FreeBSD/Linux Kernel Cross Reference
sys/kern/subr_witness.c

     /*      $OpenBSD: subr_witness.c,v 1.48 2022/02/21 14:16:49 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);
   #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_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[LOCK_CHILDCOUNT];
   static struct witness_hash w_hash;      /* The witness hash table. */
   
   /* The lock order data hash */
   static struct witness_lock_order_data w_lodata[WITNESS_LO_DATA_COUNT];
   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_sched_lock = {
           .lc_name = "sched_lock",
           .lc_flags = LC_SPINLOCK | LC_RECURSABLE
   };
   
   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_sched_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);
           }
   
           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);
   }
   
   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 (type: %s, depth: %d)",
                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 (type: %s, depth: %d)\n", 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 proc *p;
           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);
   
           p = curproc;
   
           if (class->lc_flags & LC_SLEEPLOCK) {
                   /*
                    * Since spin locks include a critical section, this check
                    * implicitly enforces a lock order of all sleep locks before
                    * all spin locks.
                    */
                   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.
                    */
                   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) &&
                       !(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 enfore a general lock order of
                            * sleepable locks before non-sleepable locks.
                            */
                           if (((lock->lo_flags & LO_SLEEPABLE) != 0 &&
                               (lock1->li_lock->lo_flags & LO_SLEEPABLE) == 0))
                                   goto reversal;
   
                           /*
                            * If we are locking Giant and this is a non-sleepable
                            * lock, then treat it as a reversal.
                            */
                           if ((lock1->li_lock->lo_flags & LO_SLEEPABLE) == 0 &&
                               is_kernel_lock(lock))
                                   goto reversal;
   
                           /*
                            * Check the lock order hierarchy for a reveresal.
                            */
                           if (!isitmydescendant(w, w1))
                                   continue;
                   reversal:
   
                           /*
                            * We have a lock order violation, check to see if it
                            * is allowed or has already been yelled about.
                            */
   
                           /* 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) {
                                  struct witness_lock_order_data *wlod1, *wlod2;
  
                                  mtx_enter(&w_mtx);
                                  wlod1 = witness_lock_order_get(w, w1);
                                  wlod2 = witness_lock_order_get(w1, w);
                                  mtx_leave(&w_mtx);
  
                                  /*
                                   * It is safe to access saved stack traces,
                                   * w_type, and w_class without the lock.
                                   * Once written, they never change.
                                   */
  
                                  if (wlod1 != NULL) {
                                          printf("lock order \"%s\"(%s) -> "
                                              "\"%s\"(%s) first seen at:\n",
                                              w->w_type->lt_name,
                                              w->w_class->lc_name,
                                              w1->w_type->lt_name,
                                              w1->w_class->lc_name);
                                          stacktrace_print(
                                              &wlod1->wlod_stack, printf);
                                  } else {
                                          printf("lock order data "
                                              "w2 -> w1 missing\n");
                                  }
                                  if (wlod2 != NULL) {
                                          printf("lock order \"%s\"(%s) -> "
                                              "\"%s\"(%s) first seen at:\n",
                                              w1->w_type->lt_name,
                                              w1->w_class->lc_name,
                                              w->w_type->lt_name,
                                              w->w_class->lc_name);
                                          stacktrace_print(
                                              &wlod2->wlod_stack, printf);
                                  } else {
                                          printf("lock order data "
                                              "w1 -> w2 missing\n");
                                  }
                          }
                          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 proc *p;
          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));
  
          p = curproc;
  
          /* Determine lock list for this lock. */
          if (LOCK_CLASS(lock)->lc_flags & LC_SLEEPLOCK)
                  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;
          struct proc *p;
          int i, j;
          int s;
  
          if (witness_cold || lock->lo_witness == NULL ||
              panicstr != NULL || db_active)
                  return;
          p = curproc;
          class = LOCK_CLASS(lock);
  
          /* Find lock instance associated with this lock. */
          if (class->lc_flags & LC_SLEEPLOCK)
                  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);
  }
  
  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 (w_mtx.mtx_owner != 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__));
  }
  
  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);
  }
  
  #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)
  {
          static struct witness tmp_w1, tmp_w2;
          static struct witness_lock_order_data tmp_data1, tmp_data2;
          struct witness_lock_order_data *data1, *data2;
          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;
  
          memset(&tmp_w1, 0, sizeof(tmp_w1));
          memset(&tmp_w2, 0, sizeof(tmp_w2));
          memset(&tmp_data1, 0, sizeof(tmp_data1));
          memset(&tmp_data2, 0, sizeof(tmp_data2));
  
  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;
                  }
  
                  /* Copy w1 locally so we can release the spin lock. */
                  tmp_w1 = *w1;
                  mtx_leave(&w_mtx);
  
                  if (tmp_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];
                          data1 = witness_lock_order_get(w1, w2);
                          data2 = witness_lock_order_get(w2, w1);
  
                          /*
                           * Copy information locally so we can release the
                           * spin lock.
                           */
                          tmp_w2 = *w2;
  
                          if (data1)
                                  tmp_data1.wlod_stack = data1->wlod_stack;
                          if (data2 && data2 != data1)
                                  tmp_data2.wlod_stack = data2->wlod_stack;
                          mtx_leave(&w_mtx);
  
                          db_printf("\nLock order reversal between \"%s\"(%s) "
                              "and \"%s\"(%s)!\n",
                              tmp_w1.w_type->lt_name, tmp_w1.w_class->lc_name,
                              tmp_w2.w_type->lt_name, tmp_w2.w_class->lc_name);
                          if (data1) {
                                  db_printf("Lock order \"%s\"(%s) -> \"%s\"(%s) "
                                      "first seen at:\n",
                                      tmp_w1.w_type->lt_name,
                                      tmp_w1.w_class->lc_name,
                                      tmp_w2.w_type->lt_name,
                                      tmp_w2.w_class->lc_name);
                                  stacktrace_print(&tmp_data1.wlod_stack,
                                      db_printf);
                                  db_printf("\n");
                          }
                          if (data2 && data2 != data1) {
                                  db_printf("Lock order \"%s\"(%s) -> \"%s\"(%s) "
                                      "first seen at:\n",
                                      tmp_w2.w_type->lt_name,
                                      tmp_w2.w_class->lc_name,
                                      tmp_w1.w_type->lt_name,
                                      tmp_w1.w_class->lc_name);
                                  stacktrace_print(&tmp_data2.wlod_stack,
                                      db_printf);
                                  db_printf("\n");
                          }
                  }
          }
          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_lofree = NULL;
          for (i = 0; i < WITNESS_LO_DATA_COUNT; i++) {
                  memset(&w_lodata[i], 0, sizeof(w_lodata[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);
  }

Cache object: 8c2a1886f84ef7804ae8ba714fbfb1c6