Obtain required table lock during cross-table updates, redux.

Commits 8319e5cb5 et al missed the fact that ATPostAlterTypeCleanup
contains three calls to ATPostAlterTypeParse, and the other two
also need protection against passing a relid that we don't yet
have lock on.  Add similar logic to those code paths, and add
some test cases demonstrating the need for it.

In v18 and master, the test cases demonstrate that there's a
behavioral discrepancy between stored generated columns and virtual
generated columns: we disallow changing the expression of a stored
column if it's used in any composite-type columns, but not that of
a virtual column.  Since the expression isn't actually relevant to
either sort of composite-type usage, this prohibition seems
unnecessary; but changing it is a matter for separate discussion.
For now we are just documenting the existing behavior.

Reported-by: jian he <jian.universality@gmail.com>
Author: jian he <jian.universality@gmail.com>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: CACJufxGKJtGNRRSXfwMW9SqVOPEMdP17BJ7DsBf=tNsv9pWU9g@mail.gmail.com
Backpatch-through: 13

1 files changed, 22 insertions, 0 deletions

diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index 6c5cb068013..cb811520c29 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -15487,6 +15487,14 @@ ATPostAlterTypeCleanup(List **wqueue, AlteredTableInfo *tab, LOCKMODE lockmode)
 		Oid			relid;
 
 		relid = IndexGetRelation(oldId, false);
+
+		/*
+		 * As above, make sure we have lock on the index's table if it's not
+		 * the same table.
+		 */
+		if (relid != tab->relid)
+			LockRelationOid(relid, AccessExclusiveLock);
+
 		ATPostAlterTypeParse(oldId, relid, InvalidOid,
 							 (char *) lfirst(def_item),
 							 wqueue, lockmode, tab->rewrite);
@@ -15503,6 +15511,20 @@ ATPostAlterTypeCleanup(List **wqueue, AlteredTableInfo *tab, LOCKMODE lockmode)
 		Oid			relid;
 
 		relid = StatisticsGetRelation(oldId, false);
+
+		/*
+		 * As above, make sure we have lock on the statistics object's table
+		 * if it's not the same table.  However, we take
+		 * ShareUpdateExclusiveLock here, aligning with the lock level used in
+		 * CreateStatistics and RemoveStatisticsById.
+		 *
+		 * CAUTION: this should be done after all cases that grab
+		 * AccessExclusiveLock, else we risk causing deadlock due to needing
+		 * to promote our table lock.
+		 */
+		if (relid != tab->relid)
+			LockRelationOid(relid, ShareUpdateExclusiveLock);
+
 		ATPostAlterTypeParse(oldId, relid, InvalidOid,
 							 (char *) lfirst(def_item),
 							 wqueue, lockmode, tab->rewrite);