agentlog: fix race condition in tests

Output of the race condition detector was:

=== FAIL: agentlog TestPsiEveIntegratedStartTwice (0.17s)
==================
WARNING: DATA RACE
Write at 0x0000029a6120 by goroutine 80:
  github.com/lf-edge/eve/pkg/pillar/agentlog_test.emulateMemoryPressureStats()
      /pillar/agentlog/agentlog_test.go:301 +0xd1
  github.com/lf-edge/eve/pkg/pillar/agentlog_test.preparePSIEnvironment()
      /pillar/agentlog/agentlog_test.go:455 +0x85
  github.com/lf-edge/eve/pkg/pillar/agentlog_test.TestPsiEveIntegratedStartTwice()
      /pillar/agentlog/agentlog_test.go:616 +0x44
  testing.tRunner()
      /usr/lib/go/src/testing/testing.go:1576 +0x216
  testing.(*T).Run.func1()
      /usr/lib/go/src/testing/testing.go:1629 +0x47

Previous read at 0x0000029a6120 by goroutine 78:
  github.com/lf-edge/eve/pkg/pillar/agentlog.collectMemoryPSI()
      /pillar/agentlog/memprofile.go:151 +0x116
  github.com/lf-edge/eve/pkg/pillar/agentlog.MemoryPSICollector()
      /pillar/agentlog/memprofile.go:248 +0x810
  github.com/lf-edge/eve/pkg/pillar/agentlog.ListenDebug.func6.1()
      /pillar/agentlog/http-debug.go:474 +0x7e

Goroutine 80 (running) created at:
  testing.(*T).Run()
      /usr/lib/go/src/testing/testing.go:1629 +0x805
  testing.runTests.func1()
      /usr/lib/go/src/testing/testing.go:2036 +0x8d
  testing.tRunner()
      /usr/lib/go/src/testing/testing.go:1576 +0x216
  testing.runTests()
      /usr/lib/go/src/testing/testing.go:2034 +0x87c
  testing.(*M).Run()
      /usr/lib/go/src/testing/testing.go:1906 +0xb44
  main.main()
      _testmain.go:102 +0x2fc

Goroutine 78 (running) created at:
  github.com/lf-edge/eve/pkg/pillar/agentlog.ListenDebug.func6()
      /pillar/agentlog/http-debug.go:473 +0x2ce
  net/http.HandlerFunc.ServeHTTP()
      /usr/lib/go/src/net/http/server.go:2122 +0x4d
  net/http.(*ServeMux).ServeHTTP()
      /usr/lib/go/src/net/http/server.go:2500 +0xc5
  net/http.serverHandler.ServeHTTP()
      /usr/lib/go/src/net/http/server.go:2936 +0x682
  net/http.(*conn).serve()
      /usr/lib/go/src/net/http/server.go:1995 +0xbd4
  net/http.(*Server).Serve.func3()
      /usr/lib/go/src/net/http/server.go:3089 +0x58
==================
    testing.go:1446: race detected during execution of test

Signed-off-by: Christoph Ostarek <[email protected]>

pkg/pillar/agentlog/agentlog_test.go

@@ -297,8 +297,8 @@ func emulateMemoryPressureStats() (cancel context.CancelFunc, err error) {
 	}
 
 	fakePSIFileName := fakePSIFileHandler.Name()
-	originalPressureMemoryFile := agentlog.PressureMemoryFile
-	agentlog.PressureMemoryFile = fakePSIFileName
+	originalPressureMemoryFile := agentlog.PressureMemoryFile()
+	agentlog.UpdatePressureMemoryFile(fakePSIFileName)
 
 	// Start a ticker to write a new line to the file every 0.5 seconds
 	ticker := time.NewTicker(500 * time.Millisecond)
@@ -342,7 +342,7 @@ func emulateMemoryPressureStats() (cancel context.CancelFunc, err error) {
 				agentlog.PsiMutex.Lock()
 				fakePSIFileHandler.Close()
 				os.Remove(fakePSIFileName)
-				agentlog.PressureMemoryFile = originalPressureMemoryFile
+				agentlog.UpdatePressureMemoryFile(originalPressureMemoryFile)
 				agentlog.PsiMutex.Unlock()
 				// We destroy this producer, so release the mutex
 				psiProducerMutex.Unlock()
@@ -371,8 +371,8 @@ func createFakePSIStatsFile() (cleanupFunc context.CancelFunc, err error) {
 	}
 
 	fakePSIFileName := fakePSIFileHandler.Name()
-	originalPressureMemoryFile := agentlog.PressureMemoryFile
-	agentlog.PressureMemoryFile = fakePSIFileName
+	originalPressureMemoryFile := agentlog.PressureMemoryFile()
+	agentlog.UpdatePressureMemoryFile(fakePSIFileName)
 
 	// Write some content to the file
 	agentlog.PsiMutex.Lock()
@@ -389,7 +389,7 @@ func createFakePSIStatsFile() (cleanupFunc context.CancelFunc, err error) {
 		agentlog.PsiMutex.Lock()
 		fakePSIFileHandler.Close()
 		os.Remove(fakePSIFileName)
-		agentlog.PressureMemoryFile = originalPressureMemoryFile
+		agentlog.UpdatePressureMemoryFile(originalPressureMemoryFile)
 		agentlog.PsiMutex.Unlock()
 		// We destroy this producer, so release the mutex
 		psiProducerMutex.Unlock()

pkg/pillar/agentlog/memprofile.go

@@ -51,9 +51,26 @@ const (
 var (
 	// PressureMemoryFile is the memory pressure file. It is a variable, not a constant, to allow
 	// changing it in tests to mock the file.
-	PressureMemoryFile = "/proc/pressure/memory"
+	pressureMemoryFile     = "/proc/pressure/memory"
+	pressureMemoryFileLock sync.RWMutex
 )
 
+// PressureMemoryFile returns the path to the memory pressure file in /proc
+func PressureMemoryFile() string {
+	pressureMemoryFileLock.RLock()
+	path := pressureMemoryFile
+	pressureMemoryFileLock.RUnlock()
+
+	return path
+}
+
+// UpdatePressureMemoryFile sets the path to the memory pressure file (mostly used for tests)
+func UpdatePressureMemoryFile(newpath string) {
+	pressureMemoryFileLock.Lock()
+	pressureMemoryFile = newpath
+	pressureMemoryFileLock.Unlock()
+}
+
 // MemAllocationSite is the return value of GetMemProfile
 type MemAllocationSite struct {
 	InUseBytes   int64
@@ -134,7 +151,7 @@ func GetMemAllocationSites(reportZeroInUse bool) (int, []MemAllocationSite) {
 var PsiMutex sync.Mutex
 
 func isPSISupported() bool {
-	_, err := os.Stat(PressureMemoryFile)
+	_, err := os.Stat(PressureMemoryFile())
 	if err != nil {
 		fmt.Println("PSI is not supported. Be sure to enable CONFIG_PSI=y in your kernel configuration.")
 		return false
@@ -148,7 +165,7 @@ func collectMemoryPSI() (*PressureStallInfo, error) {
 	if !isPSISupported() {
 		return nil, fmt.Errorf("PSI is not supported")
 	}
-	procFile, err := os.Open(PressureMemoryFile)
+	procFile, err := os.Open(PressureMemoryFile())
 	if err != nil {
 		return nil, fmt.Errorf("open: %v", err)
 	}