Fix SQL function execution to be safe with long-lived FmgrInfos.

fmgr_sql had been designed on the assumption that the FmgrInfo it's called
with has only query lifespan.  This is demonstrably unsafe in connection
with range types, as shown in bug #7881 from Andrew Gierth.  Fix things
so that we re-generate the function's cache data if the (sub)transaction
it was made in is no longer active.

Back-patch to 9.2.  This might be needed further back, but it's not clear
whether the case can realistically arise without range types, so for now
I'll desist from back-patching further.

1 files changed, 21 insertions, 0 deletions

diff --git a/src/backend/access/transam/xact.c b/src/backend/access/transam/xact.c
index 9a9724574be..e62286f9f98 100644
--- a/src/backend/access/transam/xact.c
+++ b/src/backend/access/transam/xact.c
@@ -570,6 +570,27 @@ GetCurrentSubTransactionId(void)
 	return s->subTransactionId;
 }
 
+/*
+ *	SubTransactionIsActive
+ *
+ * Test if the specified subxact ID is still active.  Note caller is
+ * responsible for checking whether this ID is relevant to the current xact.
+ */
+bool
+SubTransactionIsActive(SubTransactionId subxid)
+{
+	TransactionState s;
+
+	for (s = CurrentTransactionState; s != NULL; s = s->parent)
+	{
+		if (s->state == TRANS_ABORT)
+			continue;
+		if (s->subTransactionId == subxid)
+			return true;
+	}
+	return false;
+}
+
 
 /*
  *	GetCurrentCommandId