Index: conf/files
===================================================================
--- conf/files	(revision 256184)
+++ conf/files	(working copy)
@@ -2829,6 +2829,7 @@ kern/kern_sema.c		standard
 kern/kern_sharedpage.c		standard
 kern/kern_shutdown.c		standard
 kern/kern_sig.c			standard
+kern/kern_spinqueue.c		standard
 kern/kern_switch.c		standard
 kern/kern_sx.c			standard
 kern/kern_synch.c		standard
Index: kern/kern_spinqueue.c
===================================================================
--- kern/kern_spinqueue.c	(revision 0)
+++ kern/kern_spinqueue.c	(working copy)
@@ -0,0 +1,122 @@
+/*-
+ * Copyright (c) 2013 Davide Italiano <davide@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 unmodified, this list of conditions, and the following
+ *    disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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 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.
+ */
+
+#include <sys/param.h>
+#include <sys/systm.h>
+#include <sys/spinqueue.h>
+#include <sys/proc.h>
+#include <sys/types.h>
+#include <sys/lock.h>
+
+#include <machine/atomic.h>
+#include <machine/cpu.h>
+
+/*
+ * TODO: inline fast path for acquisition.
+ */
+
+void
+spinqueue_init(struct spinqueue *spq)
+{
+
+	/* Initialize spinqueue */
+	spq = NULL;
+}
+
+void
+spinqueue_lock(struct spinqueue **spq, struct spinqueue *me)
+{
+	struct spinqueue *tail;
+	int spincycles;
+
+	if ((*spq)->lock_owner == curthread) {
+		(*spq)->spinqueue_recurse++;
+		return;
+	}
+	me->next = NULL;
+	me->spin = 0;
+	me->lock_owner = curthread;
+	me->spinqueue_recurse = 0;
+	tail = (struct spinqueue *)atomic_swap_ptr((uintptr_t *)spq,
+	    (uintptr_t)me);
+	if (tail == NULL) {
+		spinlock_enter();
+		return;
+	}
+	tail->next = me;
+	mb();
+	spincycles = 0;
+	while (me->spin == 0) {
+//		if (spincycles++ < 60000000)
+			cpu_spinwait();
+//		else
+//			panic("Cannot lock");
+	}
+	spinlock_enter();
+	return;
+}
+
+int
+spinqueue_trylock(struct spinqueue **spq, struct spinqueue *me)
+{
+
+	me->next = NULL;
+	me->spin = 0;
+	if (atomic_cmpset_acq_ptr((uintptr_t *)spq,
+	    (uintptr_t)0, (uintptr_t)me)) {
+		spinlock_enter();
+		return (0);
+	}
+	else
+		return (EBUSY);
+}
+
+void
+spinqueue_unlock(struct spinqueue **spq, struct spinqueue *me)
+{
+	int spincycles;
+
+	if ((*spq)->spinqueue_recurse > 0) {
+		(*spq)->spinqueue_recurse--;
+		return;
+	}
+	if (me->next == NULL) {
+		if (atomic_cmpset_rel_ptr((uintptr_t *)spq, (uintptr_t)me,
+		    (uintptr_t)0)) {
+			spinlock_exit();
+			return;
+		}
+		spincycles = 0;
+		while (me->next == NULL) {
+//			if (spincycles++ < 60000000)
+				cpu_spinwait();
+//			else
+//				panic("Cannot unlock");
+		}
+	}
+	me->next->spin = 1;
+	spinlock_exit();
+}
Index: sys/spinqueue.h
===================================================================
--- sys/spinqueue.h	(revision 0)
+++ sys/spinqueue.h	(working copy)
@@ -0,0 +1,43 @@
+/*-
+ * Copyright (c) 2013 Davide Italiano <davide@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 unmodified, this list of conditions, and the following
+ *    disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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 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.
+ */
+
+#ifndef _SYS_SPINQUEUE_H_
+#define _SYS_SPINQUEUE_H_
+
+struct spinqueue {
+	/* struct lock_object lock_object */
+	struct spinqueue *next;
+	struct thread *lock_owner;
+	int spin;
+	int spinqueue_recurse;
+};
+
+void	spinqueue_init(struct spinqueue *spq);
+void	spinqueue_lock(struct spinqueue **spq, struct spinqueue *self);
+void	spinqueue_unlock(struct spinqueue **spq, struct spinqueue *self);
+int	spinqueue_trylock(struct spinqueue **spq, struct spinqueue *self);
+
+#endif /* _SYS_SPINQUEUE_H_ */