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Commiteb81b65

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committed
The previous fix in CVS HEAD and 8.4 for handling the case where a cursor
being used in a PL/pgSQL FOR loop is closed was inadequate, as Tom Lanepointed out. The bug affects FOR statement variants too, because you canclose an implicitly created cursor too by guessing the "<unnamed portal X>"name created for it.To fix that, "pin" the portal to prevent it from being dropped while it'sbeing used in a PL/pgSQL FOR loop. Backpatch all the way to 7.4 which isthe oldest supported version.
1 parent2330d9c commiteb81b65

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3 files changed

+64
-43
lines changed

3 files changed

+64
-43
lines changed

‎src/backend/utils/mmgr/portalmem.c‎

Lines changed: 49 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -12,7 +12,7 @@
1212
* Portions Copyright (c) 1994, Regents of the University of California
1313
*
1414
* IDENTIFICATION
15-
* $PostgreSQL: pgsql/src/backend/utils/mmgr/portalmem.c,v 1.118 2010/02/26 02:01:14 momjian Exp $
15+
* $PostgreSQL: pgsql/src/backend/utils/mmgr/portalmem.c,v 1.119 2010/07/05 09:27:17 heikki Exp $
1616
*
1717
*-------------------------------------------------------------------------
1818
*/
@@ -376,6 +376,28 @@ PortalCreateHoldStore(Portal portal)
376376
MemoryContextSwitchTo(oldcxt);
377377
}
378378

379+
/*
380+
* PinPortal
381+
*Protect a portal from dropping.
382+
*/
383+
void
384+
PinPortal(Portalportal)
385+
{
386+
if (portal->portalPinned)
387+
elog(ERROR,"portal already pinned");
388+
389+
portal->portalPinned= true;
390+
}
391+
392+
void
393+
UnpinPortal(Portalportal)
394+
{
395+
if (!portal->portalPinned)
396+
elog(ERROR,"portal not pinned");
397+
398+
portal->portalPinned= false;
399+
}
400+
379401
/*
380402
* PortalDrop
381403
*Destroy the portal.
@@ -385,9 +407,16 @@ PortalDrop(Portal portal, bool isTopCommit)
385407
{
386408
AssertArg(PortalIsValid(portal));
387409

388-
/* Not sure if this case can validly happen or not... */
389-
if (portal->status==PORTAL_ACTIVE)
390-
elog(ERROR,"cannot drop active portal");
410+
/*
411+
* Don't allow dropping a pinned portal, it's still needed by whoever
412+
* pinned it. Not sure if the PORTAL_ACTIVE case can validly happen or
413+
* not...
414+
*/
415+
if (portal->portalPinned||
416+
portal->status==PORTAL_ACTIVE)
417+
ereport(ERROR,
418+
(errcode(ERRCODE_INVALID_CURSOR_STATE),
419+
errmsg("cannot drop active portal \"%s\"",portal->name)));
391420

392421
/*
393422
* Remove portal from hash table. Because we do this first, we will not
@@ -630,6 +659,13 @@ AtCommit_Portals(void)
630659
continue;
631660
}
632661

662+
/*
663+
* There should be no pinned portals anymore. Complain if someone
664+
* leaked one.
665+
*/
666+
if (portal->portalPinned)
667+
elog(ERROR,"cannot commit while a portal is pinned");
668+
633669
/*
634670
* Do nothing to cursors held over from a previous transaction
635671
* (including holdable ones just frozen by CommitHoldablePortals).
@@ -738,7 +774,15 @@ AtCleanup_Portals(void)
738774
continue;
739775
}
740776

741-
/* Else zap it. */
777+
/*
778+
* If a portal is still pinned, forcibly unpin it. PortalDrop will
779+
* not let us drop the portal otherwise. Whoever pinned the portal
780+
* was interrupted by the abort too and won't try to use it anymore.
781+
*/
782+
if (portal->portalPinned)
783+
portal->portalPinned= false;
784+
785+
/* Zap it. */
742786
PortalDrop(portal, false);
743787
}
744788
}

‎src/include/utils/portal.h‎

Lines changed: 4 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -39,7 +39,7 @@
3939
* Portions Copyright (c) 1996-2010, PostgreSQL Global Development Group
4040
* Portions Copyright (c) 1994, Regents of the University of California
4141
*
42-
* $PostgreSQL: pgsql/src/include/utils/portal.h,v 1.82 2010/01/02 16:58:10 momjian Exp $
42+
* $PostgreSQL: pgsql/src/include/utils/portal.h,v 1.83 2010/07/05 09:27:17 heikki Exp $
4343
*
4444
*-------------------------------------------------------------------------
4545
*/
@@ -133,6 +133,7 @@ typedef struct PortalData
133133

134134
/* Status data */
135135
PortalStatusstatus;/* see above */
136+
boolportalPinned;/* a pinned portal can't be dropped */
136137

137138
/* If not NULL, Executor is active; call ExecutorEnd eventually: */
138139
QueryDesc*queryDesc;/* info needed for executor invocation */
@@ -199,6 +200,8 @@ extern void AtSubAbort_Portals(SubTransactionId mySubid,
199200
externvoidAtSubCleanup_Portals(SubTransactionIdmySubid);
200201
externPortalCreatePortal(constchar*name,boolallowDup,booldupSilent);
201202
externPortalCreateNewPortal(void);
203+
externvoidPinPortal(Portalportal);
204+
externvoidUnpinPortal(Portalportal);
202205
externvoidPortalDrop(Portalportal,boolisTopCommit);
203206
externPortalGetPortalByName(constchar*name);
204207
externvoidPortalDefineQuery(Portalportal,

‎src/pl/plpgsql/src/pl_exec.c‎

Lines changed: 11 additions & 37 deletions
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
88
*
99
*
1010
* IDENTIFICATION
11-
* $PostgreSQL: pgsql/src/pl/plpgsql/src/pl_exec.c,v 1.259 2010/06/21 09:47:29 heikki Exp $
11+
* $PostgreSQL: pgsql/src/pl/plpgsql/src/pl_exec.c,v 1.260 2010/07/05 09:27:18 heikki Exp $
1212
*
1313
*-------------------------------------------------------------------------
1414
*/
@@ -2002,20 +2002,11 @@ exec_stmt_forc(PLpgSQL_execstate *estate, PLpgSQL_stmt_forc *stmt)
20022002
rc=exec_for_query(estate, (PLpgSQL_stmt_forq*)stmt,portal, false);
20032003

20042004
/* ----------
2005-
* Close portal. The statements executed in the loop might've closed the
2006-
* cursor already, rendering our portal pointer invalid, so we mustn't
2007-
* trust the pointer.
2005+
* Close portal, and restore cursor variable if it was initially NULL.
20082006
* ----------
20092007
*/
2010-
portal=SPI_cursor_find(portalname);
2011-
if (portal==NULL)
2012-
ereport(ERROR,
2013-
(errcode(ERRCODE_UNDEFINED_CURSOR),
2014-
errmsg("cursor \"%s\" closed unexpectedly",
2015-
portalname)));
20162008
SPI_cursor_close(portal);
20172009

2018-
/* Restore cursor variable if it was initially NULL. */
20192010
if (curname==NULL)
20202011
{
20212012
free_var(curvar);
@@ -4278,13 +4269,6 @@ exec_run_select(PLpgSQL_execstate *estate,
42784269
* exec_for_query --- execute body of FOR loop for each row from a portal
42794270
*
42804271
* Used by exec_stmt_fors, exec_stmt_forc and exec_stmt_dynfors
4281-
*
4282-
* If the portal is for a cursor that's visible to user code, the statements
4283-
* we execute might move or close the cursor. You must pass prefetch_ok=false
4284-
* in that case to disable optimizations that rely on the portal staying
4285-
* unchanged over execution of the user statements.
4286-
* NB: With prefetch_ok=false, the portal pointer might point to garbage
4287-
* after the call. Caller beware!
42884272
*/
42894273
staticint
42904274
exec_for_query(PLpgSQL_execstate*estate,PLpgSQL_stmt_forq*stmt,
@@ -4296,10 +4280,6 @@ exec_for_query(PLpgSQL_execstate *estate, PLpgSQL_stmt_forq *stmt,
42964280
boolfound= false;
42974281
intrc=PLPGSQL_RC_OK;
42984282
intn;
4299-
constchar*portalname;
4300-
4301-
/* Remember portal name so that we can re-find it */
4302-
portalname=portal->name;
43034283

43044284
/*
43054285
* Determine if we assign to a record or a row
@@ -4311,6 +4291,12 @@ exec_for_query(PLpgSQL_execstate *estate, PLpgSQL_stmt_forq *stmt,
43114291
else
43124292
elog(ERROR,"unsupported target");
43134293

4294+
/*
4295+
* Make sure the portal doesn't get closed by the user statements
4296+
* we execute.
4297+
*/
4298+
PinPortal(portal);
4299+
43144300
/*
43154301
* Fetch the initial tuple(s).If prefetching is allowed then we grab a
43164302
* few more rows to avoid multiple trips through executor startup
@@ -4408,22 +4394,8 @@ exec_for_query(PLpgSQL_execstate *estate, PLpgSQL_stmt_forq *stmt,
44084394

44094395
/*
44104396
* Fetch more tuples. If prefetching is allowed, grab 50 at a time.
4411-
* Otherwise the statements executed in the loop might've moved or
4412-
* even closed the cursor, so check that the cursor is still open,
4413-
* and fetch only one row at a time.
44144397
*/
4415-
if (prefetch_ok)
4416-
SPI_cursor_fetch(portal, true,50);
4417-
else
4418-
{
4419-
portal=SPI_cursor_find(portalname);
4420-
if (portal==NULL)
4421-
ereport(ERROR,
4422-
(errcode(ERRCODE_UNDEFINED_CURSOR),
4423-
errmsg("cursor \"%s\" closed unexpectedly",
4424-
portalname)));
4425-
SPI_cursor_fetch(portal, true,1);
4426-
}
4398+
SPI_cursor_fetch(portal, true,prefetch_ok ?50 :1);
44274399
tuptab=SPI_tuptable;
44284400
n=SPI_processed;
44294401
}
@@ -4435,6 +4407,8 @@ exec_for_query(PLpgSQL_execstate *estate, PLpgSQL_stmt_forq *stmt,
44354407
*/
44364408
SPI_freetuptable(tuptab);
44374409

4410+
UnpinPortal(portal);
4411+
44384412
/*
44394413
* Set the FOUND variable to indicate the result of executing the loop
44404414
* (namely, whether we looped one or more times). This must be set last so

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