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 bb7078d3f8c522a9800197c55c01056d9c27f123..e02507dd1fef50280911d35fdbeae7335158a4a0 100644 (file)
--- a/src/backend/executor/execMain.c
+++ b/src/backend/executor/execMain.c
@@ -808,6 +808,10 @@ 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
index 756b9641e3f5ec345f931ccaafb5ef6f24296104..94a35a99e8bd2885b36fd0cc6bddc3924a94629b 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;