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Commitc3928b4

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Fix segfault during EvalPlanQual with mix of local and foreign partitions.
It's not sensible to re-evaluate a direct-modify Foreign Update or Deleteduring EvalPlanQual. However, ExecInitForeignScan() can still get calledif a table mixes local and foreign partitions. EvalPlanQualStart() leftthe es_result_relations array uninitialized in the child EPQ EState, butExecInitForeignScan() still expected to find it. That caused a segfault.Fix by skipping the es_result_relations lookup during EvalPlanQualprocessing. To make things a bit more robust, also skip theBeginDirectModify calls, and add a runtime check that ExecForeignScan()is not called on direct-modify foreign scans during EvalPlanQualprocessing.This is new in v14, commit1375422. Before that, EvalPlanQualStart()copied the whole ResultRelInfo array to the EPQ EState. Backpatch to v14.Report and diagnosis by Andrey Lepikhov.Discussion:https://www.postgresql.org/message-id/cb2b808d-cbaa-4772-76ee-c8809bafcf3d%40postgrespro.ru
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‎src/backend/executor/nodeForeignscan.c

Lines changed: 41 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -44,12 +44,22 @@ ForeignNext(ForeignScanState *node)
4444
TupleTableSlot*slot;
4545
ForeignScan*plan= (ForeignScan*)node->ss.ps.plan;
4646
ExprContext*econtext=node->ss.ps.ps_ExprContext;
47+
EState*estate=node->ss.ps.state;
4748
MemoryContextoldcontext;
4849

4950
/* Call the Iterate function in short-lived context */
5051
oldcontext=MemoryContextSwitchTo(econtext->ecxt_per_tuple_memory);
5152
if (plan->operation!=CMD_SELECT)
53+
{
54+
/*
55+
* direct modifications cannot be re-evaluated, so shouldn't get here
56+
* during EvalPlanQual processing
57+
*/
58+
if (estate->es_epq_active!=NULL)
59+
elog(ERROR,"cannot re-evaluate a Foreign Update or Delete during EvalPlanQual");
60+
5261
slot=node->fdwroutine->IterateDirectModify(node);
62+
}
5363
else
5464
slot=node->fdwroutine->IterateForeignScan(node);
5565
MemoryContextSwitchTo(oldcontext);
@@ -223,11 +233,25 @@ ExecInitForeignScan(ForeignScan *node, EState *estate, int eflags)
223233
scanstate->fdw_state=NULL;
224234

225235
/*
226-
* For the FDW's convenience, look up the modification target relation's.
227-
* ResultRelInfo.
236+
* For the FDW's convenience, look up the modification target relation's
237+
* ResultRelInfo. The ModifyTable node should have initialized it for us,
238+
* see ExecInitModifyTable.
239+
*
240+
* Don't try to look up the ResultRelInfo when EvalPlanQual is active,
241+
* though. Direct modififications cannot be re-evaluated as part of
242+
* EvalPlanQual. The lookup wouldn't work anyway because during
243+
* EvalPlanQual processing, EvalPlanQual only initializes the subtree
244+
* under the ModifyTable, and doesn't run ExecInitModifyTable.
228245
*/
229-
if (node->resultRelation>0)
246+
if (node->resultRelation>0&&estate->es_epq_active==NULL)
247+
{
248+
if (estate->es_result_relations==NULL||
249+
estate->es_result_relations[node->resultRelation-1]==NULL)
250+
{
251+
elog(ERROR,"result relation not initialized");
252+
}
230253
scanstate->resultRelInfo=estate->es_result_relations[node->resultRelation-1];
254+
}
231255

232256
/* Initialize any outer plan. */
233257
if (outerPlan(node))
@@ -238,7 +262,15 @@ ExecInitForeignScan(ForeignScan *node, EState *estate, int eflags)
238262
* Tell the FDW to initialize the scan.
239263
*/
240264
if (node->operation!=CMD_SELECT)
241-
fdwroutine->BeginDirectModify(scanstate,eflags);
265+
{
266+
/*
267+
* Direct modifications cannot be re-evaluated by EvalPlanQual, so
268+
* don't bother preparing the FDW. There can ForeignScan nodes in the
269+
* EvalPlanQual subtree, but ExecForeignScan should never be called.
270+
*/
271+
if (estate->es_epq_active==NULL)
272+
fdwroutine->BeginDirectModify(scanstate,eflags);
273+
}
242274
else
243275
fdwroutine->BeginForeignScan(scanstate,eflags);
244276

@@ -255,10 +287,14 @@ void
255287
ExecEndForeignScan(ForeignScanState*node)
256288
{
257289
ForeignScan*plan= (ForeignScan*)node->ss.ps.plan;
290+
EState*estate=node->ss.ps.state;
258291

259292
/* Let the FDW shut down */
260293
if (plan->operation!=CMD_SELECT)
261-
node->fdwroutine->EndDirectModify(node);
294+
{
295+
if (estate->es_epq_active==NULL)
296+
node->fdwroutine->EndDirectModify(node);
297+
}
262298
else
263299
node->fdwroutine->EndForeignScan(node);
264300

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