svn commit: r354684 - in head/sys: security/mac vm

Doug Moore dougm at FreeBSD.org
Wed Nov 13 15:56:08 UTC 2019


Author: dougm
Date: Wed Nov 13 15:56:07 2019
New Revision: 354684
URL: https://svnweb.freebsd.org/changeset/base/354684

Log:
  Define wrapper functions vm_map_entry_{succ,pred} to act as wrappers
  around entry->{next,prev} when those are used for ordered list
  traversal, and use those wrapper functions everywhere. Where the next
  field is used for maintaining a stack of deferred operations, #define
  defer_next to make that different usage clearer, and then use the
  'right' pointer instead of 'next' for that purpose.
  
  Approved by: markj
  Tested by: pho (as part of a larger patch)
  Differential Revision: https://reviews.freebsd.org/D22347

Modified:
  head/sys/security/mac/mac_process.c
  head/sys/vm/vm_map.c
  head/sys/vm/vm_map.h
  head/sys/vm/vm_mmap.c

Modified: head/sys/security/mac/mac_process.c
==============================================================================
--- head/sys/security/mac/mac_process.c	Wed Nov 13 15:31:31 2019	(r354683)
+++ head/sys/security/mac/mac_process.c	Wed Nov 13 15:56:07 2019	(r354684)
@@ -363,7 +363,8 @@ mac_proc_vm_revoke_recurse(struct thread *td, struct u
 			}
 			pmap_protect(map->pmap, vme->start, vme->end,
 			    vme->protection & ~revokeperms);
-			vm_map_try_merge_entries(map, vme->prev, vme);
+			vm_map_try_merge_entries(map, vm_map_entry_pred(vme),
+			    vme);
 		}
 	}
 	vm_map_unlock(map);

Modified: head/sys/vm/vm_map.c
==============================================================================
--- head/sys/vm/vm_map.c	Wed Nov 13 15:31:31 2019	(r354683)
+++ head/sys/vm/vm_map.c	Wed Nov 13 15:56:07 2019	(r354684)
@@ -563,6 +563,12 @@ vm_map_entry_set_vnode_text(vm_map_entry_t entry, bool
 	}
 }
 
+/*
+ * Use a different name for this vm_map_entry field when it's use
+ * is not consistent with its use as part of an ordered search tree.
+ */
+#define defer_next right
+
 static void
 vm_map_process_deferred(void)
 {
@@ -574,7 +580,7 @@ vm_map_process_deferred(void)
 	entry = td->td_map_def_user;
 	td->td_map_def_user = NULL;
 	while (entry != NULL) {
-		next = entry->next;
+		next = entry->defer_next;
 		MPASS((entry->eflags & (MAP_ENTRY_WRITECNT |
 		    MAP_ENTRY_VN_EXEC)) != (MAP_ENTRY_WRITECNT |
 		    MAP_ENTRY_VN_EXEC));
@@ -1436,7 +1442,7 @@ vm_map_insert(vm_map_t map, vm_object_t object, vm_oof
 	/*
 	 * Assert that the next entry doesn't overlap the end point.
 	 */
-	if (prev_entry->next->start < end)
+	if (vm_map_entry_succ(prev_entry)->start < end)
 		return (KERN_NO_SPACE);
 
 	if ((cow & MAP_CREATE_GUARD) != 0 && (object != NULL ||
@@ -1529,7 +1535,8 @@ charged:
 				map->size += end - prev_entry->end;
 			vm_map_entry_resize(map, prev_entry,
 			    end - prev_entry->end);
-			vm_map_try_merge_entries(map, prev_entry, prev_entry->next);
+			vm_map_try_merge_entries(map, prev_entry,
+			    vm_map_entry_succ(prev_entry));
 			return (KERN_SUCCESS);
 		}
 
@@ -1590,7 +1597,7 @@ charged:
 	 * other cases, which are less common.
 	 */
 	vm_map_try_merge_entries(map, prev_entry, new_entry);
-	vm_map_try_merge_entries(map, new_entry, new_entry->next);
+	vm_map_try_merge_entries(map, new_entry, vm_map_entry_succ(new_entry));
 
 	if ((cow & (MAP_PREFAULT | MAP_PREFAULT_PARTIAL)) != 0) {
 		vm_map_pmap_enter(map, start, prot, object, OFF_TO_IDX(offset),
@@ -2288,7 +2295,7 @@ vm_map_submap(
 	if (vm_map_lookup_entry(map, start, &entry)) {
 		vm_map_clip_start(map, entry, start);
 	} else
-		entry = entry->next;
+		entry = vm_map_entry_succ(entry);
 
 	vm_map_clip_end(map, entry, end);
 
@@ -2445,12 +2452,13 @@ again:
 	VM_MAP_RANGE_CHECK(map, start, end);
 
 	if (!vm_map_lookup_entry(map, start, &entry))
-		entry = entry->next;
+		entry = vm_map_entry_succ(entry);
 
 	/*
 	 * Make a first pass to check for protection violations.
 	 */
-	for (current = entry; current->start < end; current = current->next) {
+	for (current = entry; current->start < end;
+	    current = vm_map_entry_succ(current)) {
 		if ((current->eflags & MAP_ENTRY_GUARD) != 0)
 			continue;
 		if (current->eflags & MAP_ENTRY_IS_SUB_MAP) {
@@ -2488,7 +2496,8 @@ again:
 	 */
 	rv = KERN_SUCCESS;
 	vm_map_clip_start(map, entry, start);
-	for (current = entry; current->start < end; current = current->next) {
+	for (current = entry; current->start < end;
+	    current = vm_map_entry_succ(current)) {
 
 		vm_map_clip_end(map, current, end);
 
@@ -2546,8 +2555,8 @@ again:
 	 * [Note that clipping is not necessary the second time.]
 	 */
 	for (current = entry; current->start < end;
-	    vm_map_try_merge_entries(map, current->prev, current),
-	    current = current->next) {
+	     vm_map_try_merge_entries(map, vm_map_entry_pred(current), current),
+	    current = vm_map_entry_succ(current)) {
 		if (rv != KERN_SUCCESS ||
 		    (current->eflags & MAP_ENTRY_GUARD) != 0)
 			continue;
@@ -2585,7 +2594,7 @@ again:
 #undef	MASK
 		}
 	}
-	vm_map_try_merge_entries(map, current->prev, current);
+	vm_map_try_merge_entries(map, vm_map_entry_pred(current), current);
 	vm_map_unlock(map);
 	return (rv);
 }
@@ -2648,7 +2657,7 @@ vm_map_madvise(
 		if (modify_map)
 			vm_map_clip_start(map, entry, start);
 	} else {
-		entry = entry->next;
+		entry = vm_map_entry_succ(entry);
 	}
 
 	if (modify_map) {
@@ -2659,7 +2668,7 @@ vm_map_madvise(
 		 * limited to the specified address range.
 		 */
 		for (current = entry; current->start < end;
-		    current = current->next) {
+		    current = vm_map_entry_succ(current)) {
 			if (current->eflags & MAP_ENTRY_IS_SUB_MAP)
 				continue;
 
@@ -2690,9 +2699,11 @@ vm_map_madvise(
 			default:
 				break;
 			}
-			vm_map_try_merge_entries(map, current->prev, current);
+			vm_map_try_merge_entries(map,
+			    vm_map_entry_pred(current), current);
 		}
-		vm_map_try_merge_entries(map, current->prev, current);
+		vm_map_try_merge_entries(map, vm_map_entry_pred(current),
+		    current);
 		vm_map_unlock(map);
 	} else {
 		vm_pindex_t pstart, pend;
@@ -2705,7 +2716,7 @@ vm_map_madvise(
 		 * the vm_object pindex and count.
 		 */
 		for (current = entry; current->start < end;
-		    current = current->next) {
+		    current = vm_map_entry_succ(current)) {
 			vm_offset_t useEnd, useStart;
 
 			if (current->eflags & MAP_ENTRY_IS_SUB_MAP)
@@ -2812,16 +2823,16 @@ vm_map_inherit(vm_map_t map, vm_offset_t start, vm_off
 		entry = temp_entry;
 		vm_map_clip_start(map, entry, start);
 	} else
-		entry = temp_entry->next;
+		entry = vm_map_entry_succ(temp_entry);
 	while (entry->start < end) {
 		vm_map_clip_end(map, entry, end);
 		if ((entry->eflags & MAP_ENTRY_GUARD) == 0 ||
 		    new_inheritance != VM_INHERIT_ZERO)
 			entry->inheritance = new_inheritance;
-		vm_map_try_merge_entries(map, entry->prev, entry);
-		entry = entry->next;
+		vm_map_try_merge_entries(map, vm_map_entry_pred(entry), entry);
+		entry = vm_map_entry_succ(entry);
 	}
-	vm_map_try_merge_entries(map, entry->prev, entry);
+	vm_map_try_merge_entries(map, vm_map_entry_pred(entry), entry);
 	vm_map_unlock(map);
 	return (KERN_SUCCESS);
 }
@@ -2870,7 +2881,7 @@ vm_map_entry_in_transition(vm_map_t map, vm_offset_t i
 			*io_end = start;
 			return (NULL);
 		}
-		entry = entry->next;
+		entry = vm_map_entry_succ(entry);
 	}
 	return (entry);
 }
@@ -2896,7 +2907,7 @@ vm_map_unwire(vm_map_t map, vm_offset_t start, vm_offs
 	VM_MAP_RANGE_CHECK(map, start, end);
 	if (!vm_map_lookup_entry(map, start, &first_entry)) {
 		if (holes_ok)
-			first_entry = first_entry->next;
+			first_entry = vm_map_entry_succ(first_entry);
 		else {
 			vm_map_unlock(map);
 			return (KERN_INVALID_ADDRESS);
@@ -2940,7 +2951,8 @@ vm_map_unwire(vm_map_t map, vm_offset_t start, vm_offs
 		 * If holes_ok, skip this check.
 		 */
 		if (!holes_ok &&
-		    (entry->end < end && entry->next->start > entry->end)) {
+		    (entry->end < end &&
+		    vm_map_entry_succ(entry)->start > entry->end)) {
 			end = entry->end;
 			rv = KERN_INVALID_ADDRESS;
 			break;
@@ -2954,15 +2966,16 @@ vm_map_unwire(vm_map_t map, vm_offset_t start, vm_offs
 			rv = KERN_INVALID_ARGUMENT;
 			break;
 		}
-		entry = entry->next;
+		entry = vm_map_entry_succ(entry);
 	}
 	need_wakeup = false;
 	if (first_entry == NULL &&
 	    !vm_map_lookup_entry(map, start, &first_entry)) {
 		KASSERT(holes_ok, ("vm_map_unwire: lookup failed"));
-		first_entry = first_entry->next;
+		first_entry = vm_map_entry_succ(first_entry);
 	}
-	for (entry = first_entry; entry->start < end; entry = entry->next) {
+	for (entry = first_entry; entry->start < end;
+	    entry = vm_map_entry_succ(entry)) {
 		/*
 		 * If holes_ok was specified, an empty
 		 * space in the unwired region could have been mapped
@@ -2998,9 +3011,9 @@ vm_map_unwire(vm_map_t map, vm_offset_t start, vm_offs
 			entry->eflags &= ~MAP_ENTRY_NEEDS_WAKEUP;
 			need_wakeup = true;
 		}
-		vm_map_try_merge_entries(map, entry->prev, entry);
+		vm_map_try_merge_entries(map, vm_map_entry_pred(entry), entry);
 	}
-	vm_map_try_merge_entries(map, entry->prev, entry);
+	vm_map_try_merge_entries(map, vm_map_entry_pred(entry), entry);
 	vm_map_unlock(map);
 	if (need_wakeup)
 		vm_map_wakeup(map);
@@ -3106,7 +3119,7 @@ vm_map_wire_locked(vm_map_t map, vm_offset_t start, vm
 	VM_MAP_RANGE_CHECK(map, start, end);
 	if (!vm_map_lookup_entry(map, start, &first_entry)) {
 		if (holes_ok)
-			first_entry = first_entry->next;
+			first_entry = vm_map_entry_succ(first_entry);
 		else
 			return (KERN_INVALID_ADDRESS);
 	}
@@ -3210,7 +3223,7 @@ vm_map_wire_locked(vm_map_t map, vm_offset_t start, vm
 					    faddr < entry->end)
 						vm_map_wire_entry_failure(map,
 						    entry, faddr);
-					entry = entry->next;
+					entry = vm_map_entry_succ(entry);
 				}
 			}
 			if (rv != KERN_SUCCESS) {
@@ -3229,12 +3242,13 @@ vm_map_wire_locked(vm_map_t map, vm_offset_t start, vm
 		 * If holes_ok was specified, skip this check.
 		 */
 		if (!holes_ok &&
-		    entry->end < end && entry->next->start > entry->end) {
+		    entry->end < end &&
+		    vm_map_entry_succ(entry)->start > entry->end) {
 			end = entry->end;
 			rv = KERN_INVALID_ADDRESS;
 			goto done;
 		}
-		entry = entry->next;
+		entry = vm_map_entry_succ(entry);
 	}
 	rv = KERN_SUCCESS;
 done:
@@ -3242,9 +3256,10 @@ done:
 	if (first_entry == NULL &&
 	    !vm_map_lookup_entry(map, start, &first_entry)) {
 		KASSERT(holes_ok, ("vm_map_wire: lookup failed"));
-		first_entry = first_entry->next;
+		first_entry = vm_map_entry_succ(first_entry);
 	}
-	for (entry = first_entry; entry->start < end; entry = entry->next) {
+	for (entry = first_entry; entry->start < end;
+	    entry = vm_map_entry_succ(entry)) {
 		/*
 		 * If holes_ok was specified, an empty
 		 * space in the unwired region could have been mapped
@@ -3297,9 +3312,9 @@ done:
 			entry->eflags &= ~MAP_ENTRY_NEEDS_WAKEUP;
 			need_wakeup = true;
 		}
-		vm_map_try_merge_entries(map, entry->prev, entry);
+		vm_map_try_merge_entries(map, vm_map_entry_pred(entry), entry);
 	}
-	vm_map_try_merge_entries(map, entry->prev, entry);
+	vm_map_try_merge_entries(map, vm_map_entry_pred(entry), entry);
 	if (need_wakeup)
 		vm_map_wakeup(map);
 	return (rv);
@@ -3349,13 +3364,14 @@ vm_map_sync(
 	/*
 	 * Make a first pass to check for user-wired memory and holes.
 	 */
-	for (current = entry; current->start < end; current = current->next) {
+	for (current = entry; current->start < end;
+	    current = vm_map_entry_succ(current)) {
 		if (invalidate && (current->eflags & MAP_ENTRY_USER_WIRED)) {
 			vm_map_unlock_read(map);
 			return (KERN_INVALID_ARGUMENT);
 		}
 		if (end > current->end &&
-		    current->end != current->next->start) {
+		    current->end != vm_map_entry_succ(current)->start) {
 			vm_map_unlock_read(map);
 			return (KERN_INVALID_ADDRESS);
 		}
@@ -3399,7 +3415,7 @@ vm_map_sync(
 		vm_map_lock_read(map);
 		if (last_timestamp == map->timestamp ||
 		    !vm_map_lookup_entry(map, start, &current))
-			current = current->next;
+			current = vm_map_entry_succ(current);
 	}
 
 	vm_map_unlock_read(map);
@@ -3517,7 +3533,7 @@ vm_map_entry_delete(vm_map_t map, vm_map_entry_t entry
 	if (map->system_map)
 		vm_map_entry_deallocate(entry, TRUE);
 	else {
-		entry->next = curthread->td_map_def_user;
+		entry->defer_next = curthread->td_map_def_user;
 		curthread->td_map_def_user = entry;
 	}
 }
@@ -3542,7 +3558,7 @@ vm_map_delete(vm_map_t map, vm_offset_t start, vm_offs
 	 * Find the start of the region, and clip it
 	 */
 	if (!vm_map_lookup_entry(map, start, &first_entry))
-		entry = first_entry->next;
+		entry = vm_map_entry_succ(first_entry);
 	else {
 		entry = first_entry;
 		vm_map_clip_start(map, entry, start);
@@ -3580,7 +3596,7 @@ vm_map_delete(vm_map_t map, vm_offset_t start, vm_offs
 				 */
 				if (!vm_map_lookup_entry(map, saved_start,
 							 &tmp_entry))
-					entry = tmp_entry->next;
+					entry = vm_map_entry_succ(tmp_entry);
 				else {
 					entry = tmp_entry;
 					vm_map_clip_start(map, entry,
@@ -3591,7 +3607,7 @@ vm_map_delete(vm_map_t map, vm_offset_t start, vm_offs
 		}
 		vm_map_clip_end(map, entry, end);
 
-		next = entry->next;
+		next = vm_map_entry_succ(entry);
 
 		/*
 		 * Unwire before removing addresses from the pmap; otherwise,
@@ -3680,7 +3696,7 @@ vm_map_check_protection(vm_map_t map, vm_offset_t star
 			return (FALSE);
 		/* go to next entry */
 		start = entry->end;
-		entry = entry->next;
+		entry = vm_map_entry_succ(entry);
 	}
 	return (TRUE);
 }
@@ -3789,7 +3805,8 @@ vm_map_copy_entry(
 				fake_entry->object.vm_object = src_object;
 				fake_entry->start = src_entry->start;
 				fake_entry->end = src_entry->end;
-				fake_entry->next = curthread->td_map_def_user;
+				fake_entry->defer_next =
+				    curthread->td_map_def_user;
 				curthread->td_map_def_user = fake_entry;
 			}
 
@@ -4049,7 +4066,7 @@ vmspace_fork(struct vmspace *vm1, vm_ooffset_t *fork_c
 
 			break;
 		}
-		old_entry = old_entry->next;
+		old_entry = vm_map_entry_succ(old_entry);
 	}
 	/*
 	 * Use inlined vm_map_unlock() to postpone handling the deferred
@@ -4136,7 +4153,7 @@ vm_map_stack_locked(vm_map_t map, vm_offset_t addrbos,
 	/*
 	 * If we can't accommodate max_ssize in the current mapping, no go.
 	 */
-	if (prev_entry->next->start < addrbos + max_ssize)
+	if (vm_map_entry_succ(prev_entry)->start < addrbos + max_ssize)
 		return (KERN_NO_SPACE);
 
 	/*
@@ -4163,7 +4180,7 @@ vm_map_stack_locked(vm_map_t map, vm_offset_t addrbos,
 	rv = vm_map_insert(map, NULL, 0, bot, top, prot, max, cow);
 	if (rv != KERN_SUCCESS)
 		return (rv);
-	new_entry = prev_entry->next;
+	new_entry = vm_map_entry_succ(prev_entry);
 	KASSERT(new_entry->end == top || new_entry->start == bot,
 	    ("Bad entry start/end for new stack entry"));
 	KASSERT((orient & MAP_STACK_GROWS_DOWN) == 0 ||
@@ -4185,9 +4202,9 @@ vm_map_stack_locked(vm_map_t map, vm_offset_t addrbos,
 		 * stack_guard_page for vm_map_growstack().
 		 */
 		if (orient == MAP_STACK_GROWS_DOWN)
-			new_entry->prev->next_read = sgp;
+			vm_map_entry_pred(new_entry)->next_read = sgp;
 		else
-			new_entry->next->next_read = sgp;
+			vm_map_entry_succ(new_entry)->next_read = sgp;
 	} else {
 		(void)vm_map_delete(map, bot, top);
 	}
@@ -4241,14 +4258,14 @@ retry:
 	if ((gap_entry->eflags & MAP_ENTRY_GUARD) == 0)
 		return (KERN_SUCCESS);
 	if ((gap_entry->eflags & MAP_ENTRY_STACK_GAP_DN) != 0) {
-		stack_entry = gap_entry->next;
+		stack_entry = vm_map_entry_succ(gap_entry);
 		if ((stack_entry->eflags & MAP_ENTRY_GROWS_DOWN) == 0 ||
 		    stack_entry->start != gap_entry->end)
 			return (KERN_FAILURE);
 		grow_amount = round_page(stack_entry->start - addr);
 		grow_down = true;
 	} else if ((gap_entry->eflags & MAP_ENTRY_STACK_GAP_UP) != 0) {
-		stack_entry = gap_entry->prev;
+		stack_entry = vm_map_entry_pred(gap_entry);
 		if ((stack_entry->eflags & MAP_ENTRY_GROWS_UP) == 0 ||
 		    stack_entry->end != gap_entry->start)
 			return (KERN_FAILURE);
@@ -4826,9 +4843,10 @@ _vm_map_assert_consistent(vm_map_t map, int check)
 		KASSERT(entry->start < entry->end,
 		    ("map %p start = %jx, end = %jx", map,
 		    (uintmax_t)entry->start, (uintmax_t)entry->end));
-		KASSERT(entry->end <= entry->next->start,
+		KASSERT(entry->end <= vm_map_entry_succ(entry)->start,
 		    ("map %p end = %jx, next->start = %jx", map,
-		    (uintmax_t)entry->end, (uintmax_t)entry->next->start));
+		     (uintmax_t)entry->end,
+		     (uintmax_t)vm_map_entry_succ(entry)->start));
 		KASSERT(entry->left == NULL ||
 		    entry->left->start < entry->start,
 		    ("map %p left->start = %jx, start = %jx", map,
@@ -4837,14 +4855,16 @@ _vm_map_assert_consistent(vm_map_t map, int check)
 		    entry->start < entry->right->start,
 		    ("map %p start = %jx, right->start = %jx", map,
 		    (uintmax_t)entry->start, (uintmax_t)entry->right->start));
-		max_left = vm_map_entry_max_free_left(entry, entry->prev);
-		max_right = vm_map_entry_max_free_right(entry, entry->next);
+		max_left = vm_map_entry_max_free_left(entry,
+		    vm_map_entry_pred(entry));
+		max_right = vm_map_entry_max_free_right(entry,
+		    vm_map_entry_succ(entry));
 		KASSERT(entry->max_free == MAX(max_left, max_right),
 		    ("map %p max = %jx, max_left = %jx, max_right = %jx", map,
 		    (uintmax_t)entry->max_free,
 		    (uintmax_t)max_left, (uintmax_t)max_right));
 		prev = entry;
-	}	
+	}
 	KASSERT(prev->end <= entry->start,
 	    ("map %p prev->end = %jx, start = %jx", map,
 	    (uintmax_t)prev->end, (uintmax_t)entry->start));

Modified: head/sys/vm/vm_map.h
==============================================================================
--- head/sys/vm/vm_map.h	Wed Nov 13 15:31:31 2019	(r354683)
+++ head/sys/vm/vm_map.h	Wed Nov 13 15:56:07 2019	(r354684)
@@ -419,10 +419,25 @@ int vm_map_lookup_locked(vm_map_t *, vm_offset_t, vm_p
     vm_pindex_t *, vm_prot_t *, boolean_t *);
 void vm_map_lookup_done (vm_map_t, vm_map_entry_t);
 boolean_t vm_map_lookup_entry (vm_map_t, vm_offset_t, vm_map_entry_t *);
+
+static inline vm_map_entry_t
+vm_map_entry_succ(vm_map_entry_t entry)
+{
+
+	return (entry->next);
+}
+
+static inline vm_map_entry_t
+vm_map_entry_pred(vm_map_entry_t entry)
+{
+
+	return (entry->prev);
+}
+
 #define VM_MAP_ENTRY_FOREACH(it, map)			\
 	for ((it) = (map)->header.next;		\
 	    (it) != &(map)->header;		\
-	    (it) = (it)->next)
+	    (it) = vm_map_entry_succ(it))
 int vm_map_protect (vm_map_t, vm_offset_t, vm_offset_t, vm_prot_t, boolean_t);
 int vm_map_remove (vm_map_t, vm_offset_t, vm_offset_t);
 void vm_map_try_merge_entries(vm_map_t map, vm_map_entry_t prev,

Modified: head/sys/vm/vm_mmap.c
==============================================================================
--- head/sys/vm/vm_mmap.c	Wed Nov 13 15:31:31 2019	(r354683)
+++ head/sys/vm/vm_mmap.c	Wed Nov 13 15:56:07 2019	(r354684)
@@ -581,7 +581,7 @@ kern_munmap(struct thread *td, uintptr_t addr0, size_t
 		pkm.pm_address = (uintptr_t) NULL;
 		if (vm_map_lookup_entry(map, addr, &entry)) {
 			for (; entry->start < addr + size;
-			    entry = entry->next) {
+			    entry = vm_map_entry_succ(entry)) {
 				if (vm_map_check_protection(map, entry->start,
 					entry->end, VM_PROT_EXECUTE) == TRUE) {
 					pkm.pm_address = (uintptr_t) addr;
@@ -817,12 +817,15 @@ RestartScan:
 	 * up the pages elsewhere.
 	 */
 	lastvecindex = -1;
-	for (current = entry; current->start < end; current = current->next) {
+	while (entry->start < end) {
 
 		/*
 		 * check for contiguity
 		 */
-		if (current->end < end && current->next->start > current->end) {
+		current = entry;
+		entry = vm_map_entry_succ(current);
+		if (current->end < end &&
+		    entry->start > current->end) {
 			vm_map_unlock_read(map);
 			return (ENOMEM);
 		}


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