ADDITIONAL SYSTEM INFORMATION :
Java 10 install from PPA as described in https://stackoverflow.com/questions/49507160/how-to-install-jdk-10-under-ubuntu?utm_medium=organic&utm_source=google_rich_qa&utm_campaign=google_rich_qa.

A DESCRIPTION OF THE PROBLEM :
See below.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Snippet code:

class SH{
    ProcessBuilder pb;
    Process p;

    BufferedWriter to_subp;
    String ts;

    BufferedReader from_subp;
    String fs;

    SH(){
        try{
        pb = new ProcessBuilder("/bin/sh");
        pb.redirectErrorStream(true);
        p=pb.start();
        
       from_subp = new BufferedReader(
                    new InputStreamReader(
                    p.getInputStream()));
        
        to_subp = new BufferedWriter(
                    new OutputStreamWriter(
                    p.getOutputStream()));
        } catch (Exception ex) {
            ex.printStackTrace();
        }
    }

    void sh(String cmd){
        try {
            while ((fs = from_subp.readLine()) != null){
                System.out.println(fs);
            }
        } catch (Exception ex) {
            ex.printStackTrace();

        }
    }
 }

SH sh=new SH()

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Run 'jshell> sh.sh("ls")'. Lockup happens.
Type Ctrl-C to remove the lockuped code and go back to jshell.

ACTUAL -
Run 'jshell> sh.sh("ls")'. Lockup happens.
Close the /bin/sh, which is dash on my Ubuntu, from which I started jshell, start a new terminal, start jshell, and only then be back to jshell normal operation.

---------- BEGIN SOURCE ----------
See Steps to Reproduce above.
---------- END SOURCE ----------

FREQUENCY : always