From 010cf3b9e3f74791c3d1c892f7735cf49a15da6c Mon Sep 17 00:00:00 2001
From: David Greenman <dg@FreeBSD.org>
Date: Thu, 5 Jan 1995 04:30:40 +0000
Subject: [PATCH] Make sure that the object being collapsed doesn't go away on
 us...by gaining extra references to it.

Submitted by:	John Dyson
Obtained from:
---
 sys/vm/vm_object.c | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/sys/vm/vm_object.c b/sys/vm/vm_object.c
index 3d084cc5cfa..f529ad20d0b 100644
--- a/sys/vm/vm_object.c
+++ b/sys/vm/vm_object.c
@@ -61,7 +61,7 @@
  * any improvements or extensions that they make and grant Carnegie the
  * rights to redistribute these changes.
  *
- * $Id: vm_object.c,v 1.12 1994/12/11 01:36:53 davidg Exp $
+ * $Id: vm_object.c,v 1.13 1994/12/23 05:00:19 davidg Exp $
  */
 
 /*
@@ -251,8 +251,13 @@ vm_object_deallocate(object)
 		 */
 		vm_object_lock(object);
 		if (--(object->ref_count) != 0) {
-			if( object->ref_count == 1)
-				vm_object_rcollapse(object->reverse_shadow_head.tqh_first, object);
+			if( object->ref_count == 1) {
+				if( object->reverse_shadow_head.tqh_first) {
+					++object->reverse_shadow_head.tqh_first->ref_count;
+					vm_object_rcollapse(object->reverse_shadow_head.tqh_first, object);
+					vm_object_deallocate(object->reverse_shadow_head.tqh_first);
+				}
+			}
 
 			vm_object_unlock(object);
 			/*
@@ -1162,6 +1167,7 @@ vm_object_rcollapse(object, sobject)
 	if (backing_object->ref_count != 1)
 		return;
 
+	backing_object->ref_count += 2;
 	s = splbio();
 	while( backing_object->paging_in_progress) {
 		tsleep( backing_object, PVM, "rcolow", 0);
@@ -1201,6 +1207,7 @@ vm_object_rcollapse(object, sobject)
 		}
 		p = next;
 	}
+	backing_object->ref_count -= 2;
 }
 
 /*
@@ -1228,6 +1235,8 @@ vm_object_qcollapse(object)
 	if (backing_object->ref_count != 1)
 		return;
 
+	backing_object->ref_count += 2;
+
 	backing_offset = object->shadow_offset;
 	size = object->size;
 	p = backing_object->memq.tqh_first;
@@ -1266,6 +1275,7 @@ vm_object_qcollapse(object)
 		}
 		p = next;
 	}
+	backing_object->ref_count -= 2;
 }
 
 boolean_t	vm_object_collapse_allowed = TRUE;