From de216bab4198e0e31e1475db3f22d91706e98c0d Mon Sep 17 00:00:00 2001
From: Aliaksandr Valialkin <valyala@gmail.com>
Date: Thu, 3 Sep 2020 12:10:47 +0300
Subject: [PATCH] app/vmagent: fix data race when accessing
 writeRequest.lastFlushTime

---
 app/vmagent/remotewrite/pendingseries.go | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/app/vmagent/remotewrite/pendingseries.go b/app/vmagent/remotewrite/pendingseries.go
index 508e8932ac..31177a7fee 100644
--- a/app/vmagent/remotewrite/pendingseries.go
+++ b/app/vmagent/remotewrite/pendingseries.go
@@ -3,6 +3,7 @@ package remotewrite
 import (
 	"flag"
 	"sync"
+	"sync/atomic"
 	"time"
 
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/bytesutil"
@@ -69,7 +70,7 @@ func (ps *pendingSeries) periodicFlusher() {
 		case <-ps.stopCh:
 			mustStop = true
 		case <-ticker.C:
-			if fasttime.UnixTimestamp()-ps.wr.lastFlushTime < uint64(flushSeconds) {
+			if fasttime.UnixTimestamp()-atomic.LoadUint64(&ps.wr.lastFlushTime) < uint64(flushSeconds) {
 				continue
 			}
 		}
@@ -80,10 +81,12 @@ func (ps *pendingSeries) periodicFlusher() {
 }
 
 type writeRequest struct {
-	wr            prompbmarshal.WriteRequest
-	pushBlock     func(block []byte)
+	// Move lastFlushTime to the top of the struct in order to guarantee atomic access on 32-bit architectures.
 	lastFlushTime uint64
 
+	wr        prompbmarshal.WriteRequest
+	pushBlock func(block []byte)
+
 	tss []prompbmarshal.TimeSeries
 
 	labels  []prompbmarshal.Label
@@ -114,7 +117,7 @@ func (wr *writeRequest) reset() {
 
 func (wr *writeRequest) flush() {
 	wr.wr.Timeseries = wr.tss
-	wr.lastFlushTime = fasttime.UnixTimestamp()
+	atomic.StoreUint64(&wr.lastFlushTime, fasttime.UnixTimestamp())
 	pushWriteRequest(&wr.wr, wr.pushBlock)
 	wr.reset()
 }