text: /*-
   * 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: subr_turnstile.c,v 1.1 2004/09/22 07:28:58 t-momose Exp $
   *	and BSDI $Id: subr_turnstile.c,v 1.1 2004/09/22 07:28:58 t-momose Exp $
   */
  
  /*
   * Implementation of turnstiles used to hold queue of threads blocked on
   * non-sleepable locks.  Sleepable locks use condition variables to
   * implement their queues.  Turnstiles differ from a sleep queue in that
   * turnstile queue's are assigned to a lock held by an owning thread.  Thus,
   * when one thread is enqueued onto a turnstile, it can lend its priority
   * to the owning thread.
   *
   * We wish to avoid bloating locks with an embedded turnstile and we do not
   * want to use back-pointers in the locks for the same reason.  Thus, we
   * use a similar approach to that of Solaris 7 as described in Solaris
   * Internals by Jim Mauro and Richard McDougall.  Turnstiles are looked up
   * in a hash table based on the address of the lock.  Each entry in the
   * hash table is a linked-lists of turnstiles and is called a turnstile
   * chain.  Each chain contains a spin mutex that protects all of the
   * turnstiles in the chain.
   *
   * Each time a thread is created, a turnstile is malloc'd and attached to
   * that thread.  When a thread blocks on a lock, if it is the first thread
   * to block, it lends its turnstile to the lock.  If the lock already has
   * a turnstile, then it gives its turnstile to the lock's turnstile's free
   * list.  When a thread is woken up, it takes a turnstile from the free list
   * if there are any other waiters.  If it is the only thread blocked on the
   * lock, then it reclaims the turnstile associated with the lock and removes
   * it from the hash table.
   *
   * XXX: We should probably implement some sort of sleep queue that condition
   * variables and sleepqueue's share.  On Solaris condition variables are
   * implemented using a hash table of sleep queues similar to our current
   * sleep queues.  We might want to investigate doing that ourselves.
   */
  
  #include <sys/cdefs.h>
  __FBSDID("$FreeBSD: src/sys/kern/subr_turnstile.c,v 1.134.2.1 2003/12/11 20:01:52 jhb Exp $");
  
  #include <sys/param.h>
  #include <sys/systm.h>
  #include <sys/kernel.h>
  #include <sys/ktr.h>
  #include <sys/lock.h>
  #include <sys/malloc.h>
  #include <sys/mutex.h>
  #include <sys/proc.h>
  #include <sys/queue.h>
  #include <sys/resourcevar.h>
  #include <sys/turnstile.h>
  #include <sys/sched.h>
  
  /*
   * Constants for the hash table of turnstile chains.  TC_SHIFT is a magic
   * number chosen because the sleep queue's use the same value for the
   * shift.  Basically, we ignore the lower 8 bits of the address.
   * TC_TABLESIZE must be a power of two for TC_MASK to work properly.
   */
  #define	TC_TABLESIZE	128			/* Must be power of 2. */
  #define	TC_MASK		(TC_TABLESIZE - 1)
  #define	TC_SHIFT	8
  #define	TC_HASH(lock)	(((uintptr_t)(lock) >> TC_SHIFT) & TC_MASK)
  #define	TC_LOOKUP(lock)	&turnstile_chains[TC_HASH(lock)]
  
  /*
   * There are three different lists of turnstiles as follows.  The list
   * connected by ts_link entries is a per-thread list of all the turnstiles
   * attached to locks that we own.  This is used to fixup our priority when
   * a lock is released.  The other two lists use the ts_hash entries.  The
   * first of these two is turnstile chain list that a turnstile is on when
   * it is attached to a lock.  The second list to use ts_hash is the free
   * list hung off a turnstile that is attached to a lock.
   *
   * Each turnstile contains two lists of threads.  The ts_blocked list is
   * a linked list of threads blocked on the turnstile's lock.  The
   * ts_pending list is a linked list of threads previously awoken by
   * turnstile_signal() or turnstile_wait() that are waiting to be put on
   * the run queue.
   *
   * Locking key:
   *  c - turnstile chain lock
   *  q - td_contested lock
   */
  struct turnstile {
  	TAILQ_HEAD(, thread) ts_blocked;	/* (c + q) Blocked threads. */
  	TAILQ_HEAD(, thread) ts_pending;	/* (c) Pending threads. */
  	LIST_ENTRY(turnstile) ts_hash;		/* (c) Chain and free list. */
  	LIST_ENTRY(turnstile) ts_link;		/* (q) Contested locks. */
  	LIST_HEAD(, turnstile) ts_free;		/* (c) Free turnstiles. */
  	struct lock_object *ts_lockobj;		/* (c) Lock we reference. */
  	struct thread *ts_owner;		/* (c + q) Who owns the lock. */
  };
  
  struct turnstile_chain {
  	LIST_HEAD(, turnstile) tc_turnstiles;	/* List of turnstiles. */
  	struct mtx tc_lock;			/* Spin lock for this chain. */
  };
  
  static struct mtx td_contested_lock;
  static struct turnstile_chain turnstile_chains[TC_TABLESIZE];
  
  MALLOC_DEFINE(M_TURNSTILE, "turnstiles", "turnstiles");
  
  /*
   * Prototypes for non-exported routines.
   */
  static void	init_turnstile0(void *dummy);
  static void	propagate_priority(struct thread *);
  static void	turnstile_setowner(struct turnstile *ts, struct thread *owner);
  
  /*
   * Walks the chain of turnstiles and their owners to propagate the priority
   * of the thread being blocked to all the threads holding locks that have to
   * release their locks before this thread can run again.
   */
  static void
  propagate_priority(struct thread *td)
  {
  	struct turnstile_chain *tc;
  	struct turnstile *ts;
  	struct thread *td1;
  	int pri;
  
  	mtx_assert(&sched_lock, MA_OWNED);
  	pri = td->td_priority;
  	ts = td->td_blocked;
  	for (;;) {
  		td = ts->ts_owner;
  
  		if (td == NULL) {
  			/*
  			 * This really isn't quite right. Really
  			 * ought to bump priority of thread that
  			 * next acquires the lock.
  			 */
  			return;
  		}
  
  		MPASS(td->td_proc != NULL);
  		MPASS(td->td_proc->p_magic == P_MAGIC);
  
  		/*
  		 * XXX: The owner of a turnstile can be stale if it is the
  		 * first thread to grab a slock of a sx lock.  In that case
  		 * it is possible for us to be at SSLEEP or some other
  		 * weird state.  We should probably just return if the state
  		 * isn't SRUN or SLOCK.
  		 */
  		KASSERT(!TD_IS_SLEEPING(td),
  		    ("sleeping thread (pid %d) owns a non-sleepable lock",
  		    td->td_proc->p_pid));
  
  		/*
  		 * If this thread already has higher priority than the
  		 * thread that is being blocked, we are finished.
  		 */
  		if (td->td_priority <= pri)
  			return;
  
  		/*
  		 * If lock holder is actually running, just bump priority.
  		 */
  		if (TD_IS_RUNNING(td)) {
  			td->td_priority = pri;
  			return;
  		}
  
  #ifndef SMP
  		/*
  		 * For UP, we check to see if td is curthread (this shouldn't
  		 * ever happen however as it would mean we are in a deadlock.)
  		 */
  		KASSERT(td != curthread, ("Deadlock detected"));
  #endif
  
  		/*
  		 * If on run queue move to new run queue, and quit.
  		 * XXXKSE this gets a lot more complicated under threads
  		 * but try anyhow.
  		 */
  		if (TD_ON_RUNQ(td)) {
  			MPASS(td->td_blocked == NULL);
  			sched_prio(td, pri);
  			return;
  		}
  
  		/*
  		 * Bump this thread's priority.
  		 */
  		td->td_priority = pri;
  
  		/*
  		 * If we aren't blocked on a lock, we should be.
  		 */
  		KASSERT(TD_ON_LOCK(td), (
  		    "process %d(%s):%d holds %s but isn't blocked on a lock\n",
  		    td->td_proc->p_pid, td->td_proc->p_comm, td->td_state,
  		    ts->ts_lockobj->lo_name));
  
  		/*
  		 * Pick up the lock that td is blocked on.
  		 */
  		ts = td->td_blocked;
  		MPASS(ts != NULL);
  		tc = TC_LOOKUP(ts->ts_lockobj);
  		mtx_lock_spin(&tc->tc_lock);
  
  		/*
  		 * This thread may not be blocked on this turnstile anymore
  		 * but instead might already be woken up on another CPU
  		 * that is waiting on sched_lock in turnstile_unpend() to
  		 * finish waking this thread up.  We can detect this case
  		 * by checking to see if this thread has been given a
  		 * turnstile by either turnstile_signal() or
  		 * turnstile_wakeup().  In this case, treat the thread as
  		 * if it was already running.
  		 */
  		if (td->td_turnstile != NULL) {
  			mtx_unlock_spin(&tc->tc_lock);
  			return;
  		}
  
  		/*
  		 * Check if the thread needs to be moved up on
  		 * the blocked chain.  It doesn't need to be moved
  		 * if it is already at the head of the list or if
  		 * the item in front of it still has a higher priority.
  		 */
  		if (td == TAILQ_FIRST(&ts->ts_blocked)) {
  			mtx_unlock_spin(&tc->tc_lock);
  			continue;
  		}
  
  		td1 = TAILQ_PREV(td, threadqueue, td_lockq);
  		if (td1->td_priority <= pri) {
  			mtx_unlock_spin(&tc->tc_lock);
  			continue;
  		}
  
  		/*
  		 * Remove thread from blocked chain and determine where
  		 * it should be moved up to.  Since we know that td1 has
  		 * a lower priority than td, we know that at least one
  		 * thread in the chain has a lower priority and that
  		 * td1 will thus not be NULL after the loop.
  		 */
  		mtx_lock_spin(&td_contested_lock);
  		TAILQ_REMOVE(&ts->ts_blocked, td, td_lockq);
  		TAILQ_FOREACH(td1, &ts->ts_blocked, td_lockq) {
  			MPASS(td1->td_proc->p_magic == P_MAGIC);
  			if (td1->td_priority > pri)
  				break;
  		}
  
  		MPASS(td1 != NULL);
  		TAILQ_INSERT_BEFORE(td1, td, td_lockq);
  		mtx_unlock_spin(&td_contested_lock);
  		CTR4(KTR_LOCK,
  		    "propagate_priority: td %p moved before %p on [%p] %s",
  		    td, td1, ts->ts_lockobj, ts->ts_lockobj->lo_name);
  		mtx_unlock_spin(&tc->tc_lock);
  	}
  }
  
  /*
   * Early initialization of turnstiles.  This is not done via a SYSINIT()
   * since this needs to be initialized very early when mutexes are first
   * initialized.
   */
  void
  init_turnstiles(void)
  {
  	int i;
  
  	for (i = 0; i < TC_TABLESIZE; i++) {
  		LIST_INIT(&turnstile_chains[i].tc_turnstiles);
  		mtx_init(&turnstile_chains[i].tc_lock, "turnstile chain",
  		    NULL, MTX_SPIN);
  	}
  	mtx_init(&td_contested_lock, "td_contested", NULL, MTX_SPIN);
  	thread0.td_turnstile = NULL;
  }
  
  static void
  init_turnstile0(void *dummy)
  {
  
  	thread0.td_turnstile = turnstile_alloc();
  }
  SYSINIT(turnstile0, SI_SUB_LOCK, SI_ORDER_ANY, init_turnstile0, NULL);
  
  /*
   * Set the owner of the lock this turnstile is attached to.
   */
  static void
  turnstile_setowner(struct turnstile *ts, struct thread *owner)
  {
  
  	mtx_assert(&td_contested_lock, MA_OWNED);
  	MPASS(owner->td_proc->p_magic == P_MAGIC);
  	MPASS(ts->ts_owner == NULL);
  	ts->ts_owner = owner;
  	LIST_INSERT_HEAD(&owner->td_contested, ts, ts_link);
  }
  
  /*
   * Malloc a turnstile for a new thread, initialize it and return it.
   */
  struct turnstile *
  turnstile_alloc(void)
  {
  	struct turnstile *ts;
  
  	ts = malloc(sizeof(struct turnstile), M_TURNSTILE, M_WAITOK | M_ZERO);
  	TAILQ_INIT(&ts->ts_blocked);
  	TAILQ_INIT(&ts->ts_pending);
  	LIST_INIT(&ts->ts_free);
  	return (ts);
  }
  
  /*
   * Free a turnstile when a thread is destroyed.
   */
  void
  turnstile_free(struct turnstile *ts)
  {
  
  	MPASS(ts != NULL);
  	MPASS(TAILQ_EMPTY(&ts->ts_blocked));
  	MPASS(TAILQ_EMPTY(&ts->ts_pending));
  	free(ts, M_TURNSTILE);
  }
  
  /*
   * Look up the turnstile for a lock in the hash table locking the associated
   * turnstile chain along the way.  Return with the turnstile chain locked.
   * If no turnstile is found in the hash table, NULL is returned.
   */
  struct turnstile *
  turnstile_lookup(struct lock_object *lock)
  {
  	struct turnstile_chain *tc;
  	struct turnstile *ts;
  
  	tc = TC_LOOKUP(lock);
  	mtx_lock_spin(&tc->tc_lock);
  	LIST_FOREACH(ts, &tc->tc_turnstiles, ts_hash)
  		if (ts->ts_lockobj == lock)
  			return (ts);
  	return (NULL);
  }
  
  /*
   * Unlock the turnstile chain associated with a given lock.
   */
  void
  turnstile_release(struct lock_object *lock)
  {
  	struct turnstile_chain *tc;
  
  	tc = TC_LOOKUP(lock);
  	mtx_unlock_spin(&tc->tc_lock);
  }
  
  /*
   * Take ownership of a turnstile and adjust the priority of the new
   * owner appropriately.
   */
  void
  turnstile_claim(struct turnstile *ts)
  {
  	struct turnstile_chain *tc;
  	struct thread *td, *owner;
  
  	tc = TC_LOOKUP(ts->ts_lockobj);
  	mtx_assert(&tc->tc_lock, MA_OWNED);
  
  	owner = curthread;
  	mtx_lock_spin(&td_contested_lock);
  	turnstile_setowner(ts, owner);
  	mtx_unlock_spin(&td_contested_lock);
  
  	td = TAILQ_FIRST(&ts->ts_blocked);
  	MPASS(td != NULL);
  	MPASS(td->td_proc->p_magic == P_MAGIC);
  	mtx_unlock_spin(&tc->tc_lock);
  
  	/*
  	 * Update the priority of the new owner if needed.
  	 */
  	mtx_lock_spin(&sched_lock);
  	if (td->td_priority < owner->td_priority)
  		owner->td_priority = td->td_priority; 
  	mtx_unlock_spin(&sched_lock);
  }
  
  /*
   * Block the current thread on the turnstile ts.  This function will context
   * switch and not return until this thread has been woken back up.  This
   * function must be called with the appropriate turnstile chain locked and
   * will return with it unlocked.
   */
  void
  turnstile_wait(struct turnstile *ts, struct lock_object *lock,
      struct thread *owner)
  {
  	struct turnstile_chain *tc;
  	struct thread *td, *td1;
  
  	td = curthread;
  	tc = TC_LOOKUP(lock);
  	mtx_assert(&tc->tc_lock, MA_OWNED);
  	MPASS(td->td_turnstile != NULL);
  	MPASS(owner != NULL);
  	MPASS(owner->td_proc->p_magic == P_MAGIC);
  
  	/* If the passed in turnstile is NULL, use this thread's turnstile. */
  	if (ts == NULL) {
  		ts = td->td_turnstile;
  		LIST_INSERT_HEAD(&tc->tc_turnstiles, ts, ts_hash);
  		KASSERT(TAILQ_EMPTY(&ts->ts_pending),
  		    ("thread's turnstile has pending threads"));
  		KASSERT(TAILQ_EMPTY(&ts->ts_blocked),
  		    ("thread's turnstile has a non-empty queue"));
  		KASSERT(LIST_EMPTY(&ts->ts_free),
  		    ("thread's turnstile has a non-empty free list"));
  		KASSERT(ts->ts_lockobj == NULL, ("stale ts_lockobj pointer"));
  		ts->ts_lockobj = lock;
  		mtx_lock_spin(&td_contested_lock);
  		TAILQ_INSERT_TAIL(&ts->ts_blocked, td, td_lockq);
  		turnstile_setowner(ts, owner);
  		mtx_unlock_spin(&td_contested_lock);
  	} else {
  		TAILQ_FOREACH(td1, &ts->ts_blocked, td_lockq)
  			if (td1->td_priority > td->td_priority)
  				break;
  		mtx_lock_spin(&td_contested_lock);
  		if (td1 != NULL)
  			TAILQ_INSERT_BEFORE(td1, td, td_lockq);
  		else
  			TAILQ_INSERT_TAIL(&ts->ts_blocked, td, td_lockq);
  		mtx_unlock_spin(&td_contested_lock);
  		MPASS(td->td_turnstile != NULL);
  		LIST_INSERT_HEAD(&ts->ts_free, td->td_turnstile, ts_hash);
  		MPASS(owner == ts->ts_owner);
  	}
  	td->td_turnstile = NULL;
  	mtx_unlock_spin(&tc->tc_lock);
  
  	mtx_lock_spin(&sched_lock);
  	/*
  	 * Handle race condition where a thread on another CPU that owns
  	 * lock 'lock' could have woken us in between us dropping the
  	 * turnstile chain lock and acquiring the sched_lock.
  	 */
  	if (td->td_flags & TDF_TSNOBLOCK) {
  		td->td_flags &= ~TDF_TSNOBLOCK;
  		mtx_unlock_spin(&sched_lock);
  		return;
  	}
  		
  #ifdef notyet
  	/*
  	 * If we're borrowing an interrupted thread's VM context, we
  	 * must clean up before going to sleep.
  	 */
  	if (td->td_ithd != NULL) {
  		struct ithd *it = td->td_ithd;
  
  		if (it->it_interrupted) {
  			if (LOCK_LOG_TEST(lock, 0))
  				CTR3(KTR_LOCK, "%s: %p interrupted %p",
  				    __func__, it, it->it_interrupted);
  			intr_thd_fixup(it);
  		}
  	}
  #endif
  
  	/* Save who we are blocked on and switch. */
  	td->td_blocked = ts;
  	td->td_lockname = lock->lo_name;
  	TD_SET_LOCK(td);
  	propagate_priority(td);
  
  	if (LOCK_LOG_TEST(lock, 0))
  		CTR4(KTR_LOCK, "%s: td %p blocked on [%p] %s", __func__, td,
  		    lock, lock->lo_name);
  
  	td->td_proc->p_stats->p_ru.ru_nvcsw++;
  	mi_switch();
  
  	if (LOCK_LOG_TEST(lock, 0))
  		CTR4(KTR_LOCK, "%s: td %p free from blocked on [%p] %s",
  		    __func__, td, lock, lock->lo_name);
  
  	mtx_unlock_spin(&sched_lock);
  }
  
  /*
   * Pick the highest priority thread on this turnstile and put it on the
   * pending list.  This must be called with the turnstile chain locked.
   */
  int
  turnstile_signal(struct turnstile *ts)
  {
  	struct turnstile_chain *tc;
  	struct thread *td;
  	int empty;
  
  	MPASS(ts != NULL);
  	MPASS(curthread->td_proc->p_magic == P_MAGIC);
  	MPASS(ts->ts_owner == curthread);
  	tc = TC_LOOKUP(ts->ts_lockobj);
  	mtx_assert(&tc->tc_lock, MA_OWNED);
  
  	/*
  	 * Pick the highest priority thread blocked on this lock and
  	 * move it to the pending list.
  	 */
  	td = TAILQ_FIRST(&ts->ts_blocked);
  	MPASS(td->td_proc->p_magic == P_MAGIC);
  	mtx_lock_spin(&td_contested_lock);
  	TAILQ_REMOVE(&ts->ts_blocked, td, td_lockq);
  	mtx_unlock_spin(&td_contested_lock);
  	TAILQ_INSERT_TAIL(&ts->ts_pending, td, td_lockq);
  
  	/*
  	 * If the turnstile is now empty, remove it from its chain and
  	 * give it to the about-to-be-woken thread.  Otherwise take a
  	 * turnstile from the free list and give it to the thread.
  	 */
  	empty = TAILQ_EMPTY(&ts->ts_blocked);
  	if (empty)
  		MPASS(LIST_EMPTY(&ts->ts_free));
  	else
  		ts = LIST_FIRST(&ts->ts_free);
  	LIST_REMOVE(ts, ts_hash);
  	td->td_turnstile = ts;
  
  	return (empty);
  }
  	
  /*
   * Put all blocked threads on the pending list.  This must be called with
   * the turnstile chain locked.
   */
  void
  turnstile_wakeup(struct turnstile *ts)
  {
  	struct turnstile_chain *tc;
  	struct turnstile *ts1;
  	struct thread *td;
  
  	MPASS(ts != NULL);
  	MPASS(curthread->td_proc->p_magic == P_MAGIC);
  	MPASS(ts->ts_owner == curthread);
  	tc = TC_LOOKUP(ts->ts_lockobj);
  	mtx_assert(&tc->tc_lock, MA_OWNED);
  
  	/*
  	 * Transfer the blocked list to the pending list.
  	 */
  	mtx_lock_spin(&td_contested_lock);
  	TAILQ_CONCAT(&ts->ts_pending, &ts->ts_blocked, td_lockq);
  	mtx_unlock_spin(&td_contested_lock);
  
  	/*
  	 * Give a turnstile to each thread.  The last thread gets
  	 * this turnstile.
  	 */
  	TAILQ_FOREACH(td, &ts->ts_pending, td_lockq) {
  		if (LIST_EMPTY(&ts->ts_free)) {
  			MPASS(TAILQ_NEXT(td, td_lockq) == NULL);
  			ts1 = ts;
  		} else
  			ts1 = LIST_FIRST(&ts->ts_free);
  		LIST_REMOVE(ts1, ts_hash);
  		td->td_turnstile = ts1;
  	}
  }
  
  /*
   * Wakeup all threads on the pending list and adjust the priority of the
   * current thread appropriately.  This must be called with the turnstile
   * chain locked.
   */
  void
  turnstile_unpend(struct turnstile *ts)
  {
  	TAILQ_HEAD( ,thread) pending_threads;
  	struct turnstile_chain *tc;
  	struct thread *td;
  	int cp, pri;
  
  	MPASS(ts != NULL);
  	MPASS(ts->ts_owner == curthread);
  	tc = TC_LOOKUP(ts->ts_lockobj);
  	mtx_assert(&tc->tc_lock, MA_OWNED);
  	MPASS(!TAILQ_EMPTY(&ts->ts_pending));
  
  	/*
  	 * Move the list of pending threads out of the turnstile and
  	 * into a local variable.
  	 */
  	TAILQ_INIT(&pending_threads);
  	TAILQ_CONCAT(&pending_threads, &ts->ts_pending, td_lockq);
  #ifdef INVARIANTS
  	if (TAILQ_EMPTY(&ts->ts_blocked))
  		ts->ts_lockobj = NULL;
  #endif
  
  	/*
  	 * Remove the turnstile from this thread's list of contested locks
  	 * since this thread doesn't own it anymore.  New threads will
  	 * not be blocking on the turnstile until it is claimed by a new
  	 * owner.
  	 */
  	mtx_lock_spin(&td_contested_lock);
  	ts->ts_owner = NULL;
  	LIST_REMOVE(ts, ts_link);
  	mtx_unlock_spin(&td_contested_lock);
  	mtx_unlock_spin(&tc->tc_lock);
  
  	/*
  	 * Adjust the priority of curthread based on other contested
  	 * locks it owns.  Don't lower the priority below the base
  	 * priority however.
  	 */
  	td = curthread;
  	pri = PRI_MAX;
  	mtx_lock_spin(&sched_lock);
  	mtx_lock_spin(&td_contested_lock);
  	LIST_FOREACH(ts, &td->td_contested, ts_link) {
  		cp = TAILQ_FIRST(&ts->ts_blocked)->td_priority;
  		if (cp < pri)
  			pri = cp;
  	}
  	mtx_unlock_spin(&td_contested_lock);
  	if (pri > td->td_base_pri)
  		pri = td->td_base_pri;
  	td->td_priority = pri;
  
  	/*
  	 * Wake up all the pending threads.  If a thread is not blocked
  	 * on a lock, then it is currently executing on another CPU in
  	 * turnstile_wait() or sitting on a run queue waiting to resume
  	 * in turnstile_wait().  Set a flag to force it to try to acquire
  	 * the lock again instead of blocking.
  	 */
  	while (!TAILQ_EMPTY(&pending_threads)) {
  		td = TAILQ_FIRST(&pending_threads);
  		TAILQ_REMOVE(&pending_threads, td, td_lockq);
  		MPASS(td->td_proc->p_magic == P_MAGIC);
  		if (TD_ON_LOCK(td)) {
  			td->td_blocked = NULL;
  			td->td_lockname = NULL;
  			TD_CLR_LOCK(td);
  			MPASS(TD_CAN_RUN(td));
  			setrunqueue(td);
  		} else {
  			td->td_flags |= TDF_TSNOBLOCK;
  			MPASS(TD_IS_RUNNING(td) || TD_ON_RUNQ(td));
  		}
  	}
  	mtx_unlock_spin(&sched_lock);
  }
  
  /*
   * Return the first thread in a turnstile.
   */
  struct thread *
  turnstile_head(struct turnstile *ts)
  {
  #ifdef INVARIANTS
  	struct turnstile_chain *tc;
  
  	MPASS(ts != NULL);
  	tc = TC_LOOKUP(ts->ts_lockobj);
  	mtx_assert(&tc->tc_lock, MA_OWNED);
  #endif
  	return (TAILQ_FIRST(&ts->ts_blocked));
  }
  
  /*
   * Returns true if a turnstile is empty.
   */
  int
  turnstile_empty(struct turnstile *ts)
  {
  #ifdef INVARIANTS
  	struct turnstile_chain *tc;
  
  	MPASS(ts != NULL);
  	tc = TC_LOOKUP(ts->ts_lockobj);
  	mtx_assert(&tc->tc_lock, MA_OWNED);
  #endif
  	return (TAILQ_EMPTY(&ts->ts_blocked));
  }
  