From be2f0731006300876b008fd78a265471984cbcd9 Mon Sep 17 00:00:00 2001 From: Alvaro Herrera Date: Wed, 3 Apr 2024 17:49:44 +0200 Subject: [PATCH] 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 Also update an outdated comment in the same file -- SerialSLRULock exists no more.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 Reviewed-by: Dilip Kumar Discussion: https://postgr.es/m/2a25eaf4-a3a4-5fd1-6241-9d7c73142085@gmail.com --- src/backend/storage/lmgr/predicate.c | 19 ++++++++++++------- 1 file changed, 12 insertions(+), 7 deletions(-) diff --git a/src/backend/storage/lmgr/predicate.c b/src/backend/storage/lmgr/predicate.c index 3f378c0099b..d5bbfbd4c6f 100644 --- a/src/backend/storage/lmgr/predicate.c +++ b/src/backend/storage/lmgr/predicate.c @@ -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; -- 2.30.2