Fix ExecOpenScanRelation to take a lock on a ROW_MARK_COPY relation.

tglsfdc · tglsfdc · commit 3fbfd5dbeca7 · 2015-03-24T15:53:06.000-04:00
ExecOpenScanRelation assumed that any relation listed in the ExecRowMark
list has been locked by InitPlan; but this is not true if the rel's
markType is ROW_MARK_COPY, which is possible if it's a foreign table.

In most (possibly all) cases, failure to acquire a lock here isn't really
problematic because the parser, planner, or plancache would have taken the
appropriate lock already.  In principle though it might leave us vulnerable
to working with a relation that we hold no lock on, and in any case if the
executor isn't depending on previously-taken locks otherwise then it should
not do so for ROW_MARK_COPY relations.

Noted by Etsuro Fujita.  Back-patch to all active versions, since the
inconsistency has been there a long time.  (It's almost certainly
irrelevant in 9.0, since that predates foreign tables, but the code's
still wrong on its own terms.)
diff --git a/src/backend/executor/execMain.c b/src/backend/executor/execMain.c
@@ -804,6 +804,10 @@ InitPlan(QueryDesc *queryDesc, int eflags)
 		if (rc->isParent)
 			continue;
 
+		/*
+		 * If you change the conditions under which rel locks are acquired
+		 * here, be sure to adjust ExecOpenScanRelation to match.
+		 */
 		switch (rc->markType)
 		{
 			case ROW_MARK_EXCLUSIVE:
diff --git a/src/backend/executor/execUtils.c b/src/backend/executor/execUtils.c
@@ -819,7 +819,9 @@ ExecOpenScanRelation(EState *estate, Index scanrelid)
 		{
 			ExecRowMark *erm = lfirst(l);
 
-			if (erm->rti == scanrelid)
+			/* Keep this check in sync with InitPlan! */
+			if (erm->rti == scanrelid &&
+				erm->relation != NULL)
 			{
 				lockmode = NoLock;
 				break;

Original file line number	Diff line number	Diff line change
`@@ -819,7 +819,9 @@ ExecOpenScanRelation(EState *estate, Index scanrelid)`
`819`	`819`	`{`
`820`	`820`	`ExecRowMark *erm = lfirst(l);`
`821`	`821`
`822`		`- if (erm->rti == scanrelid)`
	`822`	`+ /* Keep this check in sync with InitPlan! */`
	`823`	`+ if (erm->rti == scanrelid &&`
	`824`	`+ erm->relation != NULL)`
`823`	`825`	`{`
`824`	`826`	`lockmode = NoLock;`
`825`	`827`	`break;`