Fix ExecOpenScanRelation to take a lock on a ROW_MARK_COPY relation.

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
index ad7e2072908a54e7cd0761027c803c7bbad62512..90d37b566ae6e2549cd97077c87989a22b7798ae 100644 (file)
--- a/src/backend/executor/execMain.c
+++ b/src/backend/executor/execMain.c
@@ -817,6 +817,10 @@ InitPlan(QueryDesc *queryDesc, int eflags)
        /* get relation's OID (will produce InvalidOid if subquery) */
        relid = getrelid(rc->rti, rangeTable);
 
+       /*
+        * 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
index 022041bea44c159acc09ecf13994207c00bae2a1..0736d2a310254e959a0fd56077c7d0b41322e587 100644 (file)
--- a/src/backend/executor/execUtils.c
+++ b/src/backend/executor/execUtils.c
@@ -820,7 +820,9 @@ ExecOpenScanRelation(EState *estate, Index scanrelid, int eflags)
        {
            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;