goleak github.com/pingcap/goleveldb/leveldb.(*DB).mpoolDrain

[hawkingrei]

Bug Report

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1. Minimal reproduce step (Required)

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

3. What did you see instead (Required)

==================== Test output for //br/pkg/restore:restore_test (shard 31 of 50):
...
...
...
goleak: Errors on successful test run: found unexpected goroutines:
[Goroutine 22847 in state select, with github.com/pingcap/goleveldb/leveldb.(*DB).mpoolDrain on top of the stack:
goroutine 22847 [select]:
github.com/pingcap/goleveldb/leveldb.(*DB).mpoolDrain(0xc007acba00)
	external/com_github_pingcap_goleveldb/leveldb/db_state.go:110 +0x205
created by github.com/pingcap/goleveldb/leveldb.openDB
	external/com_github_pingcap_goleveldb/leveldb/db.go:140 +0x9bf
] 

4. What is your TiDB version? (Required)