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Commitbe2f073

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Fix zeroing of pg_serial page without SLRU bank lock
Bug in commit53c2a97: we failed to acquire the correct SLRU banklock when iterating to zero-out intermediate pages in predicate.c.Rewrite the code block so that we follow the locking protocol correctly.Also update an outdated comment in the same file -- SerialSLRULockexists no more.Reported-by: Alexander Lakhin <exclusion@gmail.com>Reviewed-by: Dilip Kumar <dilipbalaut@gmail.com>Discussion:https://postgr.es/m/2a25eaf4-a3a4-5fd1-6241-9d7c73142085@gmail.com
1 parentbf1e650 commitbe2f073

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+12
-7
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1 file changed

+12
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‎src/backend/storage/lmgr/predicate.c

Lines changed: 12 additions & 7 deletions
Original file line numberDiff line numberDiff line change
@@ -137,7 +137,7 @@
137137
*SerialControlLock
138138
*- Protects SerialControlData members
139139
*
140-
*SerialSLRULock
140+
*SLRU per-bank locks
141141
*- Protects SerialSlruCtl
142142
*
143143
* Portions Copyright (c) 1996-2024, PostgreSQL Global Development Group
@@ -908,20 +908,25 @@ SerialAdd(TransactionId xid, SerCommitSeqNo minConflictCommitSeqNo)
908908
if (isNewPage)
909909
serialControl->headPage=targetPage;
910910

911-
LWLockAcquire(lock,LW_EXCLUSIVE);
912-
913911
if (isNewPage)
914912
{
915-
/* Initialize intervening pages. */
916-
while (firstZeroPage!=targetPage)
913+
/* Initialize intervening pages; might involve trading locks */
914+
for (;;)
917915
{
918-
(void)SimpleLruZeroPage(SerialSlruCtl,firstZeroPage);
916+
lock=SimpleLruGetBankLock(SerialSlruCtl,firstZeroPage);
917+
LWLockAcquire(lock,LW_EXCLUSIVE);
918+
slotno=SimpleLruZeroPage(SerialSlruCtl,firstZeroPage);
919+
if (firstZeroPage==targetPage)
920+
break;
919921
firstZeroPage=SerialNextPage(firstZeroPage);
922+
LWLockRelease(lock);
920923
}
921-
slotno=SimpleLruZeroPage(SerialSlruCtl,targetPage);
922924
}
923925
else
926+
{
927+
LWLockAcquire(lock,LW_EXCLUSIVE);
924928
slotno=SimpleLruReadPage(SerialSlruCtl,targetPage, true,xid);
929+
}
925930

926931
SerialValue(slotno,xid)=minConflictCommitSeqNo;
927932
SerialSlruCtl->shared->page_dirty[slotno]= true;

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