From f3bb1d69a57bea820895efaf366371463e62235d Mon Sep 17 00:00:00 2001 From: Thomas Munro Date: Fri, 7 Jun 2024 17:49:19 +1200 Subject: [PATCH] Fix RBM_ZERO_AND_LOCK. Commit 210622c6 accidentally zeroed out pages even if they were found in the buffer pool. It should always lock the page, but it should only zero pages that were not already found as an optimization to avoid I/O. Otherwise, concurrent readers that hold only a pin might see corrupted page contents changing under their feet. Reported-by: Noah Misch Reported-by: Alexander Lakhin Discussion: https://postgr.es/m/20240512171658.7e.nmisch@google.com Discussion: https://postgr.es/m/7ed10231-ce47-03d5-d3f9-4aea0dc7d5a4%40gmail.com --- src/backend/storage/buffer/bufmgr.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index 49637284f91..238fc0e3547 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1016,7 +1016,7 @@ ExtendBufferedRelTo(BufferManagerRelation bmr, * return. */ static void -ZeroBuffer(Buffer buffer, ReadBufferMode mode) +ZeroBuffer(Buffer buffer, ReadBufferMode mode, bool zero) { BufferDesc *bufHdr; uint32 buf_state; @@ -1034,7 +1034,8 @@ ZeroBuffer(Buffer buffer, ReadBufferMode mode) LockBufferForCleanup(buffer); } - memset(BufferGetPage(buffer), 0, BLCKSZ); + if (zero) + memset(BufferGetPage(buffer), 0, BLCKSZ); if (BufferIsLocal(buffer)) { @@ -1185,7 +1186,7 @@ ReadBuffer_common(Relation rel, SMgrRelation smgr, char smgr_persistence, buffer = PinBufferForBlock(rel, smgr, smgr_persistence, forkNum, blockNum, strategy, &found); - ZeroBuffer(buffer, mode); + ZeroBuffer(buffer, mode, !found); return buffer; } -- 2.45.1