From f649968c692b164fbb86e20cefb24593feb13f51 Mon Sep 17 00:00:00 2001
From: Harshavardhana <harsha@minio.io>
Date: Thu, 1 Sep 2022 13:51:06 -0700
Subject: [PATCH] tier: avoid stats infinite loop in forwardTo method (#15640)

under some sequence of events following code would
reach an infinite loop.

```
idx1, idx2 := 0, 1
for ; idx2 != idx1; idx2++ {
        fmt.Println(idx2)
}
```

fixes #15639
---
 cmd/tier-last-day-stats.go | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/cmd/tier-last-day-stats.go b/cmd/tier-last-day-stats.go
index cc8b1cbb4..b4bb8199b 100644
--- a/cmd/tier-last-day-stats.go
+++ b/cmd/tier-last-day-stats.go
@@ -38,6 +38,10 @@ func (l *lastDayTierStats) addStats(ts tierStats) {
 
 // forwardTo moves time to t, clearing entries between last update and t.
 func (l *lastDayTierStats) forwardTo(t time.Time) {
+	if t.IsZero() {
+		t = time.Now()
+	}
+
 	since := t.Sub(l.UpdatedAt).Hours()
 	// within the hour since l.UpdatedAt
 	if since < 1 {
@@ -45,15 +49,17 @@ func (l *lastDayTierStats) forwardTo(t time.Time) {
 	}
 
 	idx, lastIdx := t.Hour(), l.UpdatedAt.Hour()
-	l.UpdatedAt = t
+
+	l.UpdatedAt = t // update to the latest time index
 
 	if since >= 24 {
 		l.Bins = [24]tierStats{}
 		return
 	}
 
-	for ; lastIdx != idx; lastIdx++ {
-		l.Bins[(lastIdx+1)%24] = tierStats{}
+	for lastIdx != idx {
+		lastIdx = (lastIdx + 1) % 24
+		l.Bins[lastIdx] = tierStats{}
 	}
 }