xref: /freebsd/sys/kern/subr_witness.c (revision 1de7b4b805ddbf2429da511c053686ac4591ed89)
1 /*-
2  * SPDX-License-Identifier: BSD-3-Clause
3  *
4  * Copyright (c) 2008 Isilon Systems, Inc.
5  * Copyright (c) 2008 Ilya Maykov <ivmaykov@gmail.com>
6  * Copyright (c) 1998 Berkeley Software Design, Inc.
7  * All rights reserved.
8  *
9  * Redistribution and use in source and binary forms, with or without
10  * modification, are permitted provided that the following conditions
11  * are met:
12  * 1. Redistributions of source code must retain the above copyright
13  *    notice, this list of conditions and the following disclaimer.
14  * 2. Redistributions in binary form must reproduce the above copyright
15  *    notice, this list of conditions and the following disclaimer in the
16  *    documentation and/or other materials provided with the distribution.
17  * 3. Berkeley Software Design Inc's name may not be used to endorse or
18  *    promote products derived from this software without specific prior
19  *    written permission.
20  *
21  * THIS SOFTWARE IS PROVIDED BY BERKELEY SOFTWARE DESIGN INC ``AS IS'' AND
22  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
23  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
24  * ARE DISCLAIMED.  IN NO EVENT SHALL BERKELEY SOFTWARE DESIGN INC BE LIABLE
25  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
26  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
27  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
28  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
29  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
30  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
31  * SUCH DAMAGE.
32  *
33  *	from BSDI $Id: mutex_witness.c,v 1.1.2.20 2000/04/27 03:10:27 cp Exp $
34  *	and BSDI $Id: synch_machdep.c,v 2.3.2.39 2000/04/27 03:10:25 cp Exp $
35  */
36 
37 /*
38  * Implementation of the `witness' lock verifier.  Originally implemented for
39  * mutexes in BSD/OS.  Extended to handle generic lock objects and lock
40  * classes in FreeBSD.
41  */
42 
43 /*
44  *	Main Entry: witness
45  *	Pronunciation: 'wit-n&s
46  *	Function: noun
47  *	Etymology: Middle English witnesse, from Old English witnes knowledge,
48  *	    testimony, witness, from 2wit
49  *	Date: before 12th century
50  *	1 : attestation of a fact or event : TESTIMONY
51  *	2 : one that gives evidence; specifically : one who testifies in
52  *	    a cause or before a judicial tribunal
53  *	3 : one asked to be present at a transaction so as to be able to
54  *	    testify to its having taken place
55  *	4 : one who has personal knowledge of something
56  *	5 a : something serving as evidence or proof : SIGN
57  *	  b : public affirmation by word or example of usually
58  *	      religious faith or conviction <the heroic witness to divine
59  *	      life -- Pilot>
60  *	6 capitalized : a member of the Jehovah's Witnesses
61  */
62 
63 /*
64  * Special rules concerning Giant and lock orders:
65  *
66  * 1) Giant must be acquired before any other mutexes.  Stated another way,
67  *    no other mutex may be held when Giant is acquired.
68  *
69  * 2) Giant must be released when blocking on a sleepable lock.
70  *
71  * This rule is less obvious, but is a result of Giant providing the same
72  * semantics as spl().  Basically, when a thread sleeps, it must release
73  * Giant.  When a thread blocks on a sleepable lock, it sleeps.  Hence rule
74  * 2).
75  *
76  * 3) Giant may be acquired before or after sleepable locks.
77  *
78  * This rule is also not quite as obvious.  Giant may be acquired after
79  * a sleepable lock because it is a non-sleepable lock and non-sleepable
80  * locks may always be acquired while holding a sleepable lock.  The second
81  * case, Giant before a sleepable lock, follows from rule 2) above.  Suppose
82  * you have two threads T1 and T2 and a sleepable lock X.  Suppose that T1
83  * acquires X and blocks on Giant.  Then suppose that T2 acquires Giant and
84  * blocks on X.  When T2 blocks on X, T2 will release Giant allowing T1 to
85  * execute.  Thus, acquiring Giant both before and after a sleepable lock
86  * will not result in a lock order reversal.
87  */
88 
89 #include <sys/cdefs.h>
90 __FBSDID("$FreeBSD$");
91 
92 #include "opt_ddb.h"
93 #include "opt_hwpmc_hooks.h"
94 #include "opt_stack.h"
95 #include "opt_witness.h"
96 
97 #include <sys/param.h>
98 #include <sys/bus.h>
99 #include <sys/kdb.h>
100 #include <sys/kernel.h>
101 #include <sys/ktr.h>
102 #include <sys/lock.h>
103 #include <sys/malloc.h>
104 #include <sys/mutex.h>
105 #include <sys/priv.h>
106 #include <sys/proc.h>
107 #include <sys/sbuf.h>
108 #include <sys/sched.h>
109 #include <sys/stack.h>
110 #include <sys/sysctl.h>
111 #include <sys/syslog.h>
112 #include <sys/systm.h>
113 
114 #ifdef DDB
115 #include <ddb/ddb.h>
116 #endif
117 
118 #include <machine/stdarg.h>
119 
120 #if !defined(DDB) && !defined(STACK)
121 #error "DDB or STACK options are required for WITNESS"
122 #endif
123 
124 /* Note that these traces do not work with KTR_ALQ. */
125 #if 0
126 #define	KTR_WITNESS	KTR_SUBSYS
127 #else
128 #define	KTR_WITNESS	0
129 #endif
130 
131 #define	LI_RECURSEMASK	0x0000ffff	/* Recursion depth of lock instance. */
132 #define	LI_EXCLUSIVE	0x00010000	/* Exclusive lock instance. */
133 #define	LI_NORELEASE	0x00020000	/* Lock not allowed to be released. */
134 
135 /* Define this to check for blessed mutexes */
136 #undef BLESSING
137 
138 #ifndef WITNESS_COUNT
139 #define	WITNESS_COUNT 		1536
140 #endif
141 #define	WITNESS_HASH_SIZE	251	/* Prime, gives load factor < 2 */
142 #define	WITNESS_PENDLIST	(2048 + MAXCPU)
143 
144 /* Allocate 256 KB of stack data space */
145 #define	WITNESS_LO_DATA_COUNT	2048
146 
147 /* Prime, gives load factor of ~2 at full load */
148 #define	WITNESS_LO_HASH_SIZE	1021
149 
150 /*
151  * XXX: This is somewhat bogus, as we assume here that at most 2048 threads
152  * will hold LOCK_NCHILDREN locks.  We handle failure ok, and we should
153  * probably be safe for the most part, but it's still a SWAG.
154  */
155 #define	LOCK_NCHILDREN	5
156 #define	LOCK_CHILDCOUNT	2048
157 
158 #define	MAX_W_NAME	64
159 
160 #define	FULLGRAPH_SBUF_SIZE	512
161 
162 /*
163  * These flags go in the witness relationship matrix and describe the
164  * relationship between any two struct witness objects.
165  */
166 #define	WITNESS_UNRELATED        0x00    /* No lock order relation. */
167 #define	WITNESS_PARENT           0x01    /* Parent, aka direct ancestor. */
168 #define	WITNESS_ANCESTOR         0x02    /* Direct or indirect ancestor. */
169 #define	WITNESS_CHILD            0x04    /* Child, aka direct descendant. */
170 #define	WITNESS_DESCENDANT       0x08    /* Direct or indirect descendant. */
171 #define	WITNESS_ANCESTOR_MASK    (WITNESS_PARENT | WITNESS_ANCESTOR)
172 #define	WITNESS_DESCENDANT_MASK  (WITNESS_CHILD | WITNESS_DESCENDANT)
173 #define	WITNESS_RELATED_MASK						\
174 	(WITNESS_ANCESTOR_MASK | WITNESS_DESCENDANT_MASK)
175 #define	WITNESS_REVERSAL         0x10    /* A lock order reversal has been
176 					  * observed. */
177 #define	WITNESS_RESERVED1        0x20    /* Unused flag, reserved. */
178 #define	WITNESS_RESERVED2        0x40    /* Unused flag, reserved. */
179 #define	WITNESS_LOCK_ORDER_KNOWN 0x80    /* This lock order is known. */
180 
181 /* Descendant to ancestor flags */
182 #define	WITNESS_DTOA(x)	(((x) & WITNESS_RELATED_MASK) >> 2)
183 
184 /* Ancestor to descendant flags */
185 #define	WITNESS_ATOD(x)	(((x) & WITNESS_RELATED_MASK) << 2)
186 
187 #define	WITNESS_INDEX_ASSERT(i)						\
188 	MPASS((i) > 0 && (i) <= w_max_used_index && (i) < witness_count)
189 
190 static MALLOC_DEFINE(M_WITNESS, "Witness", "Witness");
191 
192 /*
193  * Lock instances.  A lock instance is the data associated with a lock while
194  * it is held by witness.  For example, a lock instance will hold the
195  * recursion count of a lock.  Lock instances are held in lists.  Spin locks
196  * are held in a per-cpu list while sleep locks are held in per-thread list.
197  */
198 struct lock_instance {
199 	struct lock_object	*li_lock;
200 	const char		*li_file;
201 	int			li_line;
202 	u_int			li_flags;
203 };
204 
205 /*
206  * A simple list type used to build the list of locks held by a thread
207  * or CPU.  We can't simply embed the list in struct lock_object since a
208  * lock may be held by more than one thread if it is a shared lock.  Locks
209  * are added to the head of the list, so we fill up each list entry from
210  * "the back" logically.  To ease some of the arithmetic, we actually fill
211  * in each list entry the normal way (children[0] then children[1], etc.) but
212  * when we traverse the list we read children[count-1] as the first entry
213  * down to children[0] as the final entry.
214  */
215 struct lock_list_entry {
216 	struct lock_list_entry	*ll_next;
217 	struct lock_instance	ll_children[LOCK_NCHILDREN];
218 	u_int			ll_count;
219 };
220 
221 /*
222  * The main witness structure. One of these per named lock type in the system
223  * (for example, "vnode interlock").
224  */
225 struct witness {
226 	char  			w_name[MAX_W_NAME];
227 	uint32_t 		w_index;  /* Index in the relationship matrix */
228 	struct lock_class	*w_class;
229 	STAILQ_ENTRY(witness) 	w_list;		/* List of all witnesses. */
230 	STAILQ_ENTRY(witness) 	w_typelist;	/* Witnesses of a type. */
231 	struct witness		*w_hash_next; /* Linked list in hash buckets. */
232 	const char		*w_file; /* File where last acquired */
233 	uint32_t 		w_line; /* Line where last acquired */
234 	uint32_t 		w_refcount;
235 	uint16_t 		w_num_ancestors; /* direct/indirect
236 						  * ancestor count */
237 	uint16_t 		w_num_descendants; /* direct/indirect
238 						    * descendant count */
239 	int16_t 		w_ddb_level;
240 	unsigned		w_displayed:1;
241 	unsigned		w_reversed:1;
242 };
243 
244 STAILQ_HEAD(witness_list, witness);
245 
246 /*
247  * The witness hash table. Keys are witness names (const char *), elements are
248  * witness objects (struct witness *).
249  */
250 struct witness_hash {
251 	struct witness	*wh_array[WITNESS_HASH_SIZE];
252 	uint32_t	wh_size;
253 	uint32_t	wh_count;
254 };
255 
256 /*
257  * Key type for the lock order data hash table.
258  */
259 struct witness_lock_order_key {
260 	uint16_t	from;
261 	uint16_t	to;
262 };
263 
264 struct witness_lock_order_data {
265 	struct stack			wlod_stack;
266 	struct witness_lock_order_key	wlod_key;
267 	struct witness_lock_order_data	*wlod_next;
268 };
269 
270 /*
271  * The witness lock order data hash table. Keys are witness index tuples
272  * (struct witness_lock_order_key), elements are lock order data objects
273  * (struct witness_lock_order_data).
274  */
275 struct witness_lock_order_hash {
276 	struct witness_lock_order_data	*wloh_array[WITNESS_LO_HASH_SIZE];
277 	u_int	wloh_size;
278 	u_int	wloh_count;
279 };
280 
281 #ifdef BLESSING
282 struct witness_blessed {
283 	const char	*b_lock1;
284 	const char	*b_lock2;
285 };
286 #endif
287 
288 struct witness_pendhelp {
289 	const char		*wh_type;
290 	struct lock_object	*wh_lock;
291 };
292 
293 struct witness_order_list_entry {
294 	const char		*w_name;
295 	struct lock_class	*w_class;
296 };
297 
298 /*
299  * Returns 0 if one of the locks is a spin lock and the other is not.
300  * Returns 1 otherwise.
301  */
302 static __inline int
303 witness_lock_type_equal(struct witness *w1, struct witness *w2)
304 {
305 
306 	return ((w1->w_class->lc_flags & (LC_SLEEPLOCK | LC_SPINLOCK)) ==
307 		(w2->w_class->lc_flags & (LC_SLEEPLOCK | LC_SPINLOCK)));
308 }
309 
310 static __inline int
311 witness_lock_order_key_equal(const struct witness_lock_order_key *a,
312     const struct witness_lock_order_key *b)
313 {
314 
315 	return (a->from == b->from && a->to == b->to);
316 }
317 
318 static int	_isitmyx(struct witness *w1, struct witness *w2, int rmask,
319 		    const char *fname);
320 static void	adopt(struct witness *parent, struct witness *child);
321 #ifdef BLESSING
322 static int	blessed(struct witness *, struct witness *);
323 #endif
324 static void	depart(struct witness *w);
325 static struct witness	*enroll(const char *description,
326 			    struct lock_class *lock_class);
327 static struct lock_instance	*find_instance(struct lock_list_entry *list,
328 				    const struct lock_object *lock);
329 static int	isitmychild(struct witness *parent, struct witness *child);
330 static int	isitmydescendant(struct witness *parent, struct witness *child);
331 static void	itismychild(struct witness *parent, struct witness *child);
332 static int	sysctl_debug_witness_badstacks(SYSCTL_HANDLER_ARGS);
333 static int	sysctl_debug_witness_watch(SYSCTL_HANDLER_ARGS);
334 static int	sysctl_debug_witness_fullgraph(SYSCTL_HANDLER_ARGS);
335 static int	sysctl_debug_witness_channel(SYSCTL_HANDLER_ARGS);
336 static void	witness_add_fullgraph(struct sbuf *sb, struct witness *parent);
337 #ifdef DDB
338 static void	witness_ddb_compute_levels(void);
339 static void	witness_ddb_display(int(*)(const char *fmt, ...));
340 static void	witness_ddb_display_descendants(int(*)(const char *fmt, ...),
341 		    struct witness *, int indent);
342 static void	witness_ddb_display_list(int(*prnt)(const char *fmt, ...),
343 		    struct witness_list *list);
344 static void	witness_ddb_level_descendants(struct witness *parent, int l);
345 static void	witness_ddb_list(struct thread *td);
346 #endif
347 static void	witness_debugger(int cond, const char *msg);
348 static void	witness_free(struct witness *m);
349 static struct witness	*witness_get(void);
350 static uint32_t	witness_hash_djb2(const uint8_t *key, uint32_t size);
351 static struct witness	*witness_hash_get(const char *key);
352 static void	witness_hash_put(struct witness *w);
353 static void	witness_init_hash_tables(void);
354 static void	witness_increment_graph_generation(void);
355 static void	witness_lock_list_free(struct lock_list_entry *lle);
356 static struct lock_list_entry	*witness_lock_list_get(void);
357 static int	witness_lock_order_add(struct witness *parent,
358 		    struct witness *child);
359 static int	witness_lock_order_check(struct witness *parent,
360 		    struct witness *child);
361 static struct witness_lock_order_data	*witness_lock_order_get(
362 					    struct witness *parent,
363 					    struct witness *child);
364 static void	witness_list_lock(struct lock_instance *instance,
365 		    int (*prnt)(const char *fmt, ...));
366 static int	witness_output(const char *fmt, ...) __printflike(1, 2);
367 static int	witness_voutput(const char *fmt, va_list ap) __printflike(1, 0);
368 static void	witness_setflag(struct lock_object *lock, int flag, int set);
369 
370 static SYSCTL_NODE(_debug, OID_AUTO, witness, CTLFLAG_RW, NULL,
371     "Witness Locking");
372 
373 /*
374  * If set to 0, lock order checking is disabled.  If set to -1,
375  * witness is completely disabled.  Otherwise witness performs full
376  * lock order checking for all locks.  At runtime, lock order checking
377  * may be toggled.  However, witness cannot be reenabled once it is
378  * completely disabled.
379  */
380 static int witness_watch = 1;
381 SYSCTL_PROC(_debug_witness, OID_AUTO, watch, CTLFLAG_RWTUN | CTLTYPE_INT, NULL, 0,
382     sysctl_debug_witness_watch, "I", "witness is watching lock operations");
383 
384 #ifdef KDB
385 /*
386  * When KDB is enabled and witness_kdb is 1, it will cause the system
387  * to drop into kdebug() when:
388  *	- a lock hierarchy violation occurs
389  *	- locks are held when going to sleep.
390  */
391 #ifdef WITNESS_KDB
392 int	witness_kdb = 1;
393 #else
394 int	witness_kdb = 0;
395 #endif
396 SYSCTL_INT(_debug_witness, OID_AUTO, kdb, CTLFLAG_RWTUN, &witness_kdb, 0, "");
397 #endif /* KDB */
398 
399 #if defined(DDB) || defined(KDB)
400 /*
401  * When DDB or KDB is enabled and witness_trace is 1, it will cause the system
402  * to print a stack trace:
403  *	- a lock hierarchy violation occurs
404  *	- locks are held when going to sleep.
405  */
406 int	witness_trace = 1;
407 SYSCTL_INT(_debug_witness, OID_AUTO, trace, CTLFLAG_RWTUN, &witness_trace, 0, "");
408 #endif /* DDB || KDB */
409 
410 #ifdef WITNESS_SKIPSPIN
411 int	witness_skipspin = 1;
412 #else
413 int	witness_skipspin = 0;
414 #endif
415 SYSCTL_INT(_debug_witness, OID_AUTO, skipspin, CTLFLAG_RDTUN, &witness_skipspin, 0, "");
416 
417 int badstack_sbuf_size;
418 
419 int witness_count = WITNESS_COUNT;
420 SYSCTL_INT(_debug_witness, OID_AUTO, witness_count, CTLFLAG_RDTUN,
421     &witness_count, 0, "");
422 
423 /*
424  * Output channel for witness messages.  By default we print to the console.
425  */
426 enum witness_channel {
427 	WITNESS_CONSOLE,
428 	WITNESS_LOG,
429 	WITNESS_NONE,
430 };
431 
432 static enum witness_channel witness_channel = WITNESS_CONSOLE;
433 SYSCTL_PROC(_debug_witness, OID_AUTO, output_channel, CTLTYPE_STRING |
434     CTLFLAG_RWTUN, NULL, 0, sysctl_debug_witness_channel, "A",
435     "Output channel for warnings");
436 
437 /*
438  * Call this to print out the relations between locks.
439  */
440 SYSCTL_PROC(_debug_witness, OID_AUTO, fullgraph, CTLTYPE_STRING | CTLFLAG_RD,
441     NULL, 0, sysctl_debug_witness_fullgraph, "A", "Show locks relation graphs");
442 
443 /*
444  * Call this to print out the witness faulty stacks.
445  */
446 SYSCTL_PROC(_debug_witness, OID_AUTO, badstacks, CTLTYPE_STRING | CTLFLAG_RD,
447     NULL, 0, sysctl_debug_witness_badstacks, "A", "Show bad witness stacks");
448 
449 static struct mtx w_mtx;
450 
451 /* w_list */
452 static struct witness_list w_free = STAILQ_HEAD_INITIALIZER(w_free);
453 static struct witness_list w_all = STAILQ_HEAD_INITIALIZER(w_all);
454 
455 /* w_typelist */
456 static struct witness_list w_spin = STAILQ_HEAD_INITIALIZER(w_spin);
457 static struct witness_list w_sleep = STAILQ_HEAD_INITIALIZER(w_sleep);
458 
459 /* lock list */
460 static struct lock_list_entry *w_lock_list_free = NULL;
461 static struct witness_pendhelp pending_locks[WITNESS_PENDLIST];
462 static u_int pending_cnt;
463 
464 static int w_free_cnt, w_spin_cnt, w_sleep_cnt;
465 SYSCTL_INT(_debug_witness, OID_AUTO, free_cnt, CTLFLAG_RD, &w_free_cnt, 0, "");
466 SYSCTL_INT(_debug_witness, OID_AUTO, spin_cnt, CTLFLAG_RD, &w_spin_cnt, 0, "");
467 SYSCTL_INT(_debug_witness, OID_AUTO, sleep_cnt, CTLFLAG_RD, &w_sleep_cnt, 0,
468     "");
469 
470 static struct witness *w_data;
471 static uint8_t **w_rmatrix;
472 static struct lock_list_entry w_locklistdata[LOCK_CHILDCOUNT];
473 static struct witness_hash w_hash;	/* The witness hash table. */
474 
475 /* The lock order data hash */
476 static struct witness_lock_order_data w_lodata[WITNESS_LO_DATA_COUNT];
477 static struct witness_lock_order_data *w_lofree = NULL;
478 static struct witness_lock_order_hash w_lohash;
479 static int w_max_used_index = 0;
480 static unsigned int w_generation = 0;
481 static const char w_notrunning[] = "Witness not running\n";
482 static const char w_stillcold[] = "Witness is still cold\n";
483 
484 
485 static struct witness_order_list_entry order_lists[] = {
486 	/*
487 	 * sx locks
488 	 */
489 	{ "proctree", &lock_class_sx },
490 	{ "allproc", &lock_class_sx },
491 	{ "allprison", &lock_class_sx },
492 	{ NULL, NULL },
493 	/*
494 	 * Various mutexes
495 	 */
496 	{ "Giant", &lock_class_mtx_sleep },
497 	{ "pipe mutex", &lock_class_mtx_sleep },
498 	{ "sigio lock", &lock_class_mtx_sleep },
499 	{ "process group", &lock_class_mtx_sleep },
500 	{ "process lock", &lock_class_mtx_sleep },
501 	{ "session", &lock_class_mtx_sleep },
502 	{ "uidinfo hash", &lock_class_rw },
503 #ifdef	HWPMC_HOOKS
504 	{ "pmc-sleep", &lock_class_mtx_sleep },
505 #endif
506 	{ "time lock", &lock_class_mtx_sleep },
507 	{ NULL, NULL },
508 	/*
509 	 * umtx
510 	 */
511 	{ "umtx lock", &lock_class_mtx_sleep },
512 	{ NULL, NULL },
513 	/*
514 	 * Sockets
515 	 */
516 	{ "accept", &lock_class_mtx_sleep },
517 	{ "so_snd", &lock_class_mtx_sleep },
518 	{ "so_rcv", &lock_class_mtx_sleep },
519 	{ "sellck", &lock_class_mtx_sleep },
520 	{ NULL, NULL },
521 	/*
522 	 * Routing
523 	 */
524 	{ "so_rcv", &lock_class_mtx_sleep },
525 	{ "radix node head", &lock_class_rw },
526 	{ "rtentry", &lock_class_mtx_sleep },
527 	{ "ifaddr", &lock_class_mtx_sleep },
528 	{ NULL, NULL },
529 	/*
530 	 * IPv4 multicast:
531 	 * protocol locks before interface locks, after UDP locks.
532 	 */
533 	{ "udpinp", &lock_class_rw },
534 	{ "in_multi_mtx", &lock_class_mtx_sleep },
535 	{ "igmp_mtx", &lock_class_mtx_sleep },
536 	{ "if_addr_lock", &lock_class_rw },
537 	{ NULL, NULL },
538 	/*
539 	 * IPv6 multicast:
540 	 * protocol locks before interface locks, after UDP locks.
541 	 */
542 	{ "udpinp", &lock_class_rw },
543 	{ "in6_multi_mtx", &lock_class_mtx_sleep },
544 	{ "mld_mtx", &lock_class_mtx_sleep },
545 	{ "if_addr_lock", &lock_class_rw },
546 	{ NULL, NULL },
547 	/*
548 	 * UNIX Domain Sockets
549 	 */
550 	{ "unp_link_rwlock", &lock_class_rw },
551 	{ "unp_list_lock", &lock_class_mtx_sleep },
552 	{ "unp", &lock_class_mtx_sleep },
553 	{ "so_snd", &lock_class_mtx_sleep },
554 	{ NULL, NULL },
555 	/*
556 	 * UDP/IP
557 	 */
558 	{ "udp", &lock_class_rw },
559 	{ "udpinp", &lock_class_rw },
560 	{ "so_snd", &lock_class_mtx_sleep },
561 	{ NULL, NULL },
562 	/*
563 	 * TCP/IP
564 	 */
565 	{ "tcp", &lock_class_rw },
566 	{ "tcpinp", &lock_class_rw },
567 	{ "so_snd", &lock_class_mtx_sleep },
568 	{ NULL, NULL },
569 	/*
570 	 * BPF
571 	 */
572 	{ "bpf global lock", &lock_class_mtx_sleep },
573 	{ "bpf interface lock", &lock_class_rw },
574 	{ "bpf cdev lock", &lock_class_mtx_sleep },
575 	{ NULL, NULL },
576 	/*
577 	 * NFS server
578 	 */
579 	{ "nfsd_mtx", &lock_class_mtx_sleep },
580 	{ "so_snd", &lock_class_mtx_sleep },
581 	{ NULL, NULL },
582 
583 	/*
584 	 * IEEE 802.11
585 	 */
586 	{ "802.11 com lock", &lock_class_mtx_sleep},
587 	{ NULL, NULL },
588 	/*
589 	 * Network drivers
590 	 */
591 	{ "network driver", &lock_class_mtx_sleep},
592 	{ NULL, NULL },
593 
594 	/*
595 	 * Netgraph
596 	 */
597 	{ "ng_node", &lock_class_mtx_sleep },
598 	{ "ng_worklist", &lock_class_mtx_sleep },
599 	{ NULL, NULL },
600 	/*
601 	 * CDEV
602 	 */
603 	{ "vm map (system)", &lock_class_mtx_sleep },
604 	{ "vm pagequeue", &lock_class_mtx_sleep },
605 	{ "vnode interlock", &lock_class_mtx_sleep },
606 	{ "cdev", &lock_class_mtx_sleep },
607 	{ NULL, NULL },
608 	/*
609 	 * VM
610 	 */
611 	{ "vm map (user)", &lock_class_sx },
612 	{ "vm object", &lock_class_rw },
613 	{ "vm page", &lock_class_mtx_sleep },
614 	{ "vm pagequeue", &lock_class_mtx_sleep },
615 	{ "pmap pv global", &lock_class_rw },
616 	{ "pmap", &lock_class_mtx_sleep },
617 	{ "pmap pv list", &lock_class_rw },
618 	{ "vm page free queue", &lock_class_mtx_sleep },
619 	{ NULL, NULL },
620 	/*
621 	 * kqueue/VFS interaction
622 	 */
623 	{ "kqueue", &lock_class_mtx_sleep },
624 	{ "struct mount mtx", &lock_class_mtx_sleep },
625 	{ "vnode interlock", &lock_class_mtx_sleep },
626 	{ NULL, NULL },
627 	/*
628 	 * VFS namecache
629 	 */
630 	{ "ncvn", &lock_class_mtx_sleep },
631 	{ "ncbuc", &lock_class_rw },
632 	{ "vnode interlock", &lock_class_mtx_sleep },
633 	{ "ncneg", &lock_class_mtx_sleep },
634 	{ NULL, NULL },
635 	/*
636 	 * ZFS locking
637 	 */
638 	{ "dn->dn_mtx", &lock_class_sx },
639 	{ "dr->dt.di.dr_mtx", &lock_class_sx },
640 	{ "db->db_mtx", &lock_class_sx },
641 	{ NULL, NULL },
642 	/*
643 	 * spin locks
644 	 */
645 #ifdef SMP
646 	{ "ap boot", &lock_class_mtx_spin },
647 #endif
648 	{ "rm.mutex_mtx", &lock_class_mtx_spin },
649 	{ "sio", &lock_class_mtx_spin },
650 #ifdef __i386__
651 	{ "cy", &lock_class_mtx_spin },
652 #endif
653 #ifdef __sparc64__
654 	{ "pcib_mtx", &lock_class_mtx_spin },
655 	{ "rtc_mtx", &lock_class_mtx_spin },
656 #endif
657 	{ "scc_hwmtx", &lock_class_mtx_spin },
658 	{ "uart_hwmtx", &lock_class_mtx_spin },
659 	{ "fast_taskqueue", &lock_class_mtx_spin },
660 	{ "intr table", &lock_class_mtx_spin },
661 #ifdef	HWPMC_HOOKS
662 	{ "pmc-per-proc", &lock_class_mtx_spin },
663 #endif
664 	{ "process slock", &lock_class_mtx_spin },
665 	{ "syscons video lock", &lock_class_mtx_spin },
666 	{ "sleepq chain", &lock_class_mtx_spin },
667 	{ "rm_spinlock", &lock_class_mtx_spin },
668 	{ "turnstile chain", &lock_class_mtx_spin },
669 	{ "turnstile lock", &lock_class_mtx_spin },
670 	{ "sched lock", &lock_class_mtx_spin },
671 	{ "td_contested", &lock_class_mtx_spin },
672 	{ "callout", &lock_class_mtx_spin },
673 	{ "entropy harvest mutex", &lock_class_mtx_spin },
674 #ifdef SMP
675 	{ "smp rendezvous", &lock_class_mtx_spin },
676 #endif
677 #ifdef __powerpc__
678 	{ "tlb0", &lock_class_mtx_spin },
679 #endif
680 	/*
681 	 * leaf locks
682 	 */
683 	{ "intrcnt", &lock_class_mtx_spin },
684 	{ "icu", &lock_class_mtx_spin },
685 #if defined(SMP) && defined(__sparc64__)
686 	{ "ipi", &lock_class_mtx_spin },
687 #endif
688 #ifdef __i386__
689 	{ "allpmaps", &lock_class_mtx_spin },
690 	{ "descriptor tables", &lock_class_mtx_spin },
691 #endif
692 	{ "clk", &lock_class_mtx_spin },
693 	{ "cpuset", &lock_class_mtx_spin },
694 	{ "mprof lock", &lock_class_mtx_spin },
695 	{ "zombie lock", &lock_class_mtx_spin },
696 	{ "ALD Queue", &lock_class_mtx_spin },
697 #if defined(__i386__) || defined(__amd64__)
698 	{ "pcicfg", &lock_class_mtx_spin },
699 	{ "NDIS thread lock", &lock_class_mtx_spin },
700 #endif
701 	{ "tw_osl_io_lock", &lock_class_mtx_spin },
702 	{ "tw_osl_q_lock", &lock_class_mtx_spin },
703 	{ "tw_cl_io_lock", &lock_class_mtx_spin },
704 	{ "tw_cl_intr_lock", &lock_class_mtx_spin },
705 	{ "tw_cl_gen_lock", &lock_class_mtx_spin },
706 #ifdef	HWPMC_HOOKS
707 	{ "pmc-leaf", &lock_class_mtx_spin },
708 #endif
709 	{ "blocked lock", &lock_class_mtx_spin },
710 	{ NULL, NULL },
711 	{ NULL, NULL }
712 };
713 
714 #ifdef BLESSING
715 /*
716  * Pairs of locks which have been blessed
717  * Don't complain about order problems with blessed locks
718  */
719 static struct witness_blessed blessed_list[] = {
720 };
721 #endif
722 
723 /*
724  * This global is set to 0 once it becomes safe to use the witness code.
725  */
726 static int witness_cold = 1;
727 
728 /*
729  * This global is set to 1 once the static lock orders have been enrolled
730  * so that a warning can be issued for any spin locks enrolled later.
731  */
732 static int witness_spin_warn = 0;
733 
734 /* Trim useless garbage from filenames. */
735 static const char *
736 fixup_filename(const char *file)
737 {
738 
739 	if (file == NULL)
740 		return (NULL);
741 	while (strncmp(file, "../", 3) == 0)
742 		file += 3;
743 	return (file);
744 }
745 
746 /*
747  * The WITNESS-enabled diagnostic code.  Note that the witness code does
748  * assume that the early boot is single-threaded at least until after this
749  * routine is completed.
750  */
751 static void
752 witness_initialize(void *dummy __unused)
753 {
754 	struct lock_object *lock;
755 	struct witness_order_list_entry *order;
756 	struct witness *w, *w1;
757 	int i;
758 
759 	w_data = malloc(sizeof (struct witness) * witness_count, M_WITNESS,
760 	    M_WAITOK | M_ZERO);
761 
762 	w_rmatrix = malloc(sizeof(*w_rmatrix) * (witness_count + 1),
763 	    M_WITNESS, M_WAITOK | M_ZERO);
764 
765 	for (i = 0; i < witness_count + 1; i++) {
766 		w_rmatrix[i] = malloc(sizeof(*w_rmatrix[i]) *
767 		    (witness_count + 1), M_WITNESS, M_WAITOK | M_ZERO);
768 	}
769 	badstack_sbuf_size = witness_count * 256;
770 
771 	/*
772 	 * We have to release Giant before initializing its witness
773 	 * structure so that WITNESS doesn't get confused.
774 	 */
775 	mtx_unlock(&Giant);
776 	mtx_assert(&Giant, MA_NOTOWNED);
777 
778 	CTR1(KTR_WITNESS, "%s: initializing witness", __func__);
779 	mtx_init(&w_mtx, "witness lock", NULL, MTX_SPIN | MTX_QUIET |
780 	    MTX_NOWITNESS | MTX_NOPROFILE);
781 	for (i = witness_count - 1; i >= 0; i--) {
782 		w = &w_data[i];
783 		memset(w, 0, sizeof(*w));
784 		w_data[i].w_index = i;	/* Witness index never changes. */
785 		witness_free(w);
786 	}
787 	KASSERT(STAILQ_FIRST(&w_free)->w_index == 0,
788 	    ("%s: Invalid list of free witness objects", __func__));
789 
790 	/* Witness with index 0 is not used to aid in debugging. */
791 	STAILQ_REMOVE_HEAD(&w_free, w_list);
792 	w_free_cnt--;
793 
794 	for (i = 0; i < witness_count; i++) {
795 		memset(w_rmatrix[i], 0, sizeof(*w_rmatrix[i]) *
796 		    (witness_count + 1));
797 	}
798 
799 	for (i = 0; i < LOCK_CHILDCOUNT; i++)
800 		witness_lock_list_free(&w_locklistdata[i]);
801 	witness_init_hash_tables();
802 
803 	/* First add in all the specified order lists. */
804 	for (order = order_lists; order->w_name != NULL; order++) {
805 		w = enroll(order->w_name, order->w_class);
806 		if (w == NULL)
807 			continue;
808 		w->w_file = "order list";
809 		for (order++; order->w_name != NULL; order++) {
810 			w1 = enroll(order->w_name, order->w_class);
811 			if (w1 == NULL)
812 				continue;
813 			w1->w_file = "order list";
814 			itismychild(w, w1);
815 			w = w1;
816 		}
817 	}
818 	witness_spin_warn = 1;
819 
820 	/* Iterate through all locks and add them to witness. */
821 	for (i = 0; pending_locks[i].wh_lock != NULL; i++) {
822 		lock = pending_locks[i].wh_lock;
823 		KASSERT(lock->lo_flags & LO_WITNESS,
824 		    ("%s: lock %s is on pending list but not LO_WITNESS",
825 		    __func__, lock->lo_name));
826 		lock->lo_witness = enroll(pending_locks[i].wh_type,
827 		    LOCK_CLASS(lock));
828 	}
829 
830 	/* Mark the witness code as being ready for use. */
831 	witness_cold = 0;
832 
833 	mtx_lock(&Giant);
834 }
835 SYSINIT(witness_init, SI_SUB_WITNESS, SI_ORDER_FIRST, witness_initialize,
836     NULL);
837 
838 void
839 witness_init(struct lock_object *lock, const char *type)
840 {
841 	struct lock_class *class;
842 
843 	/* Various sanity checks. */
844 	class = LOCK_CLASS(lock);
845 	if ((lock->lo_flags & LO_RECURSABLE) != 0 &&
846 	    (class->lc_flags & LC_RECURSABLE) == 0)
847 		kassert_panic("%s: lock (%s) %s can not be recursable",
848 		    __func__, class->lc_name, lock->lo_name);
849 	if ((lock->lo_flags & LO_SLEEPABLE) != 0 &&
850 	    (class->lc_flags & LC_SLEEPABLE) == 0)
851 		kassert_panic("%s: lock (%s) %s can not be sleepable",
852 		    __func__, class->lc_name, lock->lo_name);
853 	if ((lock->lo_flags & LO_UPGRADABLE) != 0 &&
854 	    (class->lc_flags & LC_UPGRADABLE) == 0)
855 		kassert_panic("%s: lock (%s) %s can not be upgradable",
856 		    __func__, class->lc_name, lock->lo_name);
857 
858 	/*
859 	 * If we shouldn't watch this lock, then just clear lo_witness.
860 	 * Otherwise, if witness_cold is set, then it is too early to
861 	 * enroll this lock, so defer it to witness_initialize() by adding
862 	 * it to the pending_locks list.  If it is not too early, then enroll
863 	 * the lock now.
864 	 */
865 	if (witness_watch < 1 || panicstr != NULL ||
866 	    (lock->lo_flags & LO_WITNESS) == 0)
867 		lock->lo_witness = NULL;
868 	else if (witness_cold) {
869 		pending_locks[pending_cnt].wh_lock = lock;
870 		pending_locks[pending_cnt++].wh_type = type;
871 		if (pending_cnt > WITNESS_PENDLIST)
872 			panic("%s: pending locks list is too small, "
873 			    "increase WITNESS_PENDLIST\n",
874 			    __func__);
875 	} else
876 		lock->lo_witness = enroll(type, class);
877 }
878 
879 void
880 witness_destroy(struct lock_object *lock)
881 {
882 	struct lock_class *class;
883 	struct witness *w;
884 
885 	class = LOCK_CLASS(lock);
886 
887 	if (witness_cold)
888 		panic("lock (%s) %s destroyed while witness_cold",
889 		    class->lc_name, lock->lo_name);
890 
891 	/* XXX: need to verify that no one holds the lock */
892 	if ((lock->lo_flags & LO_WITNESS) == 0 || lock->lo_witness == NULL)
893 		return;
894 	w = lock->lo_witness;
895 
896 	mtx_lock_spin(&w_mtx);
897 	MPASS(w->w_refcount > 0);
898 	w->w_refcount--;
899 
900 	if (w->w_refcount == 0)
901 		depart(w);
902 	mtx_unlock_spin(&w_mtx);
903 }
904 
905 #ifdef DDB
906 static void
907 witness_ddb_compute_levels(void)
908 {
909 	struct witness *w;
910 
911 	/*
912 	 * First clear all levels.
913 	 */
914 	STAILQ_FOREACH(w, &w_all, w_list)
915 		w->w_ddb_level = -1;
916 
917 	/*
918 	 * Look for locks with no parents and level all their descendants.
919 	 */
920 	STAILQ_FOREACH(w, &w_all, w_list) {
921 
922 		/* If the witness has ancestors (is not a root), skip it. */
923 		if (w->w_num_ancestors > 0)
924 			continue;
925 		witness_ddb_level_descendants(w, 0);
926 	}
927 }
928 
929 static void
930 witness_ddb_level_descendants(struct witness *w, int l)
931 {
932 	int i;
933 
934 	if (w->w_ddb_level >= l)
935 		return;
936 
937 	w->w_ddb_level = l;
938 	l++;
939 
940 	for (i = 1; i <= w_max_used_index; i++) {
941 		if (w_rmatrix[w->w_index][i] & WITNESS_PARENT)
942 			witness_ddb_level_descendants(&w_data[i], l);
943 	}
944 }
945 
946 static void
947 witness_ddb_display_descendants(int(*prnt)(const char *fmt, ...),
948     struct witness *w, int indent)
949 {
950 	int i;
951 
952  	for (i = 0; i < indent; i++)
953  		prnt(" ");
954 	prnt("%s (type: %s, depth: %d, active refs: %d)",
955 	     w->w_name, w->w_class->lc_name,
956 	     w->w_ddb_level, w->w_refcount);
957  	if (w->w_displayed) {
958  		prnt(" -- (already displayed)\n");
959  		return;
960  	}
961  	w->w_displayed = 1;
962 	if (w->w_file != NULL && w->w_line != 0)
963 		prnt(" -- last acquired @ %s:%d\n", fixup_filename(w->w_file),
964 		    w->w_line);
965 	else
966 		prnt(" -- never acquired\n");
967 	indent++;
968 	WITNESS_INDEX_ASSERT(w->w_index);
969 	for (i = 1; i <= w_max_used_index; i++) {
970 		if (db_pager_quit)
971 			return;
972 		if (w_rmatrix[w->w_index][i] & WITNESS_PARENT)
973 			witness_ddb_display_descendants(prnt, &w_data[i],
974 			    indent);
975 	}
976 }
977 
978 static void
979 witness_ddb_display_list(int(*prnt)(const char *fmt, ...),
980     struct witness_list *list)
981 {
982 	struct witness *w;
983 
984 	STAILQ_FOREACH(w, list, w_typelist) {
985 		if (w->w_file == NULL || w->w_ddb_level > 0)
986 			continue;
987 
988 		/* This lock has no anscestors - display its descendants. */
989 		witness_ddb_display_descendants(prnt, w, 0);
990 		if (db_pager_quit)
991 			return;
992 	}
993 }
994 
995 static void
996 witness_ddb_display(int(*prnt)(const char *fmt, ...))
997 {
998 	struct witness *w;
999 
1000 	KASSERT(witness_cold == 0, ("%s: witness_cold", __func__));
1001 	witness_ddb_compute_levels();
1002 
1003 	/* Clear all the displayed flags. */
1004 	STAILQ_FOREACH(w, &w_all, w_list)
1005 		w->w_displayed = 0;
1006 
1007 	/*
1008 	 * First, handle sleep locks which have been acquired at least
1009 	 * once.
1010 	 */
1011 	prnt("Sleep locks:\n");
1012 	witness_ddb_display_list(prnt, &w_sleep);
1013 	if (db_pager_quit)
1014 		return;
1015 
1016 	/*
1017 	 * Now do spin locks which have been acquired at least once.
1018 	 */
1019 	prnt("\nSpin locks:\n");
1020 	witness_ddb_display_list(prnt, &w_spin);
1021 	if (db_pager_quit)
1022 		return;
1023 
1024 	/*
1025 	 * Finally, any locks which have not been acquired yet.
1026 	 */
1027 	prnt("\nLocks which were never acquired:\n");
1028 	STAILQ_FOREACH(w, &w_all, w_list) {
1029 		if (w->w_file != NULL || w->w_refcount == 0)
1030 			continue;
1031 		prnt("%s (type: %s, depth: %d)\n", w->w_name,
1032 		    w->w_class->lc_name, w->w_ddb_level);
1033 		if (db_pager_quit)
1034 			return;
1035 	}
1036 }
1037 #endif /* DDB */
1038 
1039 int
1040 witness_defineorder(struct lock_object *lock1, struct lock_object *lock2)
1041 {
1042 
1043 	if (witness_watch == -1 || panicstr != NULL)
1044 		return (0);
1045 
1046 	/* Require locks that witness knows about. */
1047 	if (lock1 == NULL || lock1->lo_witness == NULL || lock2 == NULL ||
1048 	    lock2->lo_witness == NULL)
1049 		return (EINVAL);
1050 
1051 	mtx_assert(&w_mtx, MA_NOTOWNED);
1052 	mtx_lock_spin(&w_mtx);
1053 
1054 	/*
1055 	 * If we already have either an explicit or implied lock order that
1056 	 * is the other way around, then return an error.
1057 	 */
1058 	if (witness_watch &&
1059 	    isitmydescendant(lock2->lo_witness, lock1->lo_witness)) {
1060 		mtx_unlock_spin(&w_mtx);
1061 		return (EDOOFUS);
1062 	}
1063 
1064 	/* Try to add the new order. */
1065 	CTR3(KTR_WITNESS, "%s: adding %s as a child of %s", __func__,
1066 	    lock2->lo_witness->w_name, lock1->lo_witness->w_name);
1067 	itismychild(lock1->lo_witness, lock2->lo_witness);
1068 	mtx_unlock_spin(&w_mtx);
1069 	return (0);
1070 }
1071 
1072 void
1073 witness_checkorder(struct lock_object *lock, int flags, const char *file,
1074     int line, struct lock_object *interlock)
1075 {
1076 	struct lock_list_entry *lock_list, *lle;
1077 	struct lock_instance *lock1, *lock2, *plock;
1078 	struct lock_class *class, *iclass;
1079 	struct witness *w, *w1;
1080 	struct thread *td;
1081 	int i, j;
1082 
1083 	if (witness_cold || witness_watch < 1 || lock->lo_witness == NULL ||
1084 	    panicstr != NULL)
1085 		return;
1086 
1087 	w = lock->lo_witness;
1088 	class = LOCK_CLASS(lock);
1089 	td = curthread;
1090 
1091 	if (class->lc_flags & LC_SLEEPLOCK) {
1092 
1093 		/*
1094 		 * Since spin locks include a critical section, this check
1095 		 * implicitly enforces a lock order of all sleep locks before
1096 		 * all spin locks.
1097 		 */
1098 		if (td->td_critnest != 0 && !kdb_active)
1099 			kassert_panic("acquiring blockable sleep lock with "
1100 			    "spinlock or critical section held (%s) %s @ %s:%d",
1101 			    class->lc_name, lock->lo_name,
1102 			    fixup_filename(file), line);
1103 
1104 		/*
1105 		 * If this is the first lock acquired then just return as
1106 		 * no order checking is needed.
1107 		 */
1108 		lock_list = td->td_sleeplocks;
1109 		if (lock_list == NULL || lock_list->ll_count == 0)
1110 			return;
1111 	} else {
1112 
1113 		/*
1114 		 * If this is the first lock, just return as no order
1115 		 * checking is needed.  Avoid problems with thread
1116 		 * migration pinning the thread while checking if
1117 		 * spinlocks are held.  If at least one spinlock is held
1118 		 * the thread is in a safe path and it is allowed to
1119 		 * unpin it.
1120 		 */
1121 		sched_pin();
1122 		lock_list = PCPU_GET(spinlocks);
1123 		if (lock_list == NULL || lock_list->ll_count == 0) {
1124 			sched_unpin();
1125 			return;
1126 		}
1127 		sched_unpin();
1128 	}
1129 
1130 	/*
1131 	 * Check to see if we are recursing on a lock we already own.  If
1132 	 * so, make sure that we don't mismatch exclusive and shared lock
1133 	 * acquires.
1134 	 */
1135 	lock1 = find_instance(lock_list, lock);
1136 	if (lock1 != NULL) {
1137 		if ((lock1->li_flags & LI_EXCLUSIVE) != 0 &&
1138 		    (flags & LOP_EXCLUSIVE) == 0) {
1139 			witness_output("shared lock of (%s) %s @ %s:%d\n",
1140 			    class->lc_name, lock->lo_name,
1141 			    fixup_filename(file), line);
1142 			witness_output("while exclusively locked from %s:%d\n",
1143 			    fixup_filename(lock1->li_file), lock1->li_line);
1144 			kassert_panic("excl->share");
1145 		}
1146 		if ((lock1->li_flags & LI_EXCLUSIVE) == 0 &&
1147 		    (flags & LOP_EXCLUSIVE) != 0) {
1148 			witness_output("exclusive lock of (%s) %s @ %s:%d\n",
1149 			    class->lc_name, lock->lo_name,
1150 			    fixup_filename(file), line);
1151 			witness_output("while share locked from %s:%d\n",
1152 			    fixup_filename(lock1->li_file), lock1->li_line);
1153 			kassert_panic("share->excl");
1154 		}
1155 		return;
1156 	}
1157 
1158 	/* Warn if the interlock is not locked exactly once. */
1159 	if (interlock != NULL) {
1160 		iclass = LOCK_CLASS(interlock);
1161 		lock1 = find_instance(lock_list, interlock);
1162 		if (lock1 == NULL)
1163 			kassert_panic("interlock (%s) %s not locked @ %s:%d",
1164 			    iclass->lc_name, interlock->lo_name,
1165 			    fixup_filename(file), line);
1166 		else if ((lock1->li_flags & LI_RECURSEMASK) != 0)
1167 			kassert_panic("interlock (%s) %s recursed @ %s:%d",
1168 			    iclass->lc_name, interlock->lo_name,
1169 			    fixup_filename(file), line);
1170 	}
1171 
1172 	/*
1173 	 * Find the previously acquired lock, but ignore interlocks.
1174 	 */
1175 	plock = &lock_list->ll_children[lock_list->ll_count - 1];
1176 	if (interlock != NULL && plock->li_lock == interlock) {
1177 		if (lock_list->ll_count > 1)
1178 			plock =
1179 			    &lock_list->ll_children[lock_list->ll_count - 2];
1180 		else {
1181 			lle = lock_list->ll_next;
1182 
1183 			/*
1184 			 * The interlock is the only lock we hold, so
1185 			 * simply return.
1186 			 */
1187 			if (lle == NULL)
1188 				return;
1189 			plock = &lle->ll_children[lle->ll_count - 1];
1190 		}
1191 	}
1192 
1193 	/*
1194 	 * Try to perform most checks without a lock.  If this succeeds we
1195 	 * can skip acquiring the lock and return success.  Otherwise we redo
1196 	 * the check with the lock held to handle races with concurrent updates.
1197 	 */
1198 	w1 = plock->li_lock->lo_witness;
1199 	if (witness_lock_order_check(w1, w))
1200 		return;
1201 
1202 	mtx_lock_spin(&w_mtx);
1203 	if (witness_lock_order_check(w1, w)) {
1204 		mtx_unlock_spin(&w_mtx);
1205 		return;
1206 	}
1207 	witness_lock_order_add(w1, w);
1208 
1209 	/*
1210 	 * Check for duplicate locks of the same type.  Note that we only
1211 	 * have to check for this on the last lock we just acquired.  Any
1212 	 * other cases will be caught as lock order violations.
1213 	 */
1214 	if (w1 == w) {
1215 		i = w->w_index;
1216 		if (!(lock->lo_flags & LO_DUPOK) && !(flags & LOP_DUPOK) &&
1217 		    !(w_rmatrix[i][i] & WITNESS_REVERSAL)) {
1218 		    w_rmatrix[i][i] |= WITNESS_REVERSAL;
1219 			w->w_reversed = 1;
1220 			mtx_unlock_spin(&w_mtx);
1221 			witness_output(
1222 			    "acquiring duplicate lock of same type: \"%s\"\n",
1223 			    w->w_name);
1224 			witness_output(" 1st %s @ %s:%d\n", plock->li_lock->lo_name,
1225 			    fixup_filename(plock->li_file), plock->li_line);
1226 			witness_output(" 2nd %s @ %s:%d\n", lock->lo_name,
1227 			    fixup_filename(file), line);
1228 			witness_debugger(1, __func__);
1229 		} else
1230 			mtx_unlock_spin(&w_mtx);
1231 		return;
1232 	}
1233 	mtx_assert(&w_mtx, MA_OWNED);
1234 
1235 	/*
1236 	 * If we know that the lock we are acquiring comes after
1237 	 * the lock we most recently acquired in the lock order tree,
1238 	 * then there is no need for any further checks.
1239 	 */
1240 	if (isitmychild(w1, w))
1241 		goto out;
1242 
1243 	for (j = 0, lle = lock_list; lle != NULL; lle = lle->ll_next) {
1244 		for (i = lle->ll_count - 1; i >= 0; i--, j++) {
1245 
1246 			MPASS(j < LOCK_CHILDCOUNT * LOCK_NCHILDREN);
1247 			lock1 = &lle->ll_children[i];
1248 
1249 			/*
1250 			 * Ignore the interlock.
1251 			 */
1252 			if (interlock == lock1->li_lock)
1253 				continue;
1254 
1255 			/*
1256 			 * If this lock doesn't undergo witness checking,
1257 			 * then skip it.
1258 			 */
1259 			w1 = lock1->li_lock->lo_witness;
1260 			if (w1 == NULL) {
1261 				KASSERT((lock1->li_lock->lo_flags & LO_WITNESS) == 0,
1262 				    ("lock missing witness structure"));
1263 				continue;
1264 			}
1265 
1266 			/*
1267 			 * If we are locking Giant and this is a sleepable
1268 			 * lock, then skip it.
1269 			 */
1270 			if ((lock1->li_lock->lo_flags & LO_SLEEPABLE) != 0 &&
1271 			    lock == &Giant.lock_object)
1272 				continue;
1273 
1274 			/*
1275 			 * If we are locking a sleepable lock and this lock
1276 			 * is Giant, then skip it.
1277 			 */
1278 			if ((lock->lo_flags & LO_SLEEPABLE) != 0 &&
1279 			    lock1->li_lock == &Giant.lock_object)
1280 				continue;
1281 
1282 			/*
1283 			 * If we are locking a sleepable lock and this lock
1284 			 * isn't sleepable, we want to treat it as a lock
1285 			 * order violation to enfore a general lock order of
1286 			 * sleepable locks before non-sleepable locks.
1287 			 */
1288 			if (((lock->lo_flags & LO_SLEEPABLE) != 0 &&
1289 			    (lock1->li_lock->lo_flags & LO_SLEEPABLE) == 0))
1290 				goto reversal;
1291 
1292 			/*
1293 			 * If we are locking Giant and this is a non-sleepable
1294 			 * lock, then treat it as a reversal.
1295 			 */
1296 			if ((lock1->li_lock->lo_flags & LO_SLEEPABLE) == 0 &&
1297 			    lock == &Giant.lock_object)
1298 				goto reversal;
1299 
1300 			/*
1301 			 * Check the lock order hierarchy for a reveresal.
1302 			 */
1303 			if (!isitmydescendant(w, w1))
1304 				continue;
1305 		reversal:
1306 
1307 			/*
1308 			 * We have a lock order violation, check to see if it
1309 			 * is allowed or has already been yelled about.
1310 			 */
1311 #ifdef BLESSING
1312 
1313 			/*
1314 			 * If the lock order is blessed, just bail.  We don't
1315 			 * look for other lock order violations though, which
1316 			 * may be a bug.
1317 			 */
1318 			if (blessed(w, w1))
1319 				goto out;
1320 #endif
1321 
1322 			/* Bail if this violation is known */
1323 			if (w_rmatrix[w1->w_index][w->w_index] & WITNESS_REVERSAL)
1324 				goto out;
1325 
1326 			/* Record this as a violation */
1327 			w_rmatrix[w1->w_index][w->w_index] |= WITNESS_REVERSAL;
1328 			w_rmatrix[w->w_index][w1->w_index] |= WITNESS_REVERSAL;
1329 			w->w_reversed = w1->w_reversed = 1;
1330 			witness_increment_graph_generation();
1331 			mtx_unlock_spin(&w_mtx);
1332 
1333 #ifdef WITNESS_NO_VNODE
1334 			/*
1335 			 * There are known LORs between VNODE locks. They are
1336 			 * not an indication of a bug. VNODE locks are flagged
1337 			 * as such (LO_IS_VNODE) and we don't yell if the LOR
1338 			 * is between 2 VNODE locks.
1339 			 */
1340 			if ((lock->lo_flags & LO_IS_VNODE) != 0 &&
1341 			    (lock1->li_lock->lo_flags & LO_IS_VNODE) != 0)
1342 				return;
1343 #endif
1344 
1345 			/*
1346 			 * Ok, yell about it.
1347 			 */
1348 			if (((lock->lo_flags & LO_SLEEPABLE) != 0 &&
1349 			    (lock1->li_lock->lo_flags & LO_SLEEPABLE) == 0))
1350 				witness_output(
1351 		"lock order reversal: (sleepable after non-sleepable)\n");
1352 			else if ((lock1->li_lock->lo_flags & LO_SLEEPABLE) == 0
1353 			    && lock == &Giant.lock_object)
1354 				witness_output(
1355 		"lock order reversal: (Giant after non-sleepable)\n");
1356 			else
1357 				witness_output("lock order reversal:\n");
1358 
1359 			/*
1360 			 * Try to locate an earlier lock with
1361 			 * witness w in our list.
1362 			 */
1363 			do {
1364 				lock2 = &lle->ll_children[i];
1365 				MPASS(lock2->li_lock != NULL);
1366 				if (lock2->li_lock->lo_witness == w)
1367 					break;
1368 				if (i == 0 && lle->ll_next != NULL) {
1369 					lle = lle->ll_next;
1370 					i = lle->ll_count - 1;
1371 					MPASS(i >= 0 && i < LOCK_NCHILDREN);
1372 				} else
1373 					i--;
1374 			} while (i >= 0);
1375 			if (i < 0) {
1376 				witness_output(" 1st %p %s (%s) @ %s:%d\n",
1377 				    lock1->li_lock, lock1->li_lock->lo_name,
1378 				    w1->w_name, fixup_filename(lock1->li_file),
1379 				    lock1->li_line);
1380 				witness_output(" 2nd %p %s (%s) @ %s:%d\n", lock,
1381 				    lock->lo_name, w->w_name,
1382 				    fixup_filename(file), line);
1383 			} else {
1384 				witness_output(" 1st %p %s (%s) @ %s:%d\n",
1385 				    lock2->li_lock, lock2->li_lock->lo_name,
1386 				    lock2->li_lock->lo_witness->w_name,
1387 				    fixup_filename(lock2->li_file),
1388 				    lock2->li_line);
1389 				witness_output(" 2nd %p %s (%s) @ %s:%d\n",
1390 				    lock1->li_lock, lock1->li_lock->lo_name,
1391 				    w1->w_name, fixup_filename(lock1->li_file),
1392 				    lock1->li_line);
1393 				witness_output(" 3rd %p %s (%s) @ %s:%d\n", lock,
1394 				    lock->lo_name, w->w_name,
1395 				    fixup_filename(file), line);
1396 			}
1397 			witness_debugger(1, __func__);
1398 			return;
1399 		}
1400 	}
1401 
1402 	/*
1403 	 * If requested, build a new lock order.  However, don't build a new
1404 	 * relationship between a sleepable lock and Giant if it is in the
1405 	 * wrong direction.  The correct lock order is that sleepable locks
1406 	 * always come before Giant.
1407 	 */
1408 	if (flags & LOP_NEWORDER &&
1409 	    !(plock->li_lock == &Giant.lock_object &&
1410 	    (lock->lo_flags & LO_SLEEPABLE) != 0)) {
1411 		CTR3(KTR_WITNESS, "%s: adding %s as a child of %s", __func__,
1412 		    w->w_name, plock->li_lock->lo_witness->w_name);
1413 		itismychild(plock->li_lock->lo_witness, w);
1414 	}
1415 out:
1416 	mtx_unlock_spin(&w_mtx);
1417 }
1418 
1419 void
1420 witness_lock(struct lock_object *lock, int flags, const char *file, int line)
1421 {
1422 	struct lock_list_entry **lock_list, *lle;
1423 	struct lock_instance *instance;
1424 	struct witness *w;
1425 	struct thread *td;
1426 
1427 	if (witness_cold || witness_watch == -1 || lock->lo_witness == NULL ||
1428 	    panicstr != NULL)
1429 		return;
1430 	w = lock->lo_witness;
1431 	td = curthread;
1432 
1433 	/* Determine lock list for this lock. */
1434 	if (LOCK_CLASS(lock)->lc_flags & LC_SLEEPLOCK)
1435 		lock_list = &td->td_sleeplocks;
1436 	else
1437 		lock_list = PCPU_PTR(spinlocks);
1438 
1439 	/* Check to see if we are recursing on a lock we already own. */
1440 	instance = find_instance(*lock_list, lock);
1441 	if (instance != NULL) {
1442 		instance->li_flags++;
1443 		CTR4(KTR_WITNESS, "%s: pid %d recursed on %s r=%d", __func__,
1444 		    td->td_proc->p_pid, lock->lo_name,
1445 		    instance->li_flags & LI_RECURSEMASK);
1446 		instance->li_file = file;
1447 		instance->li_line = line;
1448 		return;
1449 	}
1450 
1451 	/* Update per-witness last file and line acquire. */
1452 	w->w_file = file;
1453 	w->w_line = line;
1454 
1455 	/* Find the next open lock instance in the list and fill it. */
1456 	lle = *lock_list;
1457 	if (lle == NULL || lle->ll_count == LOCK_NCHILDREN) {
1458 		lle = witness_lock_list_get();
1459 		if (lle == NULL)
1460 			return;
1461 		lle->ll_next = *lock_list;
1462 		CTR3(KTR_WITNESS, "%s: pid %d added lle %p", __func__,
1463 		    td->td_proc->p_pid, lle);
1464 		*lock_list = lle;
1465 	}
1466 	instance = &lle->ll_children[lle->ll_count++];
1467 	instance->li_lock = lock;
1468 	instance->li_line = line;
1469 	instance->li_file = file;
1470 	if ((flags & LOP_EXCLUSIVE) != 0)
1471 		instance->li_flags = LI_EXCLUSIVE;
1472 	else
1473 		instance->li_flags = 0;
1474 	CTR4(KTR_WITNESS, "%s: pid %d added %s as lle[%d]", __func__,
1475 	    td->td_proc->p_pid, lock->lo_name, lle->ll_count - 1);
1476 }
1477 
1478 void
1479 witness_upgrade(struct lock_object *lock, int flags, const char *file, int line)
1480 {
1481 	struct lock_instance *instance;
1482 	struct lock_class *class;
1483 
1484 	KASSERT(witness_cold == 0, ("%s: witness_cold", __func__));
1485 	if (lock->lo_witness == NULL || witness_watch == -1 || panicstr != NULL)
1486 		return;
1487 	class = LOCK_CLASS(lock);
1488 	if (witness_watch) {
1489 		if ((lock->lo_flags & LO_UPGRADABLE) == 0)
1490 			kassert_panic(
1491 			    "upgrade of non-upgradable lock (%s) %s @ %s:%d",
1492 			    class->lc_name, lock->lo_name,
1493 			    fixup_filename(file), line);
1494 		if ((class->lc_flags & LC_SLEEPLOCK) == 0)
1495 			kassert_panic(
1496 			    "upgrade of non-sleep lock (%s) %s @ %s:%d",
1497 			    class->lc_name, lock->lo_name,
1498 			    fixup_filename(file), line);
1499 	}
1500 	instance = find_instance(curthread->td_sleeplocks, lock);
1501 	if (instance == NULL) {
1502 		kassert_panic("upgrade of unlocked lock (%s) %s @ %s:%d",
1503 		    class->lc_name, lock->lo_name,
1504 		    fixup_filename(file), line);
1505 		return;
1506 	}
1507 	if (witness_watch) {
1508 		if ((instance->li_flags & LI_EXCLUSIVE) != 0)
1509 			kassert_panic(
1510 			    "upgrade of exclusive lock (%s) %s @ %s:%d",
1511 			    class->lc_name, lock->lo_name,
1512 			    fixup_filename(file), line);
1513 		if ((instance->li_flags & LI_RECURSEMASK) != 0)
1514 			kassert_panic(
1515 			    "upgrade of recursed lock (%s) %s r=%d @ %s:%d",
1516 			    class->lc_name, lock->lo_name,
1517 			    instance->li_flags & LI_RECURSEMASK,
1518 			    fixup_filename(file), line);
1519 	}
1520 	instance->li_flags |= LI_EXCLUSIVE;
1521 }
1522 
1523 void
1524 witness_downgrade(struct lock_object *lock, int flags, const char *file,
1525     int line)
1526 {
1527 	struct lock_instance *instance;
1528 	struct lock_class *class;
1529 
1530 	KASSERT(witness_cold == 0, ("%s: witness_cold", __func__));
1531 	if (lock->lo_witness == NULL || witness_watch == -1 || panicstr != NULL)
1532 		return;
1533 	class = LOCK_CLASS(lock);
1534 	if (witness_watch) {
1535 		if ((lock->lo_flags & LO_UPGRADABLE) == 0)
1536 			kassert_panic(
1537 			    "downgrade of non-upgradable lock (%s) %s @ %s:%d",
1538 			    class->lc_name, lock->lo_name,
1539 			    fixup_filename(file), line);
1540 		if ((class->lc_flags & LC_SLEEPLOCK) == 0)
1541 			kassert_panic(
1542 			    "downgrade of non-sleep lock (%s) %s @ %s:%d",
1543 			    class->lc_name, lock->lo_name,
1544 			    fixup_filename(file), line);
1545 	}
1546 	instance = find_instance(curthread->td_sleeplocks, lock);
1547 	if (instance == NULL) {
1548 		kassert_panic("downgrade of unlocked lock (%s) %s @ %s:%d",
1549 		    class->lc_name, lock->lo_name,
1550 		    fixup_filename(file), line);
1551 		return;
1552 	}
1553 	if (witness_watch) {
1554 		if ((instance->li_flags & LI_EXCLUSIVE) == 0)
1555 			kassert_panic(
1556 			    "downgrade of shared lock (%s) %s @ %s:%d",
1557 			    class->lc_name, lock->lo_name,
1558 			    fixup_filename(file), line);
1559 		if ((instance->li_flags & LI_RECURSEMASK) != 0)
1560 			kassert_panic(
1561 			    "downgrade of recursed lock (%s) %s r=%d @ %s:%d",
1562 			    class->lc_name, lock->lo_name,
1563 			    instance->li_flags & LI_RECURSEMASK,
1564 			    fixup_filename(file), line);
1565 	}
1566 	instance->li_flags &= ~LI_EXCLUSIVE;
1567 }
1568 
1569 void
1570 witness_unlock(struct lock_object *lock, int flags, const char *file, int line)
1571 {
1572 	struct lock_list_entry **lock_list, *lle;
1573 	struct lock_instance *instance;
1574 	struct lock_class *class;
1575 	struct thread *td;
1576 	register_t s;
1577 	int i, j;
1578 
1579 	if (witness_cold || lock->lo_witness == NULL || panicstr != NULL)
1580 		return;
1581 	td = curthread;
1582 	class = LOCK_CLASS(lock);
1583 
1584 	/* Find lock instance associated with this lock. */
1585 	if (class->lc_flags & LC_SLEEPLOCK)
1586 		lock_list = &td->td_sleeplocks;
1587 	else
1588 		lock_list = PCPU_PTR(spinlocks);
1589 	lle = *lock_list;
1590 	for (; *lock_list != NULL; lock_list = &(*lock_list)->ll_next)
1591 		for (i = 0; i < (*lock_list)->ll_count; i++) {
1592 			instance = &(*lock_list)->ll_children[i];
1593 			if (instance->li_lock == lock)
1594 				goto found;
1595 		}
1596 
1597 	/*
1598 	 * When disabling WITNESS through witness_watch we could end up in
1599 	 * having registered locks in the td_sleeplocks queue.
1600 	 * We have to make sure we flush these queues, so just search for
1601 	 * eventual register locks and remove them.
1602 	 */
1603 	if (witness_watch > 0) {
1604 		kassert_panic("lock (%s) %s not locked @ %s:%d", class->lc_name,
1605 		    lock->lo_name, fixup_filename(file), line);
1606 		return;
1607 	} else {
1608 		return;
1609 	}
1610 found:
1611 
1612 	/* First, check for shared/exclusive mismatches. */
1613 	if ((instance->li_flags & LI_EXCLUSIVE) != 0 && witness_watch > 0 &&
1614 	    (flags & LOP_EXCLUSIVE) == 0) {
1615 		witness_output("shared unlock of (%s) %s @ %s:%d\n",
1616 		    class->lc_name, lock->lo_name, fixup_filename(file), line);
1617 		witness_output("while exclusively locked from %s:%d\n",
1618 		    fixup_filename(instance->li_file), instance->li_line);
1619 		kassert_panic("excl->ushare");
1620 	}
1621 	if ((instance->li_flags & LI_EXCLUSIVE) == 0 && witness_watch > 0 &&
1622 	    (flags & LOP_EXCLUSIVE) != 0) {
1623 		witness_output("exclusive unlock of (%s) %s @ %s:%d\n",
1624 		    class->lc_name, lock->lo_name, fixup_filename(file), line);
1625 		witness_output("while share locked from %s:%d\n",
1626 		    fixup_filename(instance->li_file),
1627 		    instance->li_line);
1628 		kassert_panic("share->uexcl");
1629 	}
1630 	/* If we are recursed, unrecurse. */
1631 	if ((instance->li_flags & LI_RECURSEMASK) > 0) {
1632 		CTR4(KTR_WITNESS, "%s: pid %d unrecursed on %s r=%d", __func__,
1633 		    td->td_proc->p_pid, instance->li_lock->lo_name,
1634 		    instance->li_flags);
1635 		instance->li_flags--;
1636 		return;
1637 	}
1638 	/* The lock is now being dropped, check for NORELEASE flag */
1639 	if ((instance->li_flags & LI_NORELEASE) != 0 && witness_watch > 0) {
1640 		witness_output("forbidden unlock of (%s) %s @ %s:%d\n",
1641 		    class->lc_name, lock->lo_name, fixup_filename(file), line);
1642 		kassert_panic("lock marked norelease");
1643 	}
1644 
1645 	/* Otherwise, remove this item from the list. */
1646 	s = intr_disable();
1647 	CTR4(KTR_WITNESS, "%s: pid %d removed %s from lle[%d]", __func__,
1648 	    td->td_proc->p_pid, instance->li_lock->lo_name,
1649 	    (*lock_list)->ll_count - 1);
1650 	for (j = i; j < (*lock_list)->ll_count - 1; j++)
1651 		(*lock_list)->ll_children[j] =
1652 		    (*lock_list)->ll_children[j + 1];
1653 	(*lock_list)->ll_count--;
1654 	intr_restore(s);
1655 
1656 	/*
1657 	 * In order to reduce contention on w_mtx, we want to keep always an
1658 	 * head object into lists so that frequent allocation from the
1659 	 * free witness pool (and subsequent locking) is avoided.
1660 	 * In order to maintain the current code simple, when the head
1661 	 * object is totally unloaded it means also that we do not have
1662 	 * further objects in the list, so the list ownership needs to be
1663 	 * hand over to another object if the current head needs to be freed.
1664 	 */
1665 	if ((*lock_list)->ll_count == 0) {
1666 		if (*lock_list == lle) {
1667 			if (lle->ll_next == NULL)
1668 				return;
1669 		} else
1670 			lle = *lock_list;
1671 		*lock_list = lle->ll_next;
1672 		CTR3(KTR_WITNESS, "%s: pid %d removed lle %p", __func__,
1673 		    td->td_proc->p_pid, lle);
1674 		witness_lock_list_free(lle);
1675 	}
1676 }
1677 
1678 void
1679 witness_thread_exit(struct thread *td)
1680 {
1681 	struct lock_list_entry *lle;
1682 	int i, n;
1683 
1684 	lle = td->td_sleeplocks;
1685 	if (lle == NULL || panicstr != NULL)
1686 		return;
1687 	if (lle->ll_count != 0) {
1688 		for (n = 0; lle != NULL; lle = lle->ll_next)
1689 			for (i = lle->ll_count - 1; i >= 0; i--) {
1690 				if (n == 0)
1691 					witness_output(
1692 		    "Thread %p exiting with the following locks held:\n", td);
1693 				n++;
1694 				witness_list_lock(&lle->ll_children[i],
1695 				    witness_output);
1696 
1697 			}
1698 		kassert_panic(
1699 		    "Thread %p cannot exit while holding sleeplocks\n", td);
1700 	}
1701 	witness_lock_list_free(lle);
1702 }
1703 
1704 /*
1705  * Warn if any locks other than 'lock' are held.  Flags can be passed in to
1706  * exempt Giant and sleepable locks from the checks as well.  If any
1707  * non-exempt locks are held, then a supplied message is printed to the
1708  * output channel along with a list of the offending locks.  If indicated in the
1709  * flags then a failure results in a panic as well.
1710  */
1711 int
1712 witness_warn(int flags, struct lock_object *lock, const char *fmt, ...)
1713 {
1714 	struct lock_list_entry *lock_list, *lle;
1715 	struct lock_instance *lock1;
1716 	struct thread *td;
1717 	va_list ap;
1718 	int i, n;
1719 
1720 	if (witness_cold || witness_watch < 1 || panicstr != NULL)
1721 		return (0);
1722 	n = 0;
1723 	td = curthread;
1724 	for (lle = td->td_sleeplocks; lle != NULL; lle = lle->ll_next)
1725 		for (i = lle->ll_count - 1; i >= 0; i--) {
1726 			lock1 = &lle->ll_children[i];
1727 			if (lock1->li_lock == lock)
1728 				continue;
1729 			if (flags & WARN_GIANTOK &&
1730 			    lock1->li_lock == &Giant.lock_object)
1731 				continue;
1732 			if (flags & WARN_SLEEPOK &&
1733 			    (lock1->li_lock->lo_flags & LO_SLEEPABLE) != 0)
1734 				continue;
1735 			if (n == 0) {
1736 				va_start(ap, fmt);
1737 				vprintf(fmt, ap);
1738 				va_end(ap);
1739 				printf(" with the following %slocks held:\n",
1740 				    (flags & WARN_SLEEPOK) != 0 ?
1741 				    "non-sleepable " : "");
1742 			}
1743 			n++;
1744 			witness_list_lock(lock1, printf);
1745 		}
1746 
1747 	/*
1748 	 * Pin the thread in order to avoid problems with thread migration.
1749 	 * Once that all verifies are passed about spinlocks ownership,
1750 	 * the thread is in a safe path and it can be unpinned.
1751 	 */
1752 	sched_pin();
1753 	lock_list = PCPU_GET(spinlocks);
1754 	if (lock_list != NULL && lock_list->ll_count != 0) {
1755 		sched_unpin();
1756 
1757 		/*
1758 		 * We should only have one spinlock and as long as
1759 		 * the flags cannot match for this locks class,
1760 		 * check if the first spinlock is the one curthread
1761 		 * should hold.
1762 		 */
1763 		lock1 = &lock_list->ll_children[lock_list->ll_count - 1];
1764 		if (lock_list->ll_count == 1 && lock_list->ll_next == NULL &&
1765 		    lock1->li_lock == lock && n == 0)
1766 			return (0);
1767 
1768 		va_start(ap, fmt);
1769 		vprintf(fmt, ap);
1770 		va_end(ap);
1771 		printf(" with the following %slocks held:\n",
1772 		    (flags & WARN_SLEEPOK) != 0 ?  "non-sleepable " : "");
1773 		n += witness_list_locks(&lock_list, printf);
1774 	} else
1775 		sched_unpin();
1776 	if (flags & WARN_PANIC && n)
1777 		kassert_panic("%s", __func__);
1778 	else
1779 		witness_debugger(n, __func__);
1780 	return (n);
1781 }
1782 
1783 const char *
1784 witness_file(struct lock_object *lock)
1785 {
1786 	struct witness *w;
1787 
1788 	if (witness_cold || witness_watch < 1 || lock->lo_witness == NULL)
1789 		return ("?");
1790 	w = lock->lo_witness;
1791 	return (w->w_file);
1792 }
1793 
1794 int
1795 witness_line(struct lock_object *lock)
1796 {
1797 	struct witness *w;
1798 
1799 	if (witness_cold || witness_watch < 1 || lock->lo_witness == NULL)
1800 		return (0);
1801 	w = lock->lo_witness;
1802 	return (w->w_line);
1803 }
1804 
1805 static struct witness *
1806 enroll(const char *description, struct lock_class *lock_class)
1807 {
1808 	struct witness *w;
1809 	struct witness_list *typelist;
1810 
1811 	MPASS(description != NULL);
1812 
1813 	if (witness_watch == -1 || panicstr != NULL)
1814 		return (NULL);
1815 	if ((lock_class->lc_flags & LC_SPINLOCK)) {
1816 		if (witness_skipspin)
1817 			return (NULL);
1818 		else
1819 			typelist = &w_spin;
1820 	} else if ((lock_class->lc_flags & LC_SLEEPLOCK)) {
1821 		typelist = &w_sleep;
1822 	} else {
1823 		kassert_panic("lock class %s is not sleep or spin",
1824 		    lock_class->lc_name);
1825 		return (NULL);
1826 	}
1827 
1828 	mtx_lock_spin(&w_mtx);
1829 	w = witness_hash_get(description);
1830 	if (w)
1831 		goto found;
1832 	if ((w = witness_get()) == NULL)
1833 		return (NULL);
1834 	MPASS(strlen(description) < MAX_W_NAME);
1835 	strcpy(w->w_name, description);
1836 	w->w_class = lock_class;
1837 	w->w_refcount = 1;
1838 	STAILQ_INSERT_HEAD(&w_all, w, w_list);
1839 	if (lock_class->lc_flags & LC_SPINLOCK) {
1840 		STAILQ_INSERT_HEAD(&w_spin, w, w_typelist);
1841 		w_spin_cnt++;
1842 	} else if (lock_class->lc_flags & LC_SLEEPLOCK) {
1843 		STAILQ_INSERT_HEAD(&w_sleep, w, w_typelist);
1844 		w_sleep_cnt++;
1845 	}
1846 
1847 	/* Insert new witness into the hash */
1848 	witness_hash_put(w);
1849 	witness_increment_graph_generation();
1850 	mtx_unlock_spin(&w_mtx);
1851 	return (w);
1852 found:
1853 	w->w_refcount++;
1854 	if (w->w_refcount == 1)
1855 		w->w_class = lock_class;
1856 	mtx_unlock_spin(&w_mtx);
1857 	if (lock_class != w->w_class)
1858 		kassert_panic(
1859 		    "lock (%s) %s does not match earlier (%s) lock",
1860 		    description, lock_class->lc_name,
1861 		    w->w_class->lc_name);
1862 	return (w);
1863 }
1864 
1865 static void
1866 depart(struct witness *w)
1867 {
1868 	struct witness_list *list;
1869 
1870 	MPASS(w->w_refcount == 0);
1871 	if (w->w_class->lc_flags & LC_SLEEPLOCK) {
1872 		list = &w_sleep;
1873 		w_sleep_cnt--;
1874 	} else {
1875 		list = &w_spin;
1876 		w_spin_cnt--;
1877 	}
1878 	/*
1879 	 * Set file to NULL as it may point into a loadable module.
1880 	 */
1881 	w->w_file = NULL;
1882 	w->w_line = 0;
1883 	witness_increment_graph_generation();
1884 }
1885 
1886 
1887 static void
1888 adopt(struct witness *parent, struct witness *child)
1889 {
1890 	int pi, ci, i, j;
1891 
1892 	if (witness_cold == 0)
1893 		mtx_assert(&w_mtx, MA_OWNED);
1894 
1895 	/* If the relationship is already known, there's no work to be done. */
1896 	if (isitmychild(parent, child))
1897 		return;
1898 
1899 	/* When the structure of the graph changes, bump up the generation. */
1900 	witness_increment_graph_generation();
1901 
1902 	/*
1903 	 * The hard part ... create the direct relationship, then propagate all
1904 	 * indirect relationships.
1905 	 */
1906 	pi = parent->w_index;
1907 	ci = child->w_index;
1908 	WITNESS_INDEX_ASSERT(pi);
1909 	WITNESS_INDEX_ASSERT(ci);
1910 	MPASS(pi != ci);
1911 	w_rmatrix[pi][ci] |= WITNESS_PARENT;
1912 	w_rmatrix[ci][pi] |= WITNESS_CHILD;
1913 
1914 	/*
1915 	 * If parent was not already an ancestor of child,
1916 	 * then we increment the descendant and ancestor counters.
1917 	 */
1918 	if ((w_rmatrix[pi][ci] & WITNESS_ANCESTOR) == 0) {
1919 		parent->w_num_descendants++;
1920 		child->w_num_ancestors++;
1921 	}
1922 
1923 	/*
1924 	 * Find each ancestor of 'pi'. Note that 'pi' itself is counted as
1925 	 * an ancestor of 'pi' during this loop.
1926 	 */
1927 	for (i = 1; i <= w_max_used_index; i++) {
1928 		if ((w_rmatrix[i][pi] & WITNESS_ANCESTOR_MASK) == 0 &&
1929 		    (i != pi))
1930 			continue;
1931 
1932 		/* Find each descendant of 'i' and mark it as a descendant. */
1933 		for (j = 1; j <= w_max_used_index; j++) {
1934 
1935 			/*
1936 			 * Skip children that are already marked as
1937 			 * descendants of 'i'.
1938 			 */
1939 			if (w_rmatrix[i][j] & WITNESS_ANCESTOR_MASK)
1940 				continue;
1941 
1942 			/*
1943 			 * We are only interested in descendants of 'ci'. Note
1944 			 * that 'ci' itself is counted as a descendant of 'ci'.
1945 			 */
1946 			if ((w_rmatrix[ci][j] & WITNESS_ANCESTOR_MASK) == 0 &&
1947 			    (j != ci))
1948 				continue;
1949 			w_rmatrix[i][j] |= WITNESS_ANCESTOR;
1950 			w_rmatrix[j][i] |= WITNESS_DESCENDANT;
1951 			w_data[i].w_num_descendants++;
1952 			w_data[j].w_num_ancestors++;
1953 
1954 			/*
1955 			 * Make sure we aren't marking a node as both an
1956 			 * ancestor and descendant. We should have caught
1957 			 * this as a lock order reversal earlier.
1958 			 */
1959 			if ((w_rmatrix[i][j] & WITNESS_ANCESTOR_MASK) &&
1960 			    (w_rmatrix[i][j] & WITNESS_DESCENDANT_MASK)) {
1961 				printf("witness rmatrix paradox! [%d][%d]=%d "
1962 				    "both ancestor and descendant\n",
1963 				    i, j, w_rmatrix[i][j]);
1964 				kdb_backtrace();
1965 				printf("Witness disabled.\n");
1966 				witness_watch = -1;
1967 			}
1968 			if ((w_rmatrix[j][i] & WITNESS_ANCESTOR_MASK) &&
1969 			    (w_rmatrix[j][i] & WITNESS_DESCENDANT_MASK)) {
1970 				printf("witness rmatrix paradox! [%d][%d]=%d "
1971 				    "both ancestor and descendant\n",
1972 				    j, i, w_rmatrix[j][i]);
1973 				kdb_backtrace();
1974 				printf("Witness disabled.\n");
1975 				witness_watch = -1;
1976 			}
1977 		}
1978 	}
1979 }
1980 
1981 static void
1982 itismychild(struct witness *parent, struct witness *child)
1983 {
1984 	int unlocked;
1985 
1986 	MPASS(child != NULL && parent != NULL);
1987 	if (witness_cold == 0)
1988 		mtx_assert(&w_mtx, MA_OWNED);
1989 
1990 	if (!witness_lock_type_equal(parent, child)) {
1991 		if (witness_cold == 0) {
1992 			unlocked = 1;
1993 			mtx_unlock_spin(&w_mtx);
1994 		} else {
1995 			unlocked = 0;
1996 		}
1997 		kassert_panic(
1998 		    "%s: parent \"%s\" (%s) and child \"%s\" (%s) are not "
1999 		    "the same lock type", __func__, parent->w_name,
2000 		    parent->w_class->lc_name, child->w_name,
2001 		    child->w_class->lc_name);
2002 		if (unlocked)
2003 			mtx_lock_spin(&w_mtx);
2004 	}
2005 	adopt(parent, child);
2006 }
2007 
2008 /*
2009  * Generic code for the isitmy*() functions. The rmask parameter is the
2010  * expected relationship of w1 to w2.
2011  */
2012 static int
2013 _isitmyx(struct witness *w1, struct witness *w2, int rmask, const char *fname)
2014 {
2015 	unsigned char r1, r2;
2016 	int i1, i2;
2017 
2018 	i1 = w1->w_index;
2019 	i2 = w2->w_index;
2020 	WITNESS_INDEX_ASSERT(i1);
2021 	WITNESS_INDEX_ASSERT(i2);
2022 	r1 = w_rmatrix[i1][i2] & WITNESS_RELATED_MASK;
2023 	r2 = w_rmatrix[i2][i1] & WITNESS_RELATED_MASK;
2024 
2025 	/* The flags on one better be the inverse of the flags on the other */
2026 	if (!((WITNESS_ATOD(r1) == r2 && WITNESS_DTOA(r2) == r1) ||
2027 	    (WITNESS_DTOA(r1) == r2 && WITNESS_ATOD(r2) == r1))) {
2028 		/* Don't squawk if we're potentially racing with an update. */
2029 		if (!mtx_owned(&w_mtx))
2030 			return (0);
2031 		printf("%s: rmatrix mismatch between %s (index %d) and %s "
2032 		    "(index %d): w_rmatrix[%d][%d] == %hhx but "
2033 		    "w_rmatrix[%d][%d] == %hhx\n",
2034 		    fname, w1->w_name, i1, w2->w_name, i2, i1, i2, r1,
2035 		    i2, i1, r2);
2036 		kdb_backtrace();
2037 		printf("Witness disabled.\n");
2038 		witness_watch = -1;
2039 	}
2040 	return (r1 & rmask);
2041 }
2042 
2043 /*
2044  * Checks if @child is a direct child of @parent.
2045  */
2046 static int
2047 isitmychild(struct witness *parent, struct witness *child)
2048 {
2049 
2050 	return (_isitmyx(parent, child, WITNESS_PARENT, __func__));
2051 }
2052 
2053 /*
2054  * Checks if @descendant is a direct or inderect descendant of @ancestor.
2055  */
2056 static int
2057 isitmydescendant(struct witness *ancestor, struct witness *descendant)
2058 {
2059 
2060 	return (_isitmyx(ancestor, descendant, WITNESS_ANCESTOR_MASK,
2061 	    __func__));
2062 }
2063 
2064 #ifdef BLESSING
2065 static int
2066 blessed(struct witness *w1, struct witness *w2)
2067 {
2068 	int i;
2069 	struct witness_blessed *b;
2070 
2071 	for (i = 0; i < nitems(blessed_list); i++) {
2072 		b = &blessed_list[i];
2073 		if (strcmp(w1->w_name, b->b_lock1) == 0) {
2074 			if (strcmp(w2->w_name, b->b_lock2) == 0)
2075 				return (1);
2076 			continue;
2077 		}
2078 		if (strcmp(w1->w_name, b->b_lock2) == 0)
2079 			if (strcmp(w2->w_name, b->b_lock1) == 0)
2080 				return (1);
2081 	}
2082 	return (0);
2083 }
2084 #endif
2085 
2086 static struct witness *
2087 witness_get(void)
2088 {
2089 	struct witness *w;
2090 	int index;
2091 
2092 	if (witness_cold == 0)
2093 		mtx_assert(&w_mtx, MA_OWNED);
2094 
2095 	if (witness_watch == -1) {
2096 		mtx_unlock_spin(&w_mtx);
2097 		return (NULL);
2098 	}
2099 	if (STAILQ_EMPTY(&w_free)) {
2100 		witness_watch = -1;
2101 		mtx_unlock_spin(&w_mtx);
2102 		printf("WITNESS: unable to allocate a new witness object\n");
2103 		return (NULL);
2104 	}
2105 	w = STAILQ_FIRST(&w_free);
2106 	STAILQ_REMOVE_HEAD(&w_free, w_list);
2107 	w_free_cnt--;
2108 	index = w->w_index;
2109 	MPASS(index > 0 && index == w_max_used_index+1 &&
2110 	    index < witness_count);
2111 	bzero(w, sizeof(*w));
2112 	w->w_index = index;
2113 	if (index > w_max_used_index)
2114 		w_max_used_index = index;
2115 	return (w);
2116 }
2117 
2118 static void
2119 witness_free(struct witness *w)
2120 {
2121 
2122 	STAILQ_INSERT_HEAD(&w_free, w, w_list);
2123 	w_free_cnt++;
2124 }
2125 
2126 static struct lock_list_entry *
2127 witness_lock_list_get(void)
2128 {
2129 	struct lock_list_entry *lle;
2130 
2131 	if (witness_watch == -1)
2132 		return (NULL);
2133 	mtx_lock_spin(&w_mtx);
2134 	lle = w_lock_list_free;
2135 	if (lle == NULL) {
2136 		witness_watch = -1;
2137 		mtx_unlock_spin(&w_mtx);
2138 		printf("%s: witness exhausted\n", __func__);
2139 		return (NULL);
2140 	}
2141 	w_lock_list_free = lle->ll_next;
2142 	mtx_unlock_spin(&w_mtx);
2143 	bzero(lle, sizeof(*lle));
2144 	return (lle);
2145 }
2146 
2147 static void
2148 witness_lock_list_free(struct lock_list_entry *lle)
2149 {
2150 
2151 	mtx_lock_spin(&w_mtx);
2152 	lle->ll_next = w_lock_list_free;
2153 	w_lock_list_free = lle;
2154 	mtx_unlock_spin(&w_mtx);
2155 }
2156 
2157 static struct lock_instance *
2158 find_instance(struct lock_list_entry *list, const struct lock_object *lock)
2159 {
2160 	struct lock_list_entry *lle;
2161 	struct lock_instance *instance;
2162 	int i;
2163 
2164 	for (lle = list; lle != NULL; lle = lle->ll_next)
2165 		for (i = lle->ll_count - 1; i >= 0; i--) {
2166 			instance = &lle->ll_children[i];
2167 			if (instance->li_lock == lock)
2168 				return (instance);
2169 		}
2170 	return (NULL);
2171 }
2172 
2173 static void
2174 witness_list_lock(struct lock_instance *instance,
2175     int (*prnt)(const char *fmt, ...))
2176 {
2177 	struct lock_object *lock;
2178 
2179 	lock = instance->li_lock;
2180 	prnt("%s %s %s", (instance->li_flags & LI_EXCLUSIVE) != 0 ?
2181 	    "exclusive" : "shared", LOCK_CLASS(lock)->lc_name, lock->lo_name);
2182 	if (lock->lo_witness->w_name != lock->lo_name)
2183 		prnt(" (%s)", lock->lo_witness->w_name);
2184 	prnt(" r = %d (%p) locked @ %s:%d\n",
2185 	    instance->li_flags & LI_RECURSEMASK, lock,
2186 	    fixup_filename(instance->li_file), instance->li_line);
2187 }
2188 
2189 static int
2190 witness_output(const char *fmt, ...)
2191 {
2192 	va_list ap;
2193 	int ret;
2194 
2195 	va_start(ap, fmt);
2196 	ret = witness_voutput(fmt, ap);
2197 	va_end(ap);
2198 	return (ret);
2199 }
2200 
2201 static int
2202 witness_voutput(const char *fmt, va_list ap)
2203 {
2204 	int ret;
2205 
2206 	ret = 0;
2207 	switch (witness_channel) {
2208 	case WITNESS_CONSOLE:
2209 		ret = vprintf(fmt, ap);
2210 		break;
2211 	case WITNESS_LOG:
2212 		vlog(LOG_NOTICE, fmt, ap);
2213 		break;
2214 	case WITNESS_NONE:
2215 		break;
2216 	}
2217 	return (ret);
2218 }
2219 
2220 #ifdef DDB
2221 static int
2222 witness_thread_has_locks(struct thread *td)
2223 {
2224 
2225 	if (td->td_sleeplocks == NULL)
2226 		return (0);
2227 	return (td->td_sleeplocks->ll_count != 0);
2228 }
2229 
2230 static int
2231 witness_proc_has_locks(struct proc *p)
2232 {
2233 	struct thread *td;
2234 
2235 	FOREACH_THREAD_IN_PROC(p, td) {
2236 		if (witness_thread_has_locks(td))
2237 			return (1);
2238 	}
2239 	return (0);
2240 }
2241 #endif
2242 
2243 int
2244 witness_list_locks(struct lock_list_entry **lock_list,
2245     int (*prnt)(const char *fmt, ...))
2246 {
2247 	struct lock_list_entry *lle;
2248 	int i, nheld;
2249 
2250 	nheld = 0;
2251 	for (lle = *lock_list; lle != NULL; lle = lle->ll_next)
2252 		for (i = lle->ll_count - 1; i >= 0; i--) {
2253 			witness_list_lock(&lle->ll_children[i], prnt);
2254 			nheld++;
2255 		}
2256 	return (nheld);
2257 }
2258 
2259 /*
2260  * This is a bit risky at best.  We call this function when we have timed
2261  * out acquiring a spin lock, and we assume that the other CPU is stuck
2262  * with this lock held.  So, we go groveling around in the other CPU's
2263  * per-cpu data to try to find the lock instance for this spin lock to
2264  * see when it was last acquired.
2265  */
2266 void
2267 witness_display_spinlock(struct lock_object *lock, struct thread *owner,
2268     int (*prnt)(const char *fmt, ...))
2269 {
2270 	struct lock_instance *instance;
2271 	struct pcpu *pc;
2272 
2273 	if (owner->td_critnest == 0 || owner->td_oncpu == NOCPU)
2274 		return;
2275 	pc = pcpu_find(owner->td_oncpu);
2276 	instance = find_instance(pc->pc_spinlocks, lock);
2277 	if (instance != NULL)
2278 		witness_list_lock(instance, prnt);
2279 }
2280 
2281 void
2282 witness_save(struct lock_object *lock, const char **filep, int *linep)
2283 {
2284 	struct lock_list_entry *lock_list;
2285 	struct lock_instance *instance;
2286 	struct lock_class *class;
2287 
2288 	/*
2289 	 * This function is used independently in locking code to deal with
2290 	 * Giant, SCHEDULER_STOPPED() check can be removed here after Giant
2291 	 * is gone.
2292 	 */
2293 	if (SCHEDULER_STOPPED())
2294 		return;
2295 	KASSERT(witness_cold == 0, ("%s: witness_cold", __func__));
2296 	if (lock->lo_witness == NULL || witness_watch == -1 || panicstr != NULL)
2297 		return;
2298 	class = LOCK_CLASS(lock);
2299 	if (class->lc_flags & LC_SLEEPLOCK)
2300 		lock_list = curthread->td_sleeplocks;
2301 	else {
2302 		if (witness_skipspin)
2303 			return;
2304 		lock_list = PCPU_GET(spinlocks);
2305 	}
2306 	instance = find_instance(lock_list, lock);
2307 	if (instance == NULL) {
2308 		kassert_panic("%s: lock (%s) %s not locked", __func__,
2309 		    class->lc_name, lock->lo_name);
2310 		return;
2311 	}
2312 	*filep = instance->li_file;
2313 	*linep = instance->li_line;
2314 }
2315 
2316 void
2317 witness_restore(struct lock_object *lock, const char *file, int line)
2318 {
2319 	struct lock_list_entry *lock_list;
2320 	struct lock_instance *instance;
2321 	struct lock_class *class;
2322 
2323 	/*
2324 	 * This function is used independently in locking code to deal with
2325 	 * Giant, SCHEDULER_STOPPED() check can be removed here after Giant
2326 	 * is gone.
2327 	 */
2328 	if (SCHEDULER_STOPPED())
2329 		return;
2330 	KASSERT(witness_cold == 0, ("%s: witness_cold", __func__));
2331 	if (lock->lo_witness == NULL || witness_watch == -1 || panicstr != NULL)
2332 		return;
2333 	class = LOCK_CLASS(lock);
2334 	if (class->lc_flags & LC_SLEEPLOCK)
2335 		lock_list = curthread->td_sleeplocks;
2336 	else {
2337 		if (witness_skipspin)
2338 			return;
2339 		lock_list = PCPU_GET(spinlocks);
2340 	}
2341 	instance = find_instance(lock_list, lock);
2342 	if (instance == NULL)
2343 		kassert_panic("%s: lock (%s) %s not locked", __func__,
2344 		    class->lc_name, lock->lo_name);
2345 	lock->lo_witness->w_file = file;
2346 	lock->lo_witness->w_line = line;
2347 	if (instance == NULL)
2348 		return;
2349 	instance->li_file = file;
2350 	instance->li_line = line;
2351 }
2352 
2353 void
2354 witness_assert(const struct lock_object *lock, int flags, const char *file,
2355     int line)
2356 {
2357 #ifdef INVARIANT_SUPPORT
2358 	struct lock_instance *instance;
2359 	struct lock_class *class;
2360 
2361 	if (lock->lo_witness == NULL || witness_watch < 1 || panicstr != NULL)
2362 		return;
2363 	class = LOCK_CLASS(lock);
2364 	if ((class->lc_flags & LC_SLEEPLOCK) != 0)
2365 		instance = find_instance(curthread->td_sleeplocks, lock);
2366 	else if ((class->lc_flags & LC_SPINLOCK) != 0)
2367 		instance = find_instance(PCPU_GET(spinlocks), lock);
2368 	else {
2369 		kassert_panic("Lock (%s) %s is not sleep or spin!",
2370 		    class->lc_name, lock->lo_name);
2371 		return;
2372 	}
2373 	switch (flags) {
2374 	case LA_UNLOCKED:
2375 		if (instance != NULL)
2376 			kassert_panic("Lock (%s) %s locked @ %s:%d.",
2377 			    class->lc_name, lock->lo_name,
2378 			    fixup_filename(file), line);
2379 		break;
2380 	case LA_LOCKED:
2381 	case LA_LOCKED | LA_RECURSED:
2382 	case LA_LOCKED | LA_NOTRECURSED:
2383 	case LA_SLOCKED:
2384 	case LA_SLOCKED | LA_RECURSED:
2385 	case LA_SLOCKED | LA_NOTRECURSED:
2386 	case LA_XLOCKED:
2387 	case LA_XLOCKED | LA_RECURSED:
2388 	case LA_XLOCKED | LA_NOTRECURSED:
2389 		if (instance == NULL) {
2390 			kassert_panic("Lock (%s) %s not locked @ %s:%d.",
2391 			    class->lc_name, lock->lo_name,
2392 			    fixup_filename(file), line);
2393 			break;
2394 		}
2395 		if ((flags & LA_XLOCKED) != 0 &&
2396 		    (instance->li_flags & LI_EXCLUSIVE) == 0)
2397 			kassert_panic(
2398 			    "Lock (%s) %s not exclusively locked @ %s:%d.",
2399 			    class->lc_name, lock->lo_name,
2400 			    fixup_filename(file), line);
2401 		if ((flags & LA_SLOCKED) != 0 &&
2402 		    (instance->li_flags & LI_EXCLUSIVE) != 0)
2403 			kassert_panic(
2404 			    "Lock (%s) %s exclusively locked @ %s:%d.",
2405 			    class->lc_name, lock->lo_name,
2406 			    fixup_filename(file), line);
2407 		if ((flags & LA_RECURSED) != 0 &&
2408 		    (instance->li_flags & LI_RECURSEMASK) == 0)
2409 			kassert_panic("Lock (%s) %s not recursed @ %s:%d.",
2410 			    class->lc_name, lock->lo_name,
2411 			    fixup_filename(file), line);
2412 		if ((flags & LA_NOTRECURSED) != 0 &&
2413 		    (instance->li_flags & LI_RECURSEMASK) != 0)
2414 			kassert_panic("Lock (%s) %s recursed @ %s:%d.",
2415 			    class->lc_name, lock->lo_name,
2416 			    fixup_filename(file), line);
2417 		break;
2418 	default:
2419 		kassert_panic("Invalid lock assertion at %s:%d.",
2420 		    fixup_filename(file), line);
2421 
2422 	}
2423 #endif	/* INVARIANT_SUPPORT */
2424 }
2425 
2426 static void
2427 witness_setflag(struct lock_object *lock, int flag, int set)
2428 {
2429 	struct lock_list_entry *lock_list;
2430 	struct lock_instance *instance;
2431 	struct lock_class *class;
2432 
2433 	if (lock->lo_witness == NULL || witness_watch == -1 || panicstr != NULL)
2434 		return;
2435 	class = LOCK_CLASS(lock);
2436 	if (class->lc_flags & LC_SLEEPLOCK)
2437 		lock_list = curthread->td_sleeplocks;
2438 	else {
2439 		if (witness_skipspin)
2440 			return;
2441 		lock_list = PCPU_GET(spinlocks);
2442 	}
2443 	instance = find_instance(lock_list, lock);
2444 	if (instance == NULL) {
2445 		kassert_panic("%s: lock (%s) %s not locked", __func__,
2446 		    class->lc_name, lock->lo_name);
2447 		return;
2448 	}
2449 
2450 	if (set)
2451 		instance->li_flags |= flag;
2452 	else
2453 		instance->li_flags &= ~flag;
2454 }
2455 
2456 void
2457 witness_norelease(struct lock_object *lock)
2458 {
2459 
2460 	witness_setflag(lock, LI_NORELEASE, 1);
2461 }
2462 
2463 void
2464 witness_releaseok(struct lock_object *lock)
2465 {
2466 
2467 	witness_setflag(lock, LI_NORELEASE, 0);
2468 }
2469 
2470 #ifdef DDB
2471 static void
2472 witness_ddb_list(struct thread *td)
2473 {
2474 
2475 	KASSERT(witness_cold == 0, ("%s: witness_cold", __func__));
2476 	KASSERT(kdb_active, ("%s: not in the debugger", __func__));
2477 
2478 	if (witness_watch < 1)
2479 		return;
2480 
2481 	witness_list_locks(&td->td_sleeplocks, db_printf);
2482 
2483 	/*
2484 	 * We only handle spinlocks if td == curthread.  This is somewhat broken
2485 	 * if td is currently executing on some other CPU and holds spin locks
2486 	 * as we won't display those locks.  If we had a MI way of getting
2487 	 * the per-cpu data for a given cpu then we could use
2488 	 * td->td_oncpu to get the list of spinlocks for this thread
2489 	 * and "fix" this.
2490 	 *
2491 	 * That still wouldn't really fix this unless we locked the scheduler
2492 	 * lock or stopped the other CPU to make sure it wasn't changing the
2493 	 * list out from under us.  It is probably best to just not try to
2494 	 * handle threads on other CPU's for now.
2495 	 */
2496 	if (td == curthread && PCPU_GET(spinlocks) != NULL)
2497 		witness_list_locks(PCPU_PTR(spinlocks), db_printf);
2498 }
2499 
2500 DB_SHOW_COMMAND(locks, db_witness_list)
2501 {
2502 	struct thread *td;
2503 
2504 	if (have_addr)
2505 		td = db_lookup_thread(addr, true);
2506 	else
2507 		td = kdb_thread;
2508 	witness_ddb_list(td);
2509 }
2510 
2511 DB_SHOW_ALL_COMMAND(locks, db_witness_list_all)
2512 {
2513 	struct thread *td;
2514 	struct proc *p;
2515 
2516 	/*
2517 	 * It would be nice to list only threads and processes that actually
2518 	 * held sleep locks, but that information is currently not exported
2519 	 * by WITNESS.
2520 	 */
2521 	FOREACH_PROC_IN_SYSTEM(p) {
2522 		if (!witness_proc_has_locks(p))
2523 			continue;
2524 		FOREACH_THREAD_IN_PROC(p, td) {
2525 			if (!witness_thread_has_locks(td))
2526 				continue;
2527 			db_printf("Process %d (%s) thread %p (%d)\n", p->p_pid,
2528 			    p->p_comm, td, td->td_tid);
2529 			witness_ddb_list(td);
2530 			if (db_pager_quit)
2531 				return;
2532 		}
2533 	}
2534 }
2535 DB_SHOW_ALIAS(alllocks, db_witness_list_all)
2536 
2537 DB_SHOW_COMMAND(witness, db_witness_display)
2538 {
2539 
2540 	witness_ddb_display(db_printf);
2541 }
2542 #endif
2543 
2544 static void
2545 sbuf_print_witness_badstacks(struct sbuf *sb, size_t *oldidx)
2546 {
2547 	struct witness_lock_order_data *data1, *data2, *tmp_data1, *tmp_data2;
2548 	struct witness *tmp_w1, *tmp_w2, *w1, *w2;
2549 	u_int w_rmatrix1, w_rmatrix2;
2550 	int generation, i, j;
2551 
2552 	tmp_data1 = NULL;
2553 	tmp_data2 = NULL;
2554 	tmp_w1 = NULL;
2555 	tmp_w2 = NULL;
2556 
2557 	/* Allocate and init temporary storage space. */
2558 	tmp_w1 = malloc(sizeof(struct witness), M_TEMP, M_WAITOK | M_ZERO);
2559 	tmp_w2 = malloc(sizeof(struct witness), M_TEMP, M_WAITOK | M_ZERO);
2560 	tmp_data1 = malloc(sizeof(struct witness_lock_order_data), M_TEMP,
2561 	    M_WAITOK | M_ZERO);
2562 	tmp_data2 = malloc(sizeof(struct witness_lock_order_data), M_TEMP,
2563 	    M_WAITOK | M_ZERO);
2564 	stack_zero(&tmp_data1->wlod_stack);
2565 	stack_zero(&tmp_data2->wlod_stack);
2566 
2567 restart:
2568 	mtx_lock_spin(&w_mtx);
2569 	generation = w_generation;
2570 	mtx_unlock_spin(&w_mtx);
2571 	sbuf_printf(sb, "Number of known direct relationships is %d\n",
2572 	    w_lohash.wloh_count);
2573 	for (i = 1; i < w_max_used_index; i++) {
2574 		mtx_lock_spin(&w_mtx);
2575 		if (generation != w_generation) {
2576 			mtx_unlock_spin(&w_mtx);
2577 
2578 			/* The graph has changed, try again. */
2579 			*oldidx = 0;
2580 			sbuf_clear(sb);
2581 			goto restart;
2582 		}
2583 
2584 		w1 = &w_data[i];
2585 		if (w1->w_reversed == 0) {
2586 			mtx_unlock_spin(&w_mtx);
2587 			continue;
2588 		}
2589 
2590 		/* Copy w1 locally so we can release the spin lock. */
2591 		*tmp_w1 = *w1;
2592 		mtx_unlock_spin(&w_mtx);
2593 
2594 		if (tmp_w1->w_reversed == 0)
2595 			continue;
2596 		for (j = 1; j < w_max_used_index; j++) {
2597 			if ((w_rmatrix[i][j] & WITNESS_REVERSAL) == 0 || i > j)
2598 				continue;
2599 
2600 			mtx_lock_spin(&w_mtx);
2601 			if (generation != w_generation) {
2602 				mtx_unlock_spin(&w_mtx);
2603 
2604 				/* The graph has changed, try again. */
2605 				*oldidx = 0;
2606 				sbuf_clear(sb);
2607 				goto restart;
2608 			}
2609 
2610 			w2 = &w_data[j];
2611 			data1 = witness_lock_order_get(w1, w2);
2612 			data2 = witness_lock_order_get(w2, w1);
2613 
2614 			/*
2615 			 * Copy information locally so we can release the
2616 			 * spin lock.
2617 			 */
2618 			*tmp_w2 = *w2;
2619 			w_rmatrix1 = (unsigned int)w_rmatrix[i][j];
2620 			w_rmatrix2 = (unsigned int)w_rmatrix[j][i];
2621 
2622 			if (data1) {
2623 				stack_zero(&tmp_data1->wlod_stack);
2624 				stack_copy(&data1->wlod_stack,
2625 				    &tmp_data1->wlod_stack);
2626 			}
2627 			if (data2 && data2 != data1) {
2628 				stack_zero(&tmp_data2->wlod_stack);
2629 				stack_copy(&data2->wlod_stack,
2630 				    &tmp_data2->wlod_stack);
2631 			}
2632 			mtx_unlock_spin(&w_mtx);
2633 
2634 			sbuf_printf(sb,
2635 	    "\nLock order reversal between \"%s\"(%s) and \"%s\"(%s)!\n",
2636 			    tmp_w1->w_name, tmp_w1->w_class->lc_name,
2637 			    tmp_w2->w_name, tmp_w2->w_class->lc_name);
2638 			if (data1) {
2639 				sbuf_printf(sb,
2640 			"Lock order \"%s\"(%s) -> \"%s\"(%s) first seen at:\n",
2641 				    tmp_w1->w_name, tmp_w1->w_class->lc_name,
2642 				    tmp_w2->w_name, tmp_w2->w_class->lc_name);
2643 				stack_sbuf_print(sb, &tmp_data1->wlod_stack);
2644 				sbuf_printf(sb, "\n");
2645 			}
2646 			if (data2 && data2 != data1) {
2647 				sbuf_printf(sb,
2648 			"Lock order \"%s\"(%s) -> \"%s\"(%s) first seen at:\n",
2649 				    tmp_w2->w_name, tmp_w2->w_class->lc_name,
2650 				    tmp_w1->w_name, tmp_w1->w_class->lc_name);
2651 				stack_sbuf_print(sb, &tmp_data2->wlod_stack);
2652 				sbuf_printf(sb, "\n");
2653 			}
2654 		}
2655 	}
2656 	mtx_lock_spin(&w_mtx);
2657 	if (generation != w_generation) {
2658 		mtx_unlock_spin(&w_mtx);
2659 
2660 		/*
2661 		 * The graph changed while we were printing stack data,
2662 		 * try again.
2663 		 */
2664 		*oldidx = 0;
2665 		sbuf_clear(sb);
2666 		goto restart;
2667 	}
2668 	mtx_unlock_spin(&w_mtx);
2669 
2670 	/* Free temporary storage space. */
2671 	free(tmp_data1, M_TEMP);
2672 	free(tmp_data2, M_TEMP);
2673 	free(tmp_w1, M_TEMP);
2674 	free(tmp_w2, M_TEMP);
2675 }
2676 
2677 static int
2678 sysctl_debug_witness_badstacks(SYSCTL_HANDLER_ARGS)
2679 {
2680 	struct sbuf *sb;
2681 	int error;
2682 
2683 	if (witness_watch < 1) {
2684 		error = SYSCTL_OUT(req, w_notrunning, sizeof(w_notrunning));
2685 		return (error);
2686 	}
2687 	if (witness_cold) {
2688 		error = SYSCTL_OUT(req, w_stillcold, sizeof(w_stillcold));
2689 		return (error);
2690 	}
2691 	error = 0;
2692 	sb = sbuf_new(NULL, NULL, badstack_sbuf_size, SBUF_AUTOEXTEND);
2693 	if (sb == NULL)
2694 		return (ENOMEM);
2695 
2696 	sbuf_print_witness_badstacks(sb, &req->oldidx);
2697 
2698 	sbuf_finish(sb);
2699 	error = SYSCTL_OUT(req, sbuf_data(sb), sbuf_len(sb) + 1);
2700 	sbuf_delete(sb);
2701 
2702 	return (error);
2703 }
2704 
2705 #ifdef DDB
2706 static int
2707 sbuf_db_printf_drain(void *arg __unused, const char *data, int len)
2708 {
2709 
2710 	return (db_printf("%.*s", len, data));
2711 }
2712 
2713 DB_SHOW_COMMAND(badstacks, db_witness_badstacks)
2714 {
2715 	struct sbuf sb;
2716 	char buffer[128];
2717 	size_t dummy;
2718 
2719 	sbuf_new(&sb, buffer, sizeof(buffer), SBUF_FIXEDLEN);
2720 	sbuf_set_drain(&sb, sbuf_db_printf_drain, NULL);
2721 	sbuf_print_witness_badstacks(&sb, &dummy);
2722 	sbuf_finish(&sb);
2723 }
2724 #endif
2725 
2726 static int
2727 sysctl_debug_witness_channel(SYSCTL_HANDLER_ARGS)
2728 {
2729 	static const struct {
2730 		enum witness_channel channel;
2731 		const char *name;
2732 	} channels[] = {
2733 		{ WITNESS_CONSOLE, "console" },
2734 		{ WITNESS_LOG, "log" },
2735 		{ WITNESS_NONE, "none" },
2736 	};
2737 	char buf[16];
2738 	u_int i;
2739 	int error;
2740 
2741 	buf[0] = '\0';
2742 	for (i = 0; i < nitems(channels); i++)
2743 		if (witness_channel == channels[i].channel) {
2744 			snprintf(buf, sizeof(buf), "%s", channels[i].name);
2745 			break;
2746 		}
2747 
2748 	error = sysctl_handle_string(oidp, buf, sizeof(buf), req);
2749 	if (error != 0 || req->newptr == NULL)
2750 		return (error);
2751 
2752 	error = EINVAL;
2753 	for (i = 0; i < nitems(channels); i++)
2754 		if (strcmp(channels[i].name, buf) == 0) {
2755 			witness_channel = channels[i].channel;
2756 			error = 0;
2757 			break;
2758 		}
2759 	return (error);
2760 }
2761 
2762 static int
2763 sysctl_debug_witness_fullgraph(SYSCTL_HANDLER_ARGS)
2764 {
2765 	struct witness *w;
2766 	struct sbuf *sb;
2767 	int error;
2768 
2769 	if (witness_watch < 1) {
2770 		error = SYSCTL_OUT(req, w_notrunning, sizeof(w_notrunning));
2771 		return (error);
2772 	}
2773 	if (witness_cold) {
2774 		error = SYSCTL_OUT(req, w_stillcold, sizeof(w_stillcold));
2775 		return (error);
2776 	}
2777 	error = 0;
2778 
2779 	error = sysctl_wire_old_buffer(req, 0);
2780 	if (error != 0)
2781 		return (error);
2782 	sb = sbuf_new_for_sysctl(NULL, NULL, FULLGRAPH_SBUF_SIZE, req);
2783 	if (sb == NULL)
2784 		return (ENOMEM);
2785 	sbuf_printf(sb, "\n");
2786 
2787 	mtx_lock_spin(&w_mtx);
2788 	STAILQ_FOREACH(w, &w_all, w_list)
2789 		w->w_displayed = 0;
2790 	STAILQ_FOREACH(w, &w_all, w_list)
2791 		witness_add_fullgraph(sb, w);
2792 	mtx_unlock_spin(&w_mtx);
2793 
2794 	/*
2795 	 * Close the sbuf and return to userland.
2796 	 */
2797 	error = sbuf_finish(sb);
2798 	sbuf_delete(sb);
2799 
2800 	return (error);
2801 }
2802 
2803 static int
2804 sysctl_debug_witness_watch(SYSCTL_HANDLER_ARGS)
2805 {
2806 	int error, value;
2807 
2808 	value = witness_watch;
2809 	error = sysctl_handle_int(oidp, &value, 0, req);
2810 	if (error != 0 || req->newptr == NULL)
2811 		return (error);
2812 	if (value > 1 || value < -1 ||
2813 	    (witness_watch == -1 && value != witness_watch))
2814 		return (EINVAL);
2815 	witness_watch = value;
2816 	return (0);
2817 }
2818 
2819 static void
2820 witness_add_fullgraph(struct sbuf *sb, struct witness *w)
2821 {
2822 	int i;
2823 
2824 	if (w->w_displayed != 0 || (w->w_file == NULL && w->w_line == 0))
2825 		return;
2826 	w->w_displayed = 1;
2827 
2828 	WITNESS_INDEX_ASSERT(w->w_index);
2829 	for (i = 1; i <= w_max_used_index; i++) {
2830 		if (w_rmatrix[w->w_index][i] & WITNESS_PARENT) {
2831 			sbuf_printf(sb, "\"%s\",\"%s\"\n", w->w_name,
2832 			    w_data[i].w_name);
2833 			witness_add_fullgraph(sb, &w_data[i]);
2834 		}
2835 	}
2836 }
2837 
2838 /*
2839  * A simple hash function. Takes a key pointer and a key size. If size == 0,
2840  * interprets the key as a string and reads until the null
2841  * terminator. Otherwise, reads the first size bytes. Returns an unsigned 32-bit
2842  * hash value computed from the key.
2843  */
2844 static uint32_t
2845 witness_hash_djb2(const uint8_t *key, uint32_t size)
2846 {
2847 	unsigned int hash = 5381;
2848 	int i;
2849 
2850 	/* hash = hash * 33 + key[i] */
2851 	if (size)
2852 		for (i = 0; i < size; i++)
2853 			hash = ((hash << 5) + hash) + (unsigned int)key[i];
2854 	else
2855 		for (i = 0; key[i] != 0; i++)
2856 			hash = ((hash << 5) + hash) + (unsigned int)key[i];
2857 
2858 	return (hash);
2859 }
2860 
2861 
2862 /*
2863  * Initializes the two witness hash tables. Called exactly once from
2864  * witness_initialize().
2865  */
2866 static void
2867 witness_init_hash_tables(void)
2868 {
2869 	int i;
2870 
2871 	MPASS(witness_cold);
2872 
2873 	/* Initialize the hash tables. */
2874 	for (i = 0; i < WITNESS_HASH_SIZE; i++)
2875 		w_hash.wh_array[i] = NULL;
2876 
2877 	w_hash.wh_size = WITNESS_HASH_SIZE;
2878 	w_hash.wh_count = 0;
2879 
2880 	/* Initialize the lock order data hash. */
2881 	w_lofree = NULL;
2882 	for (i = 0; i < WITNESS_LO_DATA_COUNT; i++) {
2883 		memset(&w_lodata[i], 0, sizeof(w_lodata[i]));
2884 		w_lodata[i].wlod_next = w_lofree;
2885 		w_lofree = &w_lodata[i];
2886 	}
2887 	w_lohash.wloh_size = WITNESS_LO_HASH_SIZE;
2888 	w_lohash.wloh_count = 0;
2889 	for (i = 0; i < WITNESS_LO_HASH_SIZE; i++)
2890 		w_lohash.wloh_array[i] = NULL;
2891 }
2892 
2893 static struct witness *
2894 witness_hash_get(const char *key)
2895 {
2896 	struct witness *w;
2897 	uint32_t hash;
2898 
2899 	MPASS(key != NULL);
2900 	if (witness_cold == 0)
2901 		mtx_assert(&w_mtx, MA_OWNED);
2902 	hash = witness_hash_djb2(key, 0) % w_hash.wh_size;
2903 	w = w_hash.wh_array[hash];
2904 	while (w != NULL) {
2905 		if (strcmp(w->w_name, key) == 0)
2906 			goto out;
2907 		w = w->w_hash_next;
2908 	}
2909 
2910 out:
2911 	return (w);
2912 }
2913 
2914 static void
2915 witness_hash_put(struct witness *w)
2916 {
2917 	uint32_t hash;
2918 
2919 	MPASS(w != NULL);
2920 	MPASS(w->w_name != NULL);
2921 	if (witness_cold == 0)
2922 		mtx_assert(&w_mtx, MA_OWNED);
2923 	KASSERT(witness_hash_get(w->w_name) == NULL,
2924 	    ("%s: trying to add a hash entry that already exists!", __func__));
2925 	KASSERT(w->w_hash_next == NULL,
2926 	    ("%s: w->w_hash_next != NULL", __func__));
2927 
2928 	hash = witness_hash_djb2(w->w_name, 0) % w_hash.wh_size;
2929 	w->w_hash_next = w_hash.wh_array[hash];
2930 	w_hash.wh_array[hash] = w;
2931 	w_hash.wh_count++;
2932 }
2933 
2934 
2935 static struct witness_lock_order_data *
2936 witness_lock_order_get(struct witness *parent, struct witness *child)
2937 {
2938 	struct witness_lock_order_data *data = NULL;
2939 	struct witness_lock_order_key key;
2940 	unsigned int hash;
2941 
2942 	MPASS(parent != NULL && child != NULL);
2943 	key.from = parent->w_index;
2944 	key.to = child->w_index;
2945 	WITNESS_INDEX_ASSERT(key.from);
2946 	WITNESS_INDEX_ASSERT(key.to);
2947 	if ((w_rmatrix[parent->w_index][child->w_index]
2948 	    & WITNESS_LOCK_ORDER_KNOWN) == 0)
2949 		goto out;
2950 
2951 	hash = witness_hash_djb2((const char*)&key,
2952 	    sizeof(key)) % w_lohash.wloh_size;
2953 	data = w_lohash.wloh_array[hash];
2954 	while (data != NULL) {
2955 		if (witness_lock_order_key_equal(&data->wlod_key, &key))
2956 			break;
2957 		data = data->wlod_next;
2958 	}
2959 
2960 out:
2961 	return (data);
2962 }
2963 
2964 /*
2965  * Verify that parent and child have a known relationship, are not the same,
2966  * and child is actually a child of parent.  This is done without w_mtx
2967  * to avoid contention in the common case.
2968  */
2969 static int
2970 witness_lock_order_check(struct witness *parent, struct witness *child)
2971 {
2972 
2973 	if (parent != child &&
2974 	    w_rmatrix[parent->w_index][child->w_index]
2975 	    & WITNESS_LOCK_ORDER_KNOWN &&
2976 	    isitmychild(parent, child))
2977 		return (1);
2978 
2979 	return (0);
2980 }
2981 
2982 static int
2983 witness_lock_order_add(struct witness *parent, struct witness *child)
2984 {
2985 	struct witness_lock_order_data *data = NULL;
2986 	struct witness_lock_order_key key;
2987 	unsigned int hash;
2988 
2989 	MPASS(parent != NULL && child != NULL);
2990 	key.from = parent->w_index;
2991 	key.to = child->w_index;
2992 	WITNESS_INDEX_ASSERT(key.from);
2993 	WITNESS_INDEX_ASSERT(key.to);
2994 	if (w_rmatrix[parent->w_index][child->w_index]
2995 	    & WITNESS_LOCK_ORDER_KNOWN)
2996 		return (1);
2997 
2998 	hash = witness_hash_djb2((const char*)&key,
2999 	    sizeof(key)) % w_lohash.wloh_size;
3000 	w_rmatrix[parent->w_index][child->w_index] |= WITNESS_LOCK_ORDER_KNOWN;
3001 	data = w_lofree;
3002 	if (data == NULL)
3003 		return (0);
3004 	w_lofree = data->wlod_next;
3005 	data->wlod_next = w_lohash.wloh_array[hash];
3006 	data->wlod_key = key;
3007 	w_lohash.wloh_array[hash] = data;
3008 	w_lohash.wloh_count++;
3009 	stack_zero(&data->wlod_stack);
3010 	stack_save(&data->wlod_stack);
3011 	return (1);
3012 }
3013 
3014 /* Call this whenever the structure of the witness graph changes. */
3015 static void
3016 witness_increment_graph_generation(void)
3017 {
3018 
3019 	if (witness_cold == 0)
3020 		mtx_assert(&w_mtx, MA_OWNED);
3021 	w_generation++;
3022 }
3023 
3024 static int
3025 witness_output_drain(void *arg __unused, const char *data, int len)
3026 {
3027 
3028 	witness_output("%.*s", len, data);
3029 	return (len);
3030 }
3031 
3032 static void
3033 witness_debugger(int cond, const char *msg)
3034 {
3035 	char buf[32];
3036 	struct sbuf sb;
3037 	struct stack st;
3038 
3039 	if (!cond)
3040 		return;
3041 
3042 	if (witness_trace) {
3043 		sbuf_new(&sb, buf, sizeof(buf), SBUF_FIXEDLEN);
3044 		sbuf_set_drain(&sb, witness_output_drain, NULL);
3045 
3046 		stack_zero(&st);
3047 		stack_save(&st);
3048 		witness_output("stack backtrace:\n");
3049 		stack_sbuf_print_ddb(&sb, &st);
3050 
3051 		sbuf_finish(&sb);
3052 	}
3053 
3054 #ifdef KDB
3055 	if (witness_kdb)
3056 		kdb_enter(KDB_WHY_WITNESS, msg);
3057 #endif
3058 }
3059