o Introduce and use vm_map_trylock() to replace several direct uses

of lockmgr().
 o Add missing synchronization to vmspace_swap_count(): Obtain a read lock
   on the vm_map before traversing it.

sys/vm/vm_fault.c

@@ -663,9 +663,7 @@ RetryFault:;
 				/*
 				 * grab the lock if we need to
 				 */
-				(fs.lookup_still_valid ||
-				 lockmgr(&fs.map->lock, LK_EXCLUSIVE|LK_NOWAIT, (void *)0, curthread) == 0)
-			    ) {
+			    (fs.lookup_still_valid || vm_map_trylock(fs.map))) {
 				
 				fs.lookup_still_valid = 1;
 				/*

sys/vm/vm_glue.c

@@ -560,9 +560,7 @@ int action;
 			 * data structures there is a
 			 * possible deadlock.
 			 */
-			if (lockmgr(&vm->vm_map.lock,
-					LK_EXCLUSIVE | LK_NOWAIT,
-					NULL, curthread)) {
+			if (!vm_map_trylock(&vm->vm_map)) {
 				vmspace_free(vm);
 				PROC_UNLOCK(p);
 				goto nextproc;

sys/vm/vm_map.c

@@ -336,6 +336,7 @@ vmspace_swap_count(struct vmspace *vmspace)
 	vm_map_entry_t cur;
 	int count = 0;
 
+	vm_map_lock_read(map);
 	for (cur = map->header.next; cur != &map->header; cur = cur->next) {
 		vm_object_t object;
 
@@ -351,6 +352,7 @@ vmspace_swap_count(struct vmspace *vmspace)
 			}
 		}
 	}
+	vm_map_unlock_read(map);
 	return (count);
 }
 
@@ -397,6 +399,14 @@ vm_map_unlock_read(vm_map_t map)
 	lockmgr(&(map)->lock, LK_RELEASE, NULL, curthread);
 }
 
+int
+vm_map_trylock(vm_map_t map)
+{
+
+	return (lockmgr(&map->lock, LK_EXCLUSIVE | LK_NOWAIT, NULL,
+		    curthread) == 0);
+}
+
 static __inline__ int
 _vm_map_lock_upgrade(vm_map_t map, struct thread *td) {
 	int error;

sys/vm/vm_map.h

@@ -241,6 +241,7 @@ void vm_map_lock(vm_map_t map);
 void vm_map_unlock(vm_map_t map);
 void vm_map_lock_read(vm_map_t map);
 void vm_map_unlock_read(vm_map_t map);
+int vm_map_trylock(vm_map_t map);
 int vm_map_lock_upgrade(vm_map_t map);
 void vm_map_lock_downgrade(vm_map_t map);
 void vm_map_set_recursive(vm_map_t map);

sys/vm/vm_pageout.c

@@ -547,9 +547,8 @@ vm_pageout_map_deactivate_pages(map, desired)
 	int nothingwired;
 
 	GIANT_REQUIRED;
-	if (lockmgr(&map->lock, LK_EXCLUSIVE | LK_NOWAIT, (void *)0, curthread)) {
+	if (!vm_map_trylock(map))
 		return;
-	}
 
 	bigobj = NULL;
 	nothingwired = TRUE;