another mount issue on jessie

[Sebastian Kuzminsky <seb@highlab.com>]

Hi folks, I'm running in to a mount issue on Jessie, it seems different 
from the one reported here: 
https://lists.debian.org/debian-devel/2016/01/msg00750.html

I've attached a short shell script the reproduces the issue 100% of the 
time.

The pattern that triggers the failure is this: rbind-mount a directory, 
that under it has another filesystem mounted, onto a destination 
directory.  Then unmount the "submount" from under the destination 
directory, then unmount the rbind mount from the destination directory 
itself.  The destination directory is now empty, lsof shows no files 
open under the destination directory, and /proc/mounts show nothing 
mounted there.  But the destination directory cannot be removed, 
complaining of "device in use".

The problem only manifests when running the Jessie or Wheezy kernel (on 
the Jessie userspace) and Gnome is installed and colord, packagekit, and 
rtkit-daemon are all running.  Marvel at my gorgeous ascii art table:

Userspace | Kernel                                             | 
Processes running | Bug present?
----------+----------------------------------------------------+-------------------+--------------
Jessie    | linux-image-3.2.0-4-amd64 (3.2.73-2+deb7u2)        | 
Yes               | Yes
Jessie    | linux-image-3.2.0-4-amd64 (3.2.73-2+deb7u2)        | 
No                | No
----------+----------------------------------------------------+-------------------+--------------
Jessie    | linux-image-3.16.0-4-amd64 (3.16.7-ckt20-1+deb8u3) | 
Yes               | Yes
Jessie    | linux-image-3.16.0-4-amd64 (3.16.7-ckt20-1+deb8u3) | 
No                | No
----------+----------------------------------------------------+-------------------+--------------
Jessie    | linux-image-4.3.0-1-amd64 (4.3.3-7)                | 
Yes               | No
----------+----------------------------------------------------+-------------------+--------------


--
Sebastian Kuzminsky

#!/usr/bin/env bash
set -e

TEST_DIR="${PWD}/test-dir"

show_state() {
    echo ${@}:
    tree ${TEST_DIR}
    findmnt
}

if [[ $(whoami) != 'root' ]]; then
    echo "must be run as root to play with mounts"
    exit 1
fi

# clean up the left-behind mess from last time the test ran
if [[ -d ${TEST_DIR} ]]; then
    DEST=${TEST_DIR}.${BASHPID}
    echo "moving old ${TEST_DIR} to ${DEST}"
    mv ${TEST_DIR} ${DEST}
fi


#
# the test code starts here
#

echo "### setting up"

mkdir -p ${TEST_DIR}

mkdir ${TEST_DIR}/src
mkdir ${TEST_DIR}/src/subfs
mount -t tmpfs -o size=1M none ${TEST_DIR}/src/subfs

mkdir ${TEST_DIR}/dest

show_state "after setup"


echo "### bind mounting"

#mount --make-rprivate ${TEST_DIR}/src
mount -v --rbind ${TEST_DIR}/src ${TEST_DIR}/dest
mount -v --make-rprivate ${TEST_DIR}/dest

show_state after mount


echo "### recursive unmount"

umount -v -l ${TEST_DIR}/dest/subfs
umount -v -l ${TEST_DIR}/dest

show_state after recursive unmount


echo "### cleaning up"

umount -v -l ${TEST_DIR}/src/subfs

DEST_RM=0
SRC_RM=0
TEST_DIR_RM=0

# this first rm fails
rm -rf ${TEST_DIR}/dest || DEST_RM=$?

rm -rf ${TEST_DIR}/src || SRC_RM=$?
rm -rf ${TEST_DIR} || TEST_DIR_RM=$?

show_state after cleanup

if [[ ${DEST_RM} -eq 0 && ${TEST_DIR_RM} -eq 0 && ${SRC_RM} -eq 0 ]]; then
    echo "PASS!  no problem"
    RESULT=0
else
    echo "FAIL!  rm did not succeed (dest=${DEST_RM}, src=${SRC_RM}, test-dir=${TEST_DIR_RM})"
    RESULT=1
fi
exit ${RESULT}