socsvn commit: r238762 - soc2012/rudot/sys/kern

rudot at FreeBSD.org rudot at FreeBSD.org
Mon Jul 2 07:25:20 UTC 2012


Author: rudot
Date: Mon Jul  2 07:25:17 2012
New Revision: 238762
URL: http://svnweb.FreeBSD.org/socsvn/?view=rev&rev=238762

Log:
  initial version of subr_turnstile.c file

Added:
  soc2012/rudot/sys/kern/subr_turnstile.c

Added: soc2012/rudot/sys/kern/subr_turnstile.c
==============================================================================
--- /dev/null	00:00:00 1970	(empty, because file is newly added)
+++ soc2012/rudot/sys/kern/subr_turnstile.c	Mon Jul  2 07:25:17 2012	(r238762)
@@ -0,0 +1,1309 @@
+/*-
+ * Copyright (c) 1998 Berkeley Software Design, Inc. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Berkeley Software Design Inc's name may not be used to endorse or
+ *    promote products derived from this software without specific prior
+ *    written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY BERKELEY SOFTWARE DESIGN INC ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL BERKELEY SOFTWARE DESIGN INC BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ *
+ *	from BSDI $Id: mutex_witness.c,v 1.1.2.20 2000/04/27 03:10:27 cp Exp $
+ *	and BSDI $Id: synch_machdep.c,v 2.3.2.39 2000/04/27 03:10:25 cp Exp $
+ */
+
+/*
+ * Implementation of 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 allocated from a UMA zone
+ * 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.
+ */
+
+#include <sys/cdefs.h>
+__FBSDID("$FreeBSD: src/sys/kern/subr_turnstile.c,v 1.183 2012/05/15 01:30:25 rstone Exp $");
+
+#include "opt_ddb.h"
+#include "opt_kdtrace.h"
+#include "opt_turnstile_profiling.h"
+#include "opt_sched.h"
+
+#include <sys/param.h>
+#include <sys/systm.h>
+#include <sys/kdb.h>
+#include <sys/kernel.h>
+#include <sys/ktr.h>
+#include <sys/lock.h>
+#include <sys/mutex.h>
+#include <sys/proc.h>
+#include <sys/queue.h>
+#include <sys/sched.h>
+#include <sys/sdt.h>
+#include <sys/sysctl.h>
+#include <sys/turnstile.h>
+
+#include <vm/uma.h>
+
+#ifdef DDB
+#include <ddb/ddb.h>
+#include <sys/lockmgr.h>
+#include <sys/sx.h>
+#endif
+
+/*
+ * 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 the 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 of a turnstile that is attached to a lock.
+ *
+ * Each turnstile contains three lists of threads.  The two ts_blocked lists
+ * are linked list of threads blocked on the turnstile's lock.  One list is
+ * for exclusive waiters, and the other is for shared waiters.  The
+ * ts_pending list is a linked list of threads previously awakened 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 {
+	struct mtx ts_lock;			/* Spin lock for self. */
+	struct threadqueue ts_blocked[2];	/* (c + q) Blocked threads. */
+	struct threadqueue 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. */
+#ifdef TURNSTILE_PROFILING
+	u_int	tc_depth;			/* Length of tc_queues. */
+	u_int	tc_max_depth;			/* Max length of tc_queues. */
+#endif
+};
+
+#ifdef TURNSTILE_PROFILING
+u_int turnstile_max_depth;
+static SYSCTL_NODE(_debug, OID_AUTO, turnstile, CTLFLAG_RD, 0,
+    "turnstile profiling");
+static SYSCTL_NODE(_debug_turnstile, OID_AUTO, chains, CTLFLAG_RD, 0,
+    "turnstile chain stats");
+SYSCTL_UINT(_debug_turnstile, OID_AUTO, max_depth, CTLFLAG_RD,
+    &turnstile_max_depth, 0, "maximum depth achieved of a single chain");
+#endif
+static struct mtx td_contested_lock;
+static struct turnstile_chain turnstile_chains[TC_TABLESIZE];
+static uma_zone_t turnstile_zone;
+
+/*
+ * Prototypes for non-exported routines.
+ */
+static void	init_turnstile0(void *dummy);
+#ifdef TURNSTILE_PROFILING
+static void	init_turnstile_profiling(void *arg);
+#endif
+static void	propagate_priority(struct thread *td);
+static int	turnstile_adjust_thread(struct turnstile *ts,
+		    struct thread *td);
+static struct thread *turnstile_first_waiter(struct turnstile *ts);
+static void	turnstile_setowner(struct turnstile *ts, struct thread *owner);
+#ifdef INVARIANTS
+static void	turnstile_dtor(void *mem, int size, void *arg);
+#endif
+static int	turnstile_init(void *mem, int size, int flags);
+static void	turnstile_fini(void *mem, int size);
+
+SDT_PROVIDER_DECLARE(sched);
+SDT_PROBE_DEFINE(sched, , , sleep, sleep);
+SDT_PROBE_DEFINE2(sched, , , wakeup, wakeup, "struct thread *", 
+    "struct proc *");
+
+/*
+ * 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 *ts;
+	int pri;
+
+	THREAD_LOCK_ASSERT(td, MA_OWNED);
+	pri = td->td_priority;
+	ts = td->td_blocked;
+	THREAD_LOCKPTR_ASSERT(td, &ts->ts_lock);
+	/*
+	 * Grab a recursive lock on this turnstile chain so it stays locked
+	 * for the whole operation.  The caller expects us to return with
+	 * the original lock held.  We only ever lock down the chain so
+	 * the lock order is constant.
+	 */
+	mtx_lock_spin(&ts->ts_lock);
+	for (;;) {
+		td = ts->ts_owner;
+
+		if (td == NULL) {
+			/*
+			 * This might be a read lock with no owner.  There's
+			 * not much we can do, so just bail.
+			 */
+			mtx_unlock_spin(&ts->ts_lock);
+			return;
+		}
+
+		thread_lock_flags(td, MTX_DUPOK);
+		mtx_unlock_spin(&ts->ts_lock);
+		MPASS(td->td_proc != NULL);
+		MPASS(td->td_proc->p_magic == P_MAGIC);
+
+		/*
+		 * If the thread is asleep, then we are probably about
+		 * to deadlock.  To make debugging this easier, just
+		 * panic and tell the user which thread misbehaved so
+		 * they can hopefully get a stack trace from the truly
+		 * misbehaving thread.
+		 */
+		if (TD_IS_SLEEPING(td)) {
+			printf(
+		"Sleeping thread (tid %d, pid %d) owns a non-sleepable lock\n",
+			    td->td_tid, td->td_proc->p_pid);
+			kdb_backtrace_thread(td);
+			panic("sleeping thread");
+		}
+
+		/*
+		 * If this thread already has higher priority than the
+		 * thread that is being blocked, we are finished.
+		 */
+		if (td->td_priority <= pri) {
+			thread_unlock(td);
+			return;
+		}
+
+		/*
+		 * Bump this thread's priority.
+		 */
+		sched_lend_prio(td, pri);
+
+		/*
+		 * If lock holder is actually running or on the run queue
+		 * then we are done.
+		 */
+		if (TD_IS_RUNNING(td) || TD_ON_RUNQ(td)) {
+			MPASS(td->td_blocked == NULL);
+			thread_unlock(td);
+			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 we aren't blocked on a lock, we should be.
+		 */
+		KASSERT(TD_ON_LOCK(td), (
+		    "thread %d(%s):%d holds %s but isn't blocked on a lock\n",
+		    td->td_tid, td->td_name, td->td_state,
+		    ts->ts_lockobj->lo_name));
+
+		/*
+		 * Pick up the lock that td is blocked on.
+		 */
+		ts = td->td_blocked;
+		MPASS(ts != NULL);
+		THREAD_LOCKPTR_ASSERT(td, &ts->ts_lock);
+		/* Resort td on the list if needed. */
+		if (!turnstile_adjust_thread(ts, td)) {
+			mtx_unlock_spin(&ts->ts_lock);
+			return;
+		}
+		/* The thread lock is released as ts lock above. */
+	}
+}
+
+/*
+ * Adjust the thread's position on a turnstile after its priority has been
+ * changed.
+ */
+static int
+turnstile_adjust_thread(struct turnstile *ts, struct thread *td)
+{
+	struct thread *td1, *td2;
+	int queue;
+
+	THREAD_LOCK_ASSERT(td, MA_OWNED);
+	MPASS(TD_ON_LOCK(td));
+
+	/*
+	 * This thread may not be blocked on this turnstile anymore
+	 * but instead might already be woken up on another CPU
+	 * that is waiting on the thread 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_broadcast().  In this case, treat the thread as
+	 * if it was already running.
+	 */
+	if (td->td_turnstile != NULL)
+		return (0);
+
+	/*
+	 * Check if the thread needs to be moved on the blocked chain.
+	 * It needs to be moved if either its priority is lower than
+	 * the previous thread or higher than the next thread.
+	 */
+	THREAD_LOCKPTR_ASSERT(td, &ts->ts_lock);
+	td1 = TAILQ_PREV(td, threadqueue, td_lockq);
+	td2 = TAILQ_NEXT(td, td_lockq);
+	if ((td1 != NULL && td->td_priority < td1->td_priority) ||
+	    (td2 != NULL && td->td_priority > td2->td_priority)) {
+
+		/*
+		 * Remove thread from blocked chain and determine where
+		 * it should be moved to.
+		 */
+		queue = td->td_tsqueue;
+		MPASS(queue == TS_EXCLUSIVE_QUEUE || queue == TS_SHARED_QUEUE);
+		mtx_lock_spin(&td_contested_lock);
+		TAILQ_REMOVE(&ts->ts_blocked[queue], td, td_lockq);
+		TAILQ_FOREACH(td1, &ts->ts_blocked[queue], td_lockq) {
+			MPASS(td1->td_proc->p_magic == P_MAGIC);
+			if (td1->td_priority > td->td_priority)
+				break;
+		}
+
+		if (td1 == NULL)
+			TAILQ_INSERT_TAIL(&ts->ts_blocked[queue], td, td_lockq);
+		else
+			TAILQ_INSERT_BEFORE(td1, td, td_lockq);
+		mtx_unlock_spin(&td_contested_lock);
+		if (td1 == NULL)
+			CTR3(KTR_LOCK,
+		    "turnstile_adjust_thread: td %d put at tail on [%p] %s",
+			    td->td_tid, ts->ts_lockobj, ts->ts_lockobj->lo_name);
+		else
+			CTR4(KTR_LOCK,
+		    "turnstile_adjust_thread: td %d moved before %d on [%p] %s",
+			    td->td_tid, td1->td_tid, ts->ts_lockobj,
+			    ts->ts_lockobj->lo_name);
+	}
+	return (1);
+}
+
+/*
+ * 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);
+	LIST_INIT(&thread0.td_contested);
+	thread0.td_turnstile = NULL;
+}
+
+#ifdef TURNSTILE_PROFILING
+static void
+init_turnstile_profiling(void *arg)
+{
+	struct sysctl_oid *chain_oid;
+	char chain_name[10];
+	int i;
+
+	for (i = 0; i < TC_TABLESIZE; i++) {
+		snprintf(chain_name, sizeof(chain_name), "%d", i);
+		chain_oid = SYSCTL_ADD_NODE(NULL, 
+		    SYSCTL_STATIC_CHILDREN(_debug_turnstile_chains), OID_AUTO,
+		    chain_name, CTLFLAG_RD, NULL, "turnstile chain stats");
+		SYSCTL_ADD_UINT(NULL, SYSCTL_CHILDREN(chain_oid), OID_AUTO,
+		    "depth", CTLFLAG_RD, &turnstile_chains[i].tc_depth, 0,
+		    NULL);
+		SYSCTL_ADD_UINT(NULL, SYSCTL_CHILDREN(chain_oid), OID_AUTO,
+		    "max_depth", CTLFLAG_RD, &turnstile_chains[i].tc_max_depth,
+		    0, NULL);
+	}
+}
+SYSINIT(turnstile_profiling, SI_SUB_LOCK, SI_ORDER_ANY,
+    init_turnstile_profiling, NULL);
+#endif
+
+static void
+init_turnstile0(void *dummy)
+{
+
+	turnstile_zone = uma_zcreate("TURNSTILE", sizeof(struct turnstile),
+	    NULL,
+#ifdef INVARIANTS
+	    turnstile_dtor,
+#else
+	    NULL,
+#endif
+	    turnstile_init, turnstile_fini, UMA_ALIGN_CACHE, UMA_ZONE_NOFREE);
+	thread0.td_turnstile = turnstile_alloc();
+}
+SYSINIT(turnstile0, SI_SUB_LOCK, SI_ORDER_ANY, init_turnstile0, NULL);
+
+/*
+ * Update a thread on the turnstile list after it's priority has been changed.
+ * The old priority is passed in as an argument.
+ */
+void
+turnstile_adjust(struct thread *td, u_char oldpri)
+{
+	struct turnstile *ts;
+
+	MPASS(TD_ON_LOCK(td));
+
+	/*
+	 * Pick up the lock that td is blocked on.
+	 */
+	ts = td->td_blocked;
+	MPASS(ts != NULL);
+	THREAD_LOCKPTR_ASSERT(td, &ts->ts_lock);
+	mtx_assert(&ts->ts_lock, MA_OWNED);
+
+	/* Resort the turnstile on the list. */
+	if (!turnstile_adjust_thread(ts, td))
+		return;
+	/*
+	 * If our priority was lowered and we are at the head of the
+	 * turnstile, then propagate our new priority up the chain.
+	 * Note that we currently don't try to revoke lent priorities
+	 * when our priority goes up.
+	 */
+	MPASS(td->td_tsqueue == TS_EXCLUSIVE_QUEUE ||
+	    td->td_tsqueue == TS_SHARED_QUEUE);
+	if (td == TAILQ_FIRST(&ts->ts_blocked[td->td_tsqueue]) &&
+	    td->td_priority < oldpri) {
+		propagate_priority(td);
+	}
+}
+
+/*
+ * 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(ts->ts_owner == NULL);
+
+	/* A shared lock might not have an owner. */
+	if (owner == NULL)
+		return;
+
+	MPASS(owner->td_proc->p_magic == P_MAGIC);
+	ts->ts_owner = owner;
+	LIST_INSERT_HEAD(&owner->td_contested, ts, ts_link);
+}
+
+#ifdef INVARIANTS
+/*
+ * UMA zone item deallocator.
+ */
+static void
+turnstile_dtor(void *mem, int size, void *arg)
+{
+	struct turnstile *ts;
+
+	ts = mem;
+	MPASS(TAILQ_EMPTY(&ts->ts_blocked[TS_EXCLUSIVE_QUEUE]));
+	MPASS(TAILQ_EMPTY(&ts->ts_blocked[TS_SHARED_QUEUE]));
+	MPASS(TAILQ_EMPTY(&ts->ts_pending));
+}
+#endif
+
+/*
+ * UMA zone item initializer.
+ */
+static int
+turnstile_init(void *mem, int size, int flags)
+{
+	struct turnstile *ts;
+
+	bzero(mem, size);
+	ts = mem;
+	TAILQ_INIT(&ts->ts_blocked[TS_EXCLUSIVE_QUEUE]);
+	TAILQ_INIT(&ts->ts_blocked[TS_SHARED_QUEUE]);
+	TAILQ_INIT(&ts->ts_pending);
+	LIST_INIT(&ts->ts_free);
+	mtx_init(&ts->ts_lock, "turnstile lock", NULL, MTX_SPIN | MTX_RECURSE);
+	return (0);
+}
+
+static void
+turnstile_fini(void *mem, int size)
+{
+	struct turnstile *ts;
+
+	ts = mem;
+	mtx_destroy(&ts->ts_lock);
+}
+
+/*
+ * Get a turnstile for a new thread.
+ */
+struct turnstile *
+turnstile_alloc(void)
+{
+
+	return (uma_zalloc(turnstile_zone, M_WAITOK));
+}
+
+/*
+ * Free a turnstile when a thread is destroyed.
+ */
+void
+turnstile_free(struct turnstile *ts)
+{
+
+	uma_zfree(turnstile_zone, ts);
+}
+
+/*
+ * Lock the turnstile chain associated with the specified lock.
+ */
+void
+turnstile_chain_lock(struct lock_object *lock)
+{
+	struct turnstile_chain *tc;
+
+	tc = TC_LOOKUP(lock);
+	mtx_lock_spin(&tc->tc_lock);
+}
+
+struct turnstile *
+turnstile_trywait(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) {
+			mtx_lock_spin(&ts->ts_lock);
+			return (ts);
+		}
+
+	ts = curthread->td_turnstile;
+	MPASS(ts != NULL);
+	mtx_lock_spin(&ts->ts_lock);
+	KASSERT(ts->ts_lockobj == NULL, ("stale ts_lockobj pointer"));
+	ts->ts_lockobj = lock;
+
+	return (ts);
+}
+
+void
+turnstile_cancel(struct turnstile *ts)
+{
+	struct turnstile_chain *tc;
+	struct lock_object *lock;
+
+	mtx_assert(&ts->ts_lock, MA_OWNED);
+
+	mtx_unlock_spin(&ts->ts_lock);
+	lock = ts->ts_lockobj;
+	if (ts == curthread->td_turnstile)
+		ts->ts_lockobj = NULL;
+	tc = TC_LOOKUP(lock);
+	mtx_unlock_spin(&tc->tc_lock);
+}
+
+/*
+ * Look up the turnstile for a lock in the hash table locking the associated
+ * turnstile chain along the way.  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_assert(&tc->tc_lock, MA_OWNED);
+	LIST_FOREACH(ts, &tc->tc_turnstiles, ts_hash)
+		if (ts->ts_lockobj == lock) {
+			mtx_lock_spin(&ts->ts_lock);
+			return (ts);
+		}
+	return (NULL);
+}
+
+/*
+ * Unlock the turnstile chain associated with a given lock.
+ */
+void
+turnstile_chain_unlock(struct lock_object *lock)
+{
+	struct turnstile_chain *tc;
+
+	tc = TC_LOOKUP(lock);
+	mtx_unlock_spin(&tc->tc_lock);
+}
+
+/*
+ * Return a pointer to the thread waiting on this turnstile with the
+ * most important priority or NULL if the turnstile has no waiters.
+ */
+static struct thread *
+turnstile_first_waiter(struct turnstile *ts)
+{
+	struct thread *std, *xtd;
+
+	std = TAILQ_FIRST(&ts->ts_blocked[TS_SHARED_QUEUE]);
+	xtd = TAILQ_FIRST(&ts->ts_blocked[TS_EXCLUSIVE_QUEUE]);
+	if (xtd == NULL || (std != NULL && std->td_priority < xtd->td_priority))
+		return (std);
+	return (xtd);
+}
+
+/*
+ * Take ownership of a turnstile and adjust the priority of the new
+ * owner appropriately.
+ */
+void
+turnstile_claim(struct turnstile *ts)
+{
+	struct thread *td, *owner;
+	struct turnstile_chain *tc;
+
+	mtx_assert(&ts->ts_lock, MA_OWNED);
+	MPASS(ts != curthread->td_turnstile);
+
+	owner = curthread;
+	mtx_lock_spin(&td_contested_lock);
+	turnstile_setowner(ts, owner);
+	mtx_unlock_spin(&td_contested_lock);
+
+	td = turnstile_first_waiter(ts);
+	MPASS(td != NULL);
+	MPASS(td->td_proc->p_magic == P_MAGIC);
+	THREAD_LOCKPTR_ASSERT(td, &ts->ts_lock);
+
+	/*
+	 * Update the priority of the new owner if needed.
+	 */
+	thread_lock(owner);
+	if (td->td_priority < owner->td_priority)
+		sched_lend_prio(owner, td->td_priority);
+	thread_unlock(owner);
+	tc = TC_LOOKUP(ts->ts_lockobj);
+	mtx_unlock_spin(&ts->ts_lock);
+	mtx_unlock_spin(&tc->tc_lock);
+}
+
+/*
+ * Block the current thread on the turnstile assicated with 'lock'.  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 thread *owner, int queue)
+{
+	struct turnstile_chain *tc;
+	struct thread *td, *td1;
+	struct lock_object *lock;
+
+	td = curthread;
+	mtx_assert(&ts->ts_lock, MA_OWNED);
+	if (owner)
+		MPASS(owner->td_proc->p_magic == P_MAGIC);
+	MPASS(queue == TS_SHARED_QUEUE || queue == TS_EXCLUSIVE_QUEUE);
+
+	/*
+	 * If the lock does not already have a turnstile, use this thread's
+	 * turnstile.  Otherwise insert the current thread into the
+	 * turnstile already in use by this lock.
+	 */
+	tc = TC_LOOKUP(ts->ts_lockobj);
+	mtx_assert(&tc->tc_lock, MA_OWNED);
+	if (ts == td->td_turnstile) {
+#ifdef TURNSTILE_PROFILING
+		tc->tc_depth++;
+		if (tc->tc_depth > tc->tc_max_depth) {
+			tc->tc_max_depth = tc->tc_depth;
+			if (tc->tc_max_depth > turnstile_max_depth)
+				turnstile_max_depth = tc->tc_max_depth;
+		}
+#endif
+		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[TS_EXCLUSIVE_QUEUE]),
+		    ("thread's turnstile has exclusive waiters"));
+		KASSERT(TAILQ_EMPTY(&ts->ts_blocked[TS_SHARED_QUEUE]),
+		    ("thread's turnstile has shared waiters"));
+		KASSERT(LIST_EMPTY(&ts->ts_free),
+		    ("thread's turnstile has a non-empty free list"));
+		MPASS(ts->ts_lockobj != NULL);
+		mtx_lock_spin(&td_contested_lock);
+		TAILQ_INSERT_TAIL(&ts->ts_blocked[queue], td, td_lockq);
+		turnstile_setowner(ts, owner);
+		mtx_unlock_spin(&td_contested_lock);
+	} else {
+		TAILQ_FOREACH(td1, &ts->ts_blocked[queue], 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[queue], td, td_lockq);
+		MPASS(owner == ts->ts_owner);
+		mtx_unlock_spin(&td_contested_lock);
+		MPASS(td->td_turnstile != NULL);
+		LIST_INSERT_HEAD(&ts->ts_free, td->td_turnstile, ts_hash);
+	}
+	thread_lock(td);
+	thread_lock_set(td, &ts->ts_lock);
+	td->td_turnstile = NULL;
+
+	/* Save who we are blocked on and switch. */
+	lock = ts->ts_lockobj;
+	td->td_tsqueue = queue;
+	td->td_blocked = ts;
+	td->td_lockname = lock->lo_name;
+	td->td_blktick = ticks;
+	TD_SET_LOCK(td);
+	mtx_unlock_spin(&tc->tc_lock);
+	propagate_priority(td);
+
+	if (LOCK_LOG_TEST(lock, 0))
+		CTR4(KTR_LOCK, "%s: td %d blocked on [%p] %s", __func__,
+		    td->td_tid, lock, lock->lo_name);
+
+	SDT_PROBE0(sched, , , sleep);
+
+	THREAD_LOCKPTR_ASSERT(td, &ts->ts_lock);
+	mi_switch(SW_VOL | SWT_TURNSTILE, NULL);
+
+	if (LOCK_LOG_TEST(lock, 0))
+		CTR4(KTR_LOCK, "%s: td %d free from blocked on [%p] %s",
+		    __func__, td->td_tid, lock, lock->lo_name);
+	thread_unlock(td);
+}
+
+/*
+ * 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, int queue)
+{
+	struct turnstile_chain *tc;
+	struct thread *td;
+	int empty;
+
+	MPASS(ts != NULL);
+	mtx_assert(&ts->ts_lock, MA_OWNED);
+	MPASS(curthread->td_proc->p_magic == P_MAGIC);
+	MPASS(ts->ts_owner == curthread || ts->ts_owner == NULL);
+	MPASS(queue == TS_SHARED_QUEUE || queue == TS_EXCLUSIVE_QUEUE);
+
+	/*
+	 * Pick the highest priority thread blocked on this lock and
+	 * move it to the pending list.
+	 */
+	td = TAILQ_FIRST(&ts->ts_blocked[queue]);
+	MPASS(td->td_proc->p_magic == P_MAGIC);
+	mtx_lock_spin(&td_contested_lock);
+	TAILQ_REMOVE(&ts->ts_blocked[queue], 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[TS_EXCLUSIVE_QUEUE]) &&
+	    TAILQ_EMPTY(&ts->ts_blocked[TS_SHARED_QUEUE]);
+	if (empty) {
+		tc = TC_LOOKUP(ts->ts_lockobj);
+		mtx_assert(&tc->tc_lock, MA_OWNED);
+		MPASS(LIST_EMPTY(&ts->ts_free));
+#ifdef TURNSTILE_PROFILING
+		tc->tc_depth--;
+#endif
+	} else
+		ts = LIST_FIRST(&ts->ts_free);
+	MPASS(ts != NULL);
+	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_broadcast(struct turnstile *ts, int queue)
+{
+	struct turnstile_chain *tc;
+	struct turnstile *ts1;
+	struct thread *td;
+
+	MPASS(ts != NULL);
+	mtx_assert(&ts->ts_lock, MA_OWNED);
+	MPASS(curthread->td_proc->p_magic == P_MAGIC);
+	MPASS(ts->ts_owner == curthread || ts->ts_owner == NULL);
+	/*
+	 * We must have the chain locked so that we can remove the empty
+	 * turnstile from the hash queue.
+	 */
+	tc = TC_LOOKUP(ts->ts_lockobj);
+	mtx_assert(&tc->tc_lock, MA_OWNED);
+	MPASS(queue == TS_SHARED_QUEUE || queue == TS_EXCLUSIVE_QUEUE);
+
+	/*
+	 * Transfer the blocked list to the pending list.
+	 */
+	mtx_lock_spin(&td_contested_lock);
+	TAILQ_CONCAT(&ts->ts_pending, &ts->ts_blocked[queue], td_lockq);
+	mtx_unlock_spin(&td_contested_lock);
+
+	/*
+	 * Give a turnstile to each thread.  The last thread gets
+	 * this turnstile if the turnstile is empty.
+	 */
+	TAILQ_FOREACH(td, &ts->ts_pending, td_lockq) {
+		if (LIST_EMPTY(&ts->ts_free)) {
+			MPASS(TAILQ_NEXT(td, td_lockq) == NULL);
+			ts1 = ts;
+#ifdef TURNSTILE_PROFILING
+			tc->tc_depth--;
+#endif
+		} else
+			ts1 = LIST_FIRST(&ts->ts_free);
+		MPASS(ts1 != NULL);
+		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, int owner_type)
+{
+	TAILQ_HEAD( ,thread) pending_threads;
+	struct turnstile *nts;
+	struct thread *td;
+	u_char cp, pri;
+
+	MPASS(ts != NULL);
+	mtx_assert(&ts->ts_lock, MA_OWNED);
+	MPASS(ts->ts_owner == curthread || ts->ts_owner == NULL);
+	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_EXCLUSIVE_QUEUE]) &&
+	    TAILQ_EMPTY(&ts->ts_blocked[TS_SHARED_QUEUE]))
+		ts->ts_lockobj = NULL;
+#endif
+	/*
+	 * 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;
+	thread_lock(td);
+	mtx_lock_spin(&td_contested_lock);
+	/*
+	 * 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.  There might not be a current owner if this is a shared
+	 * lock.
+	 */
+	if (ts->ts_owner != NULL) {
+		ts->ts_owner = NULL;
+		LIST_REMOVE(ts, ts_link);
+	}
+	LIST_FOREACH(nts, &td->td_contested, ts_link) {
+		cp = turnstile_first_waiter(nts)->td_priority;
+		if (cp < pri)
+			pri = cp;
+	}
+	mtx_unlock_spin(&td_contested_lock);
+	sched_unlend_prio(td, pri);
+	thread_unlock(td);
+	/*
+	 * 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);
+		SDT_PROBE2(sched, , , wakeup, td, td->td_proc);
+		thread_lock(td);
+		THREAD_LOCKPTR_ASSERT(td, &ts->ts_lock);
+		MPASS(td->td_proc->p_magic == P_MAGIC);
+		MPASS(TD_ON_LOCK(td));
+		TD_CLR_LOCK(td);
+		MPASS(TD_CAN_RUN(td));
+		td->td_blocked = NULL;
+		td->td_lockname = NULL;
+		td->td_blktick = 0;
+#ifdef INVARIANTS
+		td->td_tsqueue = 0xff;
+#endif
+		sched_add(td, SRQ_BORING);
+		thread_unlock(td);
+	}
+	mtx_unlock_spin(&ts->ts_lock);
+}
+
+/*
+ * Give up ownership of a turnstile.  This must be called with the
+ * turnstile chain locked.
+ */
+void
+turnstile_disown(struct turnstile *ts)
+{
+	struct thread *td;
+	u_char cp, pri;
+
+	MPASS(ts != NULL);
+	mtx_assert(&ts->ts_lock, MA_OWNED);
+	MPASS(ts->ts_owner == curthread);
+	MPASS(TAILQ_EMPTY(&ts->ts_pending));
+	MPASS(!TAILQ_EMPTY(&ts->ts_blocked[TS_EXCLUSIVE_QUEUE]) ||
+	    !TAILQ_EMPTY(&ts->ts_blocked[TS_SHARED_QUEUE]));
+
+	/*
+	 * 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);
+
+	/*
+	 * 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;
+	thread_lock(td);
+	mtx_unlock_spin(&ts->ts_lock);
+	mtx_lock_spin(&td_contested_lock);
+	LIST_FOREACH(ts, &td->td_contested, ts_link) {
+		cp = turnstile_first_waiter(ts)->td_priority;
+		if (cp < pri)
+			pri = cp;
+	}
+	mtx_unlock_spin(&td_contested_lock);
+	sched_unlend_prio(td, pri);
+	thread_unlock(td);
+}
+
+/*
+ * Return the first thread in a turnstile.
+ */

*** DIFF OUTPUT TRUNCATED AT 1000 LINES ***


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