Jim Jones <jim.jones@uni-muenster.de> writes:
> In my environment (libxml2 v2.9.10 and Ubuntu 22.04) I couldn't
> reproduce this memory leak.
Just when you thought it was safe to go back in the water ...
Experimenting with the improved valgrind leak detection code at [1],
I discovered that XMLSERIALIZE(... INDENT) has yet a different memory
leak problem. It turns out that xmlDocSetRootElement() doesn't
merely install the given root node: it unlinks the document's old
root node and returns it to you. If you don't free it, it's leaked
(for the session, since this is a malloc not palloc). The amount of
leakage isn't that large, seems to be a couple hundred bytes per
iteration, which may explain why this escaped our notice in the
previous testing. Still, it could add up under extensive usage.
So I think we need to apply the attached, back to PG 16.
regards, tom lane
[1] https://www.postgresql.org/message-id/1295385.1747847681%40sss.pgh.pa.us
diff --git a/src/backend/utils/adt/xml.c b/src/backend/utils/adt/xml.c
index db8d0d6a7e8..73fd4fa090c 100644
--- a/src/backend/utils/adt/xml.c
+++ b/src/backend/utils/adt/xml.c
@@ -754,6 +754,7 @@ xmltotext_with_options(xmltype *data, XmlOptionType xmloption_arg, bool indent)
* content nodes, and then iterate over the nodes.
*/
xmlNodePtr root;
+ xmlNodePtr oldroot;
xmlNodePtr newline;
root = xmlNewNode(NULL, (const xmlChar *) "content-root");
@@ -761,8 +762,14 @@ xmltotext_with_options(xmltype *data, XmlOptionType xmloption_arg, bool indent)
xml_ereport(xmlerrcxt, ERROR, ERRCODE_OUT_OF_MEMORY,
"could not allocate xml node");
- /* This attaches root to doc, so we need not free it separately. */
- xmlDocSetRootElement(doc, root);
+ /*
+ * This attaches root to doc, so we need not free it separately...
+ * but instead, we have to free the old root if there was one.
+ */
+ oldroot = xmlDocSetRootElement(doc, root);
+ if (oldroot != NULL)
+ xmlFreeNode(oldroot);
+
xmlAddChildList(root, content_nodes);
/*
