text: /*-
   * 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>
  
  #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 = pcpu_find(curcpu);
  		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 = pcpu_find(curcpu);
  
  	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;
  	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 = arg;
  
  	rm_init(args->ra_rm, args->ra_desc);
  }
  
  void
  rm_sysinit_flags(void *arg)
  {
  	struct rm_args_flags *args = arg;
  
  	rm_init_flags(args->ra_rm, args->ra_desc, args->ra_opts);
  }
  
  static int
  _rm_rlock_hard(struct rmlock *rm, struct rm_priotracker *tracker, int trylock)
  {
  	struct pcpu *pc;
  
  	critical_enter();
  	pc = pcpu_find(curcpu);
  
  	/* 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. */
  	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 = pcpu_find(curcpu);
  	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(); */
  
  	__compiler_membar();
  
  	pc = cpuid_to_pcpu[td->td_oncpu]; /* pcpu_find(td->td_oncpu); */
  
  	rm_tracker_add(pc, tracker);
  
  	sched_pin();
  
  	__compiler_membar();
  
  	td->td_critnest--;
  
  	/*
  	 * Fast path to combine two common conditions into a single
  	 * conditional jump.
  	 */
  	if (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 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, TS_EXCLUSIVE_LOCK);
  		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(); */
  	pc = cpuid_to_pcpu[td->td_oncpu]; /* pcpu_find(td->td_oncpu); */
  	rm_tracker_remove(pc, tracker);
  	td->td_critnest--;
  	sched_unpin();
  
  	if (rm->lock_object.lo_flags & LO_SLEEPABLE)
  		THREAD_SLEEPING_OK();
  
  	if (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_NAND(&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_rendevous_barrier,
  		    rm_cleanIPI,
  		    smp_no_rendevous_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(pcpu_find(curcpu), 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, 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, 0, 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 (panicstr != NULL)
  		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(pcpu_find(curcpu), 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(pcpu_find(curcpu), 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
  