subr_lock.c

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/*-
 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
 *
 * Copyright (c) 2006 John Baldwin <jhb@FreeBSD.org>
 *
 * 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.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``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 THE AUTHOR OR CONTRIBUTORS 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.
 */
 
/*
 * This module holds the global variables and functions used to maintain
 * lock_object structures.
 */
 
#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");
 
#include "opt_ddb.h"
#include "opt_mprof.h"
 
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/ktr.h>
#include <sys/limits.h>
#include <sys/lock.h>
#include <sys/lock_profile.h>
#include <sys/malloc.h>
#include <sys/mutex.h>
#include <sys/pcpu.h>
#include <sys/proc.h>
#include <sys/sbuf.h>
#include <sys/sched.h>
#include <sys/smp.h>
#include <sys/sysctl.h>
 
#ifdef DDB
#include <ddb/ddb.h>
#endif
 
#include <machine/cpufunc.h>
 
/*
 * Uncomment to validate that spin argument to acquire/release routines matches
 * the flag in the lock
 */
//#define       LOCK_PROFILING_DEBUG_SPIN
 
SDT_PROVIDER_DEFINE(lock);
SDT_PROBE_DEFINE1(lock, , , starvation, "u_int");
 
CTASSERT(LOCK_CLASS_MAX == 15);
 
struct lock_class *lock_classes[LOCK_CLASS_MAX + 1] = {
        &lock_class_mtx_spin,
        &lock_class_mtx_sleep,
        &lock_class_sx,
        &lock_class_rm,
        &lock_class_rm_sleepable,
        &lock_class_rw,
        &lock_class_lockmgr,
};
 
void
lock_init(struct lock_object *lock, struct lock_class *class, const char *name,
    const char *type, int flags)
{
        int i;
 
        /* Check for double-init and zero object. */
        KASSERT(flags & LO_NEW || !lock_initialized(lock),
            ("lock \"%s\" %p already initialized", name, lock));
 
        /* Look up lock class to find its index. */
        for (i = 0; i < LOCK_CLASS_MAX; i++)
                if (lock_classes[i] == class) {
                        lock->lo_flags = i << LO_CLASSSHIFT;
                        break;
                }
        KASSERT(i < LOCK_CLASS_MAX, ("unknown lock class %p", class));
 
        /* Initialize the lock object. */
        lock->lo_name = name;
        lock->lo_flags |= flags | LO_INITIALIZED;
        LOCK_LOG_INIT(lock, 0);
        WITNESS_INIT(lock, (type != NULL) ? type : name);
}
 
void
lock_destroy(struct lock_object *lock)
{
 
        KASSERT(lock_initialized(lock), ("lock %p is not initialized", lock));
        WITNESS_DESTROY(lock);
        LOCK_LOG_DESTROY(lock, 0);
        lock->lo_flags &= ~LO_INITIALIZED;
}
 
static SYSCTL_NODE(_debug, OID_AUTO, lock, CTLFLAG_RD | CTLFLAG_MPSAFE, NULL,
    "lock debugging");
static SYSCTL_NODE(_debug_lock, OID_AUTO, delay,
    CTLFLAG_RD | CTLFLAG_MPSAFE, NULL,
    "lock delay");
 
static u_int __read_mostly starvation_limit = 131072;
SYSCTL_INT(_debug_lock_delay, OID_AUTO, starvation_limit, CTLFLAG_RW,
    &starvation_limit, 0, "");
 
static u_int __read_mostly restrict_starvation = 0;
SYSCTL_INT(_debug_lock_delay, OID_AUTO, restrict_starvation, CTLFLAG_RW,
    &restrict_starvation, 0, "");
 
void
lock_delay(struct lock_delay_arg *la)
{
        struct lock_delay_config *lc = la->config;
        u_short i;
 
        for (i = la->delay; i > 0; i--)
                cpu_spinwait();
        la->spin_cnt += la->delay;
 
        la->delay <<= 1;
        if (__predict_false(la->delay > lc->max))
                la->delay = lc->max;
 
        if (__predict_false(la->spin_cnt > starvation_limit)) {
                SDT_PROBE1(lock, , , starvation, la->delay);
                if (restrict_starvation)
                        la->delay = lc->base;
        }
}
 
static u_int
lock_roundup_2(u_int val)
{
        u_int res;
 
        for (res = 1; res <= val; res <<= 1)
                continue;
 
        return (res);
}
 
void
lock_delay_default_init(struct lock_delay_config *lc)
{
 
        lc->base = 1;
        lc->max = lock_roundup_2(mp_ncpus) * 256;
        if (lc->max > 32678)
                lc->max = 32678;
}
 
struct lock_delay_config __read_frequently locks_delay;
u_short __read_frequently locks_delay_retries;
u_short __read_frequently locks_delay_loops;
 
SYSCTL_U16(_debug_lock, OID_AUTO, delay_base, CTLFLAG_RW, &locks_delay.base,
    0, "");
SYSCTL_U16(_debug_lock, OID_AUTO, delay_max, CTLFLAG_RW, &locks_delay.max,
    0, "");
SYSCTL_U16(_debug_lock, OID_AUTO, delay_retries, CTLFLAG_RW, &locks_delay_retries,
    0, "");
SYSCTL_U16(_debug_lock, OID_AUTO, delay_loops, CTLFLAG_RW, &locks_delay_loops,
    0, "");
 
static void
locks_delay_init(void *arg __unused)
{
 
        lock_delay_default_init(&locks_delay);
        locks_delay_retries = 10;
        locks_delay_loops = max(10000, locks_delay.max);
}
LOCK_DELAY_SYSINIT(locks_delay_init);
 
#ifdef DDB
DB_SHOW_COMMAND(lock, db_show_lock)
{
        struct lock_object *lock;
        struct lock_class *class;
 
        if (!have_addr)
                return;
        lock = (struct lock_object *)addr;
        if (LO_CLASSINDEX(lock) > LOCK_CLASS_MAX) {
                db_printf("Unknown lock class: %d\n", LO_CLASSINDEX(lock));
                return;
        }
        class = LOCK_CLASS(lock);
        db_printf(" class: %s\n", class->lc_name);
        db_printf(" name: %s\n", lock->lo_name);
        class->lc_ddb_show(lock);
}
#endif
 
#ifdef LOCK_PROFILING
 
/*
 * One object per-thread for each lock the thread owns.  Tracks individual
 * lock instances.
 */
struct lock_profile_object {
        LIST_ENTRY(lock_profile_object) lpo_link;
        struct lock_object *lpo_obj;
        const char      *lpo_file;
        int             lpo_line;
        uint16_t        lpo_ref;
        uint16_t        lpo_cnt;
        uint64_t        lpo_acqtime;
        uint64_t        lpo_waittime;
        u_int           lpo_contest_locking;
};
 
/*
 * One lock_prof for each (file, line, lock object) triple.
 */
struct lock_prof {
        SLIST_ENTRY(lock_prof) link;
        struct lock_class *class;
        const char      *file;
        const char      *name;
        int             line;
        int             ticks;
        uintmax_t       cnt_wait_max;
        uintmax_t       cnt_max;
        uintmax_t       cnt_tot;
        uintmax_t       cnt_wait;
        uintmax_t       cnt_cur;
        uintmax_t       cnt_contest_locking;
};
 
SLIST_HEAD(lphead, lock_prof);
 
#define LPROF_HASH_SIZE         4096
#define LPROF_HASH_MASK         (LPROF_HASH_SIZE - 1)
#define LPROF_CACHE_SIZE        4096
 
/*
 * Array of objects and profs for each type of object for each cpu.  Spinlocks
 * are handled separately because a thread may be preempted and acquire a
 * spinlock while in the lock profiling code of a non-spinlock.  In this way
 * we only need a critical section to protect the per-cpu lists.
 */
struct lock_prof_type {
        struct lphead           lpt_lpalloc;
        struct lpohead          lpt_lpoalloc;
        struct lphead           lpt_hash[LPROF_HASH_SIZE];
        struct lock_prof        lpt_prof[LPROF_CACHE_SIZE];
        struct lock_profile_object lpt_objs[LPROF_CACHE_SIZE];
};
 
struct lock_prof_cpu {
        struct lock_prof_type   lpc_types[2]; /* One for spin one for other. */
};
 
DPCPU_DEFINE_STATIC(struct lock_prof_cpu, lp);
#define LP_CPU_SELF     (DPCPU_PTR(lp))
#define LP_CPU(cpu)     (DPCPU_ID_PTR((cpu), lp))
 
volatile int __read_mostly lock_prof_enable;
int __read_mostly lock_contested_only;
static volatile int lock_prof_resetting;
 
#define LPROF_SBUF_SIZE         256
 
static int lock_prof_rejected;
static int lock_prof_skipspin;
 
#ifndef USE_CPU_NANOSECONDS
uint64_t
nanoseconds(void)
{
        struct bintime bt;
        uint64_t ns;
 
        binuptime(&bt);
        /* From bintime2timespec */
        ns = bt.sec * (uint64_t)1000000000;
        ns += ((uint64_t)1000000000 * (uint32_t)(bt.frac >> 32)) >> 32;
        return (ns);
}
#endif
 
static void
lock_prof_init_type(struct lock_prof_type *type)
{
        int i;
 
        SLIST_INIT(&type->lpt_lpalloc);
        LIST_INIT(&type->lpt_lpoalloc);
        for (i = 0; i < LPROF_CACHE_SIZE; i++) {
                SLIST_INSERT_HEAD(&type->lpt_lpalloc, &type->lpt_prof[i],
                    link);
                LIST_INSERT_HEAD(&type->lpt_lpoalloc, &type->lpt_objs[i],
                    lpo_link);
        }
}
 
static void
lock_prof_init(void *arg)
{
        int cpu;
 
        CPU_FOREACH(cpu) {
                lock_prof_init_type(&LP_CPU(cpu)->lpc_types[0]);
                lock_prof_init_type(&LP_CPU(cpu)->lpc_types[1]);
        }
}
SYSINIT(lockprof, SI_SUB_SMP, SI_ORDER_ANY, lock_prof_init, NULL);
 
static void
lock_prof_reset_wait(void)
{
 
        /*
         * Spin relinquishing our cpu so that quiesce_all_cpus may
         * complete.
         */
        while (lock_prof_resetting)
                sched_relinquish(curthread);
}
 
static void
lock_prof_reset(void)
{
        struct lock_prof_cpu *lpc;
        int enabled, i, cpu;
 
        /*
         * We not only race with acquiring and releasing locks but also
         * thread exit.  To be certain that threads exit without valid head
         * pointers they must see resetting set before enabled is cleared.
         * Otherwise a lock may not be removed from a per-thread list due
         * to disabled being set but not wait for reset() to remove it below.
         */
        atomic_store_rel_int(&lock_prof_resetting, 1);
        enabled = lock_prof_enable;
        lock_prof_enable = 0;
        /*
         * This both publishes lock_prof_enable as disabled and makes sure
         * everyone else reads it if they are not far enough. We wait for the
         * rest down below.
         */
        cpus_fence_seq_cst();
        quiesce_all_critical();
        /*
         * Some objects may have migrated between CPUs.  Clear all links
         * before we zero the structures.  Some items may still be linked
         * into per-thread lists as well.
         */
        CPU_FOREACH(cpu) {
                lpc = LP_CPU(cpu);
                for (i = 0; i < LPROF_CACHE_SIZE; i++) {
                        LIST_REMOVE(&lpc->lpc_types[0].lpt_objs[i], lpo_link);
                        LIST_REMOVE(&lpc->lpc_types[1].lpt_objs[i], lpo_link);
                }
        }
        CPU_FOREACH(cpu) {
                lpc = LP_CPU(cpu);
                bzero(lpc, sizeof(*lpc));
                lock_prof_init_type(&lpc->lpc_types[0]);
                lock_prof_init_type(&lpc->lpc_types[1]);
        }
        /*
         * Paired with the fence from cpus_fence_seq_cst()
         */
        atomic_store_rel_int(&lock_prof_resetting, 0);
        lock_prof_enable = enabled;
}
 
static void
lock_prof_output(struct lock_prof *lp, struct sbuf *sb)
{
        const char *p;
 
        for (p = lp->file; p != NULL && strncmp(p, "../", 3) == 0; p += 3);
        sbuf_printf(sb,
            "%8ju %9ju %11ju %11ju %11ju %6ju %6ju %2ju %6ju %s:%d (%s:%s)\n",
            lp->cnt_max / 1000, lp->cnt_wait_max / 1000, lp->cnt_tot / 1000,
            lp->cnt_wait / 1000, lp->cnt_cur,
            lp->cnt_cur == 0 ? (uintmax_t)0 :
            lp->cnt_tot / (lp->cnt_cur * 1000),
            lp->cnt_cur == 0 ? (uintmax_t)0 :
            lp->cnt_wait / (lp->cnt_cur * 1000),
            (uintmax_t)0, lp->cnt_contest_locking,
            p, lp->line, lp->class->lc_name, lp->name);
}
 
static void
lock_prof_sum(struct lock_prof *match, struct lock_prof *dst, int hash,
    int spin, int t)
{
        struct lock_prof_type *type;
        struct lock_prof *l;
        int cpu;
 
        dst->file = match->file;
        dst->line = match->line;
        dst->class = match->class;
        dst->name = match->name;
 
        CPU_FOREACH(cpu) {
                type = &LP_CPU(cpu)->lpc_types[spin];
                SLIST_FOREACH(l, &type->lpt_hash[hash], link) {
                        if (l->ticks == t)
                                continue;
                        if (l->file != match->file || l->line != match->line ||
                            l->name != match->name)
                                continue;
                        l->ticks = t;
                        if (l->cnt_max > dst->cnt_max)
                                dst->cnt_max = l->cnt_max;
                        if (l->cnt_wait_max > dst->cnt_wait_max)
                                dst->cnt_wait_max = l->cnt_wait_max;
                        dst->cnt_tot += l->cnt_tot;
                        dst->cnt_wait += l->cnt_wait;
                        dst->cnt_cur += l->cnt_cur;
                        dst->cnt_contest_locking += l->cnt_contest_locking;
                }
        }
}
 
static void
lock_prof_type_stats(struct lock_prof_type *type, struct sbuf *sb, int spin,
    int t)
{
        struct lock_prof *l;
        int i;
 
        for (i = 0; i < LPROF_HASH_SIZE; ++i) {
                SLIST_FOREACH(l, &type->lpt_hash[i], link) {
                        struct lock_prof lp = {};
 
                        if (l->ticks == t)
                                continue;
                        lock_prof_sum(l, &lp, i, spin, t);
                        lock_prof_output(&lp, sb);
                }
        }
}
 
static int
dump_lock_prof_stats(SYSCTL_HANDLER_ARGS)
{
        struct sbuf *sb;
        int error, cpu, t;
        int enabled;
 
        error = sysctl_wire_old_buffer(req, 0);
        if (error != 0)
                return (error);
        sb = sbuf_new_for_sysctl(NULL, NULL, LPROF_SBUF_SIZE, req);
        sbuf_printf(sb, "\n%8s %9s %11s %11s %11s %6s %6s %2s %6s %s\n",
            "max", "wait_max", "total", "wait_total", "count", "avg", "wait_avg", "cnt_hold", "cnt_lock", "name");
        enabled = lock_prof_enable;
        lock_prof_enable = 0;
        /*
         * See the comment in lock_prof_reset
         */
        cpus_fence_seq_cst();
        quiesce_all_critical();
        t = ticks;
        CPU_FOREACH(cpu) {
                lock_prof_type_stats(&LP_CPU(cpu)->lpc_types[0], sb, 0, t);
                lock_prof_type_stats(&LP_CPU(cpu)->lpc_types[1], sb, 1, t);
        }
        atomic_thread_fence_rel();
        lock_prof_enable = enabled;
 
        error = sbuf_finish(sb);
        /* Output a trailing NUL. */
        if (error == 0)
                error = SYSCTL_OUT(req, "", 1);
        sbuf_delete(sb);
        return (error);
}
 
static int
enable_lock_prof(SYSCTL_HANDLER_ARGS)
{
        int error, v;
 
        v = lock_prof_enable;
        error = sysctl_handle_int(oidp, &v, v, req);
        if (error)
                return (error);
        if (req->newptr == NULL)
                return (error);
        if (v == lock_prof_enable)
                return (0);
        if (v == 1)
                lock_prof_reset();
        lock_prof_enable = !!v;
 
        return (0);
}
 
static int
reset_lock_prof_stats(SYSCTL_HANDLER_ARGS)
{
        int error, v;
 
        v = 0;
        error = sysctl_handle_int(oidp, &v, 0, req);
        if (error)
                return (error);
        if (req->newptr == NULL)
                return (error);
        if (v == 0)
                return (0);
        lock_prof_reset();
 
        return (0);
}
 
static struct lock_prof *
lock_profile_lookup(struct lock_object *lo, int spin, const char *file,
    int line)
{
        const char *unknown = "(unknown)";
        struct lock_prof_type *type;
        struct lock_prof *lp;
        struct lphead *head;
        const char *p;
        u_int hash;
 
        p = file;
        if (p == NULL || *p == '\0')
                p = unknown;
        hash = (uintptr_t)lo->lo_name * 31 + (uintptr_t)p * 31 + line;
        hash &= LPROF_HASH_MASK;
        type = &LP_CPU_SELF->lpc_types[spin];
        head = &type->lpt_hash[hash];
        SLIST_FOREACH(lp, head, link) {
                if (lp->line == line && lp->file == p &&
                    lp->name == lo->lo_name)
                        return (lp);
        }
        lp = SLIST_FIRST(&type->lpt_lpalloc);
        if (lp == NULL) {
                lock_prof_rejected++;
                return (lp);
        }
        SLIST_REMOVE_HEAD(&type->lpt_lpalloc, link);
        lp->file = p;
        lp->line = line;
        lp->class = LOCK_CLASS(lo);
        lp->name = lo->lo_name;
        SLIST_INSERT_HEAD(&type->lpt_hash[hash], lp, link);
        return (lp);
}
 
static struct lock_profile_object *
lock_profile_object_lookup(struct lock_object *lo, int spin, const char *file,
    int line)
{
        struct lock_profile_object *l;
        struct lock_prof_type *type;
        struct lpohead *head;
 
        head = &curthread->td_lprof[spin];
        LIST_FOREACH(l, head, lpo_link)
                if (l->lpo_obj == lo && l->lpo_file == file &&
                    l->lpo_line == line)
                        return (l);
        type = &LP_CPU_SELF->lpc_types[spin];
        l = LIST_FIRST(&type->lpt_lpoalloc);
        if (l == NULL) {
                lock_prof_rejected++;
                return (NULL);
        }
        LIST_REMOVE(l, lpo_link);
        l->lpo_obj = lo;
        l->lpo_file = file;
        l->lpo_line = line;
        l->lpo_cnt = 0;
        LIST_INSERT_HEAD(head, l, lpo_link);
 
        return (l);
}
 
void
lock_profile_obtain_lock_success(struct lock_object *lo, bool spin,
    int contested, uint64_t waittime, const char *file, int line)
{
        struct lock_profile_object *l;
 
#ifdef LOCK_PROFILING_DEBUG_SPIN
        bool is_spin = (LOCK_CLASS(lo)->lc_flags & LC_SPINLOCK);
        if ((spin && !is_spin) || (!spin && is_spin))
                printf("%s: lock %s spin mismatch (arg %d, flag %d)\n", __func__,
                    lo->lo_name, spin, is_spin);
#endif
 
        /* don't reset the timer when/if recursing */
        if (!lock_prof_enable || (lo->lo_flags & LO_NOPROFILE))
                return;
        if (lock_contested_only && !contested)
                return;
        if (spin && lock_prof_skipspin == 1)
                return;
 
        if (SCHEDULER_STOPPED())
                return;
 
        critical_enter();
        /* Recheck enabled now that we're in a critical section. */
        if (lock_prof_enable == 0)
                goto out;
        l = lock_profile_object_lookup(lo, spin, file, line);
        if (l == NULL)
                goto out;
        l->lpo_cnt++;
        if (++l->lpo_ref > 1)
                goto out;
        l->lpo_contest_locking = contested;
        l->lpo_acqtime = nanoseconds(); 
        if (waittime && (l->lpo_acqtime > waittime))
                l->lpo_waittime = l->lpo_acqtime - waittime;
        else
                l->lpo_waittime = 0;
out:
        /*
         * Paired with cpus_fence_seq_cst().
         */
        atomic_thread_fence_rel();
        critical_exit();
}
 
void
lock_profile_thread_exit(struct thread *td)
{
#ifdef INVARIANTS
        struct lock_profile_object *l;
 
        MPASS(curthread->td_critnest == 0);
#endif
        /*
         * If lock profiling was disabled we have to wait for reset to
         * clear our pointers before we can exit safely.
         */
        lock_prof_reset_wait();
#ifdef INVARIANTS
        LIST_FOREACH(l, &td->td_lprof[0], lpo_link)
                printf("thread still holds lock acquired at %s:%d\n",
                    l->lpo_file, l->lpo_line);
        LIST_FOREACH(l, &td->td_lprof[1], lpo_link)
                printf("thread still holds lock acquired at %s:%d\n",
                    l->lpo_file, l->lpo_line);
#endif
        MPASS(LIST_FIRST(&td->td_lprof[0]) == NULL);
        MPASS(LIST_FIRST(&td->td_lprof[1]) == NULL);
}
 
void
lock_profile_release_lock(struct lock_object *lo, bool spin)
{
        struct lock_profile_object *l;
        struct lock_prof_type *type;
        struct lock_prof *lp;
        uint64_t curtime, holdtime;
        struct lpohead *head;
 
#ifdef LOCK_PROFILING_DEBUG_SPIN
        bool is_spin = (LOCK_CLASS(lo)->lc_flags & LC_SPINLOCK);
        if ((spin && !is_spin) || (!spin && is_spin))
                printf("%s: lock %s spin mismatch (arg %d, flag %d)\n", __func__,
                    lo->lo_name, spin, is_spin);
#endif
 
        if (lo->lo_flags & LO_NOPROFILE)
                return;
        head = &curthread->td_lprof[spin];
        if (LIST_FIRST(head) == NULL)
                return;
        if (SCHEDULER_STOPPED())
                return;
        critical_enter();
        /* Recheck enabled now that we're in a critical section. */
        if (lock_prof_enable == 0 && lock_prof_resetting == 1)
                goto out;
        /*
         * If lock profiling is not enabled we still want to remove the
         * lpo from our queue.
         */
        LIST_FOREACH(l, head, lpo_link)
                if (l->lpo_obj == lo)
                        break;
        if (l == NULL)
                goto out;
        if (--l->lpo_ref > 0)
                goto out;
        lp = lock_profile_lookup(lo, spin, l->lpo_file, l->lpo_line);
        if (lp == NULL)
                goto release;
        curtime = nanoseconds();
        if (curtime < l->lpo_acqtime)
                goto release;
        holdtime = curtime - l->lpo_acqtime;
 
        /*
         * Record if the lock has been held longer now than ever
         * before.
         */
        if (holdtime > lp->cnt_max)
                lp->cnt_max = holdtime;
        if (l->lpo_waittime > lp->cnt_wait_max)
                lp->cnt_wait_max = l->lpo_waittime;
        lp->cnt_tot += holdtime;
        lp->cnt_wait += l->lpo_waittime;
        lp->cnt_contest_locking += l->lpo_contest_locking;
        lp->cnt_cur += l->lpo_cnt;
release:
        LIST_REMOVE(l, lpo_link);
        type = &LP_CPU_SELF->lpc_types[spin];
        LIST_INSERT_HEAD(&type->lpt_lpoalloc, l, lpo_link);
out:
        /*
         * Paired with cpus_fence_seq_cst().
         */
        atomic_thread_fence_rel();
        critical_exit();
}
 
static SYSCTL_NODE(_debug_lock, OID_AUTO, prof,
    CTLFLAG_RD | CTLFLAG_MPSAFE, NULL,
    "lock profiling");
SYSCTL_INT(_debug_lock_prof, OID_AUTO, skipspin, CTLFLAG_RW,
    &lock_prof_skipspin, 0, "Skip profiling on spinlocks.");
SYSCTL_INT(_debug_lock_prof, OID_AUTO, rejected, CTLFLAG_RD,
    &lock_prof_rejected, 0, "Number of rejected profiling records");
SYSCTL_INT(_debug_lock_prof, OID_AUTO, contested_only, CTLFLAG_RW,
    &lock_contested_only, 0, "Only profile contested acquires");
SYSCTL_PROC(_debug_lock_prof, OID_AUTO, stats,
    CTLTYPE_STRING | CTLFLAG_RD | CTLFLAG_MPSAFE, NULL, 0,
    dump_lock_prof_stats, "A",
    "Lock profiling statistics");
SYSCTL_PROC(_debug_lock_prof, OID_AUTO, reset,
    CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_NEEDGIANT, NULL, 0,
    reset_lock_prof_stats, "I",
    "Reset lock profiling statistics");
SYSCTL_PROC(_debug_lock_prof, OID_AUTO, enable,
    CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_MPSAFE, NULL, 0,
    enable_lock_prof, "I",
    "Enable lock profiling");
 
#endif