[3.4] clientv3/mvcc: fixed DATA RACE

[SimFG]

clientv3/mvcc: fixed DATA RACE between mvcc.(*store).setupMetricsReporter and mvcc.(*store).restore
issue: #14270

By comparing the code on the main branch, it is found that the main branch does not have this problem. But there is a small problem on the main branch, the code is as follows:

etcd/server/storage/mvcc/kvstore.go

Lines 349 to 364 in a3b410c

	{
	s.revMu.Lock()
	s.currentRev = <-revc
	// keys in the range [compacted revision -N, compaction] might all be deleted due to compaction.
	// the correct revision should be set to compaction revision in the case, not the largest revision
	// we have seen.
	if s.currentRev < s.compactMainRev {
	s.currentRev = s.compactMainRev
	}
	s.revMu.Unlock()
	}
	if scheduledCompact <= s.compactMainRev {
	scheduledCompact = 0
	}

L362: s.compactMainRev
I think this needs a read lock. However, I think this simple modification like this pull request is more appropriate.

{
		s.revMu.Lock()
		s.currentRev = <-revc

		// keys in the range [compacted revision -N, compaction] might all be deleted due to compaction.
		// the correct revision should be set to compaction revision in the case, not the largest revision
		// we have seen.
		if s.currentRev < s.compactMainRev {
			s.currentRev = s.compactMainRev
		}

		if scheduledCompact <= s.compactMainRev {
			scheduledCompact = 0
		}
		s.revMu.Unlock()
	}

Signed-off-by: SimFG 1142838399@qq.com

[SimFG]

cc @ahrtr

[ahrtr]

Did you manually make this change?

[SimFG]

No, it's GoLand editor.

[ahrtr]

LGTM

Thank you @SimFG

[codecov-commenter]

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