- Add a new KTR_SUBSYS in place of KTR_SPARE1 to serve as a subsystem

[FreeBSD/FreeBSD.git] / sys / kern / subr_witness.c

/*-
 * Copyright (c) 1998 Berkeley Software Design, Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Berkeley Software Design Inc's name may not be used to endorse or
 *    promote products derived from this software without specific prior
 *    written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY BERKELEY SOFTWARE DESIGN INC ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL BERKELEY SOFTWARE DESIGN INC BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *      from BSDI $Id: mutex_witness.c,v 1.1.2.20 2000/04/27 03:10:27 cp Exp $
 *      and BSDI $Id: synch_machdep.c,v 2.3.2.39 2000/04/27 03:10:25 cp Exp $
 */

/*
 * Implementation of the `witness' lock verifier.  Originally implemented for
 * mutexes in BSD/OS.  Extended to handle generic lock objects and lock
 * classes in FreeBSD.
 */

/*
 *      Main Entry: witness
 *      Pronunciation: 'wit-n&s
 *      Function: noun
 *      Etymology: Middle English witnesse, from Old English witnes knowledge,
 *          testimony, witness, from 2wit
 *      Date: before 12th century
 *      1 : attestation of a fact or event : TESTIMONY
 *      2 : one that gives evidence; specifically : one who testifies in
 *          a cause or before a judicial tribunal
 *      3 : one asked to be present at a transaction so as to be able to
 *          testify to its having taken place
 *      4 : one who has personal knowledge of something
 *      5 a : something serving as evidence or proof : SIGN
 *        b : public affirmation by word or example of usually
 *            religious faith or conviction <the heroic witness to divine
 *            life -- Pilot>
 *      6 capitalized : a member of the Jehovah's Witnesses 
 */

/*
 * Special rules concerning Giant and lock orders:
 *
 * 1) Giant must be acquired before any other mutexes.  Stated another way,
 *    no other mutex may be held when Giant is acquired.
 *
 * 2) Giant must be released when blocking on a sleepable lock.
 *
 * This rule is less obvious, but is a result of Giant providing the same
 * semantics as spl().  Basically, when a thread sleeps, it must release
 * Giant.  When a thread blocks on a sleepable lock, it sleeps.  Hence rule
 * 2).
 *
 * 3) Giant may be acquired before or after sleepable locks.
 *
 * This rule is also not quite as obvious.  Giant may be acquired after
 * a sleepable lock because it is a non-sleepable lock and non-sleepable
 * locks may always be acquired while holding a sleepable lock.  The second
 * case, Giant before a sleepable lock, follows from rule 2) above.  Suppose
 * you have two threads T1 and T2 and a sleepable lock X.  Suppose that T1
 * acquires X and blocks on Giant.  Then suppose that T2 acquires Giant and
 * blocks on X.  When T2 blocks on X, T2 will release Giant allowing T1 to
 * execute.  Thus, acquiring Giant both before and after a sleepable lock
 * will not result in a lock order reversal.
 */

#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");

#include "opt_ddb.h"
#include "opt_witness.h"

#include <sys/param.h>
#include <sys/bus.h>
#include <sys/kdb.h>
#include <sys/kernel.h>
#include <sys/ktr.h>
#include <sys/lock.h>
#include <sys/malloc.h>
#include <sys/mutex.h>
#include <sys/proc.h>
#include <sys/sysctl.h>
#include <sys/systm.h>

#include <ddb/ddb.h>

#include <machine/stdarg.h>

#if 0
#define KTR_WITNESS     KTR_SUBSYS
#else
#define KTR_WITNESS     0
#endif

/* Easier to stay with the old names. */
#define lo_list         lo_witness_data.lod_list
#define lo_witness      lo_witness_data.lod_witness

/* Define this to check for blessed mutexes */
#undef BLESSING

#define WITNESS_COUNT 1024
#define WITNESS_CHILDCOUNT (WITNESS_COUNT * 4)
/*
 * XXX: This is somewhat bogus, as we assume here that at most 1024 threads
 * will hold LOCK_NCHILDREN * 2 locks.  We handle failure ok, and we should
 * probably be safe for the most part, but it's still a SWAG.
 */
#define LOCK_CHILDCOUNT (MAXCPU + 1024) * 2

#define WITNESS_NCHILDREN 6

struct witness_child_list_entry;

struct witness {
        const   char *w_name;
        struct  lock_class *w_class;
        STAILQ_ENTRY(witness) w_list;           /* List of all witnesses. */
        STAILQ_ENTRY(witness) w_typelist;       /* Witnesses of a type. */
        struct  witness_child_list_entry *w_children;   /* Great evilness... */
        const   char *w_file;
        int     w_line;
        u_int   w_level;
        u_int   w_refcount;
        u_char  w_Giant_squawked:1;
        u_char  w_other_squawked:1;
        u_char  w_same_squawked:1;
        u_char  w_displayed:1;
};

struct witness_child_list_entry {
        struct  witness_child_list_entry *wcl_next;
        struct  witness *wcl_children[WITNESS_NCHILDREN];
        u_int   wcl_count;
};

STAILQ_HEAD(witness_list, witness);

#ifdef BLESSING
struct witness_blessed {
        const   char *b_lock1;
        const   char *b_lock2;
};
#endif

struct witness_order_list_entry {
        const   char *w_name;
        struct  lock_class *w_class;
};

#ifdef BLESSING
static int      blessed(struct witness *, struct witness *);
#endif
static int      depart(struct witness *w);
static struct   witness *enroll(const char *description,
                                struct lock_class *lock_class);
static int      insertchild(struct witness *parent, struct witness *child);
static int      isitmychild(struct witness *parent, struct witness *child);
static int      isitmydescendant(struct witness *parent, struct witness *child);
static int      itismychild(struct witness *parent, struct witness *child);
static void     removechild(struct witness *parent, struct witness *child);
static int      sysctl_debug_witness_watch(SYSCTL_HANDLER_ARGS);
static const char *fixup_filename(const char *file);
static struct   witness *witness_get(void);
static void     witness_free(struct witness *m);
static struct   witness_child_list_entry *witness_child_get(void);
static void     witness_child_free(struct witness_child_list_entry *wcl);
static struct   lock_list_entry *witness_lock_list_get(void);
static void     witness_lock_list_free(struct lock_list_entry *lle);
static struct   lock_instance *find_instance(struct lock_list_entry *lock_list,
                                             struct lock_object *lock);
static void     witness_list_lock(struct lock_instance *instance);
#ifdef DDB
static void     witness_leveldescendents(struct witness *parent, int level);
static void     witness_levelall(void);
static void     witness_displaydescendants(void(*)(const char *fmt, ...),
                                           struct witness *, int indent);
static void     witness_display_list(void(*prnt)(const char *fmt, ...),
                                     struct witness_list *list);
static void     witness_display(void(*)(const char *fmt, ...));
static void     witness_list(struct thread *td);
#endif

SYSCTL_NODE(_debug, OID_AUTO, witness, CTLFLAG_RW, 0, "Witness Locking");

/*
 * If set to 0, witness is disabled.  If set to a non-zero value, witness
 * performs full lock order checking for all locks.  At runtime, this
 * value may be set to 0 to turn off witness.  witness is not allowed be
 * turned on once it is turned off, however.
 */
static int witness_watch = 1;
TUNABLE_INT("debug.witness.watch", &witness_watch);
SYSCTL_PROC(_debug_witness, OID_AUTO, watch, CTLFLAG_RW | CTLTYPE_INT, NULL, 0,
    sysctl_debug_witness_watch, "I", "witness is watching lock operations");

#ifdef KDB
/*
 * When KDB is enabled and witness_kdb is set to 1, it will cause the system
 * to drop into kdebug() when:
 *      - a lock hierarchy violation occurs
 *      - locks are held when going to sleep.
 */
#ifdef WITNESS_KDB
int     witness_kdb = 1;
#else
int     witness_kdb = 0;
#endif
TUNABLE_INT("debug.witness.kdb", &witness_kdb);
SYSCTL_INT(_debug_witness, OID_AUTO, kdb, CTLFLAG_RW, &witness_kdb, 0, "");

/*
 * When KDB is enabled and witness_trace is set to 1, it will cause the system
 * to print a stack trace:
 *      - a lock hierarchy violation occurs
 *      - locks are held when going to sleep.
 */
int     witness_trace = 1;
TUNABLE_INT("debug.witness.trace", &witness_trace);
SYSCTL_INT(_debug_witness, OID_AUTO, trace, CTLFLAG_RW, &witness_trace, 0, "");
#endif /* KDB */

#ifdef WITNESS_SKIPSPIN
int     witness_skipspin = 1;
#else
int     witness_skipspin = 0;
#endif
TUNABLE_INT("debug.witness.skipspin", &witness_skipspin);
SYSCTL_INT(_debug_witness, OID_AUTO, skipspin, CTLFLAG_RDTUN,
    &witness_skipspin, 0, "");

static struct mtx w_mtx;
static struct witness_list w_free = STAILQ_HEAD_INITIALIZER(w_free);
static struct witness_list w_all = STAILQ_HEAD_INITIALIZER(w_all);
static struct witness_list w_spin = STAILQ_HEAD_INITIALIZER(w_spin);
static struct witness_list w_sleep = STAILQ_HEAD_INITIALIZER(w_sleep);
static struct witness_child_list_entry *w_child_free = NULL;
static struct lock_list_entry *w_lock_list_free = NULL;

static int w_free_cnt, w_spin_cnt, w_sleep_cnt, w_child_free_cnt, w_child_cnt;
SYSCTL_INT(_debug_witness, OID_AUTO, free_cnt, CTLFLAG_RD, &w_free_cnt, 0, "");
SYSCTL_INT(_debug_witness, OID_AUTO, spin_cnt, CTLFLAG_RD, &w_spin_cnt, 0, "");
SYSCTL_INT(_debug_witness, OID_AUTO, sleep_cnt, CTLFLAG_RD, &w_sleep_cnt, 0,
    "");
SYSCTL_INT(_debug_witness, OID_AUTO, child_free_cnt, CTLFLAG_RD,
    &w_child_free_cnt, 0, "");
SYSCTL_INT(_debug_witness, OID_AUTO, child_cnt, CTLFLAG_RD, &w_child_cnt, 0,
    "");

static struct witness w_data[WITNESS_COUNT];
static struct witness_child_list_entry w_childdata[WITNESS_CHILDCOUNT];
static struct lock_list_entry w_locklistdata[LOCK_CHILDCOUNT];

static struct witness_order_list_entry order_lists[] = {
        /*
         * sx locks
         */
        { "proctree", &lock_class_sx },
        { "allproc", &lock_class_sx },
        { NULL, NULL },
        /*
         * Various mutexes
         */
        { "Giant", &lock_class_mtx_sleep },
        { "filedesc structure", &lock_class_mtx_sleep },
        { "pipe mutex", &lock_class_mtx_sleep },
        { "sigio lock", &lock_class_mtx_sleep },
        { "process group", &lock_class_mtx_sleep },
        { "process lock", &lock_class_mtx_sleep },
        { "session", &lock_class_mtx_sleep },
        { "uidinfo hash", &lock_class_mtx_sleep },
        { "uidinfo struct", &lock_class_mtx_sleep },
        { "allprison", &lock_class_mtx_sleep },
        { NULL, NULL },
        /*
         * Sockets
         */
        { "filedesc structure", &lock_class_mtx_sleep },
        { "accept", &lock_class_mtx_sleep },
        { "so_snd", &lock_class_mtx_sleep },
        { "so_rcv", &lock_class_mtx_sleep },
        { "sellck", &lock_class_mtx_sleep },
        { NULL, NULL },
        /*
         * Routing
         */
        { "so_rcv", &lock_class_mtx_sleep },
        { "radix node head", &lock_class_mtx_sleep },
        { "rtentry", &lock_class_mtx_sleep },
        { "ifaddr", &lock_class_mtx_sleep },
        { NULL, NULL },
        /*
         * Multicast - protocol locks before interface locks, after UDP locks.
         */
        { "udpinp", &lock_class_mtx_sleep },
        { "in_multi_mtx", &lock_class_mtx_sleep },
        { "igmp_mtx", &lock_class_mtx_sleep },
        { "if_addr_mtx", &lock_class_mtx_sleep },
        { NULL, NULL },
        /*
         * UNIX Domain Sockets
         */
        { "unp", &lock_class_mtx_sleep },
        { "so_snd", &lock_class_mtx_sleep },
        { NULL, NULL },
        /*
         * UDP/IP
         */
        { "udp", &lock_class_mtx_sleep },
        { "udpinp", &lock_class_mtx_sleep },
        { "so_snd", &lock_class_mtx_sleep },
        { NULL, NULL },
        /*
         * TCP/IP
         */
        { "tcp", &lock_class_mtx_sleep },
        { "tcpinp", &lock_class_mtx_sleep },
        { "so_snd", &lock_class_mtx_sleep },
        { NULL, NULL },
        /*
         * SLIP
         */
        { "slip_mtx", &lock_class_mtx_sleep },
        { "slip sc_mtx", &lock_class_mtx_sleep },
        { NULL, NULL },
        /*
         * netatalk
         */
        { "ddp_list_mtx", &lock_class_mtx_sleep },
        { "ddp_mtx", &lock_class_mtx_sleep },
        { NULL, NULL },
        /*
         * BPF
         */
        { "bpf global lock", &lock_class_mtx_sleep },
        { "bpf interface lock", &lock_class_mtx_sleep },
        { "bpf cdev lock", &lock_class_mtx_sleep },
        { NULL, NULL },
        /*
         * NFS server
         */
        { "nfsd_mtx", &lock_class_mtx_sleep },
        { "so_snd", &lock_class_mtx_sleep },
        { NULL, NULL },
        /*
         * CDEV
         */
        { "system map", &lock_class_mtx_sleep },
        { "vm page queue mutex", &lock_class_mtx_sleep },
        { "vnode interlock", &lock_class_mtx_sleep },
        { "cdev", &lock_class_mtx_sleep },
        { NULL, NULL },
        /*
         * spin locks
         */
#ifdef SMP
        { "ap boot", &lock_class_mtx_spin },
#endif
        { "rm.mutex_mtx", &lock_class_mtx_spin },
        { "hptlock", &lock_class_mtx_spin },
        { "sio", &lock_class_mtx_spin },
#ifdef __i386__
        { "cy", &lock_class_mtx_spin },
#endif
        { "uart_hwmtx", &lock_class_mtx_spin },
        { "sabtty", &lock_class_mtx_spin },
        { "zstty", &lock_class_mtx_spin },
        { "ng_node", &lock_class_mtx_spin },
        { "ng_worklist", &lock_class_mtx_spin },
        { "taskqueue_fast", &lock_class_mtx_spin },
        { "intr table", &lock_class_mtx_spin },
        { "sleepq chain", &lock_class_mtx_spin },
        { "sched lock", &lock_class_mtx_spin },
        { "turnstile chain", &lock_class_mtx_spin },
        { "td_contested", &lock_class_mtx_spin },
        { "callout", &lock_class_mtx_spin },
        { "entropy harvest mutex", &lock_class_mtx_spin },
        /*
         * leaf locks
         */
        { "allpmaps", &lock_class_mtx_spin },
        { "vm page queue free mutex", &lock_class_mtx_spin },
        { "icu", &lock_class_mtx_spin },
#ifdef SMP
        { "smp rendezvous", &lock_class_mtx_spin },
#if defined(__i386__) || defined(__amd64__)
        { "tlb", &lock_class_mtx_spin },
#endif
#ifdef __sparc64__
        { "ipi", &lock_class_mtx_spin },
        { "rtc_mtx", &lock_class_mtx_spin },
#endif
#endif
        { "clk", &lock_class_mtx_spin },
        { "mutex profiling lock", &lock_class_mtx_spin },
        { "kse zombie lock", &lock_class_mtx_spin },
        { "ALD Queue", &lock_class_mtx_spin },
#ifdef __ia64__
        { "MCA spin lock", &lock_class_mtx_spin },
#endif
#if defined(__i386__) || defined(__amd64__)
        { "pcicfg", &lock_class_mtx_spin },
        { "NDIS thread lock", &lock_class_mtx_spin },
#endif
        { "tw_osl_io_lock", &lock_class_mtx_spin },
        { "tw_osl_q_lock", &lock_class_mtx_spin },
        { "tw_cl_io_lock", &lock_class_mtx_spin },
        { "tw_cl_intr_lock", &lock_class_mtx_spin },
        { "tw_cl_gen_lock", &lock_class_mtx_spin },
        { NULL, NULL },
        { NULL, NULL }
};

#ifdef BLESSING
/*
 * Pairs of locks which have been blessed
 * Don't complain about order problems with blessed locks
 */
static struct witness_blessed blessed_list[] = {
};
static int blessed_count =
        sizeof(blessed_list) / sizeof(struct witness_blessed);
#endif

/*
 * List of locks initialized prior to witness being initialized whose
 * enrollment is currently deferred.
 */
STAILQ_HEAD(, lock_object) pending_locks =
    STAILQ_HEAD_INITIALIZER(pending_locks);

/*
 * This global is set to 0 once it becomes safe to use the witness code.
 */
static int witness_cold = 1;

/*
 * This global is set to 1 once the static lock orders have been enrolled
 * so that a warning can be issued for any spin locks enrolled later.
 */
static int witness_spin_warn = 0;

/*
 * The WITNESS-enabled diagnostic code.  Note that the witness code does
 * assume that the early boot is single-threaded at least until after this
 * routine is completed.
 */
static void
witness_initialize(void *dummy __unused)
{
        struct lock_object *lock;
        struct witness_order_list_entry *order;
        struct witness *w, *w1;
        int i;

        /*
         * We have to release Giant before initializing its witness
         * structure so that WITNESS doesn't get confused.
         */
        mtx_unlock(&Giant);
        mtx_assert(&Giant, MA_NOTOWNED);

        CTR1(KTR_WITNESS, "%s: initializing witness", __func__);
        mtx_init(&w_mtx, "witness lock", NULL, MTX_SPIN | MTX_QUIET |
            MTX_NOWITNESS);
        for (i = 0; i < WITNESS_COUNT; i++)
                witness_free(&w_data[i]);
        for (i = 0; i < WITNESS_CHILDCOUNT; i++)
                witness_child_free(&w_childdata[i]);
        for (i = 0; i < LOCK_CHILDCOUNT; i++)
                witness_lock_list_free(&w_locklistdata[i]);

        /* First add in all the specified order lists. */
        for (order = order_lists; order->w_name != NULL; order++) {
                w = enroll(order->w_name, order->w_class);
                if (w == NULL)
                        continue;
                w->w_file = "order list";
                for (order++; order->w_name != NULL; order++) {
                        w1 = enroll(order->w_name, order->w_class);
                        if (w1 == NULL)
                                continue;
                        w1->w_file = "order list";
                        if (!itismychild(w, w1))
                                panic("Not enough memory for static orders!");
                        w = w1;
                }
        }
        witness_spin_warn = 1;

        /* Iterate through all locks and add them to witness. */
        while (!STAILQ_EMPTY(&pending_locks)) {
                lock = STAILQ_FIRST(&pending_locks);
                STAILQ_REMOVE_HEAD(&pending_locks, lo_list);
                KASSERT(lock->lo_flags & LO_WITNESS,
                    ("%s: lock %s is on pending list but not LO_WITNESS",
                    __func__, lock->lo_name));
                lock->lo_witness = enroll(lock->lo_type, LOCK_CLASS(lock));
        }

        /* Mark the witness code as being ready for use. */
        witness_cold = 0;

        mtx_lock(&Giant);
}
SYSINIT(witness_init, SI_SUB_WITNESS, SI_ORDER_FIRST, witness_initialize, NULL)

static int
sysctl_debug_witness_watch(SYSCTL_HANDLER_ARGS)
{
        int error, value;

        value = witness_watch;
        error = sysctl_handle_int(oidp, &value, 0, req);
        if (error != 0 || req->newptr == NULL)
                return (error);
        error = suser(req->td);
        if (error != 0)
                return (error);
        if (value == witness_watch)
                return (0);
        if (value != 0)
                return (EINVAL);
        witness_watch = 0;
        return (0);
}

void
witness_init(struct lock_object *lock)
{
        struct lock_class *class;

        /* Various sanity checks. */
        class = LOCK_CLASS(lock);
        if ((lock->lo_flags & LO_RECURSABLE) != 0 &&
            (class->lc_flags & LC_RECURSABLE) == 0)
                panic("%s: lock (%s) %s can not be recursable", __func__,
                    class->lc_name, lock->lo_name);
        if ((lock->lo_flags & LO_SLEEPABLE) != 0 &&
            (class->lc_flags & LC_SLEEPABLE) == 0)
                panic("%s: lock (%s) %s can not be sleepable", __func__,
                    class->lc_name, lock->lo_name);
        if ((lock->lo_flags & LO_UPGRADABLE) != 0 &&
            (class->lc_flags & LC_UPGRADABLE) == 0)
                panic("%s: lock (%s) %s can not be upgradable", __func__,
                    class->lc_name, lock->lo_name);

        /*
         * If we shouldn't watch this lock, then just clear lo_witness.
         * Otherwise, if witness_cold is set, then it is too early to
         * enroll this lock, so defer it to witness_initialize() by adding
         * it to the pending_locks list.  If it is not too early, then enroll
         * the lock now.
         */
        if (witness_watch == 0 || panicstr != NULL ||
            (lock->lo_flags & LO_WITNESS) == 0)
                lock->lo_witness = NULL;
        else if (witness_cold) {
                STAILQ_INSERT_TAIL(&pending_locks, lock, lo_list);
                lock->lo_flags |= LO_ENROLLPEND;
        } else
                lock->lo_witness = enroll(lock->lo_type, class);
}

void
witness_destroy(struct lock_object *lock)
{
        struct lock_class *class;
        struct witness *w;

        class = LOCK_CLASS(lock);
        if (witness_cold)
                panic("lock (%s) %s destroyed while witness_cold",
                    class->lc_name, lock->lo_name);

        /* XXX: need to verify that no one holds the lock */
        if ((lock->lo_flags & (LO_WITNESS | LO_ENROLLPEND)) == LO_WITNESS &&
            lock->lo_witness != NULL) {
                w = lock->lo_witness;
                mtx_lock_spin(&w_mtx);
                MPASS(w->w_refcount > 0);
                w->w_refcount--;

                /*
                 * Lock is already released if we have an allocation failure
                 * and depart() fails.
                 */
                if (w->w_refcount != 0 || depart(w))
                        mtx_unlock_spin(&w_mtx);
        }

        /*
         * If this lock is destroyed before witness is up and running,
         * remove it from the pending list.
         */
        if (lock->lo_flags & LO_ENROLLPEND) {
                STAILQ_REMOVE(&pending_locks, lock, lock_object, lo_list);
                lock->lo_flags &= ~LO_ENROLLPEND;
        }
}

#ifdef DDB
static void
witness_levelall (void)
{
        struct witness_list *list;
        struct witness *w, *w1;

        /*
         * First clear all levels.
         */
        STAILQ_FOREACH(w, &w_all, w_list) {
                w->w_level = 0;
        }

        /*
         * Look for locks with no parent and level all their descendants.
         */
        STAILQ_FOREACH(w, &w_all, w_list) {
                /*
                 * This is just an optimization, technically we could get
                 * away just walking the all list each time.
                 */
                if (w->w_class->lc_flags & LC_SLEEPLOCK)
                        list = &w_sleep;
                else
                        list = &w_spin;
                STAILQ_FOREACH(w1, list, w_typelist) {
                        if (isitmychild(w1, w))
                                goto skip;
                }
                witness_leveldescendents(w, 0);
        skip:
                ;       /* silence GCC 3.x */
        }
}

static void
witness_leveldescendents(struct witness *parent, int level)
{
        struct witness_child_list_entry *wcl;
        int i;

        if (parent->w_level < level)
                parent->w_level = level;
        level++;
        for (wcl = parent->w_children; wcl != NULL; wcl = wcl->wcl_next)
                for (i = 0; i < wcl->wcl_count; i++)
                        witness_leveldescendents(wcl->wcl_children[i], level);
}

static void
witness_displaydescendants(void(*prnt)(const char *fmt, ...),
                           struct witness *parent, int indent)
{
        struct witness_child_list_entry *wcl;
        int i, level;

        level = parent->w_level;
        prnt("%-2d", level);
        for (i = 0; i < indent; i++)
                prnt(" ");
        if (parent->w_refcount > 0)
                prnt("%s", parent->w_name);
        else
                prnt("(dead)");
        if (parent->w_displayed) {
                prnt(" -- (already displayed)\n");
                return;
        }
        parent->w_displayed = 1;
        if (parent->w_refcount > 0) {
                if (parent->w_file != NULL)
                        prnt(" -- last acquired @ %s:%d", parent->w_file,
                            parent->w_line);
        }
        prnt("\n");
        for (wcl = parent->w_children; wcl != NULL; wcl = wcl->wcl_next)
                for (i = 0; i < wcl->wcl_count; i++)
                            witness_displaydescendants(prnt,
                                wcl->wcl_children[i], indent + 1);
}

static void
witness_display_list(void(*prnt)(const char *fmt, ...),
                     struct witness_list *list)
{
        struct witness *w;

        STAILQ_FOREACH(w, list, w_typelist) {
                if (w->w_file == NULL || w->w_level > 0)
                        continue;
                /*
                 * This lock has no anscestors, display its descendants. 
                 */
                witness_displaydescendants(prnt, w, 0);
        }
}
        
static void
witness_display(void(*prnt)(const char *fmt, ...))
{
        struct witness *w;

        KASSERT(!witness_cold, ("%s: witness_cold", __func__));
        witness_levelall();

        /* Clear all the displayed flags. */
        STAILQ_FOREACH(w, &w_all, w_list) {
                w->w_displayed = 0;
        }

        /*
         * First, handle sleep locks which have been acquired at least
         * once.
         */
        prnt("Sleep locks:\n");
        witness_display_list(prnt, &w_sleep);
        
        /*
         * Now do spin locks which have been acquired at least once.
         */
        prnt("\nSpin locks:\n");
        witness_display_list(prnt, &w_spin);
        
        /*
         * Finally, any locks which have not been acquired yet.
         */
        prnt("\nLocks which were never acquired:\n");
        STAILQ_FOREACH(w, &w_all, w_list) {
                if (w->w_file != NULL || w->w_refcount == 0)
                        continue;
                prnt("%s\n", w->w_name);
        }
}
#endif /* DDB */

/* Trim useless garbage from filenames. */
static const char *
fixup_filename(const char *file)
{

        if (file == NULL)
                return (NULL);
        while (strncmp(file, "../", 3) == 0)
                file += 3;
        return (file);
}

int
witness_defineorder(struct lock_object *lock1, struct lock_object *lock2)
{

        if (witness_watch == 0 || panicstr != NULL)
                return (0);

        /* Require locks that witness knows about. */
        if (lock1 == NULL || lock1->lo_witness == NULL || lock2 == NULL ||
            lock2->lo_witness == NULL)
                return (EINVAL);

        MPASS(!mtx_owned(&w_mtx));
        mtx_lock_spin(&w_mtx);

        /*
         * If we already have either an explicit or implied lock order that
         * is the other way around, then return an error.
         */
        if (isitmydescendant(lock2->lo_witness, lock1->lo_witness)) {
                mtx_unlock_spin(&w_mtx);
                return (EDOOFUS);
        }
        
        /* Try to add the new order. */
        CTR3(KTR_WITNESS, "%s: adding %s as a child of %s", __func__,
            lock2->lo_type, lock1->lo_type);
        if (!itismychild(lock1->lo_witness, lock2->lo_witness))
                return (ENOMEM);
        mtx_unlock_spin(&w_mtx);
        return (0);
}

void
witness_checkorder(struct lock_object *lock, int flags, const char *file,
    int line)
{
        struct lock_list_entry **lock_list, *lle;
        struct lock_instance *lock1, *lock2;
        struct lock_class *class;
        struct witness *w, *w1;
        struct thread *td;
        int i, j;

        if (witness_cold || witness_watch == 0 || lock->lo_witness == NULL ||
            panicstr != NULL)
                return;

        /*
         * Try locks do not block if they fail to acquire the lock, thus
         * there is no danger of deadlocks or of switching while holding a
         * spin lock if we acquire a lock via a try operation.  This
         * function shouldn't even be called for try locks, so panic if
         * that happens.
         */
        if (flags & LOP_TRYLOCK)
                panic("%s should not be called for try lock operations",
                    __func__);

        w = lock->lo_witness;
        class = LOCK_CLASS(lock);
        td = curthread;
        file = fixup_filename(file);

        if (class->lc_flags & LC_SLEEPLOCK) {
                /*
                 * Since spin locks include a critical section, this check
                 * implicitly enforces a lock order of all sleep locks before
                 * all spin locks.
                 */
                if (td->td_critnest != 0 && !kdb_active)
                        panic("blockable sleep lock (%s) %s @ %s:%d",
                            class->lc_name, lock->lo_name, file, line);

                /*
                 * If this is the first lock acquired then just return as
                 * no order checking is needed.
                 */
                if (td->td_sleeplocks == NULL)
                        return;
                lock_list = &td->td_sleeplocks;
        } else {
                /*
                 * If this is the first lock, just return as no order
                 * checking is needed.  We check this in both if clauses
                 * here as unifying the check would require us to use a
                 * critical section to ensure we don't migrate while doing
                 * the check.  Note that if this is not the first lock, we
                 * are already in a critical section and are safe for the
                 * rest of the check.
                 */
                if (PCPU_GET(spinlocks) == NULL)
                        return;
                lock_list = PCPU_PTR(spinlocks);
        }

        /*
         * Check to see if we are recursing on a lock we already own.  If
         * so, make sure that we don't mismatch exclusive and shared lock
         * acquires.
         */
        lock1 = find_instance(*lock_list, lock);
        if (lock1 != NULL) {
                if ((lock1->li_flags & LI_EXCLUSIVE) != 0 &&
                    (flags & LOP_EXCLUSIVE) == 0) {
                        printf("shared lock of (%s) %s @ %s:%d\n",
                            class->lc_name, lock->lo_name, file, line);
                        printf("while exclusively locked from %s:%d\n",
                            lock1->li_file, lock1->li_line);
                        panic("share->excl");
                }
                if ((lock1->li_flags & LI_EXCLUSIVE) == 0 &&
                    (flags & LOP_EXCLUSIVE) != 0) {
                        printf("exclusive lock of (%s) %s @ %s:%d\n",
                            class->lc_name, lock->lo_name, file, line);
                        printf("while share locked from %s:%d\n",
                            lock1->li_file, lock1->li_line);
                        panic("excl->share");
                }
                return;
        }

        /*
         * Try locks do not block if they fail to acquire the lock, thus
         * there is no danger of deadlocks or of switching while holding a
         * spin lock if we acquire a lock via a try operation.
         */
        if (flags & LOP_TRYLOCK)
                return;

        /*
         * Check for duplicate locks of the same type.  Note that we only
         * have to check for this on the last lock we just acquired.  Any
         * other cases will be caught as lock order violations.
         */
        lock1 = &(*lock_list)->ll_children[(*lock_list)->ll_count - 1];
        w1 = lock1->li_lock->lo_witness;
        if (w1 == w) {
                if (w->w_same_squawked || (lock->lo_flags & LO_DUPOK) ||
                    (flags & LOP_DUPOK))
                        return;
                w->w_same_squawked = 1;
                printf("acquiring duplicate lock of same type: \"%s\"\n", 
                        lock->lo_type);
                printf(" 1st %s @ %s:%d\n", lock1->li_lock->lo_name,
                    lock1->li_file, lock1->li_line);
                printf(" 2nd %s @ %s:%d\n", lock->lo_name, file, line);
#ifdef KDB
                goto debugger;
#else
                return;
#endif
        }
        MPASS(!mtx_owned(&w_mtx));
        mtx_lock_spin(&w_mtx);
        /*
         * If we know that the the lock we are acquiring comes after
         * the lock we most recently acquired in the lock order tree,
         * then there is no need for any further checks.
         */
        if (isitmychild(w1, w)) {
                mtx_unlock_spin(&w_mtx);
                return;
        }
        for (j = 0, lle = *lock_list; lle != NULL; lle = lle->ll_next) {
                for (i = lle->ll_count - 1; i >= 0; i--, j++) {

                        MPASS(j < WITNESS_COUNT);
                        lock1 = &lle->ll_children[i];
                        w1 = lock1->li_lock->lo_witness;

                        /*
                         * If this lock doesn't undergo witness checking,
                         * then skip it.
                         */
                        if (w1 == NULL) {
                                KASSERT((lock1->li_lock->lo_flags & LO_WITNESS) == 0,
                                    ("lock missing witness structure"));
                                continue;
                        }
                        /*
                         * If we are locking Giant and this is a sleepable
                         * lock, then skip it.
                         */
                        if ((lock1->li_lock->lo_flags & LO_SLEEPABLE) != 0 &&
                            lock == &Giant.mtx_object)
                                continue;
                        /*
                         * If we are locking a sleepable lock and this lock
                         * is Giant, then skip it.
                         */
                        if ((lock->lo_flags & LO_SLEEPABLE) != 0 &&
                            lock1->li_lock == &Giant.mtx_object)
                                continue;
                        /*
                         * If we are locking a sleepable lock and this lock
                         * isn't sleepable, we want to treat it as a lock
                         * order violation to enfore a general lock order of
                         * sleepable locks before non-sleepable locks.
                         */
                        if (((lock->lo_flags & LO_SLEEPABLE) != 0 &&
                            (lock1->li_lock->lo_flags & LO_SLEEPABLE) == 0))
                                goto reversal;
                        /*
                         * If we are locking Giant and this is a non-sleepable
                         * lock, then treat it as a reversal.
                         */
                        if ((lock1->li_lock->lo_flags & LO_SLEEPABLE) == 0 &&
                            lock == &Giant.mtx_object)
                                goto reversal;
                        /*
                         * Check the lock order hierarchy for a reveresal.
                         */
                        if (!isitmydescendant(w, w1))
                                continue;
                reversal:
                        /*
                         * We have a lock order violation, check to see if it
                         * is allowed or has already been yelled about.
                         */
                        mtx_unlock_spin(&w_mtx);
#ifdef BLESSING
                        /*
                         * If the lock order is blessed, just bail.  We don't
                         * look for other lock order violations though, which
                         * may be a bug.
                         */
                        if (blessed(w, w1))
                                return;
#endif
                        if (lock1->li_lock == &Giant.mtx_object) {
                                if (w1->w_Giant_squawked)
                                        return;
                                else
                                        w1->w_Giant_squawked = 1;
                        } else {
                                if (w1->w_other_squawked)
                                        return;
                                else
                                        w1->w_other_squawked = 1;
                        }
                        /*
                         * Ok, yell about it.
                         */
                        if (((lock->lo_flags & LO_SLEEPABLE) != 0 &&
                            (lock1->li_lock->lo_flags & LO_SLEEPABLE) == 0))
                                printf(
                "lock order reversal: (sleepable after non-sleepable)\n");
                        else if ((lock1->li_lock->lo_flags & LO_SLEEPABLE) == 0
                            && lock == &Giant.mtx_object)
                                printf(
                "lock order reversal: (Giant after non-sleepable)\n");
                        else
                                printf("lock order reversal:\n");
                        /*
                         * Try to locate an earlier lock with
                         * witness w in our list.
                         */
                        do {
                                lock2 = &lle->ll_children[i];
                                MPASS(lock2->li_lock != NULL);
                                if (lock2->li_lock->lo_witness == w)
                                        break;
                                if (i == 0 && lle->ll_next != NULL) {
                                        lle = lle->ll_next;
                                        i = lle->ll_count - 1;
                                        MPASS(i >= 0 && i < LOCK_NCHILDREN);
                                } else
                                        i--;
                        } while (i >= 0);
                        if (i < 0) {
                                printf(" 1st %p %s (%s) @ %s:%d\n",
                                    lock1->li_lock, lock1->li_lock->lo_name,
                                    lock1->li_lock->lo_type, lock1->li_file,
                                    lock1->li_line);
                                printf(" 2nd %p %s (%s) @ %s:%d\n", lock,
                                    lock->lo_name, lock->lo_type, file, line);
                        } else {
                                printf(" 1st %p %s (%s) @ %s:%d\n",
                                    lock2->li_lock, lock2->li_lock->lo_name,
                                    lock2->li_lock->lo_type, lock2->li_file,
                                    lock2->li_line);
                                printf(" 2nd %p %s (%s) @ %s:%d\n",
                                    lock1->li_lock, lock1->li_lock->lo_name,
                                    lock1->li_lock->lo_type, lock1->li_file,
                                    lock1->li_line);
                                printf(" 3rd %p %s (%s) @ %s:%d\n", lock,
                                    lock->lo_name, lock->lo_type, file, line);
                        }
#ifdef KDB
                        goto debugger;
#else
                        return;
#endif
                }
        }
        lock1 = &(*lock_list)->ll_children[(*lock_list)->ll_count - 1];
        /*
         * If requested, build a new lock order.  However, don't build a new
         * relationship between a sleepable lock and Giant if it is in the
         * wrong direction.  The correct lock order is that sleepable locks
         * always come before Giant.
         */
        if (flags & LOP_NEWORDER &&
            !(lock1->li_lock == &Giant.mtx_object &&
            (lock->lo_flags & LO_SLEEPABLE) != 0)) {
                CTR3(KTR_WITNESS, "%s: adding %s as a child of %s", __func__,
                    lock->lo_type, lock1->li_lock->lo_type);
                if (!itismychild(lock1->li_lock->lo_witness, w))
                        /* Witness is dead. */
                        return;
        } 
        mtx_unlock_spin(&w_mtx);
        return;

#ifdef KDB
debugger:
        if (witness_trace)
                kdb_backtrace();
        if (witness_kdb)
                kdb_enter(__func__);
#endif
}

void
witness_lock(struct lock_object *lock, int flags, const char *file, int line)
{
        struct lock_list_entry **lock_list, *lle;
        struct lock_instance *instance;
        struct witness *w;
        struct thread *td;

        if (witness_cold || witness_watch == 0 || lock->lo_witness == NULL ||
            panicstr != NULL)
                return;
        w = lock->lo_witness;
        td = curthread;
        file = fixup_filename(file);

        /* Determine lock list for this lock. */
        if (LOCK_CLASS(lock)->lc_flags & LC_SLEEPLOCK)
                lock_list = &td->td_sleeplocks;
        else
                lock_list = PCPU_PTR(spinlocks);

        /* Check to see if we are recursing on a lock we already own. */
        instance = find_instance(*lock_list, lock);
        if (instance != NULL) {
                instance->li_flags++;
                CTR4(KTR_WITNESS, "%s: pid %d recursed on %s r=%d", __func__,
                    td->td_proc->p_pid, lock->lo_name,
                    instance->li_flags & LI_RECURSEMASK);
                instance->li_file = file;
                instance->li_line = line;
                return;
        }

        /* Update per-witness last file and line acquire. */
        w->w_file = file;
        w->w_line = line;

        /* Find the next open lock instance in the list and fill it. */
        lle = *lock_list;
        if (lle == NULL || lle->ll_count == LOCK_NCHILDREN) {
                lle = witness_lock_list_get();
                if (lle == NULL)
                        return;
                lle->ll_next = *lock_list;
                CTR3(KTR_WITNESS, "%s: pid %d added lle %p", __func__,
                    td->td_proc->p_pid, lle);
                *lock_list = lle;
        }
        instance = &lle->ll_children[lle->ll_count++];
        instance->li_lock = lock;
        instance->li_line = line;
        instance->li_file = file;
        if ((flags & LOP_EXCLUSIVE) != 0)
                instance->li_flags = LI_EXCLUSIVE;
        else
                instance->li_flags = 0;
        CTR4(KTR_WITNESS, "%s: pid %d added %s as lle[%d]", __func__,
            td->td_proc->p_pid, lock->lo_name, lle->ll_count - 1);
}

void
witness_upgrade(struct lock_object *lock, int flags, const char *file, int line)
{
        struct lock_instance *instance;
        struct lock_class *class;

        KASSERT(!witness_cold, ("%s: witness_cold", __func__));
        if (lock->lo_witness == NULL || witness_watch == 0 || panicstr != NULL)
                return;
        class = LOCK_CLASS(lock);
        file = fixup_filename(file);
        if ((lock->lo_flags & LO_UPGRADABLE) == 0)
                panic("upgrade of non-upgradable lock (%s) %s @ %s:%d",
                    class->lc_name, lock->lo_name, file, line);
        if ((flags & LOP_TRYLOCK) == 0)
                panic("non-try upgrade of lock (%s) %s @ %s:%d", class->lc_name,
                    lock->lo_name, file, line);
        if ((class->lc_flags & LC_SLEEPLOCK) == 0)
                panic("upgrade of non-sleep lock (%s) %s @ %s:%d",
                    class->lc_name, lock->lo_name, file, line);
        instance = find_instance(curthread->td_sleeplocks, lock);
        if (instance == NULL)
                panic("upgrade of unlocked lock (%s) %s @ %s:%d",
                    class->lc_name, lock->lo_name, file, line);
        if ((instance->li_flags & LI_EXCLUSIVE) != 0)
                panic("upgrade of exclusive lock (%s) %s @ %s:%d",
                    class->lc_name, lock->lo_name, file, line);
        if ((instance->li_flags & LI_RECURSEMASK) != 0)
                panic("upgrade of recursed lock (%s) %s r=%d @ %s:%d",
                    class->lc_name, lock->lo_name,
                    instance->li_flags & LI_RECURSEMASK, file, line);
        instance->li_flags |= LI_EXCLUSIVE;
}

void
witness_downgrade(struct lock_object *lock, int flags, const char *file,
    int line)
{
        struct lock_instance *instance;
        struct lock_class *class;

        KASSERT(!witness_cold, ("%s: witness_cold", __func__));
        if (lock->lo_witness == NULL || witness_watch == 0 || panicstr != NULL)
                return;
        class = LOCK_CLASS(lock);
        file = fixup_filename(file);
        if ((lock->lo_flags & LO_UPGRADABLE) == 0)
                panic("downgrade of non-upgradable lock (%s) %s @ %s:%d",
                    class->lc_name, lock->lo_name, file, line);
        if ((class->lc_flags & LC_SLEEPLOCK) == 0)
                panic("downgrade of non-sleep lock (%s) %s @ %s:%d",
                    class->lc_name, lock->lo_name, file, line);
        instance = find_instance(curthread->td_sleeplocks, lock);
        if (instance == NULL)
                panic("downgrade of unlocked lock (%s) %s @ %s:%d",
                    class->lc_name, lock->lo_name, file, line);
        if ((instance->li_flags & LI_EXCLUSIVE) == 0)
                panic("downgrade of shared lock (%s) %s @ %s:%d",
                    class->lc_name, lock->lo_name, file, line);
        if ((instance->li_flags & LI_RECURSEMASK) != 0)
                panic("downgrade of recursed lock (%s) %s r=%d @ %s:%d",
                    class->lc_name, lock->lo_name,
                    instance->li_flags & LI_RECURSEMASK, file, line);
        instance->li_flags &= ~LI_EXCLUSIVE;
}

void
witness_unlock(struct lock_object *lock, int flags, const char *file, int line)
{
        struct lock_list_entry **lock_list, *lle;
        struct lock_instance *instance;
        struct lock_class *class;
        struct thread *td;
        register_t s;
        int i, j;

        if (witness_cold || witness_watch == 0 || lock->lo_witness == NULL ||
            panicstr != NULL)
                return;
        td = curthread;
        class = LOCK_CLASS(lock);
        file = fixup_filename(file);

        /* Find lock instance associated with this lock. */
        if (class->lc_flags & LC_SLEEPLOCK)
                lock_list = &td->td_sleeplocks;
        else
                lock_list = PCPU_PTR(spinlocks);
        for (; *lock_list != NULL; lock_list = &(*lock_list)->ll_next)
                for (i = 0; i < (*lock_list)->ll_count; i++) {
                        instance = &(*lock_list)->ll_children[i];
                        if (instance->li_lock == lock)
                                goto found;
                }
        panic("lock (%s) %s not locked @ %s:%d", class->lc_name, lock->lo_name,
            file, line);
found:

        /* First, check for shared/exclusive mismatches. */
        if ((instance->li_flags & LI_EXCLUSIVE) != 0 &&
            (flags & LOP_EXCLUSIVE) == 0) {
                printf("shared unlock of (%s) %s @ %s:%d\n", class->lc_name,
                    lock->lo_name, file, line);
                printf("while exclusively locked from %s:%d\n",
                    instance->li_file, instance->li_line);
                panic("excl->ushare");
        }
        if ((instance->li_flags & LI_EXCLUSIVE) == 0 &&
            (flags & LOP_EXCLUSIVE) != 0) {
                printf("exclusive unlock of (%s) %s @ %s:%d\n", class->lc_name,
                    lock->lo_name, file, line);
                printf("while share locked from %s:%d\n", instance->li_file,
                    instance->li_line);
                panic("share->uexcl");
        }

        /* If we are recursed, unrecurse. */
        if ((instance->li_flags & LI_RECURSEMASK) > 0) {
                CTR4(KTR_WITNESS, "%s: pid %d unrecursed on %s r=%d", __func__,
                    td->td_proc->p_pid, instance->li_lock->lo_name,
                    instance->li_flags);
                instance->li_flags--;
                return;
        }

        /* Otherwise, remove this item from the list. */
        s = intr_disable();
        CTR4(KTR_WITNESS, "%s: pid %d removed %s from lle[%d]", __func__,
            td->td_proc->p_pid, instance->li_lock->lo_name,
            (*lock_list)->ll_count - 1);
        for (j = i; j < (*lock_list)->ll_count - 1; j++)
                (*lock_list)->ll_children[j] =
                    (*lock_list)->ll_children[j + 1];
        (*lock_list)->ll_count--;
        intr_restore(s);

        /* If this lock list entry is now empty, free it. */
        if ((*lock_list)->ll_count == 0) {
                lle = *lock_list;
                *lock_list = lle->ll_next;
                CTR3(KTR_WITNESS, "%s: pid %d removed lle %p", __func__,
                    td->td_proc->p_pid, lle);
                witness_lock_list_free(lle);
        }
}

/*
 * Warn if any locks other than 'lock' are held.  Flags can be passed in to
 * exempt Giant and sleepable locks from the checks as well.  If any
 * non-exempt locks are held, then a supplied message is printed to the
 * console along with a list of the offending locks.  If indicated in the
 * flags then a failure results in a panic as well.
 */
int
witness_warn(int flags, struct lock_object *lock, const char *fmt, ...)
{
        struct lock_list_entry *lle;
        struct lock_instance *lock1;
        struct thread *td;
        va_list ap;
        int i, n;

        if (witness_cold || witness_watch == 0 || panicstr != NULL)
                return (0);
        n = 0;
        td = curthread;
        for (lle = td->td_sleeplocks; lle != NULL; lle = lle->ll_next)
                for (i = lle->ll_count - 1; i >= 0; i--) {
                        lock1 = &lle->ll_children[i];
                        if (lock1->li_lock == lock)
                                continue;
                        if (flags & WARN_GIANTOK &&
                            lock1->li_lock == &Giant.mtx_object)
                                continue;
                        if (flags & WARN_SLEEPOK &&
                            (lock1->li_lock->lo_flags & LO_SLEEPABLE) != 0)
                                continue;
                        if (n == 0) {
                                va_start(ap, fmt);
                                vprintf(fmt, ap);
                                va_end(ap);
                                printf(" with the following");
                                if (flags & WARN_SLEEPOK)
                                        printf(" non-sleepable");
                                printf(" locks held:\n");
                        }
                        n++;
                        witness_list_lock(lock1);
                }
        if (PCPU_GET(spinlocks) != NULL) {
                /*
                 * Since we already hold a spinlock preemption is
                 * already blocked.
                 */
                if (n == 0) {
                        va_start(ap, fmt);
                        vprintf(fmt, ap);
                        va_end(ap);
                        printf(" with the following");
                        if (flags & WARN_SLEEPOK)
                                printf(" non-sleepable");
                        printf(" locks held:\n");
                }
                n += witness_list_locks(PCPU_PTR(spinlocks));
        }
        if (flags & WARN_PANIC && n)
                panic("witness_warn");
#ifdef KDB
        else if (witness_kdb && n)
                kdb_enter(__func__);
        else if (witness_trace && n)
                kdb_backtrace();
#endif
        return (n);
}

const char *
witness_file(struct lock_object *lock)
{
        struct witness *w;

        if (witness_cold || witness_watch == 0 || lock->lo_witness == NULL)
                return ("?");
        w = lock->lo_witness;
        return (w->w_file);
}

int
witness_line(struct lock_object *lock)
{
        struct witness *w;

        if (witness_cold || witness_watch == 0 || lock->lo_witness == NULL)
                return (0);
        w = lock->lo_witness;
        return (w->w_line);
}

static struct witness *
enroll(const char *description, struct lock_class *lock_class)
{
        struct witness *w;

        if (witness_watch == 0 || panicstr != NULL)
                return (NULL);
        if ((lock_class->lc_flags & LC_SPINLOCK) && witness_skipspin)
                return (NULL);
        mtx_lock_spin(&w_mtx);
        STAILQ_FOREACH(w, &w_all, w_list) {
                if (w->w_name == description || (w->w_refcount > 0 &&
                    strcmp(description, w->w_name) == 0)) {
                        w->w_refcount++;
                        mtx_unlock_spin(&w_mtx);
                        if (lock_class != w->w_class)
                                panic(
                                "lock (%s) %s does not match earlier (%s) lock",
                                    description, lock_class->lc_name,
                                    w->w_class->lc_name);
                        return (w);
                }
        }
        if ((w = witness_get()) == NULL)
                goto out;
        w->w_name = description;
        w->w_class = lock_class;
        w->w_refcount = 1;
        STAILQ_INSERT_HEAD(&w_all, w, w_list);
        if (lock_class->lc_flags & LC_SPINLOCK) {
                STAILQ_INSERT_HEAD(&w_spin, w, w_typelist);
                w_spin_cnt++;
        } else if (lock_class->lc_flags & LC_SLEEPLOCK) {
                STAILQ_INSERT_HEAD(&w_sleep, w, w_typelist);
                w_sleep_cnt++;
        } else {
                mtx_unlock_spin(&w_mtx);
                panic("lock class %s is not sleep or spin",
                    lock_class->lc_name);
        }
        mtx_unlock_spin(&w_mtx);
out:
        /*
         * We issue a warning for any spin locks not defined in the static
         * order list as a way to discourage their use (folks should really
         * be using non-spin mutexes most of the time).  However, several
         * 3rd part device drivers use spin locks because that is all they
         * have available on Windows and Linux and they think that normal
         * mutexes are insufficient.
         */
        if ((lock_class->lc_flags & LC_SPINLOCK) && witness_spin_warn)
                printf("WITNESS: spin lock %s not in order list\n",
                    description);
        return (w);
}

/* Don't let the door bang you on the way out... */
static int
depart(struct witness *w)
{
        struct witness_child_list_entry *wcl, *nwcl;
        struct witness_list *list;
        struct witness *parent;

        MPASS(w->w_refcount == 0);
        if (w->w_class->lc_flags & LC_SLEEPLOCK) {
                list = &w_sleep;
                w_sleep_cnt--;
        } else {
                list = &w_spin;
                w_spin_cnt--;
        }
        /*
         * First, we run through the entire tree looking for any
         * witnesses that the outgoing witness is a child of.  For
         * each parent that we find, we reparent all the direct
         * children of the outgoing witness to its parent.
         */
        STAILQ_FOREACH(parent, list, w_typelist) {
                if (!isitmychild(parent, w))
                        continue;
                removechild(parent, w);
        }

        /*
         * Now we go through and free up the child list of the
         * outgoing witness.
         */
        for (wcl = w->w_children; wcl != NULL; wcl = nwcl) {
                nwcl = wcl->wcl_next;
                w_child_cnt--;
                witness_child_free(wcl);
        }

        /*
         * Detach from various lists and free.
         */
        STAILQ_REMOVE(list, w, witness, w_typelist);
        STAILQ_REMOVE(&w_all, w, witness, w_list);
        witness_free(w);

        return (1);
}

/*
 * Add "child" as a direct child of "parent".  Returns false if
 * we fail due to out of memory.
 */
static int
insertchild(struct witness *parent, struct witness *child)
{
        struct witness_child_list_entry **wcl;

        MPASS(child != NULL && parent != NULL);

        /*
         * Insert "child" after "parent"
         */
        wcl = &parent->w_children;
        while (*wcl != NULL && (*wcl)->wcl_count == WITNESS_NCHILDREN)
                wcl = &(*wcl)->wcl_next;
        if (*wcl == NULL) {
                *wcl = witness_child_get();
                if (*wcl == NULL)
                        return (0);
                w_child_cnt++;
        }
        (*wcl)->wcl_children[(*wcl)->wcl_count++] = child;

        return (1);
}


static int
itismychild(struct witness *parent, struct witness *child)
{
        struct witness_list *list;

        MPASS(child != NULL && parent != NULL);
        if ((parent->w_class->lc_flags & (LC_SLEEPLOCK | LC_SPINLOCK)) !=
            (child->w_class->lc_flags & (LC_SLEEPLOCK | LC_SPINLOCK)))
                panic(
                "%s: parent (%s) and child (%s) are not the same lock type",
                    __func__, parent->w_class->lc_name,
                    child->w_class->lc_name);

        if (!insertchild(parent, child))
                return (0);

        if (parent->w_class->lc_flags & LC_SLEEPLOCK)
                list = &w_sleep;
        else
                list = &w_spin;
        return (1);
}

static void
removechild(struct witness *parent, struct witness *child)
{
        struct witness_child_list_entry **wcl, *wcl1;
        int i;

        for (wcl = &parent->w_children; *wcl != NULL; wcl = &(*wcl)->wcl_next)
                for (i = 0; i < (*wcl)->wcl_count; i++)
                        if ((*wcl)->wcl_children[i] == child)
                                goto found;
        return;
found:
        (*wcl)->wcl_count--;
        if ((*wcl)->wcl_count > i)
                (*wcl)->wcl_children[i] =
                    (*wcl)->wcl_children[(*wcl)->wcl_count];
        MPASS((*wcl)->wcl_children[i] != NULL);
        if ((*wcl)->wcl_count != 0)
                return;
        wcl1 = *wcl;
        *wcl = wcl1->wcl_next;
        w_child_cnt--;
        witness_child_free(wcl1);
}

static int
isitmychild(struct witness *parent, struct witness *child)
{
        struct witness_child_list_entry *wcl;
        int i;

        for (wcl = parent->w_children; wcl != NULL; wcl = wcl->wcl_next) {
                for (i = 0; i < wcl->wcl_count; i++) {
                        if (wcl->wcl_children[i] == child)
                                return (1);
                }
        }
        return (0);
}

static int
isitmydescendant(struct witness *parent, struct witness *child)
{
        struct witness_child_list_entry *wcl;
        int i, j;

        if (isitmychild(parent, child))
                return (1);
        j = 0;
        for (wcl = parent->w_children; wcl != NULL; wcl = wcl->wcl_next) {
                MPASS(j < 1000);
                for (i = 0; i < wcl->wcl_count; i++) {
                        if (isitmydescendant(wcl->wcl_children[i], child))
                                return (1);
                }
                j++;
        }
        return (0);
}

#ifdef BLESSING
static int
blessed(struct witness *w1, struct witness *w2)
{
        int i;
        struct witness_blessed *b;

        for (i = 0; i < blessed_count; i++) {
                b = &blessed_list[i];
                if (strcmp(w1->w_name, b->b_lock1) == 0) {
                        if (strcmp(w2->w_name, b->b_lock2) == 0)
                                return (1);
                        continue;
                }
                if (strcmp(w1->w_name, b->b_lock2) == 0)
                        if (strcmp(w2->w_name, b->b_lock1) == 0)
                                return (1);
        }
        return (0);
}
#endif

static struct witness *
witness_get(void)
{
        struct witness *w;

        if (witness_watch == 0) {
                mtx_unlock_spin(&w_mtx);
                return (NULL);
        }
        if (STAILQ_EMPTY(&w_free)) {
                witness_watch = 0;
                mtx_unlock_spin(&w_mtx);
                printf("%s: witness exhausted\n", __func__);
                return (NULL);
        }
        w = STAILQ_FIRST(&w_free);
        STAILQ_REMOVE_HEAD(&w_free, w_list);
        w_free_cnt--;
        bzero(w, sizeof(*w));
        return (w);
}

static void
witness_free(struct witness *w)
{

        STAILQ_INSERT_HEAD(&w_free, w, w_list);
        w_free_cnt++;
}

static struct witness_child_list_entry *
witness_child_get(void)
{
        struct witness_child_list_entry *wcl;

        if (witness_watch == 0) {
                mtx_unlock_spin(&w_mtx);
                return (NULL);
        }
        wcl = w_child_free;
        if (wcl == NULL) {
                witness_watch = 0;
                mtx_unlock_spin(&w_mtx);
                printf("%s: witness exhausted\n", __func__);
                return (NULL);
        }
        w_child_free = wcl->wcl_next;
        w_child_free_cnt--;
        bzero(wcl, sizeof(*wcl));
        return (wcl);
}

static void
witness_child_free(struct witness_child_list_entry *wcl)
{

        wcl->wcl_next = w_child_free;
        w_child_free = wcl;
        w_child_free_cnt++;
}

static struct lock_list_entry *
witness_lock_list_get(void)
{
        struct lock_list_entry *lle;

        if (witness_watch == 0)
                return (NULL);
        mtx_lock_spin(&w_mtx);
        lle = w_lock_list_free;
        if (lle == NULL) {
                witness_watch = 0;
                mtx_unlock_spin(&w_mtx);
                printf("%s: witness exhausted\n", __func__);
                return (NULL);
        }
        w_lock_list_free = lle->ll_next;
        mtx_unlock_spin(&w_mtx);
        bzero(lle, sizeof(*lle));
        return (lle);
}
                
static void
witness_lock_list_free(struct lock_list_entry *lle)
{

        mtx_lock_spin(&w_mtx);
        lle->ll_next = w_lock_list_free;
        w_lock_list_free = lle;
        mtx_unlock_spin(&w_mtx);
}

static struct lock_instance *
find_instance(struct lock_list_entry *lock_list, struct lock_object *lock)
{
        struct lock_list_entry *lle;
        struct lock_instance *instance;
        int i;

        for (lle = lock_list; lle != NULL; lle = lle->ll_next)
                for (i = lle->ll_count - 1; i >= 0; i--) {
                        instance = &lle->ll_children[i];
                        if (instance->li_lock == lock)
                                return (instance);
                }
        return (NULL);
}

static void
witness_list_lock(struct lock_instance *instance)
{
        struct lock_object *lock;

        lock = instance->li_lock;
        printf("%s %s %s", (instance->li_flags & LI_EXCLUSIVE) != 0 ?
            "exclusive" : "shared", LOCK_CLASS(lock)->lc_name, lock->lo_name);
        if (lock->lo_type != lock->lo_name)
                printf(" (%s)", lock->lo_type);
        printf(" r = %d (%p) locked @ %s:%d\n",
            instance->li_flags & LI_RECURSEMASK, lock, instance->li_file,
            instance->li_line);
}

#ifdef DDB
static int
witness_thread_has_locks(struct thread *td)
{

        return (td->td_sleeplocks != NULL);
}

static int
witness_proc_has_locks(struct proc *p)
{
        struct thread *td;

        FOREACH_THREAD_IN_PROC(p, td) {
                if (witness_thread_has_locks(td))
                        return (1);
        }
        return (0);
}
#endif

int
witness_list_locks(struct lock_list_entry **lock_list)
{
        struct lock_list_entry *lle;
        int i, nheld;

        nheld = 0;
        for (lle = *lock_list; lle != NULL; lle = lle->ll_next)
                for (i = lle->ll_count - 1; i >= 0; i--) {
                        witness_list_lock(&lle->ll_children[i]);
                        nheld++;
                }
        return (nheld);
}

/*
 * This is a bit risky at best.  We call this function when we have timed
 * out acquiring a spin lock, and we assume that the other CPU is stuck
 * with this lock held.  So, we go groveling around in the other CPU's
 * per-cpu data to try to find the lock instance for this spin lock to
 * see when it was last acquired.
 */
void
witness_display_spinlock(struct lock_object *lock, struct thread *owner)
{
        struct lock_instance *instance;
        struct pcpu *pc;

        if (owner->td_critnest == 0 || owner->td_oncpu == NOCPU)
                return;
        pc = pcpu_find(owner->td_oncpu);
        instance = find_instance(pc->pc_spinlocks, lock);
        if (instance != NULL)
                witness_list_lock(instance);
}

void
witness_save(struct lock_object *lock, const char **filep, int *linep)
{
        struct lock_list_entry *lock_list;
        struct lock_instance *instance;
        struct lock_class *class;

        KASSERT(!witness_cold, ("%s: witness_cold", __func__));
        if (lock->lo_witness == NULL || witness_watch == 0 || panicstr != NULL)
                return;
        class = LOCK_CLASS(lock);
        if (class->lc_flags & LC_SLEEPLOCK)
                lock_list = curthread->td_sleeplocks;
        else {
                if (witness_skipspin)
                        return;
                lock_list = PCPU_GET(spinlocks);
        }
        instance = find_instance(lock_list, lock);
        if (instance == NULL)
                panic("%s: lock (%s) %s not locked", __func__,
                    class->lc_name, lock->lo_name);
        *filep = instance->li_file;
        *linep = instance->li_line;
}

void
witness_restore(struct lock_object *lock, const char *file, int line)
{
        struct lock_list_entry *lock_list;
        struct lock_instance *instance;
        struct lock_class *class;

        KASSERT(!witness_cold, ("%s: witness_cold", __func__));
        if (lock->lo_witness == NULL || witness_watch == 0 || panicstr != NULL)
                return;
        class = LOCK_CLASS(lock);
        if (class->lc_flags & LC_SLEEPLOCK)
                lock_list = curthread->td_sleeplocks;
        else {
                if (witness_skipspin)
                        return;
                lock_list = PCPU_GET(spinlocks);
        }
        instance = find_instance(lock_list, lock);
        if (instance == NULL)
                panic("%s: lock (%s) %s not locked", __func__,
                    class->lc_name, lock->lo_name);
        lock->lo_witness->w_file = file;
        lock->lo_witness->w_line = line;
        instance->li_file = file;
        instance->li_line = line;
}

void
witness_assert(struct lock_object *lock, int flags, const char *file, int line)
{
#ifdef INVARIANT_SUPPORT
        struct lock_instance *instance;
        struct lock_class *class;

        if (lock->lo_witness == NULL || witness_watch == 0 || panicstr != NULL)
                return;
        class = LOCK_CLASS(lock);
        if ((class->lc_flags & LC_SLEEPLOCK) != 0)
                instance = find_instance(curthread->td_sleeplocks, lock);
        else if ((class->lc_flags & LC_SPINLOCK) != 0)
                instance = find_instance(PCPU_GET(spinlocks), lock);
        else {
                panic("Lock (%s) %s is not sleep or spin!",
                    class->lc_name, lock->lo_name);
        }
        file = fixup_filename(file);
        switch (flags) {
        case LA_UNLOCKED:
                if (instance != NULL)
                        panic("Lock (%s) %s locked @ %s:%d.",
                            class->lc_name, lock->lo_name, file, line);
                break;
        case LA_LOCKED:
        case LA_LOCKED | LA_RECURSED:
        case LA_LOCKED | LA_NOTRECURSED:
        case LA_SLOCKED:
        case LA_SLOCKED | LA_RECURSED:
        case LA_SLOCKED | LA_NOTRECURSED:
        case LA_XLOCKED:
        case LA_XLOCKED | LA_RECURSED:
        case LA_XLOCKED | LA_NOTRECURSED:
                if (instance == NULL) {
                        panic("Lock (%s) %s not locked @ %s:%d.",
                            class->lc_name, lock->lo_name, file, line);
                        break;
                }
                if ((flags & LA_XLOCKED) != 0 &&
                    (instance->li_flags & LI_EXCLUSIVE) == 0)
                        panic("Lock (%s) %s not exclusively locked @ %s:%d.",
                            class->lc_name, lock->lo_name, file, line);
                if ((flags & LA_SLOCKED) != 0 &&
                    (instance->li_flags & LI_EXCLUSIVE) != 0)
                        panic("Lock (%s) %s exclusively locked @ %s:%d.",
                            class->lc_name, lock->lo_name, file, line);
                if ((flags & LA_RECURSED) != 0 &&
                    (instance->li_flags & LI_RECURSEMASK) == 0)
                        panic("Lock (%s) %s not recursed @ %s:%d.",
                            class->lc_name, lock->lo_name, file, line);
                if ((flags & LA_NOTRECURSED) != 0 &&
                    (instance->li_flags & LI_RECURSEMASK) != 0)
                        panic("Lock (%s) %s recursed @ %s:%d.",
                            class->lc_name, lock->lo_name, file, line);
                break;
        default:
                panic("Invalid lock assertion at %s:%d.", file, line);

        }
#endif  /* INVARIANT_SUPPORT */
}

#ifdef DDB
static void
witness_list(struct thread *td)
{

        KASSERT(!witness_cold, ("%s: witness_cold", __func__));
        KASSERT(kdb_active, ("%s: not in the debugger", __func__));

        if (witness_watch == 0)
                return;

        witness_list_locks(&td->td_sleeplocks);

        /*
         * We only handle spinlocks if td == curthread.  This is somewhat broken
         * if td is currently executing on some other CPU and holds spin locks
         * as we won't display those locks.  If we had a MI way of getting
         * the per-cpu data for a given cpu then we could use
         * td->td_oncpu to get the list of spinlocks for this thread
         * and "fix" this.
         *
         * That still wouldn't really fix this unless we locked sched_lock
         * or stopped the other CPU to make sure it wasn't changing the list
         * out from under us.  It is probably best to just not try to handle
         * threads on other CPU's for now.
         */
        if (td == curthread && PCPU_GET(spinlocks) != NULL)
                witness_list_locks(PCPU_PTR(spinlocks));
}

DB_SHOW_COMMAND(locks, db_witness_list)
{
        struct thread *td;
        pid_t pid;
        struct proc *p;

        if (have_addr) {
                pid = (addr % 16) + ((addr >> 4) % 16) * 10 +
                    ((addr >> 8) % 16) * 100 + ((addr >> 12) % 16) * 1000 +
                    ((addr >> 16) % 16) * 10000;
                /* sx_slock(&allproc_lock); */
                FOREACH_PROC_IN_SYSTEM(p) {
                        if (p->p_pid == pid)
                                break;
                }
                /* sx_sunlock(&allproc_lock); */
                if (p == NULL) {
                        db_printf("pid %d not found\n", pid);
                        return;
                }
                FOREACH_THREAD_IN_PROC(p, td) {
                        witness_list(td);
                }
        } else {
                td = curthread;
                witness_list(td);
        }
}

DB_SHOW_COMMAND(alllocks, db_witness_list_all)
{
        struct thread *td;
        struct proc *p;

        /*
         * It would be nice to list only threads and processes that actually
         * held sleep locks, but that information is currently not exported
         * by WITNESS.
         */
        FOREACH_PROC_IN_SYSTEM(p) {
                if (!witness_proc_has_locks(p))
                        continue;
                FOREACH_THREAD_IN_PROC(p, td) {
                        if (!witness_thread_has_locks(td))
                                continue;
                        db_printf("Process %d (%s) thread %p (%d)\n", p->p_pid,
                            p->p_comm, td, td->td_tid);
                        witness_list(td);
                }
        }
}

DB_SHOW_COMMAND(witness, db_witness_display)
{

        witness_display(db_printf);
}
#endif