backup br stuck waiting for any response from TiKV

[Leavrth]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

1. backup

2. What did you expect to see? (Required)

success

3. What did you see instead (Required)

br stuck

goroutine 17165 [select, 1399 minutes]:
google.golang.org/grpc/internal/transport.(*Stream).waitonHleader(..)
google.golang.org/grpc/internal/transport.(*Stream).RecvCompress(..)
google.golang.org/grpc.(*csAttempt).recvMsg(..)
google.golang.org/grpc.(*clientStream).RecvMsg.func1(..)
google.golang.org/grpc.(*clientStream).withRetry(..)
google.golang.org/grpc.(*clientStream).RecvMsg(..}
github.com/pingcap/kvproto/pkg/brpb.(*backupBackupClient).Recv(..)
github.com/pingcap/tidb/br/pkg/backup.doSendBackup(..)

4. What is your TiDB version? (Required)

7.1