td;
453 		lkp->lk_exclusivecount = 1;
454 		COUNT(td, 1);
455 #if defined(DEBUG_LOCKS)
456 		stack_save(&lkp->lk_stack);
457 #endif
458 		break;
459 
460 	default:
461 		mtx_unlock(lkp->lk_interlock);
462 		panic("lockmgr: unknown locktype request %d",
463 		    flags & LK_TYPE_MASK);
464 		/* NOTREACHED */
465 	}
466 	if ((lkp->lk_flags & LK_WAITDRAIN) &&
467 	    (lkp->lk_flags & (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE |
468 		LK_SHARE_NONZERO | LK_WAIT_NONZERO)) == 0) {
469 		lkp->lk_flags &= ~LK_WAITDRAIN;
470 		wakeup((void *)&lkp->lk_flags);
471 	}
472 	mtx_unlock(lkp->lk_interlock);
473 	return (error);
474 }
475 
476 static int
477 acquiredrain(struct lock *lkp, int extflags) {
478 	int error;
479 
480 	if ((extflags & LK_NOWAIT) && (lkp->lk_flags & LK_ALL)) {
481 		return EBUSY;
482 	}
483 	while (lkp->lk_flags & LK_ALL) {
484 		lkp->lk_flags |= LK_WAITDRAIN;
485 		error = msleep(&lkp->lk_flags, lkp->lk_interlock, lkp->lk_prio,
486 			lkp->lk_wmesg,
487 			((extflags & LK_TIMELOCK) ? lkp->lk_timo : 0));
488 		if (error)
489 			return error;
490 		if (extflags & LK_SLEEPFAIL) {
491 			return ENOLCK;
492 		}
493 	}
494 	return 0;
495 }
496 
497 /*
498  * Initialize a lock; required before use.
499  */
500 void
501 lockinit(lkp, prio, wmesg, timo, flags)
502 	struct lock *lkp;
503 	int prio;
504 	const char *wmesg;
505 	int timo;
506 	int flags;
507 {
508 	CTR5(KTR_LOCK, "lockinit(): lkp == %p, prio == %d, wmesg == \"%s\", "
509 	    "timo == %d, flags = 0x%x\n", lkp, prio, wmesg, timo, flags);
510 
511 	lkp->lk_interlock = mtx_pool_alloc(mtxpool_lockbuilder);
512 	lkp->lk_flags = (flags & LK_EXTFLG_MASK);
513 	lkp->lk_sharecount = 0;
514 	lkp->lk_waitcount = 0;
515 	lkp->lk_exclusivecount = 0;
516 	lkp->lk_prio = prio;
517 	lkp->lk_timo = timo;
518 	lkp->lk_lockholder = LK_NOPROC;
519 	lkp->lk_newlock = NULL;
520 #ifdef DEBUG_LOCKS
521 	stack_zero(&lkp->lk_stack);
522 #endif
523 	lock_init(&lkp->lk_object, &lock_class_lockmgr, wmesg, NULL,
524 	    LO_RECURSABLE | LO_SLEEPABLE | LO_UPGRADABLE);
525 }
526 
527 /*
528  * Destroy a lock.
529  */
530 void
531 lockdestroy(lkp)
532 	struct lock *lkp;
533 {
534 
535 	CTR2(KTR_LOCK, "lockdestroy(): lkp == %p (lk_wmesg == \"%s\")",
536 	    lkp, lkp->lk_wmesg);
537 	lock_destroy(&lkp->lk_object);
538 }
539 
540 /*
541  * Disown the lockmgr.
542  */
543 void
544 lockmgr_disown(struct lock *lkp)
545 {
546 	struct thread *td;
547 
548 	td = curthread;
549 	KASSERT(panicstr != NULL || lkp->lk_exclusivecount,
550 	    ("%s: %p lockmgr must be exclusively locked", __func__, lkp));
551 	KASSERT(panicstr != NULL || lkp->lk_lockholder == td ||
552 	    lkp->lk_lockholder == LK_KERNPROC,
553 	    ("%s: %p lockmgr must be locked by curthread (%p)", __func__, lkp,
554 	    td));
555 
556 	/*
557 	 * Drop the lock reference and switch the owner.  This will result
558 	 * in an atomic operation like td_lock is only accessed by curthread
559 	 * and lk_lockholder only needs one write.  Note also that the lock
560 	 * owner can be alredy KERNPROC, so in that case just skip the
561 	 * decrement.
562 	 */
563 	if (lkp->lk_lockholder == td)
564 		td->td_locks--;
565 	lkp->lk_lockholder = LK_KERNPROC;
566 }
567 
568 /*
569  * Determine the status of a lock.
570  */
571 int
572 lockstatus(lkp, td)
573 	struct lock *lkp;
574 	struct thread *td;
575 {
576 	int lock_type = 0;
577 	int interlocked;
578 
579 	if (!kdb_active) {
580 		interlocked = 1;
581 		mtx_lock(lkp->lk_interlock);
582 	} else
583 		interlocked = 0;
584 	if (lkp->lk_exclusivecount != 0) {
585 		if (td == NULL || lkp->lk_lockholder == td)
586 			lock_type = LK_EXCLUSIVE;
587 		else
588 			lock_type = LK_EXCLOTHER;
589 	} else if (lkp->lk_sharecount != 0)
590 		lock_type = LK_SHARED;
591 	if (interlocked)
592 		mtx_unlock(lkp->lk_interlock);
593 	return (lock_type);
594 }
595 
596 /*
597  * Determine the number of holders of a lock.
598  */
599 int
600 lockcount(lkp)
601 	struct lock *lkp;
602 {
603 	int count;
604 
605 	mtx_lock(lkp->lk_interlock);
606 	count = lkp->lk_exclusivecount + lkp->lk_sharecount;
607 	mtx_unlock(lkp->lk_interlock);
608 	return (count);
609 }
610 
611 /*
612  * Determine the number of waiters on a lock.
613  */
614 int
615 lockwaiters(lkp)
616 	struct lock *lkp;
617 {
618 	int count;
619 
620 	mtx_lock(lkp->lk_interlock);
621 	count = lkp->lk_waitcount;
622 	mtx_unlock(lkp->lk_interlock);
623 	return (count);
624 }
625 
626 /*
627  * Print out information about state of a lock. Used by VOP_PRINT
628  * routines to display status about contained locks.
629  */
630 void
631 lockmgr_printinfo(lkp)
632 	struct lock *lkp;
633 {
634 
635 	if (lkp->lk_sharecount)
636 		printf(" lock type %s: SHARED (count %d)", lkp->lk_wmesg,
637 		    lkp->lk_sharecount);
638 	else if (lkp->lk_flags & LK_HAVE_EXCL)
639 		printf(" lock type %s: EXCL (count %d) by thread %p (pid %d)",
640 		    lkp->lk_wmesg, lkp->lk_exclusivecount,
641 		    lkp->lk_lockholder, lkp->lk_lockholder->td_proc->p_pid);
642 	if (lkp->lk_waitcount > 0)
643 		printf(" with %d pending", lkp->lk_waitcount);
644 #ifdef DEBUG_LOCKS
645 	stack_print_ddb(&lkp->lk_stack);
646 #endif
647 }
648 
649 #ifdef DDB
650 /*
651  * Check to see if a thread that is blocked on a sleep queue is actually
652  * blocked on a 'struct lock'.  If so, output some details and return true.
653  * If the lock has an exclusive owner, return that in *ownerp.
654  */
655 int
656 lockmgr_chain(struct thread *td, struct thread **ownerp)
657 {
658 	struct lock *lkp;
659 
660 	lkp = td->td_wchan;
661 
662 	/* Simple test to see if wchan points to a lockmgr lock. */
663 	if (LOCK_CLASS(&lkp->lk_object) == &lock_class_lockmgr &&
664 	    lkp->lk_wmesg == td->td_wmesg)
665 		goto ok;
666 
667 	/*
668 	 * If this thread is doing a DRAIN, then it would be asleep on
669 	 * &lkp->lk_flags rather than lkp.
670 	 */
671 	lkp = (struct lock *)((char *)td->td_wchan -
672 	    offsetof(struct lock, lk_flags));
673 	if (LOCK_CLASS(&lkp->lk_object) == &lock_class_lockmgr &&
674 	    lkp->lk_wmesg == td->td_wmesg && (lkp->lk_flags & LK_WAITDRAIN))
675 		goto ok;
676 
677 	/* Doen't seem to be a lockmgr lock. */
678 	return (0);
679 
680 ok:
681 	/* Ok, we think we have a lockmgr lock, so output some details. */
682 	db_printf("blocked on lk \"%s\" ", lkp->lk_wmesg);
683 	if (lkp->lk_sharecount) {
684 		db_printf("SHARED (count %d)\n", lkp->lk_sharecount);
685 		*ownerp = NULL;
686 	} else {
687 		db_printf("EXCL (count %d)\n", lkp->lk_exclusivecount);
688 		*ownerp = lkp->lk_lockholder;
689 	}
690 	return (1);
691 }
692 
693 void
694 db_show_lockmgr(struct lock_object *lock)
695 {
696 	struct thread *td;
697 	struct lock *lkp;
698 
699 	lkp = (struct lock *)lock;
700 
701 	db_printf(" lock type: %s\n", lkp->lk_wmesg);
702 	db_printf(" state: ");
703 	if (lkp->lk_sharecount)
704 		db_printf("SHARED (count %d)\n", lkp->lk_sharecount);
705 	else if (lkp->lk_flags & LK_HAVE_EXCL) {
706 		td = lkp->lk_lockholder;
707 		db_printf("EXCL (count %d) %p ", lkp->lk_exclusivecount, td);
708 		db_printf("(tid %d, pid %d, \"%s\")\n", td->td_tid,
709 		    td->td_proc->p_pid, td->td_name);
710 	} else
711 		db_printf("UNLOCKED\n");
712 	if (lkp->lk_waitcount > 0)
713 		db_printf(" waiters: %d\n", lkp->lk_waitcount);
714 }
715 #endif
716