Fix event triggers for partitioned tables

Index DDL cascading on partitioned tables introduced a way for ALTER
TABLE to be called reentrantly.  This caused an an important deficiency
in event trigger support to be exposed: on exiting the reentrant call,
the alter table state object was clobbered, causing a crash when the
outer alter table tries to finalize its processing.  Fix the crash by
creating a stack of event trigger state objects.  There are still ways
to cause things to misbehave (and probably other crashers) with more
elaborate tricks, but at least it now doesn't crash in the obvious
scenario.

Backpatch to 9.5, where DDL deparsing of event triggers was introduced.

Reported-by: Marco Slot
Authors: Michaël Paquier, Álvaro Herrera
Discussion: https://postgr.es/m/CANNhMLCpi+HQ7M36uPfGbJZEQLyTy7XvX=5EFkpR-b1bo0uJew@mail.gmail.com

5 files changed, 21 insertions, 9 deletions

diff --git a/src/backend/catalog/index.c b/src/backend/catalog/index.c
index 39605732b16..339bb35f9bc 100644
--- a/src/backend/catalog/index.c
+++ b/src/backend/catalog/index.c
@@ -50,6 +50,7 @@
 #include "catalog/pg_type.h"
 #include "catalog/storage.h"
 #include "commands/tablecmds.h"
+#include "commands/event_trigger.h"
 #include "commands/trigger.h"
 #include "executor/executor.h"
 #include "miscadmin.h"
@@ -212,7 +213,8 @@ relationHasPrimaryKey(Relation rel)
 void
 index_check_primary_key(Relation heapRel,
 						IndexInfo *indexInfo,
-						bool is_alter_table)
+						bool is_alter_table,
+						IndexStmt *stmt)
 {
 	List	   *cmds;
 	int			i;
@@ -280,7 +282,11 @@ index_check_primary_key(Relation heapRel,
 	 * unduly.
 	 */
 	if (cmds)
+	{
+		EventTriggerAlterTableStart((Node *) stmt);
 		AlterTableInternal(RelationGetRelid(heapRel), cmds, true);
+		EventTriggerAlterTableEnd();
+	}
 }
 
 /*
diff --git a/src/backend/commands/event_trigger.c b/src/backend/commands/event_trigger.c
index eecc85d14e5..2c1dc47541c 100644
--- a/src/backend/commands/event_trigger.c
+++ b/src/backend/commands/event_trigger.c
@@ -1696,11 +1696,6 @@ EventTriggerCollectSimpleCommand(ObjectAddress address,
  * Note we don't collect the command immediately; instead we keep it in
  * currentCommand, and only when we're done processing the subcommands we will
  * add it to the command list.
- *
- * XXX -- this API isn't considering the possibility of an ALTER TABLE command
- * being called reentrantly by an event trigger function.  Do we need stackable
- * commands at this level?	Perhaps at least we should detect the condition and
- * raise an error.
  */
 void
 EventTriggerAlterTableStart(Node *parsetree)
@@ -1725,6 +1720,7 @@ EventTriggerAlterTableStart(Node *parsetree)
 	command->d.alterTable.subcmds = NIL;
 	command->parsetree = copyObject(parsetree);
 
+	command->parent = currentEventTriggerState->currentCommand;
 	currentEventTriggerState->currentCommand = command;
 
 	MemoryContextSwitchTo(oldcxt);
@@ -1765,6 +1761,7 @@ EventTriggerCollectAlterTableSubcmd(Node *subcmd, ObjectAddress address)
 		return;
 
 	Assert(IsA(subcmd, AlterTableCmd));
+	Assert(OidIsValid(currentEventTriggerState->currentCommand));
 	Assert(OidIsValid(currentEventTriggerState->currentCommand->d.alterTable.objectId));
 
 	oldcxt = MemoryContextSwitchTo(currentEventTriggerState->cxt);
@@ -1790,11 +1787,15 @@ EventTriggerCollectAlterTableSubcmd(Node *subcmd, ObjectAddress address)
 void
 EventTriggerAlterTableEnd(void)
 {
+	CollectedCommand *parent;
+
 	/* ignore if event trigger context not set, or collection disabled */
 	if (!currentEventTriggerState ||
 		currentEventTriggerState->commandCollectionInhibited)
 		return;
 
+	parent = currentEventTriggerState->currentCommand->parent;
+
 	/* If no subcommands, don't collect */
 	if (list_length(currentEventTriggerState->currentCommand->d.alterTable.subcmds) != 0)
 	{
@@ -1805,7 +1806,7 @@ EventTriggerAlterTableEnd(void)
 	else
 		pfree(currentEventTriggerState->currentCommand);
 
-	currentEventTriggerState->currentCommand = NULL;
+	currentEventTriggerState->currentCommand = parent;
 }
 
 /*
diff --git a/src/backend/commands/indexcmds.c b/src/backend/commands/indexcmds.c
index ab3d9a0a489..3975f62c001 100644
--- a/src/backend/commands/indexcmds.c
+++ b/src/backend/commands/indexcmds.c
@@ -34,6 +34,7 @@
 #include "commands/comment.h"
 #include "commands/dbcommands.h"
 #include "commands/defrem.h"
+#include "commands/event_trigger.h"
 #include "commands/tablecmds.h"
 #include "commands/tablespace.h"
 #include "mb/pg_wchar.h"
@@ -666,7 +667,7 @@ DefineIndex(Oid relationId,
 	 * Extra checks when creating a PRIMARY KEY index.
 	 */
 	if (stmt->primary)
-		index_check_primary_key(rel, indexInfo, is_alter_table);
+		index_check_primary_key(rel, indexInfo, is_alter_table, stmt);
 
 	/*
 	 * If this table is partitioned and we're creating a unique index or a
diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index 7df1fc2a765..5d643c06d3e 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -7074,7 +7074,7 @@ ATExecAddIndexConstraint(AlteredTableInfo *tab, Relation rel,
 
 	/* Extra checks needed if making primary key */
 	if (stmt->primary)
-		index_check_primary_key(rel, indexInfo, true);
+		index_check_primary_key(rel, indexInfo, true, stmt);
 
 	/* Note we currently don't support EXCLUSION constraints here */
 	if (stmt->primary)
diff --git a/src/backend/commands/view.c b/src/backend/commands/view.c
index e73f1d8894c..b670cad8b1d 100644
--- a/src/backend/commands/view.c
+++ b/src/backend/commands/view.c
@@ -61,6 +61,8 @@ validateWithCheckOption(const char *value)
  *
  * Create a view relation and use the rules system to store the query
  * for the view.
+ *
+ * EventTriggerAlterTableStart must have been called already.
  *---------------------------------------------------------------------
  */
 static ObjectAddress
@@ -186,6 +188,7 @@ DefineVirtualRelation(RangeVar *relation, List *tlist, bool replace,
 				atcmds = lappend(atcmds, atcmd);
 			}
 
+			/* EventTriggerAlterTableStart called by ProcessUtilitySlow */
 			AlterTableInternal(viewOid, atcmds, true);
 
 			/* Make the new view columns visible */
@@ -217,6 +220,7 @@ DefineVirtualRelation(RangeVar *relation, List *tlist, bool replace,
 		atcmd->def = (Node *) options;
 		atcmds = list_make1(atcmd);
 
+		/* EventTriggerAlterTableStart called by ProcessUtilitySlow */
 		AlterTableInternal(viewOid, atcmds, true);
 
 		ObjectAddressSet(address, RelationRelationId, viewOid);