From 51fad3232fc89f871b02615ff093e52fac00b3ae Mon Sep 17 00:00:00 2001
From: niklas <niklas@openbsd.org>
Date: Tue, 24 Dec 1996 20:14:28 +0000
Subject: [PATCH] Make termination of objects wait for possible collapses
 before altering the object's shadow linkage.  Also note that the object is
 going to die so that a possible collapse can finish early.

---
 sys/vm/vm_object.c | 37 ++++++++++++++++++++++++++++---------
 sys/vm/vm_object.h |  3 ++-
 2 files changed, 30 insertions(+), 10 deletions(-)

diff --git a/sys/vm/vm_object.c b/sys/vm/vm_object.c
index 0fa0d2e92c4..722d2f583b0 100644
--- a/sys/vm/vm_object.c
+++ b/sys/vm/vm_object.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: vm_object.c,v 1.12 1996/11/06 23:24:40 niklas Exp $	*/
+/*	$OpenBSD: vm_object.c,v 1.13 1996/12/24 20:14:28 niklas Exp $	*/
 /*	$NetBSD: vm_object.c,v 1.34 1996/02/28 22:35:35 gwr Exp $	*/
 
 /* 
@@ -337,6 +337,21 @@ vm_object_terminate(object)
 	register vm_page_t	p;
 	vm_object_t		shadow_object;
 
+	/*
+	 * Setters of paging_in_progress might be interested that this object
+	 * is going away as soon as we get a grip on it.
+	 */
+	object->flags |= OBJ_FADING;
+
+	/*
+	 * Wait until the pageout daemon is through with the object or a
+	 * potential collapse operation is finished.
+	 */
+	while (object->paging_in_progress) {
+		vm_object_sleep(object, object, FALSE);
+		vm_object_lock(object);
+	}
+
 	/*
 	 *	Detach the object from its shadow if we are the shadow's
 	 *	copy.
@@ -353,14 +368,6 @@ vm_object_terminate(object)
 		vm_object_unlock(shadow_object);
 	}
 
-	/*
-	 * Wait until the pageout daemon is through with the object.
-	 */
-	while (object->paging_in_progress) {
-		vm_object_sleep(object, object, FALSE);
-		vm_object_lock(object);
-	}
-
 	/*
 	 * If not an internal object clean all the pages, removing them
 	 * from paging queues as we go.
@@ -1340,6 +1347,18 @@ vm_object_collapse_aux(object)
 				thread_wakeup(backing_object);
 				thread_wakeup(object);
 
+				/*
+				 *	During the pagein vm_object_terminate
+				 *	might have slept on our front object in
+				 *	order to remove it.  If this is the
+				 *	case, we might as well stop all the
+				 *	collapse work right here.
+				 */
+				if (object->flags & OBJ_FADING) {
+					PAGE_WAKEUP(backing_page);
+					return KERN_FAILURE;
+				}
+
 				/*
 				 *	Third, relookup in case pager changed
 				 *	page.  Pager is responsible for
diff --git a/sys/vm/vm_object.h b/sys/vm/vm_object.h
index 46a7939ac68..be739e1fb11 100644
--- a/sys/vm/vm_object.h
+++ b/sys/vm/vm_object.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: vm_object.h,v 1.3 1996/08/02 00:06:02 niklas Exp $	*/
+/*	$OpenBSD: vm_object.h,v 1.4 1996/12/24 20:14:32 niklas Exp $	*/
 /*	$NetBSD: vm_object.h,v 1.16 1995/03/29 22:10:28 briggs Exp $	*/
 
 /* 
@@ -110,6 +110,7 @@ struct vm_object {
 #define OBJ_CANPERSIST	0x0001	/* allow to persist */
 #define OBJ_INTERNAL	0x0002	/* internally created object */
 #define OBJ_ACTIVE	0x0004	/* used to mark active objects */
+#define OBJ_FADING	0x0008	/* tell others that the object is going away */
 
 TAILQ_HEAD(vm_object_hash_head, vm_object_hash_entry);
 
-- 
2.20.1