kern_rmlock.c

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/*-
 * SPDX-License-Identifier: BSD-3-Clause
 *
 * Copyright (c) 2007 Stephan Uphoff <ups@FreeBSD.org>
 * 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. Neither the name of the author nor the names of any co-contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * 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.
 */
 
/*
 * Machine independent bits of reader/writer lock implementation.
 */
 
#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");
 
#include "opt_ddb.h"
 
#include <sys/param.h>
#include <sys/systm.h>
 
#include <sys/kernel.h>
#include <sys/kdb.h>
#include <sys/ktr.h>
#include <sys/lock.h>
#include <sys/mutex.h>
#include <sys/proc.h>
#include <sys/rmlock.h>
#include <sys/sched.h>
#include <sys/smp.h>
#include <sys/turnstile.h>
#include <sys/lock_profile.h>
#include <machine/cpu.h>
#include <vm/uma.h>
 
#ifdef DDB
#include <ddb/ddb.h>
#endif
 
/*
 * A cookie to mark destroyed rmlocks.  This is stored in the head of
 * rm_activeReaders.
 */
#define RM_DESTROYED    ((void *)0xdead)
 
#define rm_destroyed(rm)                                                \
        (LIST_FIRST(&(rm)->rm_activeReaders) == RM_DESTROYED)
 
#define RMPF_ONQUEUE    1
#define RMPF_SIGNAL     2
 
#ifndef INVARIANTS
#define _rm_assert(c, what, file, line)
#endif
 
static void     assert_rm(const struct lock_object *lock, int what);
#ifdef DDB
static void     db_show_rm(const struct lock_object *lock);
#endif
static void     lock_rm(struct lock_object *lock, uintptr_t how);
#ifdef KDTRACE_HOOKS
static int      owner_rm(const struct lock_object *lock, struct thread **owner);
#endif
static uintptr_t unlock_rm(struct lock_object *lock);
 
struct lock_class lock_class_rm = {
        .lc_name = "rm",
        .lc_flags = LC_SLEEPLOCK | LC_RECURSABLE,
        .lc_assert = assert_rm,
#ifdef DDB
        .lc_ddb_show = db_show_rm,
#endif
        .lc_lock = lock_rm,
        .lc_unlock = unlock_rm,
#ifdef KDTRACE_HOOKS
        .lc_owner = owner_rm,
#endif
};
 
struct lock_class lock_class_rm_sleepable = {
        .lc_name = "sleepable rm",
        .lc_flags = LC_SLEEPLOCK | LC_SLEEPABLE | LC_RECURSABLE,
        .lc_assert = assert_rm,
#ifdef DDB
        .lc_ddb_show = db_show_rm,
#endif
        .lc_lock = lock_rm,
        .lc_unlock = unlock_rm,
#ifdef KDTRACE_HOOKS
        .lc_owner = owner_rm,
#endif
};
 
static void
assert_rm(const struct lock_object *lock, int what)
{
 
        rm_assert((const struct rmlock *)lock, what);
}
 
static void
lock_rm(struct lock_object *lock, uintptr_t how)
{
        struct rmlock *rm;
        struct rm_priotracker *tracker;
 
        rm = (struct rmlock *)lock;
        if (how == 0)
                rm_wlock(rm);
        else {
                tracker = (struct rm_priotracker *)how;
                rm_rlock(rm, tracker);
        }
}
 
static uintptr_t
unlock_rm(struct lock_object *lock)
{
        struct thread *td;
        struct pcpu *pc;
        struct rmlock *rm;
        struct rm_queue *queue;
        struct rm_priotracker *tracker;
        uintptr_t how;
 
        rm = (struct rmlock *)lock;
        tracker = NULL;
        how = 0;
        rm_assert(rm, RA_LOCKED | RA_NOTRECURSED);
        if (rm_wowned(rm))
                rm_wunlock(rm);
        else {
                /*
                 * Find the right rm_priotracker structure for curthread.
                 * The guarantee about its uniqueness is given by the fact
                 * we already asserted the lock wasn't recursively acquired.
                 */
                critical_enter();
                td = curthread;
                pc = get_pcpu();
                for (queue = pc->pc_rm_queue.rmq_next;
                    queue != &pc->pc_rm_queue; queue = queue->rmq_next) {
                        tracker = (struct rm_priotracker *)queue;
                                if ((tracker->rmp_rmlock == rm) &&
                                    (tracker->rmp_thread == td)) {
                                        how = (uintptr_t)tracker;
                                        break;
                                }
                }
                KASSERT(tracker != NULL,
                    ("rm_priotracker is non-NULL when lock held in read mode"));
                critical_exit();
                rm_runlock(rm, tracker);
        }
        return (how);
}
 
#ifdef KDTRACE_HOOKS
static int
owner_rm(const struct lock_object *lock, struct thread **owner)
{
        const struct rmlock *rm;
        struct lock_class *lc;
 
        rm = (const struct rmlock *)lock;
        lc = LOCK_CLASS(&rm->rm_wlock_object);
        return (lc->lc_owner(&rm->rm_wlock_object, owner));
}
#endif
 
static struct mtx rm_spinlock;
 
MTX_SYSINIT(rm_spinlock, &rm_spinlock, "rm_spinlock", MTX_SPIN);
 
/*
 * Add or remove tracker from per-cpu list.
 *
 * The per-cpu list can be traversed at any time in forward direction from an
 * interrupt on the *local* cpu.
 */
static void inline
rm_tracker_add(struct pcpu *pc, struct rm_priotracker *tracker)
{
        struct rm_queue *next;
 
        /* Initialize all tracker pointers */
        tracker->rmp_cpuQueue.rmq_prev = &pc->pc_rm_queue;
        next = pc->pc_rm_queue.rmq_next;
        tracker->rmp_cpuQueue.rmq_next = next;
 
        /* rmq_prev is not used during froward traversal. */
        next->rmq_prev = &tracker->rmp_cpuQueue;
 
        /* Update pointer to first element. */
        pc->pc_rm_queue.rmq_next = &tracker->rmp_cpuQueue;
}
 
/*
 * Return a count of the number of trackers the thread 'td' already
 * has on this CPU for the lock 'rm'.
 */
static int
rm_trackers_present(const struct pcpu *pc, const struct rmlock *rm,
    const struct thread *td)
{
        struct rm_queue *queue;
        struct rm_priotracker *tracker;
        int count;
 
        count = 0;
        for (queue = pc->pc_rm_queue.rmq_next; queue != &pc->pc_rm_queue;
            queue = queue->rmq_next) {
                tracker = (struct rm_priotracker *)queue;
                if ((tracker->rmp_rmlock == rm) && (tracker->rmp_thread == td))
                        count++;
        }
        return (count);
}
 
static void inline
rm_tracker_remove(struct pcpu *pc, struct rm_priotracker *tracker)
{
        struct rm_queue *next, *prev;
 
        next = tracker->rmp_cpuQueue.rmq_next;
        prev = tracker->rmp_cpuQueue.rmq_prev;
 
        /* Not used during forward traversal. */
        next->rmq_prev = prev;
 
        /* Remove from list. */
        prev->rmq_next = next;
}
 
static void
rm_cleanIPI(void *arg)
{
        struct pcpu *pc;
        struct rmlock *rm = arg;
        struct rm_priotracker *tracker;
        struct rm_queue *queue;
        pc = get_pcpu();
 
        for (queue = pc->pc_rm_queue.rmq_next; queue != &pc->pc_rm_queue;
            queue = queue->rmq_next) {
                tracker = (struct rm_priotracker *)queue;
                if (tracker->rmp_rmlock == rm && tracker->rmp_flags == 0) {
                        tracker->rmp_flags = RMPF_ONQUEUE;
                        mtx_lock_spin(&rm_spinlock);
                        LIST_INSERT_HEAD(&rm->rm_activeReaders, tracker,
                            rmp_qentry);
                        mtx_unlock_spin(&rm_spinlock);
                }
        }
}
 
void
rm_init_flags(struct rmlock *rm, const char *name, int opts)
{
        struct lock_class *lc;
        int liflags, xflags;
 
        liflags = 0;
        if (!(opts & RM_NOWITNESS))
                liflags |= LO_WITNESS;
        if (opts & RM_RECURSE)
                liflags |= LO_RECURSABLE;
        if (opts & RM_NEW)
                liflags |= LO_NEW;
        if (opts & RM_DUPOK)
                liflags |= LO_DUPOK;
        rm->rm_writecpus = all_cpus;
        LIST_INIT(&rm->rm_activeReaders);
        if (opts & RM_SLEEPABLE) {
                liflags |= LO_SLEEPABLE;
                lc = &lock_class_rm_sleepable;
                xflags = (opts & RM_NEW ? SX_NEW : 0);
                sx_init_flags(&rm->rm_lock_sx, "rmlock_sx",
                    xflags | SX_NOWITNESS);
        } else {
                lc = &lock_class_rm;
                xflags = (opts & RM_NEW ? MTX_NEW : 0);
                mtx_init(&rm->rm_lock_mtx, name, "rmlock_mtx",
                    xflags | MTX_NOWITNESS);
        }
        lock_init(&rm->lock_object, lc, name, NULL, liflags);
}
 
void
rm_init(struct rmlock *rm, const char *name)
{
 
        rm_init_flags(rm, name, 0);
}
 
void
rm_destroy(struct rmlock *rm)
{
 
        rm_assert(rm, RA_UNLOCKED);
        LIST_FIRST(&rm->rm_activeReaders) = RM_DESTROYED;
        if (rm->lock_object.lo_flags & LO_SLEEPABLE)
                sx_destroy(&rm->rm_lock_sx);
        else
                mtx_destroy(&rm->rm_lock_mtx);
        lock_destroy(&rm->lock_object);
}
 
int
rm_wowned(const struct rmlock *rm)
{
 
        if (rm->lock_object.lo_flags & LO_SLEEPABLE)
                return (sx_xlocked(&rm->rm_lock_sx));
        else
                return (mtx_owned(&rm->rm_lock_mtx));
}
 
void
rm_sysinit(void *arg)
{
        struct rm_args *args;
 
        args = arg;
        rm_init_flags(args->ra_rm, args->ra_desc, args->ra_flags);
}
 
static __noinline int
_rm_rlock_hard(struct rmlock *rm, struct rm_priotracker *tracker, int trylock)
{
        struct pcpu *pc;
 
        critical_enter();
        pc = get_pcpu();
 
        /* Check if we just need to do a proper critical_exit. */
        if (!CPU_ISSET(pc->pc_cpuid, &rm->rm_writecpus)) {
                critical_exit();
                return (1);
        }
 
        /* Remove our tracker from the per-cpu list. */
        rm_tracker_remove(pc, tracker);
 
        /*
         * Check to see if the IPI granted us the lock after all.  The load of
         * rmp_flags must happen after the tracker is removed from the list.
         */
        atomic_interrupt_fence();
        if (tracker->rmp_flags) {
                /* Just add back tracker - we hold the lock. */
                rm_tracker_add(pc, tracker);
                critical_exit();
                return (1);
        }
 
        /*
         * We allow readers to acquire a lock even if a writer is blocked if
         * the lock is recursive and the reader already holds the lock.
         */
        if ((rm->lock_object.lo_flags & LO_RECURSABLE) != 0) {
                /*
                 * Just grant the lock if this thread already has a tracker
                 * for this lock on the per-cpu queue.
                 */
                if (rm_trackers_present(pc, rm, curthread) != 0) {
                        mtx_lock_spin(&rm_spinlock);
                        LIST_INSERT_HEAD(&rm->rm_activeReaders, tracker,
                            rmp_qentry);
                        tracker->rmp_flags = RMPF_ONQUEUE;
                        mtx_unlock_spin(&rm_spinlock);
                        rm_tracker_add(pc, tracker);
                        critical_exit();
                        return (1);
                }
        }
 
        sched_unpin();
        critical_exit();
 
        if (trylock) {
                if (rm->lock_object.lo_flags & LO_SLEEPABLE) {
                        if (!sx_try_xlock(&rm->rm_lock_sx))
                                return (0);
                } else {
                        if (!mtx_trylock(&rm->rm_lock_mtx))
                                return (0);
                }
        } else {
                if (rm->lock_object.lo_flags & LO_SLEEPABLE) {
                        THREAD_SLEEPING_OK();
                        sx_xlock(&rm->rm_lock_sx);
                        THREAD_NO_SLEEPING();
                } else
                        mtx_lock(&rm->rm_lock_mtx);
        }
 
        critical_enter();
        pc = get_pcpu();
        CPU_CLR(pc->pc_cpuid, &rm->rm_writecpus);
        rm_tracker_add(pc, tracker);
        sched_pin();
        critical_exit();
 
        if (rm->lock_object.lo_flags & LO_SLEEPABLE)
                sx_xunlock(&rm->rm_lock_sx);
        else
                mtx_unlock(&rm->rm_lock_mtx);
 
        return (1);
}
 
int
_rm_rlock(struct rmlock *rm, struct rm_priotracker *tracker, int trylock)
{
        struct thread *td = curthread;
        struct pcpu *pc;
 
        if (SCHEDULER_STOPPED())
                return (1);
 
        tracker->rmp_flags  = 0;
        tracker->rmp_thread = td;
        tracker->rmp_rmlock = rm;
 
        if (rm->lock_object.lo_flags & LO_SLEEPABLE)
                THREAD_NO_SLEEPING();
 
        td->td_critnest++;      /* critical_enter(); */
        atomic_interrupt_fence();
 
        pc = cpuid_to_pcpu[td->td_oncpu];
        rm_tracker_add(pc, tracker);
        sched_pin();
 
        atomic_interrupt_fence();
        td->td_critnest--;
 
        /*
         * Fast path to combine two common conditions into a single
         * conditional jump.
         */
        if (__predict_true(0 == (td->td_owepreempt |
            CPU_ISSET(pc->pc_cpuid, &rm->rm_writecpus))))
                return (1);
 
        /* We do not have a read token and need to acquire one. */
        return _rm_rlock_hard(rm, tracker, trylock);
}
 
static __noinline void
_rm_unlock_hard(struct thread *td,struct rm_priotracker *tracker)
{
 
        if (td->td_owepreempt) {
                td->td_critnest++;
                critical_exit();
        }
 
        if (!tracker->rmp_flags)
                return;
 
        mtx_lock_spin(&rm_spinlock);
        LIST_REMOVE(tracker, rmp_qentry);
 
        if (tracker->rmp_flags & RMPF_SIGNAL) {
                struct rmlock *rm;
                struct turnstile *ts;
 
                rm = tracker->rmp_rmlock;
 
                turnstile_chain_lock(&rm->lock_object);
                mtx_unlock_spin(&rm_spinlock);
 
                ts = turnstile_lookup(&rm->lock_object);
 
                turnstile_signal(ts, TS_EXCLUSIVE_QUEUE);
                turnstile_unpend(ts);
                turnstile_chain_unlock(&rm->lock_object);
        } else
                mtx_unlock_spin(&rm_spinlock);
}
 
void
_rm_runlock(struct rmlock *rm, struct rm_priotracker *tracker)
{
        struct pcpu *pc;
        struct thread *td = tracker->rmp_thread;
 
        if (SCHEDULER_STOPPED())
                return;
 
        td->td_critnest++;      /* critical_enter(); */
        atomic_interrupt_fence();
 
        pc = cpuid_to_pcpu[td->td_oncpu];
        rm_tracker_remove(pc, tracker);
 
        atomic_interrupt_fence();
        td->td_critnest--;
        sched_unpin();
 
        if (rm->lock_object.lo_flags & LO_SLEEPABLE)
                THREAD_SLEEPING_OK();
 
        if (__predict_true(0 == (td->td_owepreempt | tracker->rmp_flags)))
                return;
 
        _rm_unlock_hard(td, tracker);
}
 
void
_rm_wlock(struct rmlock *rm)
{
        struct rm_priotracker *prio;
        struct turnstile *ts;
        cpuset_t readcpus;
 
        if (SCHEDULER_STOPPED())
                return;
 
        if (rm->lock_object.lo_flags & LO_SLEEPABLE)
                sx_xlock(&rm->rm_lock_sx);
        else
                mtx_lock(&rm->rm_lock_mtx);
 
        if (CPU_CMP(&rm->rm_writecpus, &all_cpus)) {
                /* Get all read tokens back */
                readcpus = all_cpus;
                CPU_ANDNOT(&readcpus, &readcpus, &rm->rm_writecpus);
                rm->rm_writecpus = all_cpus;
 
                /*
                 * Assumes rm->rm_writecpus update is visible on other CPUs
                 * before rm_cleanIPI is called.
                 */
#ifdef SMP
                smp_rendezvous_cpus(readcpus,
                    smp_no_rendezvous_barrier,
                    rm_cleanIPI,
                    smp_no_rendezvous_barrier,
                    rm);
 
#else
                rm_cleanIPI(rm);
#endif
 
                mtx_lock_spin(&rm_spinlock);
                while ((prio = LIST_FIRST(&rm->rm_activeReaders)) != NULL) {
                        ts = turnstile_trywait(&rm->lock_object);
                        prio->rmp_flags = RMPF_ONQUEUE | RMPF_SIGNAL;
                        mtx_unlock_spin(&rm_spinlock);
                        turnstile_wait(ts, prio->rmp_thread,
                            TS_EXCLUSIVE_QUEUE);
                        mtx_lock_spin(&rm_spinlock);
                }
                mtx_unlock_spin(&rm_spinlock);
        }
}
 
void
_rm_wunlock(struct rmlock *rm)
{
 
        if (rm->lock_object.lo_flags & LO_SLEEPABLE)
                sx_xunlock(&rm->rm_lock_sx);
        else
                mtx_unlock(&rm->rm_lock_mtx);
}
 
#if LOCK_DEBUG > 0
 
void
_rm_wlock_debug(struct rmlock *rm, const char *file, int line)
{
 
        if (SCHEDULER_STOPPED())
                return;
 
        KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
            ("rm_wlock() by idle thread %p on rmlock %s @ %s:%d",
            curthread, rm->lock_object.lo_name, file, line));
        KASSERT(!rm_destroyed(rm),
            ("rm_wlock() of destroyed rmlock @ %s:%d", file, line));
        _rm_assert(rm, RA_UNLOCKED, file, line);
 
        WITNESS_CHECKORDER(&rm->lock_object, LOP_NEWORDER | LOP_EXCLUSIVE,
            file, line, NULL);
 
        _rm_wlock(rm);
 
        LOCK_LOG_LOCK("RMWLOCK", &rm->lock_object, 0, 0, file, line);
        WITNESS_LOCK(&rm->lock_object, LOP_EXCLUSIVE, file, line);
        TD_LOCKS_INC(curthread);
}
 
void
_rm_wunlock_debug(struct rmlock *rm, const char *file, int line)
{
 
        if (SCHEDULER_STOPPED())
                return;
 
        KASSERT(!rm_destroyed(rm),
            ("rm_wunlock() of destroyed rmlock @ %s:%d", file, line));
        _rm_assert(rm, RA_WLOCKED, file, line);
        WITNESS_UNLOCK(&rm->lock_object, LOP_EXCLUSIVE, file, line);
        LOCK_LOG_LOCK("RMWUNLOCK", &rm->lock_object, 0, 0, file, line);
        _rm_wunlock(rm);
        TD_LOCKS_DEC(curthread);
}
 
int
_rm_rlock_debug(struct rmlock *rm, struct rm_priotracker *tracker,
    int trylock, const char *file, int line)
{
 
        if (SCHEDULER_STOPPED())
                return (1);
 
#ifdef INVARIANTS
        if (!(rm->lock_object.lo_flags & LO_RECURSABLE) && !trylock) {
                critical_enter();
                KASSERT(rm_trackers_present(get_pcpu(), rm,
                    curthread) == 0,
                    ("rm_rlock: recursed on non-recursive rmlock %s @ %s:%d\n",
                    rm->lock_object.lo_name, file, line));
                critical_exit();
        }
#endif
        KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
            ("rm_rlock() by idle thread %p on rmlock %s @ %s:%d",
            curthread, rm->lock_object.lo_name, file, line));
        KASSERT(!rm_destroyed(rm),
            ("rm_rlock() of destroyed rmlock @ %s:%d", file, line));
        if (!trylock) {
                KASSERT(!rm_wowned(rm),
                    ("rm_rlock: wlock already held for %s @ %s:%d",
                    rm->lock_object.lo_name, file, line));
                WITNESS_CHECKORDER(&rm->lock_object,
                    LOP_NEWORDER | LOP_NOSLEEP, file, line, NULL);
        }
 
        if (_rm_rlock(rm, tracker, trylock)) {
                if (trylock)
                        LOCK_LOG_TRY("RMRLOCK", &rm->lock_object, 0, 1, file,
                            line);
                else
                        LOCK_LOG_LOCK("RMRLOCK", &rm->lock_object, 0, 0, file,
                            line);
                WITNESS_LOCK(&rm->lock_object, LOP_NOSLEEP, file, line);
                TD_LOCKS_INC(curthread);
                return (1);
        } else if (trylock)
                LOCK_LOG_TRY("RMRLOCK", &rm->lock_object, 0, 0, file, line);
 
        return (0);
}
 
void
_rm_runlock_debug(struct rmlock *rm, struct rm_priotracker *tracker,
    const char *file, int line)
{
 
        if (SCHEDULER_STOPPED())
                return;
 
        KASSERT(!rm_destroyed(rm),
            ("rm_runlock() of destroyed rmlock @ %s:%d", file, line));
        _rm_assert(rm, RA_RLOCKED, file, line);
        WITNESS_UNLOCK(&rm->lock_object, 0, file, line);
        LOCK_LOG_LOCK("RMRUNLOCK", &rm->lock_object, 0, 0, file, line);
        _rm_runlock(rm, tracker);
        TD_LOCKS_DEC(curthread);
}
 
#else
 
/*
 * Just strip out file and line arguments if no lock debugging is enabled in
 * the kernel - we are called from a kernel module.
 */
void
_rm_wlock_debug(struct rmlock *rm, const char *file, int line)
{
 
        _rm_wlock(rm);
}
 
void
_rm_wunlock_debug(struct rmlock *rm, const char *file, int line)
{
 
        _rm_wunlock(rm);
}
 
int
_rm_rlock_debug(struct rmlock *rm, struct rm_priotracker *tracker,
    int trylock, const char *file, int line)
{
 
        return _rm_rlock(rm, tracker, trylock);
}
 
void
_rm_runlock_debug(struct rmlock *rm, struct rm_priotracker *tracker,
    const char *file, int line)
{
 
        _rm_runlock(rm, tracker);
}
 
#endif
 
#ifdef INVARIANT_SUPPORT
#ifndef INVARIANTS
#undef _rm_assert
#endif
 
/*
 * Note that this does not need to use witness_assert() for read lock
 * assertions since an exact count of read locks held by this thread
 * is computable.
 */
void
_rm_assert(const struct rmlock *rm, int what, const char *file, int line)
{
        int count;
 
        if (SCHEDULER_STOPPED())
                return;
        switch (what) {
        case RA_LOCKED:
        case RA_LOCKED | RA_RECURSED:
        case RA_LOCKED | RA_NOTRECURSED:
        case RA_RLOCKED:
        case RA_RLOCKED | RA_RECURSED:
        case RA_RLOCKED | RA_NOTRECURSED:
                /*
                 * Handle the write-locked case.  Unlike other
                 * primitives, writers can never recurse.
                 */
                if (rm_wowned(rm)) {
                        if (what & RA_RLOCKED)
                                panic("Lock %s exclusively locked @ %s:%d\n",
                                    rm->lock_object.lo_name, file, line);
                        if (what & RA_RECURSED)
                                panic("Lock %s not recursed @ %s:%d\n",
                                    rm->lock_object.lo_name, file, line);
                        break;
                }
 
                critical_enter();
                count = rm_trackers_present(get_pcpu(), rm, curthread);
                critical_exit();
 
                if (count == 0)
                        panic("Lock %s not %slocked @ %s:%d\n",
                            rm->lock_object.lo_name, (what & RA_RLOCKED) ?
                            "read " : "", file, line);
                if (count > 1) {
                        if (what & RA_NOTRECURSED)
                                panic("Lock %s recursed @ %s:%d\n",
                                    rm->lock_object.lo_name, file, line);
                } else if (what & RA_RECURSED)
                        panic("Lock %s not recursed @ %s:%d\n",
                            rm->lock_object.lo_name, file, line);
                break;
        case RA_WLOCKED:
                if (!rm_wowned(rm))
                        panic("Lock %s not exclusively locked @ %s:%d\n",
                            rm->lock_object.lo_name, file, line);
                break;
        case RA_UNLOCKED:
                if (rm_wowned(rm))
                        panic("Lock %s exclusively locked @ %s:%d\n",
                            rm->lock_object.lo_name, file, line);
 
                critical_enter();
                count = rm_trackers_present(get_pcpu(), rm, curthread);
                critical_exit();
 
                if (count != 0)
                        panic("Lock %s read locked @ %s:%d\n",
                            rm->lock_object.lo_name, file, line);
                break;
        default:
                panic("Unknown rm lock assertion: %d @ %s:%d", what, file,
                    line);
        }
}
#endif /* INVARIANT_SUPPORT */
 
#ifdef DDB
static void
print_tracker(struct rm_priotracker *tr)
{
        struct thread *td;
 
        td = tr->rmp_thread;
        db_printf("   thread %p (tid %d, pid %d, \"%s\") {", td, td->td_tid,
            td->td_proc->p_pid, td->td_name);
        if (tr->rmp_flags & RMPF_ONQUEUE) {
                db_printf("ONQUEUE");
                if (tr->rmp_flags & RMPF_SIGNAL)
                        db_printf(",SIGNAL");
        } else
                db_printf("0");
        db_printf("}\n");
}
 
static void
db_show_rm(const struct lock_object *lock)
{
        struct rm_priotracker *tr;
        struct rm_queue *queue;
        const struct rmlock *rm;
        struct lock_class *lc;
        struct pcpu *pc;
 
        rm = (const struct rmlock *)lock;
        db_printf(" writecpus: ");
        ddb_display_cpuset(__DEQUALIFY(const cpuset_t *, &rm->rm_writecpus));
        db_printf("\n");
        db_printf(" per-CPU readers:\n");
        STAILQ_FOREACH(pc, &cpuhead, pc_allcpu)
                for (queue = pc->pc_rm_queue.rmq_next;
                    queue != &pc->pc_rm_queue; queue = queue->rmq_next) {
                        tr = (struct rm_priotracker *)queue;
                        if (tr->rmp_rmlock == rm)
                                print_tracker(tr);
                }
        db_printf(" active readers:\n");
        LIST_FOREACH(tr, &rm->rm_activeReaders, rmp_qentry)
                print_tracker(tr);
        lc = LOCK_CLASS(&rm->rm_wlock_object);
        db_printf("Backing write-lock (%s):\n", lc->lc_name);
        lc->lc_ddb_show(&rm->rm_wlock_object);
}
#endif
 
/*
 * Read-mostly sleepable locks.
 *
 * These primitives allow both readers and writers to sleep. However, neither
 * readers nor writers are tracked and subsequently there is no priority
 * propagation.
 *
 * They are intended to be only used when write-locking is almost never needed
 * (e.g., they can guard against unloading a kernel module) while read-locking
 * happens all the time.
 *
 * Concurrent writers take turns taking the lock while going off cpu. If this is
 * of concern for your usecase, this is not the right primitive.
 *
 * Neither rms_rlock nor rms_runlock use thread fences. Instead interrupt
 * fences are inserted to ensure ordering with the code executed in the IPI
 * handler.
 *
 * No attempt is made to track which CPUs read locked at least once,
 * consequently write locking sends IPIs to all of them. This will become a
 * problem at some point. The easiest way to lessen it is to provide a bitmap.
 */
 
#define RMS_NOOWNER     ((void *)0x1)
#define RMS_TRANSIENT   ((void *)0x2)
#define RMS_FLAGMASK    0xf
 
struct rmslock_pcpu {
        int influx;
        int readers;
};
 
_Static_assert(sizeof(struct rmslock_pcpu) == 8, "bad size");
 
/*
 * Internal routines
 */
static struct rmslock_pcpu *
rms_int_pcpu(struct rmslock *rms)
{
 
        CRITICAL_ASSERT(curthread);
        return (zpcpu_get(rms->pcpu));
}
 
static struct rmslock_pcpu *
rms_int_remote_pcpu(struct rmslock *rms, int cpu)
{
 
        return (zpcpu_get_cpu(rms->pcpu, cpu));
}
 
static void
rms_int_influx_enter(struct rmslock *rms, struct rmslock_pcpu *pcpu)
{
 
        CRITICAL_ASSERT(curthread);
        MPASS(pcpu->influx == 0);
        pcpu->influx = 1;
}
 
static void
rms_int_influx_exit(struct rmslock *rms, struct rmslock_pcpu *pcpu)
{
 
        CRITICAL_ASSERT(curthread);
        MPASS(pcpu->influx == 1);
        pcpu->influx = 0;
}
 
#ifdef INVARIANTS
static void
rms_int_debug_readers_inc(struct rmslock *rms)
{
        int old;
        old = atomic_fetchadd_int(&rms->debug_readers, 1);
        KASSERT(old >= 0, ("%s: bad readers count %d\n", __func__, old));
}
 
static void
rms_int_debug_readers_dec(struct rmslock *rms)
{
        int old;
 
        old = atomic_fetchadd_int(&rms->debug_readers, -1);
        KASSERT(old > 0, ("%s: bad readers count %d\n", __func__, old));
}
#else
static void
rms_int_debug_readers_inc(struct rmslock *rms)
{
}
 
static void
rms_int_debug_readers_dec(struct rmslock *rms)
{
}
#endif
 
static void
rms_int_readers_inc(struct rmslock *rms, struct rmslock_pcpu *pcpu)
{
 
        CRITICAL_ASSERT(curthread);
        rms_int_debug_readers_inc(rms);
        pcpu->readers++;
}
 
static void
rms_int_readers_dec(struct rmslock *rms, struct rmslock_pcpu *pcpu)
{
 
        CRITICAL_ASSERT(curthread);
        rms_int_debug_readers_dec(rms);
        pcpu->readers--;
}
 
/*
 * Public API
 */
void
rms_init(struct rmslock *rms, const char *name)
{
 
        rms->owner = RMS_NOOWNER;
        rms->writers = 0;
        rms->readers = 0;
        rms->debug_readers = 0;
        mtx_init(&rms->mtx, name, NULL, MTX_DEF | MTX_NEW);
        rms->pcpu = uma_zalloc_pcpu(pcpu_zone_8, M_WAITOK | M_ZERO);
}
 
void
rms_destroy(struct rmslock *rms)
{
 
        MPASS(rms->writers == 0);
        MPASS(rms->readers == 0);
        mtx_destroy(&rms->mtx);
        uma_zfree_pcpu(pcpu_zone_8, rms->pcpu);
}
 
static void __noinline
rms_rlock_fallback(struct rmslock *rms)
{
 
        rms_int_influx_exit(rms, rms_int_pcpu(rms));
        critical_exit();
 
        mtx_lock(&rms->mtx);
        while (rms->writers > 0)
                msleep(&rms->readers, &rms->mtx, PUSER - 1, mtx_name(&rms->mtx), 0);
        critical_enter();
        rms_int_readers_inc(rms, rms_int_pcpu(rms));
        mtx_unlock(&rms->mtx);
        critical_exit();
        TD_LOCKS_INC(curthread);
}
 
void
rms_rlock(struct rmslock *rms)
{
        struct rmslock_pcpu *pcpu;
 
        WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL, __func__);
        MPASS(atomic_load_ptr(&rms->owner) != curthread);
 
        critical_enter();
        pcpu = rms_int_pcpu(rms);
        rms_int_influx_enter(rms, pcpu);
        atomic_interrupt_fence();
        if (__predict_false(rms->writers > 0)) {
                rms_rlock_fallback(rms);
                return;
        }
        atomic_interrupt_fence();
        rms_int_readers_inc(rms, pcpu);
        atomic_interrupt_fence();
        rms_int_influx_exit(rms, pcpu);
        critical_exit();
        TD_LOCKS_INC(curthread);
}
 
int
rms_try_rlock(struct rmslock *rms)
{
        struct rmslock_pcpu *pcpu;
 
        MPASS(atomic_load_ptr(&rms->owner) != curthread);
 
        critical_enter();
        pcpu = rms_int_pcpu(rms);
        rms_int_influx_enter(rms, pcpu);
        atomic_interrupt_fence();
        if (__predict_false(rms->writers > 0)) {
                rms_int_influx_exit(rms, pcpu);
                critical_exit();
                return (0);
        }
        atomic_interrupt_fence();
        rms_int_readers_inc(rms, pcpu);
        atomic_interrupt_fence();
        rms_int_influx_exit(rms, pcpu);
        critical_exit();
        TD_LOCKS_INC(curthread);
        return (1);
}
 
static void __noinline
rms_runlock_fallback(struct rmslock *rms)
{
 
        rms_int_influx_exit(rms, rms_int_pcpu(rms));
        critical_exit();
 
        mtx_lock(&rms->mtx);
        MPASS(rms->writers > 0);
        MPASS(rms->readers > 0);
        MPASS(rms->debug_readers == rms->readers);
        rms_int_debug_readers_dec(rms);
        rms->readers--;
        if (rms->readers == 0)
                wakeup_one(&rms->writers);
        mtx_unlock(&rms->mtx);
        TD_LOCKS_DEC(curthread);
}
 
void
rms_runlock(struct rmslock *rms)
{
        struct rmslock_pcpu *pcpu;
 
        critical_enter();
        pcpu = rms_int_pcpu(rms);
        rms_int_influx_enter(rms, pcpu);
        atomic_interrupt_fence();
        if (__predict_false(rms->writers > 0)) {
                rms_runlock_fallback(rms);
                return;
        }
        atomic_interrupt_fence();
        rms_int_readers_dec(rms, pcpu);
        atomic_interrupt_fence();
        rms_int_influx_exit(rms, pcpu);
        critical_exit();
        TD_LOCKS_DEC(curthread);
}
 
struct rmslock_ipi {
        struct rmslock *rms;
        struct smp_rendezvous_cpus_retry_arg srcra;
};
 
static void
rms_action_func(void *arg)
{
        struct rmslock_ipi *rmsipi;
        struct rmslock_pcpu *pcpu;
        struct rmslock *rms;
 
        rmsipi = __containerof(arg, struct rmslock_ipi, srcra);
        rms = rmsipi->rms;
        pcpu = rms_int_pcpu(rms);
 
        if (pcpu->influx)
                return;
        if (pcpu->readers != 0) {
                atomic_add_int(&rms->readers, pcpu->readers);
                pcpu->readers = 0;
        }
        smp_rendezvous_cpus_done(arg);
}
 
static void
rms_wait_func(void *arg, int cpu)
{
        struct rmslock_ipi *rmsipi;
        struct rmslock_pcpu *pcpu;
        struct rmslock *rms;
 
        rmsipi = __containerof(arg, struct rmslock_ipi, srcra);
        rms = rmsipi->rms;
        pcpu = rms_int_remote_pcpu(rms, cpu);
 
        while (atomic_load_int(&pcpu->influx))
                cpu_spinwait();
}
 
#ifdef INVARIANTS
static void
rms_assert_no_pcpu_readers(struct rmslock *rms)
{
        struct rmslock_pcpu *pcpu;
        int cpu;
 
        CPU_FOREACH(cpu) {
                pcpu = rms_int_remote_pcpu(rms, cpu);
                if (pcpu->readers != 0) {
                        panic("%s: got %d readers on cpu %d\n", __func__,
                            pcpu->readers, cpu);
                }
        }
}
#else
static void
rms_assert_no_pcpu_readers(struct rmslock *rms)
{
}
#endif
 
static void
rms_wlock_switch(struct rmslock *rms)
{
        struct rmslock_ipi rmsipi;
 
        MPASS(rms->readers == 0);
        MPASS(rms->writers == 1);
 
        rmsipi.rms = rms;
 
        smp_rendezvous_cpus_retry(all_cpus,
            smp_no_rendezvous_barrier,
            rms_action_func,
            smp_no_rendezvous_barrier,
            rms_wait_func,
            &rmsipi.srcra);
}
 
void
rms_wlock(struct rmslock *rms)
{
 
        WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL, __func__);
        MPASS(atomic_load_ptr(&rms->owner) != curthread);
 
        mtx_lock(&rms->mtx);
        rms->writers++;
        if (rms->writers > 1) {
                msleep(&rms->owner, &rms->mtx, (PUSER - 1),
                    mtx_name(&rms->mtx), 0);
                MPASS(rms->readers == 0);
                KASSERT(rms->owner == RMS_TRANSIENT,
                    ("%s: unexpected owner value %p\n", __func__,
                    rms->owner));
                goto out_grab;
        }
 
        KASSERT(rms->owner == RMS_NOOWNER,
            ("%s: unexpected owner value %p\n", __func__, rms->owner));
 
        rms_wlock_switch(rms);
        rms_assert_no_pcpu_readers(rms);
 
        if (rms->readers > 0) {
                msleep(&rms->writers, &rms->mtx, (PUSER - 1),
                    mtx_name(&rms->mtx), 0);
        }
 
out_grab:
        rms->owner = curthread;
        rms_assert_no_pcpu_readers(rms);
        mtx_unlock(&rms->mtx);
        MPASS(rms->readers == 0);
        TD_LOCKS_INC(curthread);
}
 
void
rms_wunlock(struct rmslock *rms)
{
 
        mtx_lock(&rms->mtx);
        KASSERT(rms->owner == curthread,
            ("%s: unexpected owner value %p\n", __func__, rms->owner));
        MPASS(rms->writers >= 1);
        MPASS(rms->readers == 0);
        rms->writers--;
        if (rms->writers > 0) {
                wakeup_one(&rms->owner);
                rms->owner = RMS_TRANSIENT;
        } else {
                wakeup(&rms->readers);
                rms->owner = RMS_NOOWNER;
        }
        mtx_unlock(&rms->mtx);
        TD_LOCKS_DEC(curthread);
}
 
void
rms_unlock(struct rmslock *rms)
{
 
        if (rms_wowned(rms))
                rms_wunlock(rms);
        else
                rms_runlock(rms);
}