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Fix zeroing of pg_serial page without SLRU bank lock 

Bug in commit 53c2a97a9266: we failed to acquire the correct SLRU bank
lock 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Also update an outdated comment in the same file -- SerialSLRULock
exists 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
This commit is contained in:
Alvaro Herrera 2024-04-03 17:49:44 +02:00
parent bf1e650806
commit be2f073100
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GPG Key ID: 1C20ACB9D5C564AE
1 changed files with 12 additions and 7 deletions
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19
src/backend/storage/lmgr/predicate.c
View File

@ -137,7 +137,7 @@
* SerialControlLock
* - Protects SerialControlData members
*
* SerialSLRULock
* SLRU per-bank locks
* - Protects SerialSlruCtl
*
* Portions Copyright (c) 1996-2024, PostgreSQL Global Development Group
@ -908,20 +908,25 @@ SerialAdd(TransactionId xid, SerCommitSeqNo minConflictCommitSeqNo)
if (isNewPage)
serialControl->headPage = targetPage;
LWLockAcquire(lock, LW_EXCLUSIVE);
if (isNewPage)
{
/* Initialize intervening pages. */
while (firstZeroPage != targetPage)
/* Initialize intervening pages; might involve trading locks */
for (;;)
{
(void) SimpleLruZeroPage(SerialSlruCtl, firstZeroPage);
lock = SimpleLruGetBankLock(SerialSlruCtl, firstZeroPage);
LWLockAcquire(lock, LW_EXCLUSIVE);
slotno = SimpleLruZeroPage(SerialSlruCtl, firstZeroPage);
if (firstZeroPage == targetPage)
break;
firstZeroPage = SerialNextPage(firstZeroPage);
LWLockRelease(lock);
}
slotno = SimpleLruZeroPage(SerialSlruCtl, targetPage);
}
else
{
LWLockAcquire(lock, LW_EXCLUSIVE);
slotno = SimpleLruReadPage(SerialSlruCtl, targetPage, true, xid);
}
SerialValue(slotno, xid) = minConflictCommitSeqNo;
SerialSlruCtl->shared->page_dirty[slotno] = true;