From 577843f1b99ff6edfca2e7edcbd49c4d66a70185 Mon Sep 17 00:00:00 2001
From: tiancaiamao <tiancaiamao@gmail.com>
Date: Thu, 28 Apr 2022 14:21:51 +0800
Subject: [PATCH] internal/unionstore: avoid panic and add log for tidb
 issue/34307 (#482)

Signed-off-by: tiancaiamao <tiancaiamao@gmail.com>
---
 internal/unionstore/memdb_arena.go | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/internal/unionstore/memdb_arena.go b/internal/unionstore/memdb_arena.go
index 5addc883..db83e465 100644
--- a/internal/unionstore/memdb_arena.go
+++ b/internal/unionstore/memdb_arena.go
@@ -39,7 +39,9 @@ import (
 	"math"
 	"unsafe"
 
+	"github.com/tikv/client-go/v2/internal/logutil"
 	"github.com/tikv/client-go/v2/kv"
+	"go.uber.org/zap"
 )
 
 const (
@@ -61,7 +63,17 @@ type memdbArenaAddr struct {
 }
 
 func (addr memdbArenaAddr) isNull() bool {
-	return addr == nullAddr
+	if addr == nullAddr {
+		return true
+	}
+	if addr.idx == math.MaxUint32 || addr.off == math.MaxUint32 {
+		// defensive programming, the code should never run to here.
+		// it always means something wrong... (maybe caused by data race?)
+		// because we never set part of idx/off to math.MaxUint64
+		logutil.BgLogger().Warn("Invalid memdbArenaAddr", zap.Uint32("idx", addr.idx), zap.Uint32("off", addr.off))
+		return true
+	}
+	return false
 }
 
 // store and load is used by vlog, due to pointer in vlog is not aligned.