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Fix reference-after-free when waiting for another xact due to constraint. 

If an insertion or update had to wait for another transaction to finish,
because there was another insertion with conflicting key in progress,
we would pass a just-free'd item pointer to XactLockTableWait().

All calls to XactLockTableWait() and MultiXactIdWait() had similar issues.
Some passed a pointer to a buffer in the buffer cache, after already
releasing the lock. The call in EvalPlanQualFetch had already released the
pin too. All but the call in execUtils.c would merely lead to reporting a
bogus ctid, however (or an assertion failure, if enabled).

All the callers that passed HeapTuple->t_data->t_ctid were slightly bogus
anyway: if the tuple was updated (again) in the same transaction, its ctid
field would point to the next tuple in the chain, not the tuple itself.

Backpatch to 9.4, where the 'ctid' argument to XactLockTableWait was added
(in commit f88d4cfc)
This commit is contained in:
Heikki Linnakangas 2015-02-04 16:00:34 +02:00
parent 370b3a4618
commit 57fe246890
4 changed files with 14 additions and 12 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

16
src/backend/access/heap/heapam.c
View File

@ -2717,7 +2717,7 @@ l1:
{
/* wait for multixact */
MultiXactIdWait((MultiXactId) xwait, MultiXactStatusUpdate, infomask,
relation, &tp.t_data->t_ctid, XLTW_Delete,
relation, &(tp.t_self), XLTW_Delete,
NULL);
LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
@ -2744,7 +2744,7 @@ l1:
else
{
/* wait for regular transaction to end */
XactLockTableWait(xwait, relation, &tp.t_data->t_ctid, XLTW_Delete);
XactLockTableWait(xwait, relation, &(tp.t_self), XLTW_Delete);
LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
/*
@ -3261,7 +3261,7 @@ l2:
/* wait for multixact */
MultiXactIdWait((MultiXactId) xwait, mxact_status, infomask,
relation, &oldtup.t_data->t_ctid, XLTW_Update,
relation, &oldtup.t_self, XLTW_Update,
&remain);
LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
@ -3341,7 +3341,7 @@ l2:
*/
heap_acquire_tuplock(relation, &(oldtup.t_self), *lockmode,
LockWaitBlock, &have_tuple_lock);
XactLockTableWait(xwait, relation, &oldtup.t_data->t_ctid,
XactLockTableWait(xwait, relation, &oldtup.t_self,
XLTW_Update);
LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
@ -4365,7 +4365,7 @@ l3:
{
case LockWaitBlock:
MultiXactIdWait((MultiXactId) xwait, status, infomask,
relation, &tuple->t_data->t_ctid, XLTW_Lock, NULL);
relation, &tuple->t_self, XLTW_Lock, NULL);
break;
case LockWaitSkip:
if (!ConditionalMultiXactIdWait((MultiXactId) xwait,
@ -4437,7 +4437,7 @@ l3:
switch (wait_policy)
{
case LockWaitBlock:
XactLockTableWait(xwait, relation, &tuple->t_data->t_ctid,
XactLockTableWait(xwait, relation, &tuple->t_self,
XLTW_Lock);
break;
case LockWaitSkip:
@ -5181,7 +5181,7 @@ l4:
{
LockBuffer(buf, BUFFER_LOCK_UNLOCK);
XactLockTableWait(members[i].xid, rel,
&mytup.t_data->t_ctid,
&mytup.t_self,
XLTW_LockUpdated);
pfree(members);
goto l4;
@ -5242,7 +5242,7 @@ l4:
if (needwait)
{
LockBuffer(buf, BUFFER_LOCK_UNLOCK);
XactLockTableWait(rawxmax, rel, &mytup.t_data->t_ctid,
XactLockTableWait(rawxmax, rel, &mytup.t_self,
XLTW_LockUpdated);
goto l4;
}

4
src/backend/catalog/index.c
View File

@ -2328,7 +2328,7 @@ IndexBuildHeapRangeScan(Relation heapRelation,
*/
LockBuffer(scan->rs_cbuf, BUFFER_LOCK_UNLOCK);
XactLockTableWait(xwait, heapRelation,
&heapTuple->t_data->t_ctid,
&heapTuple->t_self,
XLTW_InsertIndexUnique);
CHECK_FOR_INTERRUPTS();
goto recheck;
@ -2377,7 +2377,7 @@ IndexBuildHeapRangeScan(Relation heapRelation,
*/
LockBuffer(scan->rs_cbuf, BUFFER_LOCK_UNLOCK);
XactLockTableWait(xwait, heapRelation,
&heapTuple->t_data->t_ctid,
&heapTuple->t_self,
XLTW_InsertIndexUnique);
CHECK_FOR_INTERRUPTS();
goto recheck;

2
src/backend/executor/execMain.c
View File

@ -2118,7 +2118,7 @@ EvalPlanQualFetch(EState *estate, Relation relation, int lockmode,
{
case LockWaitBlock:
XactLockTableWait(SnapshotDirty.xmax,
relation, &tuple.t_data->t_ctid,
relation, &tuple.t_self,
XLTW_FetchUpdated);
break;
case LockWaitSkip:

4
src/backend/executor/execUtils.c
View File

@ -1245,6 +1245,7 @@ retry:
ForwardScanDirection)) != NULL)
{
TransactionId xwait;
ItemPointerData ctid_wait;
Datum existing_values[INDEX_MAX_KEYS];
bool existing_isnull[INDEX_MAX_KEYS];
char *error_new;
@ -1306,8 +1307,9 @@ retry:
if (TransactionIdIsValid(xwait))
{
ctid_wait = tup->t_data->t_ctid;
index_endscan(index_scan);
XactLockTableWait(xwait, heap, &tup->t_data->t_ctid,
XactLockTableWait(xwait, heap, &ctid_wait,
XLTW_RecheckExclusionConstr);
goto retry;
}