consider updating logrus

[siddontang]

Bug Report

In our test, we find there are too many mutex used

268847702 2712 @ 0x473024 0x6f0c40 0x6ef80c 0xf94517 0x1028925 0x1032e46 0x102c0fb 0x102cf3e 0x102c5e9 0x106068c 0x105963e 0x10571b6 0x1055d0e 0x106fce4 0x45bc71
#	0x473023	sync.(*Mutex).Unlock+0x73								/home/qupeng/.local/opt/go/src/sync/mutex.go:201
#	0x6f0c3f	github.com/pingcap/tidb/vendor/github.com/sirupsen/logrus.(*MutexWrap).Unlock+0x3f	/home/qupeng/.go/src/github.com/pingcap/tidb/vendor/github.com/sirupsen/logrus/logger.go:49
#	0x6ef80b	github.com/pingcap/tidb/vendor/github.com/sirupsen/logrus.GetLevel+0x7b			/home/qupeng/.go/src/github.com/pingcap/tidb/vendor/github.com/sirupsen/logrus/exported.go:41
#	0xf94516	github.com/pingcap/tidb/executor.(*ExecStmt).LogSlowQuery+0x36				/home/qupeng/.go/src/github.com/pingcap/tidb/executor/adapter.go:336
#	0x1028924	github.com/pingcap/tidb/session.(*session).CommitTxn+0x124				/home/qupeng/.go/src/github.com/pingcap/tidb/session/session.go:388
#	0x1032e45	github.com/pingcap/tidb/session.runStmt+0x245						/home/qupeng/.go/src/github.com/pingcap/tidb/session/tidb.go:170
#	0x102c0fa	github.com/pingcap/tidb/session.(*session).executeStatement+0x1ea			/home/qupeng/.go/src/github.com/pingcap/tidb/session/session.go:741
#	0x102cf3d	github.com/pingcap/tidb/session.(*session).execute+0x87d				/home/qupeng/.go/src/github.com/pingcap/tidb/session/session.go:812
#	0x102c5e8	github.com/pingcap/tidb/session.(*session).Execute+0x68					/home/qupeng/.go/src/github.com/pingcap/tidb/session/session.go:762
#	0x106068b	github.com/pingcap/tidb/server.(*TiDBContext).Execute+0x7b				/home/qupeng/.go/src/github.com/pingcap/tidb/server/driver_tidb.go:240
#	0x105963d	github.com/pingcap/tidb/server.(*clientConn).handleQuery+0x8d				/home/qupeng/.go/src/github.com/pingcap/tidb/server/conn.go:874
#	0x10571b5	github.com/pingcap/tidb/server.(*clientConn).dispatch+0x685				/home/qupeng/.go/src/github.com/pingcap/tidb/server/conn.go:626
#	0x1055d0d	github.com/pingcap/tidb/server.(*clientConn).Run+0x1bd					/home/qupeng/.go/src/github.com/pingcap/tidb/server/conn.go:470
#	0x106fce3	github.com/pingcap/tidb/server.(*Server).onConn+0x223					/home/qupeng/.go/src/github.com/pingcap/tidb/server/server.go:324

This is cause by the logrus GetLevel function which uses a global mutex. In the latest logrus, it has already switched to using atomic.

I write a simple benchmark https://gist.github.com/siddontang/ee4cee6115b9d8d16286543c734f04d4 and find the atomic has a better performance than mutex.

Luckily, the latest logrus has already used atomic, we can update it directly.

[tiancaiamao]

I'm moving to go mod #7922
Maybe I can update logrus after that.
I know update logrus and support module are two different things, but update them once maybe save some time for me. @siddontang