Fix labelset race condition (#6573)

Signed-off-by: SungJin1212 <[email protected]>

Author: SungJin1212

Diff for: CHANGELOG.md

@@ -6,6 +6,7 @@
 * [ENHANCEMENT] Querier: Apply bytes limiter to LabelNames and LabelValuesForLabelNames. #6568
 * [ENHANCEMENT] Query Frontend: Add a `too_many_tenants` reason label value to `cortex_rejected_queries_total` metric to track the rejected query count due to the # of tenant limits. #6569
 * [BUGFIX] Ingester: Avoid error or early throttling when READONLY ingesters are present in the ring #6517
+* [BUGFIX] Ingester: Fix labelset data race condition. #6573
 
 ## 1.19.0 in progress
 

Diff for: pkg/ingester/user_state.go

@@ -131,15 +131,14 @@ func (m *labelSetCounter) canAddSeriesForLabelSet(ctx context.Context, u *userTS
 
 func (m *labelSetCounter) backFillLimit(ctx context.Context, u *userTSDB, forceBackfill bool, allLimits []validation.LimitsPerLabelSet, limit validation.LimitsPerLabelSet, s *labelSetCounterShard) (int, error) {
 	s.Lock()
+	defer s.Unlock()
 	// If not force backfill, use existing counter value.
 	if !forceBackfill {
 		if r, ok := s.valuesCounter[limit.Hash]; ok {
-			s.Unlock()
 			return r.count, nil
 		}
 	}
 
-	defer s.Unlock()
 	ir, err := u.db.Head().Index()
 	if err != nil {
 		return 0, err