logtail: fix race condition with sockstats label (#8578)

Updates tailscale/corp#8427

Signed-off-by: Joe Tsai <joetsai@digital-static.net>

logtail/logtail.go

@@ -146,7 +146,6 @@ func NewLogger(cfg Config, logf tslogger.Logf) *Logger {
 		flushDelayFn:   cfg.FlushDelayFn,
 		timeNow:        cfg.TimeNow,
 		metricsDelta:   cfg.MetricsDelta,
-		sockstatsLabel: sockstats.LabelLogtailLogger,
 
 		procID:              procID,
 		includeProcSequence: cfg.IncludeProcSequence,
@@ -154,6 +153,7 @@ func NewLogger(cfg Config, logf tslogger.Logf) *Logger {
 		shutdownStart: make(chan struct{}),
 		shutdownDone:  make(chan struct{}),
 	}
+	l.SetSockstatsLabel(sockstats.LabelLogtailLogger)
 	if cfg.NewZstdEncoder != nil {
 		l.zstdEncoder = cfg.NewZstdEncoder()
 	}
@@ -188,7 +188,7 @@ type Logger struct {
 	metricsDelta   func() string // or nil
 	privateID      logid.PrivateID
 	httpDoCalls    atomic.Int32
-	sockstatsLabel sockstats.Label
+	sockstatsLabel atomicSocktatsLabel
 
 	procID              uint32
 	includeProcSequence bool
@@ -202,6 +202,11 @@ type Logger struct {
 	shutdownDone    chan struct{} // closed when shutdown complete
 }
 
+type atomicSocktatsLabel struct{ p atomic.Uint32 }
+
+func (p *atomicSocktatsLabel) Load() sockstats.Label       { return sockstats.Label(p.p.Load()) }
+func (p *atomicSocktatsLabel) Store(label sockstats.Label) { p.p.Store(uint32(label)) }
+
 // SetVerbosityLevel controls the verbosity level that should be
 // written to stderr. 0 is the default (not verbose). Levels 1 or higher
 // are increasingly verbose.
@@ -219,7 +224,7 @@ func (l *Logger) SetNetMon(lm *netmon.Monitor) {
 
 // SetSockstatsLabel sets the label used in sockstat logs to identify network traffic from this logger.
 func (l *Logger) SetSockstatsLabel(label sockstats.Label) {
-	l.sockstatsLabel = label
+	l.sockstatsLabel.Store(label)
 }
 
 // PrivateID returns the logger's private log ID.
@@ -445,7 +450,7 @@ func (l *Logger) awaitInternetUp(ctx context.Context) {
 // origlen of -1 indicates that the body is not compressed.
 func (l *Logger) upload(ctx context.Context, body []byte, origlen int) (retryAfter time.Duration, err error) {
 	const maxUploadTime = 45 * time.Second
-	ctx = sockstats.WithSockStats(ctx, l.sockstatsLabel, l.Logf)
+	ctx = sockstats.WithSockStats(ctx, l.sockstatsLabel.Load(), l.Logf)
 	ctx, cancel := context.WithTimeout(ctx, maxUploadTime)
 	defer cancel()