chore(ci): added checklocks static analyzer (#1838)

From https://github.com/google/gvisor/tree/master/tools/checklocks

This will perform static verification that we're using
`sync.Mutex`, `sync.RWMutex` and `atomic` correctly to guard access
to certain fields.

This was mostly just a matter of adding annotations to indicate which
fields are guarded by which mutex.

In a handful of places the code had to be refactored to allow static
analyzer to do its job better or to not be confused by some
constructs.

In one place this actually uncovered a bug where a function was not
releasing a lock properly in an error case.

The check is part of `make lint` but can also be invoked by
`make check-locks`.

cli/cli_progress.go

@@ -35,33 +35,47 @@ type cliProgress struct {
 	snapshotfs.NullUploadProgress
 
 	// all int64 must precede all int32 due to alignment requirements on ARM
-	uploadedBytes  int64
-	cachedBytes    int64
+	// +checkatomic
+	uploadedBytes int64
+	// +checkatomic
+	cachedBytes int64
+	// +checkatomic
 	hashedBytes    int64
 	outputThrottle timetrack.Throttle // is int64
 
-	cachedFiles       int32
+	// +checkatomic
+	cachedFiles int32
+	// +checkatomic
 	inProgressHashing int32
-	hashedFiles       int32
-	uploadedFiles     int32
+	// +checkatomic
+	hashedFiles int32
+	// +checkatomic
+	uploadedFiles int32
+	// +checkatomic
 	ignoredErrorCount int32
-	fatalErrorCount   int32
+	// +checkatomic
+	fatalErrorCount int32
 
-	uploading      int32
+	// +checkatomic
+	uploading int32
+	// +checkatomic
 	uploadFinished int32
 
-	lastLineLength  int
-	spinPhase       int
-	uploadStartTime timetrack.Estimator
+	outputMutex sync.Mutex
 
-	estimatedFileCount  int
-	estimatedTotalBytes int64
+	// +checklocks:outputMutex
+	lastLineLength int
+	// +checklocks:outputMutex
+	spinPhase int
+
+	uploadStartTime timetrack.Estimator // +checklocksignore
+
+	estimatedFileCount  int   // +checklocksignore
+	estimatedTotalBytes int64 // +checklocksignore
 
 	// indicates shared instance that does not reset counters at the beginning of upload.
 	shared bool
 
-	outputMutex sync.Mutex
-
 	progressFlags
 }
 
@@ -181,6 +195,7 @@ func (p *cliProgress) output(col *color.Color, msg string) {
 	p.out.printStderr("\r%v%v", line, extraSpaces)
 }
 
+// +checklocks:p.outputMutex
 func (p *cliProgress) spinnerCharacter() string {
 	if atomic.LoadInt32(&p.uploadFinished) == 1 {
 		return "*"
@@ -193,6 +208,7 @@ func (p *cliProgress) spinnerCharacter() string {
 	return s
 }
 
+// +checklocksignore.
 func (p *cliProgress) StartShared() {
 	*p = cliProgress{
 		uploading:       1,
@@ -207,6 +223,7 @@ func (p *cliProgress) FinishShared() {
 	p.output(defaultColor, "")
 }
 
+// +checklocksignore.
 func (p *cliProgress) UploadStarted() {
 	if p.shared {
 		// do nothing