Hi, 

Comint can stall emacs while waiting for subproces output. I attach a
trivial patch.

Here is a short explanation. First comint calls comint-input-sender 

╭──────── #1842 ─ /home/vitoshka/TVC/emacs/lisp/comint.el ──
│         (let ((comint-input-sender-no-newline no-newline))
│           (funcall comint-input-sender proc input))
╰──────── #1843 ─

Then, if process echoes, comint first waits for process output:

╭──────── #1850 ─ /home/vitoshka/TVC/emacs/lisp/comint.el ──
│             (while (and (accept-process-output proc)
│                         (> (+ comint-last-input-end echo-len)
│                            (point-max))
╰──────── #1852 ─

The problem is that, occasionally, comint-input-sender might be a
non-trivial function and could take care of process output itself. Thus,
accept-process-output will wait for nonexistent output, and stall
emacs. The patch just reverts the order in the (and ...) above.

    Thanks, 
    Vitalie