fix; race in bucket replication stats (#13942)

- r.ulock was not locked when r.UsageCache was being modified

Bonus:

- simplify code by removing some unnecessary clone methods - we can 
do this because go arrays are values (not pointers/references) that are 
automatically copied on assignment.

- remove some unnecessary map allocation calls

cmd/bucket-replication-stats.go

@@ -51,6 +51,9 @@ func (r *ReplicationStats) Delete(bucket string) {
 	r.Lock()
 	defer r.Unlock()
 	delete(r.Cache, bucket)
+
+	r.ulock.Lock()
+	defer r.ulock.Unlock()
 	delete(r.UsageCache, bucket)
 
 }
@@ -82,10 +85,12 @@ func (r *ReplicationStats) Update(bucket string, arn string, n int64, duration t
 	bs, ok := r.Cache[bucket]
 	if !ok {
 		bs = &BucketReplicationStats{Stats: make(map[string]*BucketReplicationStat)}
+		r.Cache[bucket] = bs
 	}
 	b, ok := bs.Stats[arn]
 	if !ok {
 		b = &BucketReplicationStat{}
+		bs.Stats[arn] = b
 	}
 	switch status {
 	case replication.Completed:
@@ -115,9 +120,6 @@ func (r *ReplicationStats) Update(bucket string, arn string, n int64, duration t
 			b.ReplicaSize += n
 		}
 	}
-
-	bs.Stats[arn] = b
-	r.Cache[bucket] = bs
 }
 
 // GetInitialUsage get replication metrics available at the time of cluster initialization
@@ -128,10 +130,10 @@ func (r *ReplicationStats) GetInitialUsage(bucket string) BucketReplicationStats
 	r.ulock.RLock()
 	defer r.ulock.RUnlock()
 	st, ok := r.UsageCache[bucket]
-	if ok {
+	if !ok {
-		return st.Clone()
+		return BucketReplicationStats{}
 	}
-	return BucketReplicationStats{Stats: make(map[string]*BucketReplicationStat)}
+	return st.Clone()
 }
 
 // Get replication metrics for a bucket from this node since this node came up.
@@ -145,7 +147,7 @@ func (r *ReplicationStats) Get(bucket string) BucketReplicationStats {
 
 	st, ok := r.Cache[bucket]
 	if !ok {
-		return BucketReplicationStats{Stats: make(map[string]*BucketReplicationStat)}
+		return BucketReplicationStats{}
 	}
 	return st.Clone()
 }
@@ -162,19 +164,27 @@ func NewReplicationStats(ctx context.Context, objectAPI ObjectLayer) *Replicatio
 func (r *ReplicationStats) loadInitialReplicationMetrics(ctx context.Context) {
 	rTimer := time.NewTimer(time.Minute * 1)
 	defer rTimer.Stop()
+	var (
+		dui DataUsageInfo
+		err error
+	)
+outer:
 	for {
 		select {
 		case <-ctx.Done():
 			return
 		case <-rTimer.C:
-			dui, err := loadDataUsageFromBackend(GlobalContext, newObjectLayerFn())
+			dui, err = loadDataUsageFromBackend(GlobalContext, newObjectLayerFn())
 			if err != nil {
 				continue
 			}
-			// data usage has not captured any data yet.
+			// If LastUpdate is set, data usage is available.
-			if dui.LastUpdate.IsZero() {
+			if !dui.LastUpdate.IsZero() {
-				continue
+				break outer
 			}
+		}
+	}
+
 	m := make(map[string]*BucketReplicationStats)
 	for bucket, usage := range dui.BucketsUsage {
 		b := &BucketReplicationStats{
@@ -196,7 +206,4 @@ func (r *ReplicationStats) loadInitialReplicationMetrics(ctx context.Context) {
 	r.ulock.Lock()
 	defer r.ulock.Unlock()
 	r.UsageCache = m
-			return
-		}
-	}
 }

cmd/bucket-replication.go

@@ -1808,23 +1808,16 @@ func getLatestReplicationStats(bucket string, u BucketUsageInfo) (s BucketReplic
 	// add initial usage stat to cluster stats
 	usageStat := globalReplicationStats.GetInitialUsage(bucket)
 	totReplicaSize += usageStat.ReplicaSize
-	if usageStat.Stats != nil {
 	for arn, stat := range usageStat.Stats {
-			st := stats[arn]
+		st, ok := stats[arn]
-			if st == nil {
+		if !ok {
-				st = &BucketReplicationStat{
+			st = &BucketReplicationStat{}
-					ReplicatedSize: stat.ReplicatedSize,
+			stats[arn] = st
-					FailedSize:     stat.FailedSize,
-					FailedCount:    stat.FailedCount,
 		}
-			} else {
 		st.ReplicatedSize += stat.ReplicatedSize
 		st.FailedSize += stat.FailedSize
 		st.FailedCount += stat.FailedCount
 	}
-			stats[arn] = st
-		}
-	}
 	s = BucketReplicationStats{
 		Stats: make(map[string]*BucketReplicationStat, len(stats)),
 	}

cmd/bucket-stats.go

@@ -18,7 +18,6 @@
 package cmd
 
 import (
-	"sync/atomic"
 	"time"
 )
 
@@ -52,13 +51,6 @@ func (rl *ReplicationLatency) update(size int64, duration time.Duration) {
 	rl.UploadHistogram.Add(size, duration)
 }
 
-// Clone replication latency
-func (rl ReplicationLatency) clone() ReplicationLatency {
-	return ReplicationLatency{
-		UploadHistogram: rl.UploadHistogram.Clone(),
-	}
-}
-
 // BucketStats bucket statistics
 type BucketStats struct {
 	ReplicationStats BucketReplicationStats
@@ -88,29 +80,18 @@ func (brs *BucketReplicationStats) Empty() bool {
 }
 
 // Clone creates a new BucketReplicationStats copy
-func (brs BucketReplicationStats) Clone() BucketReplicationStats {
+func (brs BucketReplicationStats) Clone() (c BucketReplicationStats) {
-	c := BucketReplicationStats{
+	// This is called only by replicationStats cache and already holds a
-		Stats: make(map[string]*BucketReplicationStat, len(brs.Stats)),
+	// read lock before calling Clone()
-	}
+
-	// This is called only by replicationStats cache and already holds a read lock before calling Clone()
+	c = brs
+	// We need to copy the map, so we do not reference the one in `brs`.
+	c.Stats = make(map[string]*BucketReplicationStat, len(brs.Stats))
 	for arn, st := range brs.Stats {
-		c.Stats[arn] = &BucketReplicationStat{
+		// make a copy of `*st`
-			FailedSize:     atomic.LoadInt64(&st.FailedSize),
+		s := *st
-			ReplicatedSize: atomic.LoadInt64(&st.ReplicatedSize),
+		c.Stats[arn] = &s
-			ReplicaSize:    atomic.LoadInt64(&st.ReplicaSize),
-			FailedCount:    atomic.LoadInt64(&st.FailedCount),
-			PendingSize:    atomic.LoadInt64(&st.PendingSize),
-			PendingCount:   atomic.LoadInt64(&st.PendingCount),
-			Latency:        st.Latency.clone(),
 	}
-	}
-	// update total counts across targets
-	c.FailedSize = atomic.LoadInt64(&brs.FailedSize)
-	c.FailedCount = atomic.LoadInt64(&brs.FailedCount)
-	c.PendingCount = atomic.LoadInt64(&brs.PendingCount)
-	c.PendingSize = atomic.LoadInt64(&brs.PendingSize)
-	c.ReplicaSize = atomic.LoadInt64(&brs.ReplicaSize)
-	c.ReplicatedSize = atomic.LoadInt64(&brs.ReplicatedSize)
 	return c
 }
 

cmd/last-minute.go

@@ -102,39 +102,21 @@ type LastMinuteLatencies struct {
 	LastSec int64
 }
 
-// Clone safely returns a copy for a LastMinuteLatencies structure
-func (l *LastMinuteLatencies) Clone() LastMinuteLatencies {
-	n := LastMinuteLatencies{}
-	n.LastSec = l.LastSec
-	for i := range l.Totals {
-		for j := range l.Totals[i] {
-			n.Totals[i][j] = AccElem{
-				Total: l.Totals[i][j].Total,
-				N:     l.Totals[i][j].N,
-			}
-		}
-	}
-	return n
-}
-
 // Merge safely merges two LastMinuteLatencies structures into one
 func (l LastMinuteLatencies) Merge(o LastMinuteLatencies) (merged LastMinuteLatencies) {
-	cl := l.Clone()
+	if l.LastSec > o.LastSec {
-	co := o.Clone()
+		o.forwardTo(l.LastSec)
-
+		merged.LastSec = l.LastSec
-	if cl.LastSec > co.LastSec {
-		co.forwardTo(cl.LastSec)
-		merged.LastSec = cl.LastSec
 	} else {
-		cl.forwardTo(co.LastSec)
+		l.forwardTo(o.LastSec)
-		merged.LastSec = co.LastSec
+		merged.LastSec = o.LastSec
 	}
 
-	for i := range cl.Totals {
+	for i := range merged.Totals {
-		for j := range cl.Totals[i] {
+		for j := range merged.Totals[i] {
 			merged.Totals[i][j] = AccElem{
-				Total: cl.Totals[i][j].Total + co.Totals[i][j].Total,
+				Total: l.Totals[i][j].Total + o.Totals[i][j].Total,
-				N:     cl.Totals[i][j].N + co.Totals[i][j].N,
+				N:     l.Totals[i][j].N + o.Totals[i][j].N,
 			}
 		}
 	}