Remove TID from task start

This was used to map kernel.Task to goroutines before
kernel.Task.GoroutineID was available. It's not needed anymore.

PiperOrigin-RevId: 445452190

pkg/sentry/kernel/kernel.go

@@ -1090,9 +1090,7 @@ func (k *Kernel) CreateProcess(args CreateProcessArgs) (*ThreadGroup, ThreadID,
 
 // StartProcess starts running a process that was created with CreateProcess.
 func (k *Kernel) StartProcess(tg *ThreadGroup) {
-	t := tg.Leader()
-	tid := k.tasks.Root.IDOfTask(t)
-	t.Start(tid)
+	tg.Leader().Start()
 }
 
 // Start starts execution of all tasks in k.
@@ -1122,8 +1120,8 @@ func (k *Kernel) Start() error {
 	// Start task goroutines.
 	k.tasks.mu.RLock()
 	defer k.tasks.mu.RUnlock()
-	for t, tid := range k.tasks.Root.tids {
-		t.Start(tid)
+	for t := range k.tasks.Root.tids {
+		t.Start()
 	}
 	return nil
 }

pkg/sentry/kernel/task_clone.go

@@ -243,8 +243,7 @@ func (t *Task) Clone(args *linux.CloneArgs) (ThreadID, *SyscallControl, error) {
 
 	// This has to happen last, because e.g. ptraceClone may send a SIGSTOP to
 	// nt that it must receive before its task goroutine starts running.
-	tid := nt.k.tasks.Root.IDOfTask(nt)
-	defer nt.Start(tid)
+	defer nt.Start()
 
 	if args.Flags&linux.CLONE_THREAD == 0 && seccheck.Global.Enabled(seccheck.PointCloneProcess) {
 		mask, info := getCloneSeccheckInfo(t, nt)
@@ -288,7 +287,7 @@ func (t *Task) Clone(args *linux.CloneArgs) (ThreadID, *SyscallControl, error) {
 		ntid.CopyOut(t, hostarch.Addr(args.ParentTID))
 	}
 
-	t.traceCloneEvent(tid)
+	t.traceCloneEvent(nt.k.tasks.Root.IDOfTask(nt))
 	kind := ptraceCloneKindClone
 	if args.Flags&linux.CLONE_VFORK != 0 {
 		kind = ptraceCloneKindVfork

pkg/sentry/kernel/task_run.go

@@ -51,11 +51,7 @@ type taskRunState interface {
 }
 
 // run runs the task goroutine.
-//
-// threadID a dummy value set to the task's TID in the root PID namespace to
-// make it visible in stack dumps. A goroutine for a given task can be identified
-// searching for Task.run()'s argument value.
-func (t *Task) run(threadID uintptr) {
+func (t *Task) run() {
 	t.goid.Store(goid.Get())
 
 	// Construct t.blockingTimer here. We do this here because we can't
@@ -103,8 +99,6 @@ func (t *Task) run(threadID uintptr) {
 			// Deferring this store triggers a false positive in the race
 			// detector (https://github.com/golang/go/issues/42599).
 			t.goid.Store(0)
-			// Keep argument alive because stack trace for dead variables may not be correct.
-			runtime.KeepAlive(threadID)
 			return
 		}
 	}

pkg/sentry/kernel/task_start.go

@@ -347,11 +347,7 @@ func (ns *PIDNamespace) allocateTID() (ThreadID, error) {
 
 // Start starts the task goroutine. Start must be called exactly once for each
 // task returned by NewTask.
-//
-// 'tid' must be the task's TID in the root PID namespace and it's used for
-// debugging purposes only (set as parameter to Task.run to make it visible
-// in stack dumps).
-func (t *Task) Start(tid ThreadID) {
+func (t *Task) Start() {
 	// If the task was restored, it may be "starting" after having already exited.
 	if t.runState == nil {
 		return
@@ -364,6 +360,5 @@ func (t *Task) Start(tid ThreadID) {
 	// Task is now running in system mode.
 	t.accountTaskGoroutineLeave(TaskGoroutineNonexistent)
 
-	// Use the task's TID in the root PID namespace to make it visible in stack dumps.
-	go t.run(uintptr(tid)) // S/R-SAFE: synchronizes with saving through stops
+	go t.run() // S/R-SAFE: synchronizes with saving through stops
 }