Docker shared bind mounts bug reproducer

docker-shared-bind-mounts-bug.sh

#!/bin/bash

# possible Docker bug when doing nested shared bind mounts
# happens since at least Docker 17.10 (could be earlier)
# currently tested with Docker 20.10.5
# see also https://bugs.launchpad.net/kolla-ansible/+bug/1783978

# the formula below is built this way: (origin mounts)+(submounts)=(total)

# the behaviour described below is observed both on container recreation
# (as given here) and container restart

# in certain cases mounts are being preserved and happen to grow exponentially

set -x

mkdir -p $HOME/bombastic-host
mkdir -p $HOME/bombastic-host-sub




# (1) - bind in shared-bind - BAD behaviour (possibly expected)

docker run --rm \
    -v $HOME/bombastic-host:/bombastic-container:shared \
    -v $HOME/bombastic-host-sub:/bombastic-container/sub \
    busybox /bin/true

mount | grep bombastic | sort | cut -f 1-3 -d' '

# after 1: 0+1=1
# /dev/sdb on /home/radek/bombastic-host/sub

docker run --rm \
    -v $HOME/bombastic-host:/bombastic-container:shared \
    -v $HOME/bombastic-host-sub:/bombastic-container/sub \
    busybox /bin/true

mount | grep bombastic | sort | cut -f 1-3 -d' '

# after 2: 1+2=3
# /dev/sdb on /home/radek/bombastic-host-sub
# /dev/sdb on /home/radek/bombastic-host/sub
# /dev/sdb on /home/radek/bombastic-host/sub

docker run --rm \
    -v $HOME/bombastic-host:/bombastic-container:shared \
    -v $HOME/bombastic-host-sub:/bombastic-container/sub \
    busybox /bin/true

mount | grep bombastic | sort | cut -f 1-3 -d' '

# after 3: 3+4=7
# /dev/sdb on /home/radek/bombastic-host-sub
# /dev/sdb on /home/radek/bombastic-host-sub
# /dev/sdb on /home/radek/bombastic-host-sub
# /dev/sdb on /home/radek/bombastic-host/sub
# /dev/sdb on /home/radek/bombastic-host/sub
# /dev/sdb on /home/radek/bombastic-host/sub
# /dev/sdb on /home/radek/bombastic-host/sub

# and on it goes...

# cleanup (must be in this order)

sudo umount $HOME/bombastic-host-sub
sudo umount $HOME/bombastic-host/sub




# (2) - shared-bind in bind - OK

docker run --rm \
    -v $HOME/bombastic-host:/bombastic-container \
    -v $HOME/bombastic-host-sub:/bombastic-container/sub:shared \
    busybox /bin/true

mount | grep bombastic | sort | cut -f 1-3 -d' '




# (3) - volume in shared-bind - BAD (analogously to 1)

docker run --rm \
    -v bombastic-sub-volume:/bombastic-container/sub \
    -v $HOME/bombastic-host:/bombastic-container:shared \
    busybox /bin/true

mount | grep bombastic | sort | cut -f 1-3 -d' '

# after 1: 0+1=1
# /dev/sdb on /home/radek/bombastic-host/sub

docker run --rm \
    -v bombastic-sub-volume:/bombastic-container/sub \
    -v $HOME/bombastic-host:/bombastic-container:shared \
    busybox /bin/true

mount | grep bombastic | sort | cut -f 1-3 -d' '

# after 2: 1+2=3
# /dev/sdb on /home/radek/bombastic-host/sub
# /dev/sdb on /home/radek/bombastic-host/sub
# /dev/sdb on /var/lib/docker/volumes/bombastic-sub-volume/_data

docker run --rm \
    -v bombastic-sub-volume:/bombastic-container/sub \
    -v $HOME/bombastic-host:/bombastic-container:shared \
    busybox /bin/true

mount | grep bombastic | sort | cut -f 1-3 -d' '

# after 3: 3+4=7
# /dev/sdb on /home/radek/bombastic-host/sub
# /dev/sdb on /home/radek/bombastic-host/sub
# /dev/sdb on /home/radek/bombastic-host/sub
# /dev/sdb on /home/radek/bombastic-host/sub
# /dev/sdb on /var/lib/docker/volumes/bombastic-sub-volume/_data
# /dev/sdb on /var/lib/docker/volumes/bombastic-sub-volume/_data
# /dev/sdb on /var/lib/docker/volumes/bombastic-sub-volume/_data

# and on it goes...

# cleanup (must be in this order)

sudo umount /var/lib/docker/volumes/bombastic-sub-volume/_data
sudo umount /home/radek/bombastic-host/sub




# (4) - shared-bind in volume - BAD (unlike analogous 2, I expect this case to be OK)
# could be related to https://github.com/moby/moby/issues/35323

docker run --rm \
    -v bombastic-volume:/bombastic-container \
    -v $HOME/bombastic-host-sub:/bombastic-container/sub:shared \
    busybox /bin/true

mount | grep bombastic | sort | cut -f 1-3 -d' '

# after 1: 0+1=1
# /dev/sdb on /var/lib/docker/volumes/bombastic-volume/_data/sub

docker run --rm \
    -v bombastic-volume:/bombastic-container \
    -v $HOME/bombastic-host-sub:/bombastic-container/sub:shared \
    busybox /bin/true

mount | grep bombastic | sort | cut -f 1-3 -d' '

# after 2: 1+2=3
# /dev/sdb on /home/radek/bombastic-host-sub
# /dev/sdb on /var/lib/docker/volumes/bombastic-volume/_data/sub
# /dev/sdb on /var/lib/docker/volumes/bombastic-volume/_data/sub

docker run --rm \
    -v bombastic-volume:/bombastic-container \
    -v $HOME/bombastic-host-sub:/bombastic-container/sub:shared \
    busybox /bin/true

mount | grep bombastic | sort | cut -f 1-3 -d' '

# after 3: 3+4=7
# /dev/sdb on /home/radek/bombastic-host-sub
# /dev/sdb on /home/radek/bombastic-host-sub
# /dev/sdb on /home/radek/bombastic-host-sub
# /dev/sdb on /var/lib/docker/volumes/bombastic-volume/_data/sub
# /dev/sdb on /var/lib/docker/volumes/bombastic-volume/_data/sub
# /dev/sdb on /var/lib/docker/volumes/bombastic-volume/_data/sub
# /dev/sdb on /var/lib/docker/volumes/bombastic-volume/_data/sub

# and on it goes...

# cleanup (must be in this order)

sudo umount $HOME/bombastic-host-sub
sudo umount /var/lib/docker/volumes/bombastic-volume/_data/sub