Fix cleanup lock acquisition in SPLIT_ALLOCATE_PAGE replay.

Amit Kapila · Amit Kapila · commit e848be60b5cf · 2022-11-14T10:43:33.000+05:30
During XLOG_HASH_SPLIT_ALLOCATE_PAGE replay, we were checking for a cleanup lock on the new bucket page after acquiring an exclusive lock on it and raising a PANIC error on failure. However, it is quite possible that checkpointer can acquire the pin on the same page before acquiring a lock on it, and then the replay will lead to an error. So instead, directly acquire the cleanup lock on the new bucket page during XLOG_HASH_SPLIT_ALLOCATE_PAGE replay operation. Reported-by: Andres Freund Author: Robert Haas Reviewed-By: Amit Kapila, Andres Freund, Vignesh C Backpatch-through: 11 Discussion: https://postgr.es/m/20220810022617.fvjkjiauaykwrbse@awork3.anarazel.de
diff --git a/src/backend/access/hash/hash_xlog.c b/src/backend/access/hash/hash_xlog.c
@@ -351,11 +351,10 @@ hash_xlog_split_allocate_page(XLogReaderState *record)
 	}
 
 	/* replay the record for new bucket */
-	newbuf = XLogInitBufferForRedo(record, 1);
+	XLogReadBufferForRedoExtended(record, 1, RBM_ZERO_AND_CLEANUP_LOCK, true,
+								  &newbuf);
 	_hash_initbuf(newbuf, xlrec->new_bucket, xlrec->new_bucket,
 				  xlrec->new_bucket_flag, true);
-	if (!IsBufferCleanupOK(newbuf))
-		elog(PANIC, "hash_xlog_split_allocate_page: failed to acquire cleanup lock");
 	MarkBufferDirty(newbuf);
 	PageSetLSN(BufferGetPage(newbuf), lsn);
 
diff --git a/src/backend/access/hash/hashpage.c b/src/backend/access/hash/hashpage.c
@@ -805,9 +805,13 @@ _hash_expandtable(Relation rel, Buffer metabuf)
 	/*
 	 * Physically allocate the new bucket's primary page.  We want to do this
 	 * before changing the metapage's mapping info, in case we can't get the
-	 * disk space.  Ideally, we don't need to check for cleanup lock on new
-	 * bucket as no other backend could find this bucket unless meta page is
-	 * updated.  However, it is good to be consistent with old bucket locking.
+	 * disk space.
+	 *
+	 * XXX It doesn't make sense to call _hash_getnewbuf first, zeroing the
+	 * buffer, and then only afterwards check whether we have a cleanup lock.
+	 * However, since no scan can be accessing the buffer yet, any concurrent
+	 * accesses will just be from processes like the bgwriter or checkpointer
+	 * which don't care about its contents, so it doesn't really matter.
 	 */
 	buf_nblkno = _hash_getnewbuf(rel, start_nblkno, MAIN_FORKNUM);
 	if (!IsBufferCleanupOK(buf_nblkno))
