postgres.git / summary / log / commit / refs

commit    692df425b6883dd3edcc15bb984415ef349fafb1
Author:   Tom Lane <tgl@sss.pgh.pa.us>
Date:     Sat Aug 06 15:50:23 2022 +0000
First released in: 16.0, 15.0

    Fix data-corruption hazard in WAL-logged CREATE DATABASE.
    
    RelationCopyStorageUsingBuffer thought it could skip copying
    empty pages, but of course that does not work at all, because
    subsequent blocks will be out of place.
    
    Also fix it to acquire share lock on the source buffer.  It *might*
    be safe to not do that, but it's not very certain, and I don't think
    this code deserves any benefit of the doubt.
    
    Dilip Kumar, per complaint from me
    
    Discussion: https://postgr.es/m/3679800.1659654066@sss.pgh.pa.us


 src/backend/storage/buffer/bufmgr.c | 10 +++-------
 1 file changed, 3 insertions(+), 7 deletions(-)

diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c
index 6b30138ab32..8ef0436c521 100644
--- a/src/backend/storage/buffer/bufmgr.c
+++ b/src/backend/storage/buffer/bufmgr.c
@@ -3741,23 +3741,19 @@ RelationCopyStorageUsingBuffer(Relation src, Relation dst, ForkNumber forkNum,
 		srcBuf = ReadBufferWithoutRelcache(src->rd_locator, forkNum, blkno,
 										   RBM_NORMAL, bstrategy_src,
 										   permanent);
+		LockBuffer(srcBuf, BUFFER_LOCK_SHARE);
 		srcPage = BufferGetPage(srcBuf);
-		if (PageIsNew(srcPage) || PageIsEmpty(srcPage))
-		{
-			ReleaseBuffer(srcBuf);
-			continue;
-		}
 
 		/* Use P_NEW to extend the destination relation. */
 		dstBuf = ReadBufferWithoutRelcache(dst->rd_locator, forkNum, P_NEW,
 										   RBM_NORMAL, bstrategy_dst,
 										   permanent);
 		LockBuffer(dstBuf, BUFFER_LOCK_EXCLUSIVE);
+		dstPage = BufferGetPage(dstBuf);
 
 		START_CRIT_SECTION();
 
 		/* Copy page data from the source to the destination. */
-		dstPage = BufferGetPage(dstBuf);
 		memcpy(dstPage, srcPage, BLCKSZ);
 		MarkBufferDirty(dstBuf);
 
@@ -3768,7 +3764,7 @@ RelationCopyStorageUsingBuffer(Relation src, Relation dst, ForkNumber forkNum,
 		END_CRIT_SECTION();
 
 		UnlockReleaseBuffer(dstBuf);
-		ReleaseBuffer(srcBuf);
+		UnlockReleaseBuffer(srcBuf);
 	}
 }
 


[parent: 922a8fa09840]