Module Name: src
Committed By: rmind
Date: Sat Jun 18 21:14:43 UTC 2011
Modified Files:
src/sys/uvm: uvm_bio.c uvm_object.c
Log Message:
- Move pre-check from uvm_obj_destroy() to ubc_purge(), keep it abstracted.
- Add comments noting the race between ubc_alloc() and ubc_purge().
To generate a diff of this commit:
cvs rdiff -u -r1.75 -r1.76 src/sys/uvm/uvm_bio.c
cvs rdiff -u -r1.9 -r1.10 src/sys/uvm/uvm_object.c
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/sys/uvm/uvm_bio.c
diff -u src/sys/uvm/uvm_bio.c:1.75 src/sys/uvm/uvm_bio.c:1.76
--- src/sys/uvm/uvm_bio.c:1.75 Fri Jun 17 09:50:52 2011
+++ src/sys/uvm/uvm_bio.c Sat Jun 18 21:14:43 2011
@@ -1,4 +1,4 @@
-/* $NetBSD: uvm_bio.c,v 1.75 2011/06/17 09:50:52 hannken Exp $ */
+/* $NetBSD: uvm_bio.c,v 1.76 2011/06/18 21:14:43 rmind Exp $ */
/*
* Copyright (c) 1998 Chuck Silvers.
@@ -34,7 +34,7 @@
*/
#include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: uvm_bio.c,v 1.75 2011/06/17 09:50:52 hannken Exp $");
+__KERNEL_RCSID(0, "$NetBSD: uvm_bio.c,v 1.76 2011/06/18 21:14:43 rmind Exp $");
#include "opt_uvmhist.h"
#include "opt_ubc.h"
@@ -481,12 +481,12 @@
slot_offset = (vaddr_t)(offset & ((voff_t)ubc_winsize - 1));
*lenp = MIN(*lenp, ubc_winsize - slot_offset);
+ mutex_enter(ubc_object.uobj.vmobjlock);
+again:
/*
- * The object is already referenced, so we do not need to add a ref.
+ * The UVM object is already referenced.
* Lock order: UBC object -> ubc_map::uobj.
*/
- mutex_enter(ubc_object.uobj.vmobjlock);
-again:
umap = ubc_find_mapping(uobj, umap_offset);
if (umap == NULL) {
struct uvm_object *oobj;
@@ -503,10 +503,14 @@
oobj = umap->uobj;
/*
- * remove from old hash (if any), add to new hash.
+ * Remove from old hash (if any), add to new hash.
*/
if (oobj != NULL) {
+ /*
+ * Mapping must be removed before the list entry,
+ * since there is a race with ubc_purge().
+ */
if (umap->flags & UMAP_MAPPING_CACHED) {
umap->flags &= ~UMAP_MAPPING_CACHED;
mutex_enter(oobj->vmobjlock);
@@ -792,6 +796,13 @@
KASSERT(uobj->uo_npages == 0);
+ /*
+ * Safe to check without lock held, as ubc_alloc() removes
+ * the mapping and list entry in the correct order.
+ */
+ if (__predict_true(LIST_EMPTY(&uobj->uo_ubc))) {
+ return;
+ }
mutex_enter(ubc_object.uobj.vmobjlock);
while ((umap = LIST_FIRST(&uobj->uo_ubc)) != NULL) {
KASSERT(umap->refcount == 0);
Index: src/sys/uvm/uvm_object.c
diff -u src/sys/uvm/uvm_object.c:1.9 src/sys/uvm/uvm_object.c:1.10
--- src/sys/uvm/uvm_object.c:1.9 Sun Jun 12 06:36:38 2011
+++ src/sys/uvm/uvm_object.c Sat Jun 18 21:14:43 2011
@@ -1,4 +1,4 @@
-/* $NetBSD: uvm_object.c,v 1.9 2011/06/12 06:36:38 mrg Exp $ */
+/* $NetBSD: uvm_object.c,v 1.10 2011/06/18 21:14:43 rmind Exp $ */
/*
* Copyright (c) 2006, 2010 The NetBSD Foundation, Inc.
@@ -37,7 +37,7 @@
*/
#include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: uvm_object.c,v 1.9 2011/06/12 06:36:38 mrg Exp $");
+__KERNEL_RCSID(0, "$NetBSD: uvm_object.c,v 1.10 2011/06/18 21:14:43 rmind Exp $");
#include "opt_ddb.h"
@@ -84,10 +84,9 @@
KASSERT(rb_tree_iterate(&uo->rb_tree, NULL, RB_DIR_LEFT) == NULL);
- /* Purge any UBC entries with this object. */
- if (__predict_false(!LIST_EMPTY(&uo->uo_ubc))) {
- ubc_purge(uo);
- }
+ /* Purge any UBC entries associated with this object. */
+ ubc_purge(uo);
+
/* Destroy the lock, if requested. */
if (dlock) {
mutex_obj_free(uo->vmobjlock);
