diff --git a/block.c b/block.c
index 5b4ebfe..459412e 100644
--- a/block.c
+++ b/block.c
@@ -2513,12 +2513,15 @@ static void bdrv_replace_child_noperm(BdrvChild *child,
  * If @new_bs is not NULL, bdrv_check_perm() must be called beforehand, as this
  * function uses bdrv_set_perm() to update the permissions according to the new
  * reference that @new_bs gets.
+ *
+ * Callers must ensure that child->frozen is false.
  */
 static void bdrv_replace_child(BdrvChild *child, BlockDriverState *new_bs)
 {
     BlockDriverState *old_bs = child->bs;
     uint64_t perm, shared_perm;
 
+    /* Asserts that child->frozen == false */
     bdrv_replace_child_noperm(child, new_bs);
 
     /*
@@ -2676,6 +2679,7 @@ static void bdrv_detach_child(BdrvChild *child)
     g_free(child);
 }
 
+/* Callers must ensure that child->frozen is false. */
 void bdrv_root_unref_child(BdrvChild *child)
 {
     BlockDriverState *child_bs;
@@ -2685,10 +2689,6 @@ void bdrv_root_unref_child(BdrvChild *child)
     bdrv_unref(child_bs);
 }
 
-/**
- * Clear all inherits_from pointers from children and grandchildren of
- * @root that point to @root, where necessary.
- */
 static void bdrv_unset_inherits_from(BlockDriverState *root, BdrvChild *child)
 {
     BdrvChild *c;
@@ -2713,6 +2713,7 @@ static void bdrv_unset_inherits_from(BlockDriverState *root, BdrvChild *child)
     }
 }
 
+/* Callers must ensure that child->frozen is false. */
 void bdrv_unref_child(BlockDriverState *parent, BdrvChild *child)
 {
     if (child == NULL) {
@@ -2756,7 +2757,7 @@ void bdrv_set_backing_hd(BlockDriverState *bs, BlockDriverState *backing_hd,
     bool update_inherits_from = bdrv_chain_contains(bs, backing_hd) &&
         bdrv_inherits_from_recursive(backing_hd, bs);
 
-    if (bdrv_is_backing_chain_frozen(bs, backing_bs(bs), errp)) {
+    if (bdrv_is_chain_frozen(bs, child_bs(bs->backing), errp)) {
         return;
     }
 
@@ -2765,6 +2766,7 @@ void bdrv_set_backing_hd(BlockDriverState *bs, BlockDriverState *backing_hd,
     }
 
     if (bs->backing) {
+        /* Cannot be frozen, we checked that above */
         bdrv_unref_child(bs, bs->backing);
         bs->backing = NULL;
     }
@@ -3912,8 +3914,7 @@ static int bdrv_reopen_parse_backing(BDRVReopenState *reopen_state,
             return -EPERM;
         }
         /* Check if the backing link that we want to replace is frozen */
-        if (bdrv_is_backing_chain_frozen(overlay_bs, backing_bs(overlay_bs),
-                                         errp)) {
+        if (bdrv_is_chain_frozen(overlay_bs, backing_bs(overlay_bs), errp)) {
             return -EPERM;
         }
         reopen_state->replace_backing_bs = true;
@@ -4248,6 +4249,7 @@ static void bdrv_close(BlockDriverState *bs)
 
     if (bs->drv) {
         if (bs->drv->bdrv_close) {
+            /* Must unfreeze all children, so bdrv_unref_child() works */
             bs->drv->bdrv_close(bs);
         }
         bs->drv = NULL;
@@ -4617,20 +4619,22 @@ BlockDriverState *bdrv_find_base(BlockDriverState *bs)
 }
 
 /*
- * Return true if at least one of the backing links between @bs and
- * @base is frozen. @errp is set if that's the case.
+ * Return true if at least one of the (COW and R/W) filter links
+ * between @bs and @base is frozen. @errp is set if that's the case.
  * @base must be reachable from @bs, or NULL.
  */
-bool bdrv_is_backing_chain_frozen(BlockDriverState *bs, BlockDriverState *base,
-                                  Error **errp)
+bool bdrv_is_chain_frozen(BlockDriverState *bs, BlockDriverState *base,
+                          Error **errp)
 {
     BlockDriverState *i;
+    BdrvChild *child;
+
+    for (i = bs; i != base; i = child_bs(child)) {
+        child = bdrv_filtered_child(i);
 
-    for (i = bs; i != base; i = backing_bs(i)) {
-        if (i->backing && i->backing->frozen) {
+        if (child && child->frozen) {
             error_setg(errp, "Cannot change '%s' link from '%s' to '%s'",
-                       i->backing->name, i->node_name,
-                       backing_bs(i)->node_name);
+                       child->name, i->node_name, child->bs->node_name);
             return true;
         }
     }
@@ -4639,32 +4643,35 @@ bool bdrv_is_backing_chain_frozen(BlockDriverState *bs, BlockDriverState *base,
 }
 
 /*
- * Freeze all backing links between @bs and @base.
+ * Freeze all (COW and R/W) filter links between @bs and @base.
  * If any of the links is already frozen the operation is aborted and
  * none of the links are modified.
  * @base must be reachable from @bs, or NULL.
  * Returns 0 on success. On failure returns < 0 and sets @errp.
  */
-int bdrv_freeze_backing_chain(BlockDriverState *bs, BlockDriverState *base,
-                              Error **errp)
+int bdrv_freeze_chain(BlockDriverState *bs, BlockDriverState *base,
+                      Error **errp)
 {
     BlockDriverState *i;
+    BdrvChild *child;
 
-    if (bdrv_is_backing_chain_frozen(bs, base, errp)) {
+    if (bdrv_is_chain_frozen(bs, base, errp)) {
         return -EPERM;
     }
 
-    for (i = bs; i != base; i = backing_bs(i)) {
-        if (i->backing && backing_bs(i)->never_freeze) {
+    for (i = bs; i != base; i = child_bs(child)) {
+        child = bdrv_filtered_child(i);
+        if (child && child->bs->never_freeze) {
             error_setg(errp, "Cannot freeze '%s' link to '%s'",
-                       i->backing->name, backing_bs(i)->node_name);
+                       child->name, child->bs->node_name);
             return -EPERM;
         }
     }
 
-    for (i = bs; i != base; i = backing_bs(i)) {
-        if (i->backing) {
-            i->backing->frozen = true;
+    for (i = bs; i != base; i = child_bs(child)) {
+        child = bdrv_filtered_child(i);
+        if (child) {
+            child->frozen = true;
         }
     }
 
@@ -4672,18 +4679,21 @@ int bdrv_freeze_backing_chain(BlockDriverState *bs, BlockDriverState *base,
 }
 
 /*
- * Unfreeze all backing links between @bs and @base. The caller must
- * ensure that all links are frozen before using this function.
+ * Unfreeze all (COW and R/W) filter links between @bs and @base. The
+ * caller must ensure that all links are frozen before using this
+ * function.
  * @base must be reachable from @bs, or NULL.
  */
-void bdrv_unfreeze_backing_chain(BlockDriverState *bs, BlockDriverState *base)
+void bdrv_unfreeze_chain(BlockDriverState *bs, BlockDriverState *base)
 {
     BlockDriverState *i;
+    BdrvChild *child;
 
-    for (i = bs; i != base; i = backing_bs(i)) {
-        if (i->backing) {
-            assert(i->backing->frozen);
-            i->backing->frozen = false;
+    for (i = bs; i != base; i = child_bs(child)) {
+        child = bdrv_filtered_child(i);
+        if (child) {
+            assert(child->frozen);
+            child->frozen = false;
         }
     }
 }
@@ -4786,8 +4796,11 @@ int bdrv_drop_intermediate(BlockDriverState *top, BlockDriverState *base,
             }
         }
 
-        /* Do the actual switch in the in-memory graph.
-         * Completes bdrv_check_update_perm() transaction internally. */
+        /*
+         * Do the actual switch in the in-memory graph.
+         * Completes bdrv_check_update_perm() transaction internally.
+         * c->frozen is false, we have checked that above.
+         */
         bdrv_ref(base);
         bdrv_replace_child(c, base);
         bdrv_unref(top);
diff --git a/block/commit.c b/block/commit.c
index 445a280..e1f45a4 100644
--- a/block/commit.c
+++ b/block/commit.c
@@ -47,7 +47,7 @@ static int commit_prepare(Job *job)
 {
     CommitBlockJob *s = container_of(job, CommitBlockJob, common.job);
 
-    bdrv_unfreeze_backing_chain(s->commit_top_bs, s->base_bs);
+    bdrv_unfreeze_chain(s->commit_top_bs, s->base_bs);
     s->chain_frozen = false;
 
     /* Remove base node parent that still uses BLK_PERM_WRITE/RESIZE before
@@ -67,7 +67,7 @@ static void commit_abort(Job *job)
     BlockDriverState *top_bs = blk_bs(s->top);
 
     if (s->chain_frozen) {
-        bdrv_unfreeze_backing_chain(s->commit_top_bs, s->base_bs);
+        bdrv_unfreeze_chain(s->commit_top_bs, s->base_bs);
     }
 
     /* Make sure commit_top_bs and top stay around until bdrv_replace_node() */
@@ -317,7 +317,7 @@ void commit_start(const char *job_id, BlockDriverState *bs,
         }
     }
 
-    if (bdrv_freeze_backing_chain(commit_top_bs, base, errp) < 0) {
+    if (bdrv_freeze_chain(commit_top_bs, base, errp) < 0) {
         goto fail;
     }
     s->chain_frozen = true;
@@ -358,7 +358,7 @@ void commit_start(const char *job_id, BlockDriverState *bs,
 
 fail:
     if (s->chain_frozen) {
-        bdrv_unfreeze_backing_chain(commit_top_bs, base);
+        bdrv_unfreeze_chain(commit_top_bs, base);
     }
     if (s->base) {
         blk_unref(s->base);
diff --git a/block/mirror.c b/block/mirror.c
index b6de24b..4b187e6 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -648,7 +648,7 @@ static int mirror_exit_common(Job *job)
     target_bs = blk_bs(s->target);
 
     if (bdrv_chain_contains(src, target_bs)) {
-        bdrv_unfreeze_backing_chain(mirror_top_bs, target_bs);
+        bdrv_unfreeze_chain(mirror_top_bs, target_bs);
     }
 
     bdrv_release_dirty_bitmap(s->dirty_bitmap);
@@ -1713,7 +1713,7 @@ static BlockJob *mirror_start_job(
             }
         }
 
-        if (bdrv_freeze_backing_chain(mirror_top_bs, target, errp) < 0) {
+        if (bdrv_freeze_chain(mirror_top_bs, target, errp) < 0) {
             goto fail;
         }
     }
diff --git a/block/stream.c b/block/stream.c
index aa2e7af..3cca1f9 100644
--- a/block/stream.c
+++ b/block/stream.c
@@ -53,7 +53,7 @@ static void stream_abort(Job *job)
 
     if (s->chain_frozen) {
         BlockJob *bjob = &s->common;
-        bdrv_unfreeze_backing_chain(blk_bs(bjob->blk), s->bottom);
+        bdrv_unfreeze_chain(blk_bs(bjob->blk), s->bottom);
     }
 }
 
@@ -66,7 +66,7 @@ static int stream_prepare(Job *job)
     Error *local_err = NULL;
     int ret = 0;
 
-    bdrv_unfreeze_backing_chain(bs, s->bottom);
+    bdrv_unfreeze_chain(bs, s->bottom);
     s->chain_frozen = false;
 
     if (bs->backing) {
@@ -225,7 +225,7 @@ void stream_start(const char *job_id, BlockDriverState *bs,
     int basic_flags = BLK_PERM_CONSISTENT_READ | BLK_PERM_WRITE_UNCHANGED;
     BlockDriverState *bottom = bdrv_find_overlay(bs, base);
 
-    if (bdrv_freeze_backing_chain(bs, bottom, errp) < 0) {
+    if (bdrv_freeze_chain(bs, bottom, errp) < 0) {
         return;
     }
 
@@ -276,5 +276,5 @@ fail:
     if (bs_read_only) {
         bdrv_reopen_set_read_only(bs, true, NULL);
     }
-    bdrv_unfreeze_backing_chain(bs, bottom);
+    bdrv_unfreeze_chain(bs, bottom);
 }
diff --git a/include/block/block.h b/include/block/block.h
index 4de8d8f..e55143d 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -360,11 +360,11 @@ int bdrv_drop_intermediate(BlockDriverState *top, BlockDriverState *base,
 BlockDriverState *bdrv_find_overlay(BlockDriverState *active,
                                     BlockDriverState *bs);
 BlockDriverState *bdrv_find_base(BlockDriverState *bs);
-bool bdrv_is_backing_chain_frozen(BlockDriverState *bs, BlockDriverState *base,
+bool bdrv_is_chain_frozen(BlockDriverState *bs, BlockDriverState *base,
                                   Error **errp);
-int bdrv_freeze_backing_chain(BlockDriverState *bs, BlockDriverState *base,
+int bdrv_freeze_chain(BlockDriverState *bs, BlockDriverState *base,
                               Error **errp);
-void bdrv_unfreeze_backing_chain(BlockDriverState *bs, BlockDriverState *base);
+void bdrv_unfreeze_chain(BlockDriverState *bs, BlockDriverState *base);
 int coroutine_fn bdrv_co_delete_file(BlockDriverState *bs, Error **errp);
 
 
