From c8ca055935f21e8b740292d0c30b221ea8a21d3a Mon Sep 17 00:00:00 2001
From: Klaus Post <klauspost@gmail.com>
Date: Tue, 24 Aug 2021 16:11:38 +0200
Subject: [PATCH] Fix concurrent map read/write (#13052)

Clones were not independent.

Fixes race:

```
WARNING: DATA RACE
Read at 0x00c002040cc0 by goroutine 50:
  runtime.mapiterinit()
      c:/go/src/runtime/map.go:802 +0x0
  github.com/minio/minio/cmd.(*dataUsageCache).flatten()
      d:/minio/minio/cmd/data-usage-cache.go:551 +0xad
  github.com/minio/minio/cmd.(*dataUsageCache).dui()
      d:/minio/minio/cmd/data-usage-cache.go:352 +0x144
  github.com/minio/minio/cmd.(*erasureServerPools).NSScanner.func3.1()
      d:/minio/minio/cmd/erasure-server-pool.go:542 +0x2a4
  github.com/minio/minio/cmd.(*erasureServerPools).NSScanner.func3()
      d:/minio/minio/cmd/erasure-server-pool.go:561 +0x24b

Previous write at 0x00c002040cc0 by goroutine 1391:
  runtime.mapassign_faststr()
      c:/go/src/runtime/map_faststr.go:202 +0x0
  github.com/minio/minio/cmd.(*dataUsageEntry).addChild()
      d:/minio/minio/cmd/data-usage-cache.go:231 +0x313
  github.com/minio/minio/cmd.(*dataUsageCache).replace()
      d:/minio/minio/cmd/data-usage-cache.go:383 +0x293
  github.com/minio/minio/cmd.erasureObjects.nsScanner.func1()
      d:/minio/minio/cmd/erasure.go:428 +0x3a6
```
---
 cmd/data-usage-cache.go | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/cmd/data-usage-cache.go b/cmd/data-usage-cache.go
index ea802a18c..bb6ef11d8 100644
--- a/cmd/data-usage-cache.go
+++ b/cmd/data-usage-cache.go
@@ -238,6 +238,24 @@ func (e *dataUsageEntry) removeChild(hash dataUsageHash) {
 	}
 }
 
+// Create a clone of the entry.
+func (e dataUsageEntry) clone() dataUsageEntry {
+	// We operate on a copy from the receiver.
+	if e.Children != nil {
+		ch := make(dataUsageHashMap, len(e.Children))
+		for k, v := range e.Children {
+			ch[k] = v
+		}
+		e.Children = ch
+	}
+	if e.ReplicationStats != nil {
+		// Copy to new struct
+		r := *e.ReplicationStats
+		e.ReplicationStats = &r
+	}
+	return e
+}
+
 // find a path in the cache.
 // Returns nil if not found.
 func (d *dataUsageCache) find(path string) *dataUsageEntry {
@@ -672,7 +690,7 @@ func (d *dataUsageCache) clone() dataUsageCache {
 		Cache: make(map[string]dataUsageEntry, len(d.Cache)),
 	}
 	for k, v := range d.Cache {
-		clone.Cache[k] = v
+		clone.Cache[k] = v.clone()
 	}
 	return clone
 }