/*      $OpenBSD: subr_witness.c,v 1.59 2026/03/23 08:37:35 jsg Exp $   */

/*-
 * Copyright (c) 2008 Isilon Systems, Inc.
 * Copyright (c) 2008 Ilya Maykov <ivmaykov@gmail.com>
 * 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/param.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/malloc.h>
#ifdef MULTIPROCESSOR
#include <sys/mplock.h>
#endif
#include <sys/mutex.h>
#include <sys/percpu.h>
#include <sys/proc.h>
#include <sys/sched.h>
#include <sys/stacktrace.h>
#include <sys/stdint.h>
#include <sys/sysctl.h>
#include <sys/syslog.h>
#include <sys/witness.h>

#include <machine/cpu.h>

#include <uvm/uvm_extern.h>     /* uvm_pageboot_alloc */

#ifndef DDB
#error "DDB is required for WITNESS"
#endif

#include <machine/db_machdep.h>

#include <ddb/db_access.h>
#include <ddb/db_var.h>
#include <ddb/db_output.h>

#define LI_RECURSEMASK  0x0000ffff      /* Recursion depth of lock instance. */
#define LI_EXCLUSIVE    0x00010000      /* Exclusive lock instance. */
#define LI_NORELEASE    0x00020000      /* Lock not allowed to be released. */

#ifndef WITNESS_COUNT
#define WITNESS_COUNT           1536
#endif
#define WITNESS_HASH_SIZE       251     /* Prime, gives load factor < 2 */
#define WITNESS_PENDLIST        (1024 + MAXCPUS)

/* Allocate 256 KB of stack data space */
#define WITNESS_LO_DATA_COUNT   2048

/* Prime, gives load factor of ~2 at full load */
#define WITNESS_LO_HASH_SIZE    1021

/*
 * XXX: This is somewhat bogus, as we assume here that at most 2048 threads
 * will hold LOCK_NCHILDREN locks.  We handle failure ok, and we should
 * probably be safe for the most part, but it's still a SWAG.
 */
#define LOCK_NCHILDREN  5
#define LOCK_CHILDCOUNT 2048

#define FULLGRAPH_SBUF_SIZE     512

/*
 * These flags go in the witness relationship matrix and describe the
 * relationship between any two struct witness objects.
 */
#define WITNESS_UNRELATED        0x00    /* No lock order relation. */
#define WITNESS_PARENT           0x01    /* Parent, aka direct ancestor. */
#define WITNESS_ANCESTOR         0x02    /* Direct or indirect ancestor. */
#define WITNESS_CHILD            0x04    /* Child, aka direct descendant. */
#define WITNESS_DESCENDANT       0x08    /* Direct or indirect descendant. */
#define WITNESS_ANCESTOR_MASK    (WITNESS_PARENT | WITNESS_ANCESTOR)
#define WITNESS_DESCENDANT_MASK  (WITNESS_CHILD | WITNESS_DESCENDANT)
#define WITNESS_RELATED_MASK                                            \
        (WITNESS_ANCESTOR_MASK | WITNESS_DESCENDANT_MASK)
#define WITNESS_REVERSAL         0x10    /* A lock order reversal has been
                                          * observed. */
#define WITNESS_RESERVED1        0x20    /* Unused flag, reserved. */
#define WITNESS_RESERVED2        0x40    /* Unused flag, reserved. */
#define WITNESS_LOCK_ORDER_KNOWN 0x80    /* This lock order is known. */

/* Descendant to ancestor flags */
#define WITNESS_DTOA(x) (((x) & WITNESS_RELATED_MASK) >> 2)

/* Ancestor to descendant flags */
#define WITNESS_ATOD(x) (((x) & WITNESS_RELATED_MASK) << 2)

#define WITNESS_INDEX_ASSERT(i)                                         \
        KASSERT((i) > 0 && (i) <= w_max_used_index && (i) < witness_count)

/*
 * Lock classes.  Each lock has a class which describes characteristics
 * common to all types of locks of a given class.
 *
 * Spin locks in general must always protect against preemption, as it is
 * an error to perform any type of context switch while holding a spin lock.
 * Also, for an individual lock to be recursable, its class must allow
 * recursion and the lock itself must explicitly allow recursion.
 */

struct lock_class {
        const           char *lc_name;
        u_int           lc_flags;
};

union lock_stack {
        union lock_stack        *ls_next;
        struct stacktrace        ls_stack;
};

#define LC_SLEEPLOCK    0x00000001      /* Sleep lock. */
#define LC_SPINLOCK     0x00000002      /* Spin lock. */
#define LC_SLEEPABLE    0x00000004      /* Sleeping allowed with this lock. */
#define LC_RECURSABLE   0x00000008      /* Locks of this type may recurse. */
#define LC_UPGRADABLE   0x00000010      /* Upgrades and downgrades permitted. */

/*
 * Lock instances.  A lock instance is the data associated with a lock while
 * it is held by witness.  For example, a lock instance will hold the
 * recursion count of a lock.  Lock instances are held in lists.  Spin locks
 * are held in a per-cpu list while sleep locks are held in per-thread list.
 */
struct lock_instance {
        struct lock_object      *li_lock;
        union lock_stack        *li_stack;
        u_int                   li_flags;
};

/*
 * A simple list type used to build the list of locks held by a thread
 * or CPU.  We can't simply embed the list in struct lock_object since a
 * lock may be held by more than one thread if it is a shared lock.  Locks
 * are added to the head of the list, so we fill up each list entry from
 * "the back" logically.  To ease some of the arithmetic, we actually fill
 * in each list entry the normal way (children[0] then children[1], etc.) but
 * when we traverse the list we read children[count-1] as the first entry
 * down to children[0] as the final entry.
 */
struct lock_list_entry {
        struct lock_list_entry  *ll_next;
        struct lock_instance    ll_children[LOCK_NCHILDREN];
        int                     ll_count;
};

/*
 * The main witness structure. One of these per named lock type in the system
 * (for example, "vnode interlock").
 */
struct witness {
        const struct lock_type  *w_type;
        const char              *w_subtype;
        uint32_t                w_index;  /* Index in the relationship matrix */
        struct lock_class       *w_class;
        SLIST_ENTRY(witness)    w_list;         /* List of all witnesses. */
        SLIST_ENTRY(witness)    w_typelist;     /* Witnesses of a type. */
        SLIST_ENTRY(witness)    w_hash_next;    /* Linked list in
                                                 * hash buckets. */
        uint16_t                w_num_ancestors; /* direct/indirect
                                                  * ancestor count */
        uint16_t                w_num_descendants; /* direct/indirect
                                                    * descendant count */
        int16_t                 w_ddb_level;
        unsigned                w_acquired:1;
        unsigned                w_displayed:1;
        unsigned                w_reversed:1;
};

SLIST_HEAD(witness_list, witness);

/*
 * The witness hash table. Keys are witness names (const char *), elements are
 * witness objects (struct witness *).
 */
struct witness_hash {
        struct witness_list     wh_array[WITNESS_HASH_SIZE];
        uint32_t                wh_size;
        uint32_t                wh_count;
};

/*
 * Key type for the lock order data hash table.
 */
struct witness_lock_order_key {
        uint16_t        from;
        uint16_t        to;
};

struct witness_lock_order_data {
        struct stacktrace               wlod_stack;
        struct witness_lock_order_key   wlod_key;
        struct witness_lock_order_data  *wlod_next;
};

/*
 * The witness lock order data hash table. Keys are witness index tuples
 * (struct witness_lock_order_key), elements are lock order data objects
 * (struct witness_lock_order_data).
 */
struct witness_lock_order_hash {
        struct witness_lock_order_data  *wloh_array[WITNESS_LO_HASH_SIZE];
        u_int   wloh_size;
        u_int   wloh_count;
};

struct witness_pendhelp {
        const struct lock_type  *wh_type;
        struct lock_object      *wh_lock;
};

struct witness_cpu {
        struct lock_list_entry  *wc_spinlocks;
        struct lock_list_entry  *wc_lle_cache;
        union lock_stack        *wc_stk_cache;
        unsigned int             wc_lle_count;
        unsigned int             wc_stk_count;
} __aligned(CACHELINESIZE);

#define WITNESS_LLE_CACHE_MAX   8
#define WITNESS_STK_CACHE_MAX   (WITNESS_LLE_CACHE_MAX * LOCK_NCHILDREN)

struct witness_cpu witness_cpu[MAXCPUS];

/*
 * Returns 0 if one of the locks is a spin lock and the other is not.
 * Returns 1 otherwise.
 */
static __inline int
witness_lock_type_equal(struct witness *w1, struct witness *w2)
{

        return ((w1->w_class->lc_flags & (LC_SLEEPLOCK | LC_SPINLOCK)) ==
                (w2->w_class->lc_flags & (LC_SLEEPLOCK | LC_SPINLOCK)));
}

static __inline int
witness_lock_order_key_equal(const struct witness_lock_order_key *a,
    const struct witness_lock_order_key *b)
{

        return (a->from == b->from && a->to == b->to);
}

static int      _isitmyx(struct witness *w1, struct witness *w2, int rmask,
                    const char *fname);
static void     adopt(struct witness *parent, struct witness *child);
static struct witness   *enroll(const struct lock_type *, const char *,
                            struct lock_class *);
static struct lock_instance     *find_instance(struct lock_list_entry *list,
                                    const struct lock_object *lock);
static int      isitmychild(struct witness *parent, struct witness *child);
static int      isitmydescendant(struct witness *parent, struct witness *child);
static void     itismychild(struct witness *parent, struct witness *child);
static int      islockmychild(struct lock_object *parent,
                    struct lock_object *child);
#ifdef DDB
static void     db_witness_add_fullgraph(struct witness *parent);
static void     witness_ddb_compute_levels(void);
static void     witness_ddb_display(int(*)(const char *fmt, ...));
static void     witness_ddb_display_descendants(int(*)(const char *fmt, ...),
                    struct witness *, int indent);
static void     witness_ddb_display_list(int(*prnt)(const char *fmt, ...),
                    struct witness_list *list);
static void     witness_ddb_level_descendants(struct witness *parent, int l);
static void     witness_ddb_list(struct proc *td);
#endif
static int      witness_alloc_stacks(void);
static void     witness_debugger(int dump);
static void     witness_free(struct witness *m);
static struct witness   *witness_get(void);
static uint32_t witness_hash_djb2(const uint8_t *key, uint32_t size);
static struct witness   *witness_hash_get(const struct lock_type *,
                    const char *);
static void     witness_hash_put(struct witness *w);
static void     witness_init_hash_tables(void);
static void     witness_increment_graph_generation(void);
static int      witness_list_locks(struct lock_list_entry **,
                    int (*)(const char *, ...));
static void     witness_lock_list_free(struct lock_list_entry *lle);
static struct lock_list_entry   *witness_lock_list_get(void);
static void     witness_lock_stack_free(union lock_stack *stack);
static union lock_stack         *witness_lock_stack_get(void);
static int      witness_lock_order_add(struct witness *parent,
                    struct witness *child);
static int      witness_lock_order_check(struct witness *parent,
                    struct witness *child);
static struct witness_lock_order_data   *witness_lock_order_get(
                                            struct witness *parent,
                                            struct witness *child);
static void     witness_list_lock(struct lock_instance *instance,
                    int (*prnt)(const char *fmt, ...));
static void     witness_print_cycle(int (*prnt)(const char *fmt, ...),
                    struct witness *parent, struct witness *child);
static void     witness_print_cycle_edge(int (*prnt)(const char *fmt, ...),
                    struct witness *parent, struct witness *child,
                    int step, int last);
static int      witness_search(struct witness *w, struct witness *target,
                    struct witness **path, int depth, int *remaining);
static void     witness_setflag(struct lock_object *lock, int flag, int set);

/*
 * If set to 0, lock order checking is disabled.  If set to -1,
 * witness is completely disabled.  Otherwise witness performs full
 * lock order checking for all locks.  At runtime, lock order checking
 * may be toggled.  However, witness cannot be reenabled once it is
 * completely disabled.
 */
#ifdef WITNESS_WATCH
static int witness_watch = 3;
#else
static int witness_watch = 2;
#endif

#ifdef WITNESS_LOCKTRACE
static int witness_locktrace = 1;
#else
static int witness_locktrace = 0;
#endif

int witness_count = WITNESS_COUNT;
int witness_uninitialized_report = 5;

static struct mutex w_mtx;
static struct rwlock w_ctlock = RWLOCK_INITIALIZER("w_ctlock");

/* w_list */
static struct witness_list w_free = SLIST_HEAD_INITIALIZER(w_free);
static struct witness_list w_all = SLIST_HEAD_INITIALIZER(w_all);

/* w_typelist */
static struct witness_list w_spin = SLIST_HEAD_INITIALIZER(w_spin);
static struct witness_list w_sleep = SLIST_HEAD_INITIALIZER(w_sleep);

/* lock list */
static struct lock_list_entry *w_lock_list_free = NULL;
static struct witness_pendhelp pending_locks[WITNESS_PENDLIST];
static u_int pending_cnt;

static int w_free_cnt, w_spin_cnt, w_sleep_cnt;

static struct witness *w_data;
static uint8_t **w_rmatrix;
static struct lock_list_entry *w_locklistdata;
static struct witness_hash w_hash;      /* The witness hash table. */

/* The lock order data hash */
static struct witness_lock_order_data *w_lodata;
static struct witness_lock_order_data *w_lofree = NULL;
static struct witness_lock_order_hash w_lohash;
static int w_max_used_index = 0;
static unsigned int w_generation = 0;

static union lock_stack *w_lock_stack_free;
static unsigned int w_lock_stack_num;

static struct lock_class lock_class_kernel_lock = {
        .lc_name = "kernel_lock",
        .lc_flags = LC_SLEEPLOCK | LC_RECURSABLE | LC_SLEEPABLE
};

static struct lock_class lock_class_mutex = {
        .lc_name = "mutex",
        .lc_flags = LC_SPINLOCK
};

static struct lock_class lock_class_rwlock = {
        .lc_name = "rwlock",
        .lc_flags = LC_SLEEPLOCK | LC_SLEEPABLE | LC_UPGRADABLE
};

static struct lock_class lock_class_rrwlock = {
        .lc_name = "rrwlock",
        .lc_flags = LC_SLEEPLOCK | LC_RECURSABLE | LC_SLEEPABLE |
            LC_UPGRADABLE
};

static struct lock_class *lock_classes[] = {
        &lock_class_kernel_lock,
        &lock_class_mutex,
        &lock_class_rwlock,
        &lock_class_rrwlock,
};

/*
 * 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.
 */
void
witness_initialize(void)
{
        struct lock_object *lock;
        union lock_stack *stacks;
        struct witness *w;
        int i, s;

        w_data = (void *)uvm_pageboot_alloc(sizeof(struct witness) *
            witness_count);
        memset(w_data, 0, sizeof(struct witness) * witness_count);

        w_rmatrix = (void *)uvm_pageboot_alloc(sizeof(*w_rmatrix) *
            (witness_count + 1));

        for (i = 0; i < witness_count + 1; i++) {
                w_rmatrix[i] = (void *)uvm_pageboot_alloc(
                    sizeof(*w_rmatrix[i]) * (witness_count + 1));
                memset(w_rmatrix[i], 0, sizeof(*w_rmatrix[i]) *
                    (witness_count + 1));
        }

        mtx_init_flags(&w_mtx, IPL_HIGH, "witness lock", MTX_NOWITNESS);
        for (i = witness_count - 1; i >= 0; i--) {
                w = &w_data[i];
                memset(w, 0, sizeof(*w));
                w_data[i].w_index = i;  /* Witness index never changes. */
                witness_free(w);
        }
        KASSERTMSG(SLIST_FIRST(&w_free)->w_index == 0,
            "%s: Invalid list of free witness objects", __func__);

        /* Witness with index 0 is not used to aid in debugging. */
        SLIST_REMOVE_HEAD(&w_free, w_list);
        w_free_cnt--;

        for (i = 0; i < witness_count; i++) {
                memset(w_rmatrix[i], 0, sizeof(*w_rmatrix[i]) *
                    (witness_count + 1));
        }

        if (witness_locktrace) {
                w_lock_stack_num = LOCK_CHILDCOUNT * LOCK_NCHILDREN;
                stacks = (void *)uvm_pageboot_alloc(sizeof(*stacks) *
                    w_lock_stack_num);
        }

        w_locklistdata = (void *)uvm_pageboot_alloc(
            sizeof(struct lock_list_entry) * LOCK_CHILDCOUNT);
        memset(w_locklistdata, 0, sizeof(struct lock_list_entry) *
            LOCK_CHILDCOUNT);

        s = splhigh();
        for (i = 0; i < w_lock_stack_num; i++)
                witness_lock_stack_free(&stacks[i]);
        for (i = 0; i < LOCK_CHILDCOUNT; i++)
                witness_lock_list_free(&w_locklistdata[i]);
        splx(s);
        witness_init_hash_tables();
        witness_spin_warn = 1;

        /* Iterate through all locks and add them to witness. */
        for (i = 0; pending_locks[i].wh_lock != NULL; i++) {
                lock = pending_locks[i].wh_lock;
                KASSERTMSG(lock->lo_flags & LO_WITNESS,
                    "%s: lock %s is on pending list but not LO_WITNESS",
                    __func__, lock->lo_name);
                lock->lo_witness = enroll(pending_locks[i].wh_type,
                    lock->lo_name, LOCK_CLASS(lock));
        }

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

void
witness_init(struct lock_object *lock, const struct lock_type *type)
{
        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.
         * Record the type in case the lock becomes watched later.
         * 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 < 1 || panicstr != NULL || db_active ||
            (lock->lo_flags & LO_WITNESS) == 0) {
                lock->lo_witness = NULL;
                lock->lo_type = type;
        } else if (witness_cold) {
                pending_locks[pending_cnt].wh_lock = lock;
                pending_locks[pending_cnt++].wh_type = type;
                if (pending_cnt > WITNESS_PENDLIST)
                        panic("%s: pending locks list is too small, "
                            "increase WITNESS_PENDLIST",
                            __func__);
        } else
                lock->lo_witness = enroll(type, lock->lo_name, class);

        lock->lo_relative = NULL;
}

static inline int
is_kernel_lock(const struct lock_object *lock)
{
#ifdef MULTIPROCESSOR
        return (lock == &kernel_lock.mpl_lock_obj);
#else
        return (0);
#endif
}

#ifdef DDB
static void
witness_ddb_compute_levels(void)
{
        struct witness *w;

        /*
         * First clear all levels.
         */
        SLIST_FOREACH(w, &w_all, w_list)
                w->w_ddb_level = -1;

        /*
         * Look for locks with no parents and level all their descendants.
         */
        SLIST_FOREACH(w, &w_all, w_list) {
                /* If the witness has ancestors (is not a root), skip it. */
                if (w->w_num_ancestors > 0)
                        continue;
                witness_ddb_level_descendants(w, 0);
        }
}

static void
witness_ddb_level_descendants(struct witness *w, int l)
{
        int i;

        if (w->w_ddb_level >= l)
                return;

        w->w_ddb_level = l;
        l++;

        for (i = 1; i <= w_max_used_index; i++) {
                if (w_rmatrix[w->w_index][i] & WITNESS_PARENT)
                        witness_ddb_level_descendants(&w_data[i], l);
        }
}

static void
witness_ddb_display_descendants(int(*prnt)(const char *fmt, ...),
    struct witness *w, int indent)
{
        int i;

        for (i = 0; i < indent; i++)
                prnt(" ");
        prnt("%s (%s) (type: %s, depth: %d)",
            w->w_subtype, w->w_type->lt_name,
            w->w_class->lc_name, w->w_ddb_level);
        if (w->w_displayed) {
                prnt(" -- (already displayed)\n");
                return;
        }
        w->w_displayed = 1;
        if (!w->w_acquired)
                prnt(" -- never acquired\n");
        else
                prnt("\n");
        indent++;
        WITNESS_INDEX_ASSERT(w->w_index);
        for (i = 1; i <= w_max_used_index; i++) {
                if (w_rmatrix[w->w_index][i] & WITNESS_PARENT)
                        witness_ddb_display_descendants(prnt, &w_data[i],
                            indent);
        }
}

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

        SLIST_FOREACH(w, list, w_typelist) {
                if (!w->w_acquired || w->w_ddb_level > 0)
                        continue;

                /* This lock has no ancestors - display its descendants. */
                witness_ddb_display_descendants(prnt, w, 0);
        }
}

static void
witness_ddb_display(int(*prnt)(const char *fmt, ...))
{
        struct witness *w;

        KASSERTMSG(witness_cold == 0, "%s: witness_cold", __func__);
        witness_ddb_compute_levels();

        /* Clear all the displayed flags. */
        SLIST_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_ddb_display_list(prnt, &w_sleep);

        /*
         * Now do spin locks which have been acquired at least once.
         */
        prnt("\nSpin locks:\n");
        witness_ddb_display_list(prnt, &w_spin);

        /*
         * Finally, any locks which have not been acquired yet.
         */
        prnt("\nLocks which were never acquired:\n");
        SLIST_FOREACH(w, &w_all, w_list) {
                if (w->w_acquired)
                        continue;
                prnt("%s (%s) (type: %s, depth: %d)\n",
                    w->w_subtype, w->w_type->lt_name,
                    w->w_class->lc_name, w->w_ddb_level);
        }
}
#endif /* DDB */

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

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

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

        MUTEX_ASSERT_UNLOCKED(&w_mtx);
        mtx_enter(&w_mtx);

        /*
         * If we already have either an explicit or implied lock order that
         * is the other way around, then return an error.
         */
        if (witness_watch &&
            isitmydescendant(lock2->lo_witness, lock1->lo_witness)) {
                mtx_leave(&w_mtx);
                return (EINVAL);
        }

        /* Try to add the new order. */
        itismychild(lock1->lo_witness, lock2->lo_witness);
        mtx_leave(&w_mtx);
        return (0);
}

void
witness_checkorder(struct lock_object *lock, int flags,
    struct lock_object *interlock)
{
        struct lock_list_entry *lock_list, *lle;
        struct lock_instance *lock1, *lock2, *plock;
        struct lock_class *class, *iclass;
        struct witness *w, *w1;
        int i, j, s;

        if (witness_cold || witness_watch < 1 || panicstr != NULL || db_active)
                return;

        if ((lock->lo_flags & LO_INITIALIZED) == 0) {
                if (witness_uninitialized_report > 0) {
                        witness_uninitialized_report--;
                        printf("witness: lock_object uninitialized: %p\n", lock);
                        witness_debugger(1);
                }
                lock->lo_flags |= LO_INITIALIZED;
        }

        if ((lock->lo_flags & LO_WITNESS) == 0)
                return;

        w = lock->lo_witness;
        class = LOCK_CLASS(lock);

        if (w == NULL)
                w = lock->lo_witness =
                    enroll(lock->lo_type, lock->lo_name, class);

        if (class->lc_flags & LC_SLEEPLOCK) {
                struct proc *p;

                /*
                 * Since spin locks include a critical section, this check
                 * implicitly enforces a lock order of all sleep locks before
                 * all spin locks.
                 */
                lock_list = witness_cpu[cpu_number()].wc_spinlocks;
                if (lock_list != NULL && lock_list->ll_count > 0) {
                        panic("acquiring blockable sleep lock with "
                            "spinlock or critical section held (%s) %s",
                            class->lc_name, lock->lo_name);
                }

                /*
                 * If this is the first lock acquired then just return as
                 * no order checking is needed.
                 */
                p = curproc;
                if (p == NULL)
                        return;
                lock_list = p->p_sleeplocks;
                if (lock_list == NULL || lock_list->ll_count == 0)
                        return;
        } else {

                /*
                 * If this is the first lock, just return as no order
                 * checking is needed.
                 */
                lock_list = witness_cpu[cpu_number()].wc_spinlocks;
                if (lock_list == NULL || lock_list->ll_count == 0)
                        return;
        }

        s = splhigh();

        /*
         * 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("witness: shared lock of (%s) %s "
                            "while exclusively locked\n",
                            class->lc_name, lock->lo_name);
                        panic("excl->share");
                }
                if ((lock1->li_flags & LI_EXCLUSIVE) == 0 &&
                    (flags & LOP_EXCLUSIVE) != 0) {
                        printf("witness: exclusive lock of (%s) %s "
                            "while share locked\n",
                            class->lc_name, lock->lo_name);
                        panic("share->excl");
                }
                goto out_splx;
        }

        /* Warn if the interlock is not locked exactly once. */
        if (interlock != NULL) {
                iclass = LOCK_CLASS(interlock);
                lock1 = find_instance(lock_list, interlock);
                if (lock1 == NULL)
                        panic("interlock (%s) %s not locked",
                            iclass->lc_name, interlock->lo_name);
                else if ((lock1->li_flags & LI_RECURSEMASK) != 0)
                        panic("interlock (%s) %s recursed",
                            iclass->lc_name, interlock->lo_name);
        }

        /*
         * Find the previously acquired lock, but ignore interlocks.
         */
        plock = &lock_list->ll_children[lock_list->ll_count - 1];
        if (interlock != NULL && plock->li_lock == interlock) {
                if (lock_list->ll_count > 1)
                        plock =
                            &lock_list->ll_children[lock_list->ll_count - 2];
                else {
                        lle = lock_list->ll_next;

                        /*
                         * The interlock is the only lock we hold, so
                         * simply return.
                         */
                        if (lle == NULL)
                                goto out_splx;
                        plock = &lle->ll_children[lle->ll_count - 1];
                }
        }

        /*
         * Try to perform most checks without a lock.  If this succeeds we
         * can skip acquiring the lock and return success.  Otherwise we redo
         * the check with the lock held to handle races with concurrent updates.
         */
        w1 = plock->li_lock->lo_witness;
        if (witness_lock_order_check(w1, w))
                goto out_splx;

        mtx_enter(&w_mtx);
        if (witness_lock_order_check(w1, w))
                goto out;

        witness_lock_order_add(w1, w);

        /*
         * 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.
         */
        if (w1 == w) {
                i = w->w_index;
                if (!(lock->lo_flags & LO_DUPOK) && !(flags & LOP_DUPOK) &&
                    !islockmychild(plock->li_lock, lock) &&
                    !(w_rmatrix[i][i] & WITNESS_REVERSAL)) {
                        w_rmatrix[i][i] |= WITNESS_REVERSAL;
                        w->w_reversed = 1;
                        mtx_leave(&w_mtx);
                        printf("witness: acquiring duplicate lock of "
                            "same type: \"%s\"\n", w->w_type->lt_name);
                        printf(" 1st %s\n", plock->li_lock->lo_name);
                        printf(" 2nd %s\n", lock->lo_name);
                        witness_debugger(1);
                } else
                        mtx_leave(&w_mtx);
                goto out_splx;
        }
        MUTEX_ASSERT_LOCKED(&w_mtx);

        /*
         * If we know that 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))
                goto out;

        for (j = 0, lle = lock_list; lle != NULL; lle = lle->ll_next) {
                for (i = lle->ll_count - 1; i >= 0; i--, j++) {

                        KASSERT(j < LOCK_CHILDCOUNT * LOCK_NCHILDREN);
                        lock1 = &lle->ll_children[i];

                        /*
                         * Ignore the interlock.
                         */
                        if (interlock == lock1->li_lock)
                                continue;

                        /*
                         * If this lock doesn't undergo witness checking,
                         * then skip it.
                         */
                        w1 = lock1->li_lock->lo_witness;
                        if (w1 == NULL) {
                                KASSERTMSG((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 &&
                            is_kernel_lock(lock))
                                continue;

                        /*
                         * If we are locking a sleepable lock and this lock
                         * is Giant, then skip it.
                         */
                        if ((lock->lo_flags & LO_SLEEPABLE) != 0 &&
                            is_kernel_lock(lock1->li_lock))
                                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 enforce 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 &&
                            is_kernel_lock(lock))
                                goto reversal;

                        /*
                         * Check the lock order hierarchy for a reversal.
                         */
                        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.
                         */

                        /* Bail if this violation is known */
                        if (w_rmatrix[w1->w_index][w->w_index] & WITNESS_REVERSAL)
                                goto out;

                        /* Record this as a violation */
                        w_rmatrix[w1->w_index][w->w_index] |= WITNESS_REVERSAL;
                        w_rmatrix[w->w_index][w1->w_index] |= WITNESS_REVERSAL;
                        w->w_reversed = w1->w_reversed = 1;
                        witness_increment_graph_generation();
                        mtx_leave(&w_mtx);

                        /*
                         * There are known LORs between VNODE locks. They are
                         * not an indication of a bug. VNODE locks are flagged
                         * as such (LO_IS_VNODE) and we don't yell if the LOR
                         * is between 2 VNODE locks.
                         */
                        if ((lock->lo_flags & LO_IS_VNODE) != 0 &&
                            (lock1->li_lock->lo_flags & LO_IS_VNODE) != 0)
                                goto out_splx;

                        /*
                         * Ok, yell about it.
                         */
                        printf("witness: ");
                        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
                            && is_kernel_lock(lock))
                                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];
                                KASSERT(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;
                                        KASSERT(i >= 0 && i < LOCK_NCHILDREN);
                                } else
                                        i--;
                        } while (i >= 0);
                        if (i < 0) {
                                printf(" 1st %p %s (%s)\n",
                                    lock1->li_lock, lock1->li_lock->lo_name,
                                    w1->w_type->lt_name);
                                printf(" 2nd %p %s (%s)\n",
                                    lock, lock->lo_name, w->w_type->lt_name);
                        } else {
                                printf(" 1st %p %s (%s)\n",
                                    lock2->li_lock, lock2->li_lock->lo_name,
                                    lock2->li_lock->lo_witness->w_type->
                                      lt_name);
                                printf(" 2nd %p %s (%s)\n",
                                    lock1->li_lock, lock1->li_lock->lo_name,
                                    w1->w_type->lt_name);
                                printf(" 3rd %p %s (%s)\n", lock,
                                    lock->lo_name, w->w_type->lt_name);
                        }
                        if (witness_watch > 1)
                                witness_print_cycle(printf, w1, w);
                        witness_debugger(0);
                        goto out_splx;
                }
        }

        /*
         * 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 &&
            !(is_kernel_lock(plock->li_lock) &&
            (lock->lo_flags & LO_SLEEPABLE) != 0))
                itismychild(plock->li_lock->lo_witness, w);
out:
        mtx_leave(&w_mtx);
out_splx:
        splx(s);
}

void
witness_lock(struct lock_object *lock, int flags)
{
        struct lock_list_entry **lock_list, *lle;
        struct lock_instance *instance;
        struct witness *w;
        int s;

        if (witness_cold || witness_watch < 0 || panicstr != NULL ||
            db_active || (lock->lo_flags & LO_WITNESS) == 0)
                return;

        w = lock->lo_witness;
        if (w == NULL)
                w = lock->lo_witness =
                    enroll(lock->lo_type, lock->lo_name, LOCK_CLASS(lock));

        /* Determine lock list for this lock. */
        if (LOCK_CLASS(lock)->lc_flags & LC_SLEEPLOCK) {
                struct proc *p;

                p = curproc;
                if (p == NULL)
                        return;
                lock_list = &p->p_sleeplocks;
        } else
                lock_list = &witness_cpu[cpu_number()].wc_spinlocks;

        s = splhigh();

        /* 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++;
                goto out;
        }

        w->w_acquired = 1;

        /* 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)
                        goto out;
                lle->ll_next = *lock_list;
                *lock_list = lle;
        }
        instance = &lle->ll_children[lle->ll_count++];
        instance->li_lock = lock;
        if ((flags & LOP_EXCLUSIVE) != 0)
                instance->li_flags = LI_EXCLUSIVE;
        else
                instance->li_flags = 0;
        instance->li_stack = NULL;
        if (witness_locktrace) {
                instance->li_stack = witness_lock_stack_get();
                if (instance->li_stack != NULL)
                        stacktrace_save(&instance->li_stack->ls_stack);
        }
out:
        splx(s);
}

void
witness_upgrade(struct lock_object *lock, int flags)
{
        struct lock_instance *instance;
        struct lock_class *class;
        int s;

        KASSERTMSG(witness_cold == 0, "%s: witness_cold", __func__);
        if (lock->lo_witness == NULL || witness_watch < 0 ||
            panicstr != NULL || db_active)
                return;
        class = LOCK_CLASS(lock);
        if (witness_watch) {
                if ((lock->lo_flags & LO_UPGRADABLE) == 0)
                        panic("upgrade of non-upgradable lock (%s) %s",
                            class->lc_name, lock->lo_name);
                if ((class->lc_flags & LC_SLEEPLOCK) == 0)
                        panic("upgrade of non-sleep lock (%s) %s",
                            class->lc_name, lock->lo_name);
        }
        s = splhigh();
        instance = find_instance(curproc->p_sleeplocks, lock);
        if (instance == NULL) {
                panic("upgrade of unlocked lock (%s) %s",
                    class->lc_name, lock->lo_name);
                goto out;
        }
        if (witness_watch) {
                if ((instance->li_flags & LI_EXCLUSIVE) != 0)
                        panic("upgrade of exclusive lock (%s) %s",
                            class->lc_name, lock->lo_name);
                if ((instance->li_flags & LI_RECURSEMASK) != 0)
                        panic("upgrade of recursed lock (%s) %s r=%d",
                            class->lc_name, lock->lo_name,
                            instance->li_flags & LI_RECURSEMASK);
        }
        instance->li_flags |= LI_EXCLUSIVE;
out:
        splx(s);
}

void
witness_downgrade(struct lock_object *lock, int flags)
{
        struct lock_instance *instance;
        struct lock_class *class;
        int s;

        KASSERTMSG(witness_cold == 0, "%s: witness_cold", __func__);
        if (lock->lo_witness == NULL || witness_watch < 0 ||
            panicstr != NULL || db_active)
                return;
        class = LOCK_CLASS(lock);
        if (witness_watch) {
                if ((lock->lo_flags & LO_UPGRADABLE) == 0)
                        panic(
                            "downgrade of non-upgradable lock (%s) %s",
                            class->lc_name, lock->lo_name);
                if ((class->lc_flags & LC_SLEEPLOCK) == 0)
                        panic("downgrade of non-sleep lock (%s) %s",
                            class->lc_name, lock->lo_name);
        }
        s = splhigh();
        instance = find_instance(curproc->p_sleeplocks, lock);
        if (instance == NULL) {
                panic("downgrade of unlocked lock (%s) %s",
                    class->lc_name, lock->lo_name);
                goto out;
        }
        if (witness_watch) {
                if ((instance->li_flags & LI_EXCLUSIVE) == 0)
                        panic("downgrade of shared lock (%s) %s",
                            class->lc_name, lock->lo_name);
                if ((instance->li_flags & LI_RECURSEMASK) != 0)
                        panic("downgrade of recursed lock (%s) %s r=%d",
                            class->lc_name, lock->lo_name,
                            instance->li_flags & LI_RECURSEMASK);
        }
        instance->li_flags &= ~LI_EXCLUSIVE;
out:
        splx(s);
}

void
witness_unlock(struct lock_object *lock, int flags)
{
        struct lock_list_entry **lock_list, *lle;
        struct lock_instance *instance;
        struct lock_class *class;
        int i, j;
        int s;

        if (witness_cold || lock->lo_witness == NULL ||
            panicstr != NULL || db_active)
                return;
        class = LOCK_CLASS(lock);

        /* Find lock instance associated with this lock. */
        if (class->lc_flags & LC_SLEEPLOCK) {
                struct proc *p;

                p = curproc;
                if (p == NULL)
                        return;
                lock_list = &p->p_sleeplocks;
        } else
                lock_list = &witness_cpu[cpu_number()].wc_spinlocks;

        s = splhigh();

        lle = *lock_list;
        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;
                }

        /*
         * When disabling WITNESS through witness_watch we could end up in
         * having registered locks in the p_sleeplocks queue.
         * We have to make sure we flush these queues, so just search for
         * eventual register locks and remove them.
         */
        if (witness_watch > 0) {
                panic("lock (%s) %s not locked", class->lc_name, lock->lo_name);
        }
        goto out;

found:

        /* First, check for shared/exclusive mismatches. */
        if ((instance->li_flags & LI_EXCLUSIVE) != 0 && witness_watch > 0 &&
            (flags & LOP_EXCLUSIVE) == 0) {
                printf("witness: shared unlock of (%s) %s "
                    "while exclusively locked\n",
                    class->lc_name, lock->lo_name);
                panic("excl->ushare");
        }
        if ((instance->li_flags & LI_EXCLUSIVE) == 0 && witness_watch > 0 &&
            (flags & LOP_EXCLUSIVE) != 0) {
                printf("witness: exclusive unlock of (%s) %s "
                    "while share locked\n", class->lc_name, lock->lo_name);
                panic("share->uexcl");
        }
        /* If we are recursed, unrecurse. */
        if ((instance->li_flags & LI_RECURSEMASK) > 0) {
                instance->li_flags--;
                goto out;
        }
        /* The lock is now being dropped, check for NORELEASE flag */
        if ((instance->li_flags & LI_NORELEASE) != 0 && witness_watch > 0) {
                printf("witness: forbidden unlock of (%s) %s\n",
                    class->lc_name, lock->lo_name);
                panic("lock marked norelease");
        }

        /* Release the stack buffer, if any. */
        if (instance->li_stack != NULL) {
                witness_lock_stack_free(instance->li_stack);
                instance->li_stack = NULL;
        }

        /* Remove this item from the list. */
        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--;

        /*
         * In order to reduce contention on w_mtx, we want to keep always an
         * head object into lists so that frequent allocation from the
         * free witness pool (and subsequent locking) is avoided.
         * In order to maintain the current code simple, when the head
         * object is totally unloaded it means also that we do not have
         * further objects in the list, so the list ownership needs to be
         * hand over to another object if the current head needs to be freed.
         */
        if ((*lock_list)->ll_count == 0) {
                if (*lock_list == lle) {
                        if (lle->ll_next == NULL)
                                goto out;
                } else
                        lle = *lock_list;
                *lock_list = lle->ll_next;
                witness_lock_list_free(lle);
        }
out:
        splx(s);
}

/*
 * Set the permitted parent/child relation for the given lock.
 * This allows the nesting of two locks that are of the same type.
 *
 * Once a lock relation has been set, the caller is not allowed
 * to change the type (parent/child), as doing so is indicative of a bug.
 *
 * This function is allowed only when the caller has exclusive access
 * to @lock.
 */
void
witness_setrelative(struct lock_object *lock, struct lock_object *relative,
    int is_parent)
{
        if (witness_watch < 0 || panicstr != NULL || db_active)
                return;

        mtx_enter(&w_mtx);
        if (is_parent) {
                KASSERT(lock->lo_relative == NULL ||
                    (lock->lo_flags & LO_HASPARENT));
                lock->lo_flags |= LO_HASPARENT;
        } else {
                KASSERT(lock->lo_relative == NULL ||
                    !(lock->lo_flags & LO_HASPARENT));
                lock->lo_flags &= ~LO_HASPARENT;
        }
        lock->lo_relative = relative;
        mtx_leave(&w_mtx);
}

void
witness_thread_exit(struct proc *p)
{
        struct lock_list_entry *lle;
        int i, n, s;

        lle = p->p_sleeplocks;
        if (lle == NULL || panicstr != NULL || db_active)
                return;
        if (lle->ll_count != 0) {
                for (n = 0; lle != NULL; lle = lle->ll_next)
                        for (i = lle->ll_count - 1; i >= 0; i--) {
                                if (n == 0)
                                        printf("witness: thread %p exiting "
                                            "with the following locks held:\n",
                                            p);
                                n++;
                                witness_list_lock(&lle->ll_children[i],
                                    printf);
                        }
                panic("thread %p cannot exit while holding sleeplocks", p);
        }
        KASSERT(lle->ll_next == NULL);
        s = splhigh();
        witness_lock_list_free(lle);
        splx(s);
}

/*
 * 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
 * output channel 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 *lock_list, *lle;
        struct lock_instance *lock1;
        struct proc *p;
        va_list ap;
        int i, n;

        if (witness_cold || witness_watch < 1 || panicstr != NULL || db_active)
                return (0);
        n = 0;
        p = curproc;
        for (lle = p->p_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_KERNELOK &&
                            is_kernel_lock(lock1->li_lock))
                                continue;
                        if (flags & WARN_SLEEPOK &&
                            (lock1->li_lock->lo_flags & LO_SLEEPABLE) != 0)
                                continue;
                        if (n == 0) {
                                printf("witness: ");
                                va_start(ap, fmt);
                                vprintf(fmt, ap);
                                va_end(ap);
                                printf(" with the following %slocks held:\n",
                                    (flags & WARN_SLEEPOK) != 0 ?
                                    "non-sleepable " : "");
                        }
                        n++;
                        witness_list_lock(lock1, printf);
                }

        lock_list = witness_cpu[cpu_number()].wc_spinlocks;
        if (lock_list != NULL && lock_list->ll_count != 0) {
                /*
                 * We should only have one spinlock and as long as
                 * the flags cannot match for this locks class,
                 * check if the first spinlock is the one curproc
                 * should hold.
                 */
                lock1 = &lock_list->ll_children[lock_list->ll_count - 1];
                if (lock_list->ll_count == 1 && lock_list->ll_next == NULL &&
                    lock1->li_lock == lock && n == 0)
                        return (0);

                printf("witness: ");
                va_start(ap, fmt);
                vprintf(fmt, ap);
                va_end(ap);
                printf(" with the following %slocks held:\n",
                    (flags & WARN_SLEEPOK) != 0 ?  "non-sleepable " : "");
                n += witness_list_locks(&lock_list, printf);
        }
        if (n > 0) {
                if (flags & WARN_PANIC)
                        panic("%s", __func__);
                else
                        witness_debugger(1);
        }
        return (n);
}

static struct witness *
enroll(const struct lock_type *type, const char *subtype,
    struct lock_class *lock_class)
{
        struct witness *w;
        struct witness_list *typelist;

        KASSERT(type != NULL);

        if (witness_watch < 0 || panicstr != NULL || db_active)
                return (NULL);
        if ((lock_class->lc_flags & LC_SPINLOCK)) {
                typelist = &w_spin;
        } else if ((lock_class->lc_flags & LC_SLEEPLOCK)) {
                typelist = &w_sleep;
        } else {
                panic("lock class %s is not sleep or spin",
                    lock_class->lc_name);
                return (NULL);
        }

        mtx_enter(&w_mtx);
        w = witness_hash_get(type, subtype);
        if (w)
                goto found;
        if ((w = witness_get()) == NULL)
                return (NULL);
        w->w_type = type;
        w->w_subtype = subtype;
        w->w_class = lock_class;
        SLIST_INSERT_HEAD(&w_all, w, w_list);
        if (lock_class->lc_flags & LC_SPINLOCK) {
                SLIST_INSERT_HEAD(&w_spin, w, w_typelist);
                w_spin_cnt++;
        } else if (lock_class->lc_flags & LC_SLEEPLOCK) {
                SLIST_INSERT_HEAD(&w_sleep, w, w_typelist);
                w_sleep_cnt++;
        }

        /* Insert new witness into the hash */
        witness_hash_put(w);
        witness_increment_graph_generation();
        mtx_leave(&w_mtx);
        return (w);
found:
        mtx_leave(&w_mtx);
        if (lock_class != w->w_class)
                panic("lock (%s) %s does not match earlier (%s) lock",
                    type->lt_name, lock_class->lc_name, w->w_class->lc_name);
        return (w);
}

static void
adopt(struct witness *parent, struct witness *child)
{
        int pi, ci, i, j;

        if (witness_cold == 0)
                MUTEX_ASSERT_LOCKED(&w_mtx);

        /* If the relationship is already known, there's no work to be done. */
        if (isitmychild(parent, child))
                return;

        /* When the structure of the graph changes, bump up the generation. */
        witness_increment_graph_generation();

        /*
         * The hard part ... create the direct relationship, then propagate all
         * indirect relationships.
         */
        pi = parent->w_index;
        ci = child->w_index;
        WITNESS_INDEX_ASSERT(pi);
        WITNESS_INDEX_ASSERT(ci);
        KASSERT(pi != ci);
        w_rmatrix[pi][ci] |= WITNESS_PARENT;
        w_rmatrix[ci][pi] |= WITNESS_CHILD;

        /*
         * If parent was not already an ancestor of child,
         * then we increment the descendant and ancestor counters.
         */
        if ((w_rmatrix[pi][ci] & WITNESS_ANCESTOR) == 0) {
                parent->w_num_descendants++;
                child->w_num_ancestors++;
        }

        /*
         * Find each ancestor of 'pi'. Note that 'pi' itself is counted as
         * an ancestor of 'pi' during this loop.
         */
        for (i = 1; i <= w_max_used_index; i++) {
                if ((w_rmatrix[i][pi] & WITNESS_ANCESTOR_MASK) == 0 &&
                    (i != pi))
                        continue;

                /* Find each descendant of 'i' and mark it as a descendant. */
                for (j = 1; j <= w_max_used_index; j++) {

                        /*
                         * Skip children that are already marked as
                         * descendants of 'i'.
                         */
                        if (w_rmatrix[i][j] & WITNESS_ANCESTOR_MASK)
                                continue;

                        /*
                         * We are only interested in descendants of 'ci'. Note
                         * that 'ci' itself is counted as a descendant of 'ci'.
                         */
                        if ((w_rmatrix[ci][j] & WITNESS_ANCESTOR_MASK) == 0 &&
                            (j != ci))
                                continue;
                        w_rmatrix[i][j] |= WITNESS_ANCESTOR;
                        w_rmatrix[j][i] |= WITNESS_DESCENDANT;
                        w_data[i].w_num_descendants++;
                        w_data[j].w_num_ancestors++;

                        /*
                         * Make sure we aren't marking a node as both an
                         * ancestor and descendant. We should have caught
                         * this as a lock order reversal earlier.
                         */
                        if ((w_rmatrix[i][j] & WITNESS_ANCESTOR_MASK) &&
                            (w_rmatrix[i][j] & WITNESS_DESCENDANT_MASK)) {
                                printf("witness: rmatrix paradox! [%d][%d]=%d "
                                    "both ancestor and descendant\n",
                                    i, j, w_rmatrix[i][j]);
#ifdef DDB
                                db_stack_dump();
#endif
                                printf("witness disabled\n");
                                witness_watch = -1;
                        }
                        if ((w_rmatrix[j][i] & WITNESS_ANCESTOR_MASK) &&
                            (w_rmatrix[j][i] & WITNESS_DESCENDANT_MASK)) {
                                printf("witness: rmatrix paradox! [%d][%d]=%d "
                                    "both ancestor and descendant\n",
                                    j, i, w_rmatrix[j][i]);
#ifdef DDB
                                db_stack_dump();
#endif
                                printf("witness disabled\n");
                                witness_watch = -1;
                        }
                }
        }
}

static void
itismychild(struct witness *parent, struct witness *child)
{
        KASSERT(child != NULL && parent != NULL);
        if (witness_cold == 0)
                MUTEX_ASSERT_LOCKED(&w_mtx);

        if (!witness_lock_type_equal(parent, child)) {
                if (witness_cold == 0)
                        mtx_leave(&w_mtx);
                panic(
                    "%s: parent \"%s\" (%s) and child \"%s\" (%s) are not "
                    "the same lock type", __func__, parent->w_type->lt_name,
                    parent->w_class->lc_name, child->w_type->lt_name,
                    child->w_class->lc_name);
        }
        adopt(parent, child);
}

/*
 * Generic code for the isitmy*() functions. The rmask parameter is the
 * expected relationship of w1 to w2.
 */
static int
_isitmyx(struct witness *w1, struct witness *w2, int rmask, const char *fname)
{
        unsigned char r1, r2;
        int i1, i2;

        i1 = w1->w_index;
        i2 = w2->w_index;
        WITNESS_INDEX_ASSERT(i1);
        WITNESS_INDEX_ASSERT(i2);
        r1 = w_rmatrix[i1][i2] & WITNESS_RELATED_MASK;
        r2 = w_rmatrix[i2][i1] & WITNESS_RELATED_MASK;

        /* The flags on one better be the inverse of the flags on the other */
        if (!((WITNESS_ATOD(r1) == r2 && WITNESS_DTOA(r2) == r1) ||
            (WITNESS_DTOA(r1) == r2 && WITNESS_ATOD(r2) == r1))) {
                /* Don't squawk if we're potentially racing with an update. */
                if (mtx_owner(&w_mtx) != mtx_curcpu())
                        return (0);
                printf("witness: %s: rmatrix mismatch between %s (index %d) "
                    "and %s (index %d): w_rmatrix[%d][%d] == %x but "
                    "w_rmatrix[%d][%d] == %x\n",
                    fname, w1->w_type->lt_name, i1, w2->w_type->lt_name,
                    i2, i1, i2, r1,
                    i2, i1, r2);
#ifdef DDB
                db_stack_dump();
#endif
                printf("witness disabled\n");
                witness_watch = -1;
        }
        return (r1 & rmask);
}

/*
 * Checks if @child is a direct child of @parent.
 */
static int
isitmychild(struct witness *parent, struct witness *child)
{

        return (_isitmyx(parent, child, WITNESS_PARENT, __func__));
}

/*
 * Checks if @descendant is a direct or indirect descendant of @ancestor.
 */
static int
isitmydescendant(struct witness *ancestor, struct witness *descendant)
{

        return (_isitmyx(ancestor, descendant, WITNESS_ANCESTOR_MASK,
            __func__));
}

/*
 * Checks if the @parent/@child relation is allowed.
 */
static int
islockmychild(struct lock_object *parent, struct lock_object *child)
{
        if (!(parent->lo_flags & LO_HASPARENT) &&
            parent->lo_relative == child)
                return (1);
        if ((child->lo_flags & LO_HASPARENT) &&
            child->lo_relative == parent)
                return (1);
        return (0);
}

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

        if (witness_cold == 0)
                MUTEX_ASSERT_LOCKED(&w_mtx);

        if (witness_watch < 0) {
                mtx_leave(&w_mtx);
                return (NULL);
        }
        if (SLIST_EMPTY(&w_free)) {
                witness_watch = -1;
                mtx_leave(&w_mtx);
                printf("WITNESS: unable to allocate a new witness object\n");
                return (NULL);
        }
        w = SLIST_FIRST(&w_free);
        SLIST_REMOVE_HEAD(&w_free, w_list);
        w_free_cnt--;
        index = w->w_index;
        KASSERT(index > 0 && index == w_max_used_index + 1 &&
            index < witness_count);
        memset(w, 0, sizeof(*w));
        w->w_index = index;
        if (index > w_max_used_index)
                w_max_used_index = index;
        return (w);
}

static void
witness_free(struct witness *w)
{
        SLIST_INSERT_HEAD(&w_free, w, w_list);
        w_free_cnt++;
}

static struct lock_list_entry *
witness_lock_list_get(void)
{
        struct lock_list_entry *lle;
        struct witness_cpu *wcpu = &witness_cpu[cpu_number()];

        if (witness_watch < 0)
                return (NULL);

        splassert(IPL_HIGH);

        if (wcpu->wc_lle_count > 0) {
                lle = wcpu->wc_lle_cache;
                wcpu->wc_lle_cache = lle->ll_next;
                wcpu->wc_lle_count--;
                memset(lle, 0, sizeof(*lle));
                return (lle);
        }

        mtx_enter(&w_mtx);
        lle = w_lock_list_free;
        if (lle == NULL) {
                witness_watch = -1;
                mtx_leave(&w_mtx);
                printf("%s: witness exhausted\n", __func__);
                return (NULL);
        }
        w_lock_list_free = lle->ll_next;
        mtx_leave(&w_mtx);
        memset(lle, 0, sizeof(*lle));
        return (lle);
}

static void
witness_lock_list_free(struct lock_list_entry *lle)
{
        struct witness_cpu *wcpu = &witness_cpu[cpu_number()];

        splassert(IPL_HIGH);

        if (wcpu->wc_lle_count < WITNESS_LLE_CACHE_MAX) {
                lle->ll_next = wcpu->wc_lle_cache;
                wcpu->wc_lle_cache = lle;
                wcpu->wc_lle_count++;
                return;
        }

        mtx_enter(&w_mtx);
        lle->ll_next = w_lock_list_free;
        w_lock_list_free = lle;
        mtx_leave(&w_mtx);
}

static union lock_stack *
witness_lock_stack_get(void)
{
        union lock_stack *stack = NULL;
        struct witness_cpu *wcpu = &witness_cpu[cpu_number()];

        splassert(IPL_HIGH);

        if (wcpu->wc_stk_count > 0) {
                stack = wcpu->wc_stk_cache;
                wcpu->wc_stk_cache = stack->ls_next;
                wcpu->wc_stk_count--;
                return (stack);
        }

        mtx_enter(&w_mtx);
        if (w_lock_stack_free != NULL) {
                stack = w_lock_stack_free;
                w_lock_stack_free = stack->ls_next;
        }
        mtx_leave(&w_mtx);
        return (stack);
}

static void
witness_lock_stack_free(union lock_stack *stack)
{
        struct witness_cpu *wcpu = &witness_cpu[cpu_number()];

        splassert(IPL_HIGH);

        if (wcpu->wc_stk_count < WITNESS_STK_CACHE_MAX) {
                stack->ls_next = wcpu->wc_stk_cache;
                wcpu->wc_stk_cache = stack;
                wcpu->wc_stk_count++;
                return;
        }

        mtx_enter(&w_mtx);
        stack->ls_next = w_lock_stack_free;
        w_lock_stack_free = stack;
        mtx_leave(&w_mtx);
}

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

        for (lle = 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,
    int (*prnt)(const char *fmt, ...))
{
        struct lock_object *lock;

        lock = instance->li_lock;
        prnt("%s %s %s", (instance->li_flags & LI_EXCLUSIVE) != 0 ?
            "exclusive" : "shared", LOCK_CLASS(lock)->lc_name, lock->lo_name);
        prnt(" r = %d (%p)\n", instance->li_flags & LI_RECURSEMASK, lock);
        if (instance->li_stack != NULL)
                stacktrace_print(&instance->li_stack->ls_stack, prnt);
}

static int
witness_search(struct witness *w, struct witness *target,
    struct witness **path, int depth, int *remaining)
{
        int i, any_remaining;

        if (depth == 0) {
                *remaining = 1;
                return (w == target);
        }

        any_remaining = 0;
        for (i = 1; i <= w_max_used_index; i++) {
                if (w_rmatrix[w->w_index][i] & WITNESS_PARENT) {
                        if (witness_search(&w_data[i], target, path, depth - 1,
                            remaining)) {
                                path[depth - 1] = &w_data[i];
                                *remaining = 1;
                                return 1;
                        }
                        if (remaining)
                                any_remaining = 1;
                }
        }
        *remaining = any_remaining;
        return 0;
}

static void
witness_print_cycle_edge(int(*prnt)(const char *fmt, ...),
    struct witness *parent, struct witness *child, int step, int last)
{
        struct witness_lock_order_data *wlod;
        int next;

        if (last)
                next = 1;
        else
                next = step + 1;
        prnt("lock order [%d] %s (%s) -> [%d] %s (%s)\n",
            step, parent->w_subtype, parent->w_type->lt_name,
            next, child->w_subtype, child->w_type->lt_name);
        if (witness_watch > 1) {
                mtx_enter(&w_mtx);
                wlod = witness_lock_order_get(parent, child);
                mtx_leave(&w_mtx);

                if (wlod != NULL)
                        stacktrace_print(&wlod->wlod_stack, printf);
                else
                        prnt("lock order data %p -> %p is missing\n",
                            parent->w_type->lt_name, child->w_type->lt_name);
        }
}

static void
witness_print_cycle(int(*prnt)(const char *fmt, ...),
    struct witness *parent, struct witness *child)
{
        struct witness *path[4];
        struct witness *w;
        int depth, remaining;
        int step = 0;

        /*
         * Use depth-limited search to find the shortest path
         * from child to parent.
         */
        for (depth = 1; depth < nitems(path); depth++) {
                if (witness_search(child, parent, path, depth, &remaining))
                        goto found;
                if (!remaining)
                        break;
        }
        prnt("witness: incomplete path, depth %d\n", depth);
        return;

found:
        witness_print_cycle_edge(prnt, parent, child, ++step, 0);
        for (w = child; depth > 0; depth--) {
                witness_print_cycle_edge(prnt, w, path[depth - 1], ++step,
                    depth == 1);
                w = path[depth - 1];
        }
}

#ifdef DDB
static int
witness_thread_has_locks(struct proc *p)
{

        if (p->p_sleeplocks == NULL)
                return (0);
        return (p->p_sleeplocks->ll_count != 0);
}

static int
witness_process_has_locks(struct process *pr)
{
        struct proc *p;

        TAILQ_FOREACH(p, &pr->ps_threads, p_thr_link) {
                if (witness_thread_has_locks(p))
                        return (1);
        }
        return (0);
}
#endif

int
witness_list_locks(struct lock_list_entry **lock_list,
    int (*prnt)(const char *fmt, ...))
{
        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], prnt);
                        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 proc *owner,
    int (*prnt)(const char *fmt, ...))
{
        struct lock_instance *instance;

        if (owner->p_stat != SONPROC)
                return;
        instance = find_instance(
            witness_cpu[owner->p_cpu->ci_cpuid].wc_spinlocks, lock);
        if (instance != NULL)
                witness_list_lock(instance, prnt);
}

void
witness_assert(const struct lock_object *lock, int flags)
{
        struct lock_instance *instance;
        struct lock_class *class;

        if (lock->lo_witness == NULL || witness_watch < 1 ||
            panicstr != NULL || db_active)
                return;
        class = LOCK_CLASS(lock);
        if ((class->lc_flags & LC_SLEEPLOCK) != 0)
                instance = find_instance(curproc->p_sleeplocks, lock);
        else if ((class->lc_flags & LC_SPINLOCK) != 0)
                instance = find_instance(
                    witness_cpu[cpu_number()].wc_spinlocks, lock);
        else {
                panic("lock (%s) %s is not sleep or spin!",
                    class->lc_name, lock->lo_name);
                return;
        }
        switch (flags) {
        case LA_UNLOCKED:
                if (instance != NULL)
                        panic("lock (%s) %s locked",
                            class->lc_name, lock->lo_name);
                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",
                            class->lc_name, lock->lo_name);
                        break;
                }
                if ((flags & LA_XLOCKED) != 0 &&
                    (instance->li_flags & LI_EXCLUSIVE) == 0)
                        panic(
                            "lock (%s) %s not exclusively locked",
                            class->lc_name, lock->lo_name);
                if ((flags & LA_SLOCKED) != 0 &&
                    (instance->li_flags & LI_EXCLUSIVE) != 0)
                        panic(
                            "lock (%s) %s exclusively locked",
                            class->lc_name, lock->lo_name);
                if ((flags & LA_RECURSED) != 0 &&
                    (instance->li_flags & LI_RECURSEMASK) == 0)
                        panic("lock (%s) %s not recursed",
                            class->lc_name, lock->lo_name);
                if ((flags & LA_NOTRECURSED) != 0 &&
                    (instance->li_flags & LI_RECURSEMASK) != 0)
                        panic("lock (%s) %s recursed",
                            class->lc_name, lock->lo_name);
                break;
        default:
                panic("invalid lock assertion");

        }
}

static void
witness_setflag(struct lock_object *lock, int flag, int set)
{
        struct lock_list_entry *lock_list;
        struct lock_instance *instance;
        struct lock_class *class;

        if (lock->lo_witness == NULL || witness_watch < 0 ||
            panicstr != NULL || db_active)
                return;
        class = LOCK_CLASS(lock);
        if (class->lc_flags & LC_SLEEPLOCK)
                lock_list = curproc->p_sleeplocks;
        else
                lock_list = witness_cpu[cpu_number()].wc_spinlocks;
        instance = find_instance(lock_list, lock);
        if (instance == NULL) {
                panic("%s: lock (%s) %s not locked", __func__,
                    class->lc_name, lock->lo_name);
                return;
        }

        if (set)
                instance->li_flags |= flag;
        else
                instance->li_flags &= ~flag;
}

void
witness_norelease(struct lock_object *lock)
{

        witness_setflag(lock, LI_NORELEASE, 1);
}

void
witness_releaseok(struct lock_object *lock)
{

        witness_setflag(lock, LI_NORELEASE, 0);
}

#ifdef DDB
static void
witness_ddb_list(struct proc *p)
{
        struct witness_cpu *wc = &witness_cpu[cpu_number()];

        KASSERTMSG(witness_cold == 0, "%s: witness_cold", __func__);
        KASSERTMSG(db_active, "%s: not in the debugger", __func__);

        if (witness_watch < 1)
                return;

        witness_list_locks(&p->p_sleeplocks, db_printf);

        /*
         * We only handle spinlocks if td == curproc.  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 the scheduler
         * 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 (p == curproc && wc->wc_spinlocks != NULL)
                witness_list_locks(&wc->wc_spinlocks, db_printf);
}

void
db_witness_list(db_expr_t addr, int have_addr, db_expr_t count, char *modif)
{
        struct proc *p;

        if (have_addr)
                p = (struct proc *)addr;
        else
                p = curproc;
        witness_ddb_list(p);
}

void
db_witness_list_all(db_expr_t addr, int have_addr, db_expr_t count, char *modif)
{
        CPU_INFO_ITERATOR cii;
        struct cpu_info *ci;
        struct lock_list_entry *lock_list;
        struct process *pr;
        struct proc *p;

        CPU_INFO_FOREACH(cii, ci) {
                lock_list = witness_cpu[CPU_INFO_UNIT(ci)].wc_spinlocks;
                if (lock_list == NULL || lock_list->ll_count == 0)
                        continue;
                db_printf("CPU %d:\n", CPU_INFO_UNIT(ci));
                witness_list_locks(&lock_list, db_printf);
        }

        /*
         * It would be nice to list only threads and processes that actually
         * held sleep locks, but that information is currently not exported
         * by WITNESS.
         */
        LIST_FOREACH(pr, &allprocess, ps_list) {
                if (!witness_process_has_locks(pr))
                        continue;
                TAILQ_FOREACH(p, &pr->ps_threads, p_thr_link) {
                        if (!witness_thread_has_locks(p))
                                continue;
                        db_printf("Process %d (%s) thread %p (%d)\n",
                            pr->ps_pid, pr->ps_comm, p, p->p_tid);
                        witness_ddb_list(p);
                }
        }
}

void
witness_print_badstacks(void)
{
        struct witness *w1, *w2;
        int error, generation, i, j;

        if (witness_watch < 1) {
                db_printf("witness watch is disabled\n");
                return;
        }
        if (witness_cold) {
                db_printf("witness is cold\n");
                return;
        }
        error = 0;

restart:
        mtx_enter(&w_mtx);
        generation = w_generation;
        mtx_leave(&w_mtx);
        db_printf("Number of known direct relationships is %d\n",
            w_lohash.wloh_count);
        for (i = 1; i < w_max_used_index; i++) {
                mtx_enter(&w_mtx);
                if (generation != w_generation) {
                        mtx_leave(&w_mtx);

                        /* The graph has changed, try again. */
                        db_printf("Lock graph changed, restarting trace.\n");
                        goto restart;
                }

                w1 = &w_data[i];
                if (w1->w_reversed == 0) {
                        mtx_leave(&w_mtx);
                        continue;
                }
                mtx_leave(&w_mtx);

                if (w1->w_reversed == 0)
                        continue;
                for (j = 1; j < w_max_used_index; j++) {
                        if ((w_rmatrix[i][j] & WITNESS_REVERSAL) == 0 || i > j)
                                continue;

                        mtx_enter(&w_mtx);
                        if (generation != w_generation) {
                                mtx_leave(&w_mtx);

                                /* The graph has changed, try again. */
                                db_printf("Lock graph changed, "
                                    "restarting trace.\n");
                                goto restart;
                        }

                        w2 = &w_data[j];
                        mtx_leave(&w_mtx);

                        db_printf("\nLock order reversal between \"%s\"(%s) "
                            "and \"%s\"(%s)!\n",
                            w1->w_type->lt_name, w1->w_class->lc_name,
                            w2->w_type->lt_name, w2->w_class->lc_name);
                        witness_print_cycle(db_printf, w1, w2);
                }
        }
        mtx_enter(&w_mtx);
        if (generation != w_generation) {
                mtx_leave(&w_mtx);

                /*
                 * The graph changed while we were printing stack data,
                 * try again.
                 */
                db_printf("Lock graph changed, restarting trace.\n");
                goto restart;
        }
        mtx_leave(&w_mtx);
}

void
db_witness_display(db_expr_t addr, int have_addr, db_expr_t count, char *modif)
{
        switch (modif[0]) {
        case 'b':
                witness_print_badstacks();
                break;
        default:
                witness_ddb_display(db_printf);
                break;
        }
}
#endif

void
db_witness_print_fullgraph(void)
{
        struct witness *w;
        int error;

        if (witness_watch < 1) {
                db_printf("witness watch is disabled\n");
                return;
        }
        if (witness_cold) {
                db_printf("witness is cold\n");
                return;
        }
        error = 0;

        mtx_enter(&w_mtx);
        SLIST_FOREACH(w, &w_all, w_list)
                w->w_displayed = 0;
        SLIST_FOREACH(w, &w_all, w_list)
                db_witness_add_fullgraph(w);
        mtx_leave(&w_mtx);
}

static void
db_witness_add_fullgraph(struct witness *w)
{
        int i;

        if (w->w_displayed != 0 || w->w_acquired == 0)
                return;
        w->w_displayed = 1;

        WITNESS_INDEX_ASSERT(w->w_index);
        for (i = 1; i <= w_max_used_index; i++) {
                if (w_rmatrix[w->w_index][i] & WITNESS_PARENT) {
                        db_printf("\"%s\",\"%s\"\n", w->w_type->lt_name,
                            w_data[i].w_type->lt_name);
                        db_witness_add_fullgraph(&w_data[i]);
                }
        }
}

/*
 * A simple hash function. Takes a key pointer and a key size. If size == 0,
 * interprets the key as a string and reads until the null
 * terminator. Otherwise, reads the first size bytes. Returns an unsigned 32-bit
 * hash value computed from the key.
 */
static uint32_t
witness_hash_djb2(const uint8_t *key, uint32_t size)
{
        unsigned int hash = 5381;
        int i;

        /* hash = hash * 33 + key[i] */
        if (size)
                for (i = 0; i < size; i++)
                        hash = ((hash << 5) + hash) + (unsigned int)key[i];
        else
                for (i = 0; key[i] != 0; i++)
                        hash = ((hash << 5) + hash) + (unsigned int)key[i];

        return (hash);
}


/*
 * Initializes the two witness hash tables. Called exactly once from
 * witness_initialize().
 */
static void
witness_init_hash_tables(void)
{
        int i;

        KASSERT(witness_cold);

        /* Initialize the hash tables. */
        for (i = 0; i < WITNESS_HASH_SIZE; i++)
                SLIST_INIT(&w_hash.wh_array[i]);

        w_hash.wh_size = WITNESS_HASH_SIZE;
        w_hash.wh_count = 0;

        /* Initialize the lock order data hash. */
        w_lodata = (void *)uvm_pageboot_alloc(
            sizeof(struct witness_lock_order_data) * WITNESS_LO_DATA_COUNT);
        memset(w_lodata, 0, sizeof(struct witness_lock_order_data) *
            WITNESS_LO_DATA_COUNT);
        w_lofree = NULL;
        for (i = 0; i < WITNESS_LO_DATA_COUNT; i++) {
                w_lodata[i].wlod_next = w_lofree;
                w_lofree = &w_lodata[i];
        }
        w_lohash.wloh_size = WITNESS_LO_HASH_SIZE;
        w_lohash.wloh_count = 0;
        for (i = 0; i < WITNESS_LO_HASH_SIZE; i++)
                w_lohash.wloh_array[i] = NULL;
}

static struct witness *
witness_hash_get(const struct lock_type *type, const char *subtype)
{
        struct witness *w;
        uint32_t hash;

        KASSERT(type != NULL);
        if (witness_cold == 0)
                MUTEX_ASSERT_LOCKED(&w_mtx);
        hash = (uint32_t)((uintptr_t)type ^ (uintptr_t)subtype) %
            w_hash.wh_size;
        SLIST_FOREACH(w, &w_hash.wh_array[hash], w_hash_next) {
                if (w->w_type == type && w->w_subtype == subtype)
                        goto out;
        }

out:
        return (w);
}

static void
witness_hash_put(struct witness *w)
{
        uint32_t hash;

        KASSERT(w != NULL);
        KASSERT(w->w_type != NULL);
        if (witness_cold == 0)
                MUTEX_ASSERT_LOCKED(&w_mtx);
        KASSERTMSG(witness_hash_get(w->w_type, w->w_subtype) == NULL,
            "%s: trying to add a hash entry that already exists!", __func__);
        KASSERTMSG(SLIST_NEXT(w, w_hash_next) == NULL,
            "%s: w->w_hash_next != NULL", __func__);

        hash = (uint32_t)((uintptr_t)w->w_type ^ (uintptr_t)w->w_subtype) %
            w_hash.wh_size;
        SLIST_INSERT_HEAD(&w_hash.wh_array[hash], w, w_hash_next);
        w_hash.wh_count++;
}


static struct witness_lock_order_data *
witness_lock_order_get(struct witness *parent, struct witness *child)
{
        struct witness_lock_order_data *data = NULL;
        struct witness_lock_order_key key;
        unsigned int hash;

        KASSERT(parent != NULL && child != NULL);
        key.from = parent->w_index;
        key.to = child->w_index;
        WITNESS_INDEX_ASSERT(key.from);
        WITNESS_INDEX_ASSERT(key.to);
        if ((w_rmatrix[parent->w_index][child->w_index]
            & WITNESS_LOCK_ORDER_KNOWN) == 0)
                goto out;

        hash = witness_hash_djb2((const char*)&key,
            sizeof(key)) % w_lohash.wloh_size;
        data = w_lohash.wloh_array[hash];
        while (data != NULL) {
                if (witness_lock_order_key_equal(&data->wlod_key, &key))
                        break;
                data = data->wlod_next;
        }

out:
        return (data);
}

/*
 * Verify that parent and child have a known relationship, are not the same,
 * and child is actually a child of parent.  This is done without w_mtx
 * to avoid contention in the common case.
 */
static int
witness_lock_order_check(struct witness *parent, struct witness *child)
{

        if (parent != child &&
            w_rmatrix[parent->w_index][child->w_index]
            & WITNESS_LOCK_ORDER_KNOWN &&
            isitmychild(parent, child))
                return (1);

        return (0);
}

static int
witness_lock_order_add(struct witness *parent, struct witness *child)
{
        static int lofree_empty_reported = 0;
        struct witness_lock_order_data *data = NULL;
        struct witness_lock_order_key key;
        unsigned int hash;

        KASSERT(parent != NULL && child != NULL);
        key.from = parent->w_index;
        key.to = child->w_index;
        WITNESS_INDEX_ASSERT(key.from);
        WITNESS_INDEX_ASSERT(key.to);
        if (w_rmatrix[parent->w_index][child->w_index]
            & WITNESS_LOCK_ORDER_KNOWN)
                return (1);

        hash = witness_hash_djb2((const char*)&key,
            sizeof(key)) % w_lohash.wloh_size;
        w_rmatrix[parent->w_index][child->w_index] |= WITNESS_LOCK_ORDER_KNOWN;
        data = w_lofree;
        if (data == NULL) {
                if (!lofree_empty_reported) {
                        lofree_empty_reported = 1;
                        printf("witness: out of free lock order entries\n");
                }
                return (0);
        }
        w_lofree = data->wlod_next;
        data->wlod_next = w_lohash.wloh_array[hash];
        data->wlod_key = key;
        w_lohash.wloh_array[hash] = data;
        w_lohash.wloh_count++;
        stacktrace_save_at(&data->wlod_stack, 1);
        return (1);
}

/* Call this whenever the structure of the witness graph changes. */
static void
witness_increment_graph_generation(void)
{

        if (witness_cold == 0)
                MUTEX_ASSERT_LOCKED(&w_mtx);
        w_generation++;
}

static void
witness_debugger(int dump)
{
        switch (witness_watch) {
        case 1:
                break;
        case 2:
                if (dump)
                        db_stack_dump();
                break;
        case 3:
                if (dump)
                        db_stack_dump();
                db_enter();
                break;
        default:
                panic("witness: locking error");
        }
}

static int
witness_alloc_stacks(void)
{
        union lock_stack *stacks;
        unsigned int i, nstacks = LOCK_CHILDCOUNT * LOCK_NCHILDREN;

        rw_assert_wrlock(&w_ctlock);

        if (w_lock_stack_num >= nstacks)
                return (0);

        nstacks -= w_lock_stack_num;
        stacks = mallocarray(nstacks, sizeof(*stacks), M_WITNESS,
            M_WAITOK | M_CANFAIL | M_ZERO);
        if (stacks == NULL)
                return (ENOMEM);

        mtx_enter(&w_mtx);
        for (i = 0; i < nstacks; i++) {
                stacks[i].ls_next = w_lock_stack_free;
                w_lock_stack_free = &stacks[i];
        }
        mtx_leave(&w_mtx);
        w_lock_stack_num += nstacks;

        return (0);
}

int
witness_sysctl(int *name, u_int namelen, void *oldp, size_t *oldlenp,
    void *newp, size_t newlen)
{
        int error, value;

        if (namelen != 1)
                return (ENOTDIR);

        rw_enter_write(&w_ctlock);

        switch (name[0]) {
        case KERN_WITNESS_WATCH:
                error = witness_sysctl_watch(oldp, oldlenp, newp, newlen);
                break;
        case KERN_WITNESS_LOCKTRACE:
                value = witness_locktrace;
                error = sysctl_int(oldp, oldlenp, newp, newlen, &value);
                if (error == 0 && newp != NULL) {
                        switch (value) {
                        case 1:
                                error = witness_alloc_stacks();
                                /* FALLTHROUGH */
                        case 0:
                                if (error == 0)
                                        witness_locktrace = value;
                                break;
                        default:
                                error = EINVAL;
                                break;
                        }
                }
                break;
        default:
                error = EOPNOTSUPP;
                break;
        }

        rw_exit_write(&w_ctlock);

        return (error);
}

int
witness_sysctl_watch(void *oldp, size_t *oldlenp, void *newp, size_t newlen)
{
        int error;
        int value;

        value = witness_watch;
        error = sysctl_int_bounded(oldp, oldlenp, newp, newlen,
            &value, -1, 3);
        if (error == 0 && newp != NULL) {
                mtx_enter(&w_mtx);
                if (value < 0 || witness_watch >= 0)
                        witness_watch = value;
                else
                        error = EINVAL;
                mtx_leave(&w_mtx);
        }
        return (error);
}