From eb10ac346f7ee91da6b823738704c6a0c57b673d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Micha=C5=82=20Matczuk?= <michal@scylladb.com>
Date: Fri, 3 Jan 2020 14:55:30 +0100
Subject: [PATCH] fs/accounting: Added StatsInfo locking in statsGroups sum
 function (#3844)

Without the fix we can have a race, example:

```
Write at 0x00c000432039 by goroutine 187:
  github.com/rclone/rclone/fs/accounting.(*StatsInfo).Error()
      fs/accounting/stats.go:495 +0x3f1
  github.com/rclone/rclone/fs/accounting.(*StatsInfo).Error-fm()
      fs/accounting/stats.go:477 +0x55
  github.com/rclone/rclone/fs/walk.listRwalk.func1()
      fs/walk/walk.go:162 +0xd2
  github.com/rclone/rclone/fs/walk.walk.func2()
      fs/walk/walk.go:402 +0x30f

Previous read at 0x00c000432039 by goroutine 184:
  github.com/rclone/rclone/fs/accounting.(*statsGroups).sum()
      fs/accounting/stats_groups.go:351 +0xcae
  github.com/rclone/rclone/fs/accounting.rcTransferredStats()
      fs/accounting/stats_groups.go:132 +0x1f4
```

Fixes #3844
---
 fs/accounting/stats_groups.go | 31 ++++++++++++++++++-------------
 1 file changed, 18 insertions(+), 13 deletions(-)

diff --git a/fs/accounting/stats_groups.go b/fs/accounting/stats_groups.go
index c96061052..35b750bd6 100644
--- a/fs/accounting/stats_groups.go
+++ b/fs/accounting/stats_groups.go
@@ -344,22 +344,27 @@ func (sg *statsGroups) names() []string {
 func (sg *statsGroups) sum() *StatsInfo {
 	sg.mu.Lock()
 	defer sg.mu.Unlock()
+
 	sum := NewStats()
 	for _, stats := range sg.m {
-		sum.bytes += stats.bytes
-		sum.errors += stats.errors
-		sum.fatalError = sum.fatalError || stats.fatalError
-		sum.retryError = sum.retryError || stats.retryError
-		sum.checks += stats.checks
-		sum.transfers += stats.transfers
-		sum.deletes += stats.deletes
-		sum.checking.merge(stats.checking)
-		sum.transferring.merge(stats.transferring)
-		sum.inProgress.merge(stats.inProgress)
-		if sum.lastError == nil && stats.lastError != nil {
-			sum.lastError = stats.lastError
+		stats.mu.RLock()
+		{
+			sum.bytes += stats.bytes
+			sum.errors += stats.errors
+			sum.fatalError = sum.fatalError || stats.fatalError
+			sum.retryError = sum.retryError || stats.retryError
+			sum.checks += stats.checks
+			sum.transfers += stats.transfers
+			sum.deletes += stats.deletes
+			sum.checking.merge(stats.checking)
+			sum.transferring.merge(stats.transferring)
+			sum.inProgress.merge(stats.inProgress)
+			if sum.lastError == nil && stats.lastError != nil {
+				sum.lastError = stats.lastError
+			}
+			sum.startedTransfers = append(sum.startedTransfers, stats.startedTransfers...)
 		}
-		sum.startedTransfers = append(sum.startedTransfers, stats.startedTransfers...)
+		stats.mu.RUnlock()
 	}
 	return sum
 }