[Bug 1087704] New: repetition of signal 21 with --sig-proxy and SIGSTOP of docker

[Red Hat Bugzilla]

https://bugzilla.redhat.com/show_bug.cgi?id=1087704

Bug ID: 1087704
           Summary: repetition of signal 21 with --sig-proxy and SIGSTOP
                    of docker
           Product: Fedora
           Version: 20
         Component: docker-io
          Severity: low
          Assignee: [e-mail]
          Reporter: [e-mail]
        QA Contact: [e-mail]
                CC: [e-mail], [e-mail],
                    [e-mail], [e-mail],
                    [e-mail], [e-mail],
                    [e-mail]

Description of problem:
I noticed weird reaction to SIGSTOP signal. When you start container with
--sig-proxy, ignore all signals in container and from OS use kill -SIGSTOP to
the `docker run` process, it's put into background. (so far correct behavior)
Than when you use kill -SIGCONT, it's resumed (still in background) and it's
continuing to send signal 21 to the container (100% CPU utilization).
This disappears once you attach the process with fg.

Version-Release number of selected component (if applicable):
docker-io-0.9.1-1.fc21.x86_64

How reproducible:
always

Steps to Reproduce:
1. /usr/bin/docker -D run --tty=false --rm -i --name test_eoly
localhost:5000/ldoktor/fedora:latest bash -c 'for NUM in `seq 1 64`; do trap
"echo Received $NUM, ignoring..." $NUM; done; while :; do sleep 1; done'
2. ps ax |grep docker
3. kill -SIGSTOP $PID
4. kill -SIGCONT $PID

Actual results:
[1]+  Pozastavena             /usr/bin/docker -D run --tty=false --rm -i --name
test_eoly localhost:5000/ldoktor/fedora:latest bash -c 'for NUM in `seq 1 64`;
do trap "echo Received $NUM, ignoring..." $NUM; done; while :; do sleep 1;
done'
[root@t530 ~]# Received 21, ignoring...
Received 21, ignoring...
Received 21, ignoring...
Received 21, ignoring...
Received 21, ignoring...
Received 21, ignoring...
... (100% CPU utilization, when you use fg it stops and you can use the
container again...)

Expected results:
[1]+  Pozastavena             /usr/bin/docker -D run --tty=false --rm -i --name
test_eoly localhost:5000/ldoktor/fedora:latest bash -c 'for NUM in `seq 1 64`;
do trap "echo Received $NUM, ignoring..." $NUM; done; while :; do sleep 1;
done'
[root@t530 ~]# Received 21, ignoring...

Additional info:
I'm not definitely sure if this is really required as it's not a common usage.
But as there is no way to detach the process apart from kill -SIGSTOP people
might use it and get to this problem...