Re: postgres_fdw uninterruptible during connection establishment / ProcSignalBarrier

[Nathan Bossart]

On Mon, Jan 30, 2023 at 11:49:37AM -0800, Andres Freund wrote:
> Why don't the dblink tests catch this?  Any chance you or Robins could prepare
> a patch with fix and test, given that you know how to trigger this?

It's trivially reproducible by calling 1-argument dblink_connect() multiple
times and then calling dblink_disconnect().  Here's a patch.

-- 
Nathan Bossart
Amazon Web Services: https://aws.amazon.com

diff --git a/contrib/dblink/dblink.c b/contrib/dblink/dblink.c
index 8982d623d3..78a8bcee6e 100644
--- a/contrib/dblink/dblink.c
+++ b/contrib/dblink/dblink.c
@@ -321,7 +321,7 @@ dblink_connect(PG_FUNCTION_ARGS)
 	else
 	{
 		if (pconn->conn)
-			libpqsrv_disconnect(conn);
+			libpqsrv_disconnect(pconn->conn);
 		pconn->conn = conn;
 	}
 
diff --git a/contrib/dblink/expected/dblink.out b/contrib/dblink/expected/dblink.out
index 14d015e4d5..0f5050b409 100644
--- a/contrib/dblink/expected/dblink.out
+++ b/contrib/dblink/expected/dblink.out
@@ -938,6 +938,25 @@ DROP SERVER fdtest;
 ALTER FOREIGN DATA WRAPPER dblink_fdw OPTIONS (nonexistent 'fdw');
 ERROR:  invalid option "nonexistent"
 HINT:  There are no valid options in this context.
+-- test repeated calls to dblink_connect
+SELECT dblink_connect(connection_parameters());
+ dblink_connect 
+----------------
+ OK
+(1 row)
+
+SELECT dblink_connect(connection_parameters());
+ dblink_connect 
+----------------
+ OK
+(1 row)
+
+SELECT dblink_disconnect();
+ dblink_disconnect 
+-------------------
+ OK
+(1 row)
+
 -- test asynchronous notifications
 SELECT dblink_connect(connection_parameters());
  dblink_connect 
diff --git a/contrib/dblink/sql/dblink.sql b/contrib/dblink/sql/dblink.sql
index e560260bfc..7870ce5d5a 100644
--- a/contrib/dblink/sql/dblink.sql
+++ b/contrib/dblink/sql/dblink.sql
@@ -489,6 +489,11 @@ DROP SERVER fdtest;
 -- should fail
 ALTER FOREIGN DATA WRAPPER dblink_fdw OPTIONS (nonexistent 'fdw');
 
+-- test repeated calls to dblink_connect
+SELECT dblink_connect(connection_parameters());
+SELECT dblink_connect(connection_parameters());
+SELECT dblink_disconnect();
+
 -- test asynchronous notifications
 SELECT dblink_connect(connection_parameters());