Fix failure due to accessing an already-freed tuple descriptor in a plan

involving HashAggregate over SubqueryScan (this is the known case, there
may well be more).  The bug is only latent in releases before 8.2 since they
didn't try to access tupletable slots' descriptors during ExecDropTupleTable.
The least bogus fix seems to be to make subqueries share the parent query's
memory context, so that tupdescs they create will have the same lifespan as
those of the parent query.  There are comments in the code envisioning going
even further by not having a separate child EState at all, but that will
require rethinking executor access to range tables, which I don't want to
tackle right now.  Per bug report from Jean-Pierre Pelletier.

diff --git a/src/backend/executor/execMain.c b/src/backend/executor/execMain.c
index a0bac10ce86acdc2e8891219e73daa2d2601109e..f8cc84dd45ce5a28f8796f29e72a20ed7d9b1c82 100644 (file)
--- a/src/backend/executor/execMain.c
+++ b/src/backend/executor/execMain.c
@@ -2223,6 +2223,10 @@ EvalPlanQualStart(evalPlanQual *epq, EState *estate, evalPlanQual *priorepq)
 
        rtsize = list_length(estate->es_range_table);
 
+       /*
+        * It's tempting to think about using CreateSubExecutorState here, but
+        * at present we can't because of memory leakage concerns ...
+        */
        epq->estate = epqstate = CreateExecutorState();
 
        oldcontext = MemoryContextSwitchTo(epqstate->es_query_cxt);

diff --git a/src/backend/executor/execUtils.c b/src/backend/executor/execUtils.c
index 41a87bdbfb5c59cd45ded2373b4096eaf2668d54..dd672be81d7ab8179845782f98f0a92672ac7dd8 100644 (file)
--- a/src/backend/executor/execUtils.c
+++ b/src/backend/executor/execUtils.c
@@ -15,6 +15,7 @@
 /*
  * INTERFACE ROUTINES
  *             CreateExecutorState             Create/delete executor working state
+ *             CreateSubExecutorState
  *             FreeExecutorState
  *             CreateExprContext
  *             CreateStandaloneExprContext
@@ -65,6 +66,8 @@ int                   NIndexTupleInserted;
 int                    NIndexTupleProcessed;
 
 
+static EState *InternalCreateExecutorState(MemoryContext qcontext,
+                                                                                  bool is_subquery);
 static void ShutdownExprContext(ExprContext *econtext);
 
 
@@ -149,9 +152,7 @@ DisplayTupleCount(FILE *statfp)
 EState *
 CreateExecutorState(void)
 {
-       EState     *estate;
        MemoryContext qcontext;
-       MemoryContext oldcontext;
 
        /*
         * Create the per-query context for this Executor run.
@@ -162,6 +163,37 @@ CreateExecutorState(void)
                                                                         ALLOCSET_DEFAULT_INITSIZE,
                                                                         ALLOCSET_DEFAULT_MAXSIZE);
 
+       return InternalCreateExecutorState(qcontext, false);
+}
+
+/* ----------------
+ *             CreateSubExecutorState
+ *
+ *             Create and initialize an EState node for a sub-query.
+ *
+ * Ideally, sub-queries probably shouldn't have their own EState at all,
+ * but right now this is necessary because they have their own rangetables
+ * and we access the rangetable via the EState.  It is critical that a
+ * sub-query share the parent's es_query_cxt, else structures allocated by
+ * the sub-query (especially its result tuple descriptor) may disappear
+ * too soon during executor shutdown.
+ * ----------------
+ */
+EState *
+CreateSubExecutorState(EState *parent_estate)
+{
+       return InternalCreateExecutorState(parent_estate->es_query_cxt, true);
+}
+
+/*
+ * Guts of CreateExecutorState/CreateSubExecutorState
+ */
+static EState *
+InternalCreateExecutorState(MemoryContext qcontext, bool is_subquery)
+{
+       EState     *estate;
+       MemoryContext oldcontext;
+
        /*
         * Make the EState node within the per-query context.  This way, we don't
         * need a separate pfree() operation for it at shutdown.
@@ -200,6 +232,8 @@ CreateExecutorState(void)
        estate->es_lastoid = InvalidOid;
        estate->es_rowMarks = NIL;
 
+       estate->es_is_subquery = is_subquery;
+
        estate->es_instrument = false;
        estate->es_select_into = false;
        estate->es_into_oids = false;
@@ -258,9 +292,12 @@ FreeExecutorState(EState *estate)
 
        /*
         * Free the per-query memory context, thereby releasing all working
-        * memory, including the EState node itself.
+        * memory, including the EState node itself.  In a subquery, we don't
+        * do this, leaving the memory cleanup to happen when the topmost query
+        * is closed down.
         */
-       MemoryContextDelete(estate->es_query_cxt);
+       if (!estate->es_is_subquery)
+               MemoryContextDelete(estate->es_query_cxt);
 }
 
 /* ----------------

diff --git a/src/backend/executor/nodeSubplan.c b/src/backend/executor/nodeSubplan.c
index e30363e87474324818065e1161ceaabf7670ec4e..a24de2b2b9201a21e369994ff03189f41e15344e 100644 (file)
--- a/src/backend/executor/nodeSubplan.c
+++ b/src/backend/executor/nodeSubplan.c
@@ -635,7 +635,6 @@ ExecInitSubPlan(SubPlanState *node, EState *estate, int eflags)
 {
        SubPlan    *subplan = (SubPlan *) node->xprstate.expr;
        EState     *sp_estate;
-       MemoryContext oldcontext;
 
        /*
         * Do access checking on the rangetable entries in the subquery.
@@ -661,15 +660,13 @@ ExecInitSubPlan(SubPlanState *node, EState *estate, int eflags)
         * create an EState for the subplan
         *
         * The subquery needs its own EState because it has its own rangetable. It
-        * shares our Param ID space, however.  XXX if rangetable access were done
-        * differently, the subquery could share our EState, which would eliminate
-        * some thrashing about in this module...
+        * shares our Param ID space and es_query_cxt, however.  XXX if rangetable
+        * access were done differently, the subquery could share our EState,
+        * which would eliminate some thrashing about in this module...
         */
-       sp_estate = CreateExecutorState();
+       sp_estate = CreateSubExecutorState(estate);
        node->sub_estate = sp_estate;
 
-       oldcontext = MemoryContextSwitchTo(sp_estate->es_query_cxt);
-
        sp_estate->es_range_table = subplan->rtable;
        sp_estate->es_param_list_info = estate->es_param_list_info;
        sp_estate->es_param_exec_vals = estate->es_param_exec_vals;
@@ -694,8 +691,6 @@ ExecInitSubPlan(SubPlanState *node, EState *estate, int eflags)
 
        node->needShutdown = true;      /* now we need to shutdown the subplan */
 
-       MemoryContextSwitchTo(oldcontext);
-
        /*
         * If this plan is un-correlated or undirect correlated one and want to
         * set params for parent plan then mark parameters as needing evaluation.
@@ -1036,11 +1031,7 @@ ExecEndSubPlan(SubPlanState *node)
 {
        if (node->needShutdown)
        {
-               MemoryContext oldcontext;
-
-               oldcontext = MemoryContextSwitchTo(node->sub_estate->es_query_cxt);
                ExecEndPlan(node->planstate, node->sub_estate);
-               MemoryContextSwitchTo(oldcontext);
                FreeExecutorState(node->sub_estate);
                node->sub_estate = NULL;
                node->planstate = NULL;

diff --git a/src/backend/executor/nodeSubqueryscan.c b/src/backend/executor/nodeSubqueryscan.c
index 3213f7ca4beb7e539e7ead431232659bbed78c20..35826f9c1a0686f60570e68dfcd593aaf6f3798a 100644 (file)
--- a/src/backend/executor/nodeSubqueryscan.c
+++ b/src/backend/executor/nodeSubqueryscan.c
@@ -49,7 +49,6 @@ SubqueryNext(SubqueryScanState *node)
        EState     *estate;
        ScanDirection direction;
        TupleTableSlot *slot;
-       MemoryContext oldcontext;
 
        /*
         * get information from the estate and scan state
@@ -63,17 +62,12 @@ SubqueryNext(SubqueryScanState *node)
         */
 
        /*
-        * Get the next tuple from the sub-query.  We have to be careful to run it
-        * in its appropriate memory context.
+        * Get the next tuple from the sub-query.
         */
        node->sss_SubEState->es_direction = direction;
 
-       oldcontext = MemoryContextSwitchTo(node->sss_SubEState->es_query_cxt);
-
        slot = ExecProcNode(node->subplan);
 
-       MemoryContextSwitchTo(oldcontext);
-
        /*
         * We just overwrite our ScanTupleSlot with the subplan's result slot,
         * rather than expending the cycles for ExecCopySlot().
@@ -112,7 +106,6 @@ ExecInitSubqueryScan(SubqueryScan *node, EState *estate, int eflags)
        SubqueryScanState *subquerystate;
        RangeTblEntry *rte;
        EState     *sp_estate;
-       MemoryContext oldcontext;
 
        /* check for unsupported flags */
        Assert(!(eflags & EXEC_FLAG_MARK));
@@ -170,15 +163,13 @@ ExecInitSubqueryScan(SubqueryScan *node, EState *estate, int eflags)
 
        /*
         * The subquery needs its own EState because it has its own rangetable. It
-        * shares our Param ID space, however.  XXX if rangetable access were done
-        * differently, the subquery could share our EState, which would eliminate
-        * some thrashing about in this module...
+        * shares our Param ID space and es_query_cxt, however.  XXX if rangetable
+        * access were done differently, the subquery could share our EState,
+        * which would eliminate some thrashing about in this module...
         */
-       sp_estate = CreateExecutorState();
+       sp_estate = CreateSubExecutorState(estate);
        subquerystate->sss_SubEState = sp_estate;
 
-       oldcontext = MemoryContextSwitchTo(sp_estate->es_query_cxt);
-
        sp_estate->es_range_table = rte->subquery->rtable;
        sp_estate->es_param_list_info = estate->es_param_list_info;
        sp_estate->es_param_exec_vals = estate->es_param_exec_vals;
@@ -193,8 +184,6 @@ ExecInitSubqueryScan(SubqueryScan *node, EState *estate, int eflags)
         */
        subquerystate->subplan = ExecInitNode(node->subplan, sp_estate, eflags);
 
-       MemoryContextSwitchTo(oldcontext);
-
        subquerystate->ss.ps.ps_TupFromTlist = false;
 
        /*
@@ -235,8 +224,6 @@ ExecCountSlotsSubqueryScan(SubqueryScan *node)
 void
 ExecEndSubqueryScan(SubqueryScanState *node)
 {
-       MemoryContext oldcontext;
-
        /*
         * Free the exprcontext
         */
@@ -251,12 +238,8 @@ ExecEndSubqueryScan(SubqueryScanState *node)
        /*
         * close down subquery
         */
-       oldcontext = MemoryContextSwitchTo(node->sss_SubEState->es_query_cxt);
-
        ExecEndPlan(node->subplan, node->sss_SubEState);
 
-       MemoryContextSwitchTo(oldcontext);
-
        FreeExecutorState(node->sss_SubEState);
 }
 
@@ -270,12 +253,9 @@ void
 ExecSubqueryReScan(SubqueryScanState *node, ExprContext *exprCtxt)
 {
        EState     *estate;
-       MemoryContext oldcontext;
 
        estate = node->ss.ps.state;
 
-       oldcontext = MemoryContextSwitchTo(node->sss_SubEState->es_query_cxt);
-
        /*
         * ExecReScan doesn't know about my subplan, so I have to do
         * changed-parameter signaling myself.  This is just as well, because the
@@ -291,8 +271,6 @@ ExecSubqueryReScan(SubqueryScanState *node, ExprContext *exprCtxt)
        if (node->subplan->chgParam == NULL)
                ExecReScan(node->subplan, NULL);
 
-       MemoryContextSwitchTo(oldcontext);
-
        node->ss.ss_ScanTupleSlot = NULL;
        node->ss.ps.ps_TupFromTlist = false;
 }

diff --git a/src/include/executor/executor.h b/src/include/executor/executor.h
index 45836fea94bc2cdd878d0e646b9b5b17a4d7a5ef..766ef4b46a1456698abe268a1df95298bfe98bca 100644 (file)
--- a/src/include/executor/executor.h
+++ b/src/include/executor/executor.h
@@ -223,6 +223,7 @@ extern void end_tup_output(TupOutputState *tstate);
  * prototypes from functions in execUtils.c
  */
 extern EState *CreateExecutorState(void);
+extern EState *CreateSubExecutorState(EState *parent_estate);
 extern void FreeExecutorState(EState *estate);
 extern ExprContext *CreateExprContext(EState *estate);
 extern ExprContext *CreateStandaloneExprContext(void);

diff --git a/src/include/nodes/execnodes.h b/src/include/nodes/execnodes.h
index 43bf753ecef4e6302124de1879e9fad1e5d66961..a7123f9f711fbc149b47f6f9098ee72da83f60aa 100644 (file)
--- a/src/include/nodes/execnodes.h
+++ b/src/include/nodes/execnodes.h
@@ -323,6 +323,8 @@ typedef struct EState
        Oid                     es_lastoid;             /* last oid processed (by INSERT) */
        List       *es_rowMarks;        /* not good place, but there is no other */
 
+       bool            es_is_subquery; /* true if subquery (es_query_cxt not mine) */
+
        bool            es_instrument;  /* true requests runtime instrumentation */
        bool            es_select_into; /* true if doing SELECT INTO */
        bool            es_into_oids;   /* true to generate OIDs in SELECT INTO */