pty.spawn'd sh shell doesn't exit via 'exit' or CTRL-D (^D) about gvisor HOT 4 OPEN

I think the failure to exit has something to do with an ignored SIGCHILD. I can see this in the debug logs:

D0901 23:13:30.747875  529435 task_signals.go:443] [   1:   1] Discarding ignored signal 17

and if I modify the Python program to handle SIGCHILD I can get the shell to exit using the exit program.

import os
import pty
import signal


def handler(signum, frame):
    print('Signal handler called with signal', signum)
    os.waitpid(-1, 0)
    raise KeyboardInterrupt()

# gVisor is ignoring the SIGCHILD 'Discarding ignored signal 17'
signal.signal(signal.SIGCHLD, handler)

try:
    pty.spawn("sh")
except KeyboardInterrupt:
    print("child exited")

$ docker run -it --runtime=runsc python:3.9.9-slim-bullseye python3 -c "$(cat minimal_exit.py)"
# exit
Signal handler called with signal 17
                                    child exited
$

from gvisor.

The issue with CTRL-D handling appears to be that inputQueueRead in line_discipline.go cannot send EOF (return 0, nil) to the replicaFD when a CTRL-D is sent and the buffer is empty.

from gvisor.

Thanks for digging into the issue! Do you have a ready patch for a fix? I am happy to review and merge the PR

from gvisor.

I've opened #9336 which attempts to address the CTRL-D issue, but haven't yet looked at the signal issue.

from gvisor.