Make clear_exited_pid work on running processes

src/tasking.rs

@@ -354,10 +354,13 @@ impl Tasking {
 
 
     pub fn clear_exited_pid(&self, pid: usize) -> Result<(), ()> {
+        if self.current_pid() == Some(pid) {
+            return Err(());
+        }
         let mut processes = self.processes.write();
         let process = processes.get(pid).ok_or(())?;
-        if *process.sleeping.read() != Some(SleepReason::Exited) {
-            return Err(());
+        if process.sleeping.read().is_none() {
+            self.ready_to_run.lock().retain(|e| *e != pid);
         }
         self.freeable_kstacks.lock().push(processes.remove(pid).kernel_stack);
         Ok(())