postgres.git / summary / log / commit / refs
commit 608cf2bfd9ec33e741ba6a1c07c78c7e8f1cb171
Author: Tom Lane <tgl@sss.pgh.pa.us>
Date: Tue Feb 02 18:49:08 2021 +0000
First released in: 14.0, 9.5.25, 9.6.21, 10.16, 11.11, 12.6, 13.2
Fix ancient memory leak in contrib/auto_explain.
The ExecutorEnd hook is invoked in a context that could be quite
long-lived, not the executor's own per-query context as I think
we were sort of assuming. Thus, any cruft generated while producing
the EXPLAIN output could accumulate over multiple queries. This can
result in spectacular leakage if log_nested_statements is on, and
even without that I'm surprised nobody complained before.
To fix, just switch into the executor's context so that anything we
allocate will be released when standard_ExecutorEnd frees the executor
state. We might as well nuke the code's retail pfree of the explain
output string, too; that's laughably inadequate to the need.
Japin Li, per report from Jeff Janes. This bug is old, so
back-patch to all supported branches.
Discussion: https://postgr.es/m/CAMkU=1wCVtbeRn0s9gt12KwQ7PLXovbpM8eg25SYocKW3BT4hg@mail.gmail.com
contrib/auto_explain/auto_explain.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)
diff --git a/contrib/auto_explain/auto_explain.c b/contrib/auto_explain/auto_explain.c
index 11349b65a75..2d6abf43b10 100644
--- a/contrib/auto_explain/auto_explain.c
+++ b/contrib/auto_explain/auto_explain.c
@@ -320,8 +320,15 @@ explain_ExecutorEnd(QueryDesc *queryDesc)
{
if (queryDesc->totaltime && auto_explain_enabled())
{
+ MemoryContext oldcxt;
double msec;
+ /*
+ * Make sure we operate in the per-query context, so any cruft will be
+ * discarded later during ExecutorEnd.
+ */
+ oldcxt = MemoryContextSwitchTo(queryDesc->estate->es_query_cxt);
+
/*
* Make sure stats accumulation is done. (Note: it's okay if several
* levels of hook all do this.)
@@ -369,9 +376,9 @@ explain_ExecutorEnd(QueryDesc *queryDesc)
(errmsg("duration: %.3f ms plan:\n%s",
msec, es->str->data),
errhidestmt(true)));
-
- pfree(es->str->data);
}
+
+ MemoryContextSwitchTo(oldcxt);
}
if (prev_ExecutorEnd)
[parent: d683d6528dba]