Add an injection_points isolation test suite.

Make the isolation harness recognize injection_points wait events as a
type of blocked state.  Test an extant inplace-update bug.

Reviewed by Robert Haas and Michael Paquier.

Discussion: https://postgr.es/m/20240512232923.aa.nmisch@google.com

src/test/modules/injection_points/specs/inplace.spec

@@ -0,0 +1,83 @@
+# Test race conditions involving:
+# - s1: VACUUM inplace-updating a pg_class row
+# - s2: GRANT/REVOKE making pg_class rows dead
+# - s3: "VACUUM pg_class" making dead rows LP_UNUSED; DDL reusing them
+
+# Need GRANT to make a non-HOT update.  Otherwise, "VACUUM pg_class" would
+# leave an LP_REDIRECT that persists.  To get non-HOT, make rels so the
+# pg_class row for vactest.orig50 is on a filled page (assuming BLCKSZ=8192).
+# Just to save on filesystem syscalls, use relkind=c for every other rel.
+setup
+{
+	CREATE EXTENSION injection_points;
+	CREATE SCHEMA vactest;
+	CREATE FUNCTION vactest.mkrels(text, int, int) RETURNS void
+		LANGUAGE plpgsql SET search_path = vactest AS $$
+	DECLARE
+		tname text;
+	BEGIN
+		FOR i in $2 .. $3 LOOP
+			tname := $1 || i;
+			EXECUTE FORMAT('CREATE TYPE ' || tname || ' AS ()');
+			RAISE DEBUG '% at %', tname, ctid
+				FROM pg_class WHERE oid = tname::regclass;
+		END LOOP;
+	END
+	$$;
+}
+setup	{ VACUUM FULL pg_class;  -- reduce free space }
+setup
+{
+	SELECT vactest.mkrels('orig', 1, 49);
+	CREATE TABLE vactest.orig50 ();
+	SELECT vactest.mkrels('orig', 51, 100);
+}
+
+# XXX DROP causes an assertion failure; adopt DROP once fixed
+teardown
+{
+	--DROP SCHEMA vactest CASCADE;
+	DO $$BEGIN EXECUTE 'ALTER SCHEMA vactest RENAME TO schema' || oid FROM pg_namespace where nspname = 'vactest'; END$$;
+	DROP EXTENSION injection_points;
+}
+
+# Wait during inplace update, in a VACUUM of vactest.orig50.
+session s1
+setup	{
+	SELECT injection_points_set_local();
+	SELECT injection_points_attach('inplace-before-pin', 'wait');
+}
+step vac1	{ VACUUM vactest.orig50;  -- wait during inplace update }
+# One bug scenario leaves two live pg_class tuples for vactest.orig50 and zero
+# live tuples for one of the "intruder" rels.  REINDEX observes the duplicate.
+step read1	{
+	REINDEX TABLE pg_class;  -- look for duplicates
+	SELECT reltuples = -1 AS reltuples_unknown
+	FROM pg_class WHERE oid = 'vactest.orig50'::regclass;
+}
+
+
+# Transactional updates of the tuple vac1 is waiting to inplace-update.
+session s2
+step grant2		{ GRANT SELECT ON TABLE vactest.orig50 TO PUBLIC; }
+
+
+# Non-blocking actions.
+session s3
+step vac3		{ VACUUM pg_class; }
+# Reuse the lp that vac1 is waiting to change.  I've observed reuse at the 1st
+# or 18th CREATE, so create excess.
+step mkrels3	{
+	SELECT vactest.mkrels('intruder', 1, 100);  -- repopulate LP_UNUSED
+	SELECT injection_points_detach('inplace-before-pin');
+	SELECT injection_points_wakeup('inplace-before-pin');
+}
+
+
+# XXX extant bug
+permutation
+	vac1(mkrels3)	# reads pg_class tuple T0 for vactest.orig50, xmax invalid
+	grant2			# T0 becomes eligible for pruning, T1 is successor
+	vac3			# T0 becomes LP_UNUSED
+	mkrels3			# T0 reused; vac1 wakes and overwrites the reused T0
+	read1