kernel: answer ESRCH for a thread the detached-thread reaper has joined

src/kernel/pthread.cpp

@@ -3389,6 +3389,11 @@ int KYTY_SYSV_ABI PthreadCancel(Pthread thread) {
 		return KERNEL_ERROR_EINVAL;
 	}
 
+	// A joined thread's native handle is gone; the guest may still hold its handle.
+	if (thread->free) {
+		return KERNEL_ERROR_ESRCH;
+	}
+
 	int result = pthread_cancel(thread->p);
 
 	LOGF("\tthread cancel: %s, %d\n", thread->name.c_str(), result);
@@ -3492,10 +3497,8 @@ int KYTY_SYSV_ABI PthreadGetprio(Pthread thread, int* prio) {
 
 	EXIT_NOT_IMPLEMENTED(prio == nullptr);
 
-	sched_param native_param {};
+	if (thread->free) {
-	int         native_policy = 0;
+		return KERNEL_ERROR_ESRCH;
-	if (pthread_getschedparam(thread->p, &native_policy, &native_param) != 0) {
-		return KERNEL_ERROR_EINVAL;
 	}
 
 	*prio = thread->attr->guest_priority;
@@ -3510,6 +3513,11 @@ int KYTY_SYSV_ABI PthreadSetprio(Pthread thread, int prio) {
 		return KERNEL_ERROR_ESRCH;
 	}
 
+	// A joined thread's native handle is gone; the guest may still hold its handle.
+	if (thread->free) {
+		return KERNEL_ERROR_ESRCH;
+	}
+
 	sched_param param {};
 	int         pol = 0;