Fix waits of REINDEX CONCURRENTLY for indexes with predicates or expressions

As introduced by f9900df5f9, a REINDEX CONCURRENTLY job done for an
index with predicates or expressions would set PROC_IN_SAFE_IC in its
MyProc->statusFlags, causing it to be ignored by other concurrent
operations.

Such concurrent index rebuilds should never be ignored, as a predicate
or an expression could call a user-defined function that accesses a
different table than the table where the index is rebuilt.

A test that uses injection points is added, backpatched down to 17.
Michail has proposed a different test, but I have added something
simpler with more coverage.

Oversight in f9900df5f9.

Author: Michail Nikolaev
Discussion: https://postgr.es/m/CANtu0oj9A3kZVduFTG0vrmGnKB+DCHgEpzOp0qAyOgmks84j0w@mail.gmail.com
Backpatch-through: 14

src/backend/commands/indexcmds.c

@@ -61,6 +61,7 @@
 #include "utils/builtins.h"
 #include "utils/fmgroids.h"
 #include "utils/guc.h"
+#include "utils/injection_point.h"
 #include "utils/inval.h"
 #include "utils/lsyscache.h"
 #include "utils/memutils.h"
@@ -3782,8 +3783,16 @@ ReindexRelationConcurrently(const ReindexStmt *stmt, Oid relationOid, const Rein
 		RestrictSearchPath();
 
 		/* determine safety of this index for set_indexsafe_procflags */
-		idx->safe = (indexRel->rd_indexprs == NIL &&
-					 indexRel->rd_indpred == NIL);
+		idx->safe = (RelationGetIndexExpressions(indexRel) == NIL &&
+					 RelationGetIndexPredicate(indexRel) == NIL);
+
+#ifdef USE_INJECTION_POINTS
+		if (idx->safe)
+			INJECTION_POINT("reindex-conc-index-safe");
+		else
+			INJECTION_POINT("reindex-conc-index-not-safe");
+#endif
+
 		idx->tableId = RelationGetRelid(heapRel);
 		idx->amId = indexRel->rd_rel->relam;
 

src/test/modules/injection_points/Makefile

@@ -10,7 +10,7 @@ EXTENSION = injection_points
 DATA = injection_points--1.0.sql
 PGFILEDESC = "injection_points - facility for injection points"
 
-REGRESS = injection_points
+REGRESS = injection_points reindex_conc
 REGRESS_OPTS = --dlpath=$(top_builddir)/src/test/regress
 
 ISOLATION = inplace

src/test/modules/injection_points/expected/reindex_conc.out

@@ -0,0 +1,51 @@
+-- Tests for REINDEX CONCURRENTLY
+CREATE EXTENSION injection_points;
+-- Check safety of indexes with predicates and expressions.
+SELECT injection_points_set_local();
+ injection_points_set_local 
+----------------------------
+ 
+(1 row)
+
+SELECT injection_points_attach('reindex-conc-index-safe', 'notice');
+ injection_points_attach 
+-------------------------
+ 
+(1 row)
+
+SELECT injection_points_attach('reindex-conc-index-not-safe', 'notice');
+ injection_points_attach 
+-------------------------
+ 
+(1 row)
+
+CREATE SCHEMA reindex_inj;
+CREATE TABLE reindex_inj.tbl(i int primary key, updated_at timestamp);
+CREATE UNIQUE INDEX ind_simple ON reindex_inj.tbl(i);
+CREATE UNIQUE INDEX ind_expr ON reindex_inj.tbl(ABS(i));
+CREATE UNIQUE INDEX ind_pred ON reindex_inj.tbl(i) WHERE mod(i, 2) = 0;
+CREATE UNIQUE INDEX ind_expr_pred ON reindex_inj.tbl(abs(i)) WHERE mod(i, 2) = 0;
+REINDEX INDEX CONCURRENTLY reindex_inj.ind_simple;
+NOTICE:  notice triggered for injection point reindex-conc-index-safe
+REINDEX INDEX CONCURRENTLY reindex_inj.ind_expr;
+NOTICE:  notice triggered for injection point reindex-conc-index-not-safe
+REINDEX INDEX CONCURRENTLY reindex_inj.ind_pred;
+NOTICE:  notice triggered for injection point reindex-conc-index-not-safe
+REINDEX INDEX CONCURRENTLY reindex_inj.ind_expr_pred;
+NOTICE:  notice triggered for injection point reindex-conc-index-not-safe
+-- Cleanup
+SELECT injection_points_detach('reindex-conc-index-safe');
+ injection_points_detach 
+-------------------------
+ 
+(1 row)
+
+SELECT injection_points_detach('reindex-conc-index-not-safe');
+ injection_points_detach 
+-------------------------
+ 
+(1 row)
+
+DROP TABLE reindex_inj.tbl;
+DROP SCHEMA reindex_inj;
+DROP EXTENSION injection_points;

src/test/modules/injection_points/meson.build

@@ -34,6 +34,7 @@ tests += {
   'regress': {
     'sql': [
       'injection_points',
+      'reindex_conc',
     ],
     'regress_args': ['--dlpath', meson.build_root() / 'src/test/regress'],
     # The injection points are cluster-wide, so disable installcheck

src/test/modules/injection_points/sql/reindex_conc.sql

@@ -0,0 +1,28 @@
+-- Tests for REINDEX CONCURRENTLY
+CREATE EXTENSION injection_points;
+
+-- Check safety of indexes with predicates and expressions.
+SELECT injection_points_set_local();
+SELECT injection_points_attach('reindex-conc-index-safe', 'notice');
+SELECT injection_points_attach('reindex-conc-index-not-safe', 'notice');
+
+CREATE SCHEMA reindex_inj;
+CREATE TABLE reindex_inj.tbl(i int primary key, updated_at timestamp);
+
+CREATE UNIQUE INDEX ind_simple ON reindex_inj.tbl(i);
+CREATE UNIQUE INDEX ind_expr ON reindex_inj.tbl(ABS(i));
+CREATE UNIQUE INDEX ind_pred ON reindex_inj.tbl(i) WHERE mod(i, 2) = 0;
+CREATE UNIQUE INDEX ind_expr_pred ON reindex_inj.tbl(abs(i)) WHERE mod(i, 2) = 0;
+
+REINDEX INDEX CONCURRENTLY reindex_inj.ind_simple;
+REINDEX INDEX CONCURRENTLY reindex_inj.ind_expr;
+REINDEX INDEX CONCURRENTLY reindex_inj.ind_pred;
+REINDEX INDEX CONCURRENTLY reindex_inj.ind_expr_pred;
+
+-- Cleanup
+SELECT injection_points_detach('reindex-conc-index-safe');
+SELECT injection_points_detach('reindex-conc-index-not-safe');
+DROP TABLE reindex_inj.tbl;
+DROP SCHEMA reindex_inj;
+
+DROP EXTENSION injection_points;