Modified reproducer of https://github.com/systemd/systemd/issues/10872

reproducer.sh

#!/bin/bash
set -eu

# Based on:
# https://gist.githubusercontent.com/bboozzoo/d4b142229b1915ef7cc0cf8593599ad9/raw/367f593d7ef61a3659951f42c699e86820a8db75/reproduce.sh

export LC_ALL=C

LOOPS=40
COUNT="${COUNT-20}"

PREFIX=/tmp/mounttest

systemd_mp() {
    local id
    id="$1"
    systemd-escape -p "$PREFIX/mount/$id"
}

cleanup() {
    echo "--- cleaning up"
    # cleanup
    systemctl daemon-reload
    for i in $(seq $COUNT); do
        systemctl stop "$(systemd_mp "$i").mount" || true
        rm -f "/etc/systemd/system/$(systemd_mp "$i").mount"
    done
    systemctl daemon-reload
    for m in $(grep "$PREFIX/mount/" /proc/self/mountinfo | awk '{print $5}'); do
        umount "$m"
    done
    losetup -D
}

random_sleep() {
    local long
    long="${1-5}"
    sleep $(bc <<< "scale=4; $long*$RANDOM/32767")
}


if ! which bc 2>/dev/null; then
    echo "error: bc not found, install proper package"
    exit 1
fi

variant=0

case "${1-}" in
    --cleanup)
        cleanup
        exit 0
        ;;
    --variant-before)
        variant=1
        ;;
    --variant-systemd-mount)
        variant=2
        ;;
    --variant-mount)
        variant=3
        ;;
    --variant-many-reloads)
        variant=4
        ;;
    --variant-static-lodev)
        variant=5
        ;;
esac

mkdir -p $PREFIX
# create a bunch of disks
for i in $(seq $COUNT); do
    what="$PREFIX/disk-$i.img"
    where="$PREFIX/mount/$i"
    if [ ! -e "$what" ];then
        dd if=/dev/zero of="$PREFIX/disk-$i.img" bs=1M count=10 >/dev/null
        mkfs.ext4 -F "$PREFIX/disk-$i.img" >/dev/null
        echo "$i" > "$PREFIX/canary"
        debugfs -w -R "write $PREFIX/canary canary" "$PREFIX/disk-$i.img"
    fi
    mkdir -p "$PREFIX/mount/$i"
    systemd_unit="$PREFIX/$(systemd_mp "$i").mount"
    if [[ "$variant" = "5" ]]; then
        losetup -f $what
        lodev=$(losetup -l -O NAME -n -j "$what")
        if [[ "$lodev" ]]; then
           what=$lodev
        else
           echo "Failed to find loop dev for $what"
           cleanup
           exit 1
        fi
    fi
    cat <<EOF > "$systemd_unit"
[Unit]
Description=mount unit for test $i

[Mount]
What=$what
Where=$where
Type=ext4
Options=nodev
EOF
done

trap "echo interrupted: run with --cleanup" SIGINT

if [[ "$variant" = "1" ]]; then
    for i in $(seq $COUNT); do
        unit_name="$(systemd_mp "$i").mount"
        cp "$PREFIX/$unit_name" "/etc/systemd/system/$unit_name"
    done
    systemctl daemon-reload
fi

verify() {
    local i
    i="$1"

    text="$(findmnt -ln)"
    if ! echo "$text" | grep -q "$PREFIX/mount/$i "; then
        date
        echo "disk-$i missing"
        echo "unit: tmp-mounttest-mount-$i.mount"
        echo "mountinfo: $text"

        sleep 10
        return 1
    fi

    local content
    content="$(cat "$PREFIX/mount/$i/canary")"
    if [[ "$content"  != "$i" ]]; then
        echo "unexpected content in disk $i: '$content'"
        return 1
    fi
}

variant_0() {
    local i
    i="$1"
    unit_name="$(systemd_mp "$i").mount"
    cp "$PREFIX/$unit_name" "/etc/systemd/system/$unit_name"
    random_sleep
    systemctl daemon-reload

    systemctl start "$unit_name"
    random_sleep

    verify "$i"

    systemctl stop "$unit_name"

    rm -f "/etc/systemd/system/$unit_name"
    systemctl daemon-reload
}

variant_1() {
    local i
    i="$1"
    unit_name="$(systemd_mp "$i").mount"

    systemctl start "$unit_name"
    random_sleep

    verify "$i"

    systemctl stop "$unit_name"
}

variant_2() {
    local i
    i="$1"
    what="$PREFIX/disk-$i.img"
    where="$PREFIX/mount/$i"

    systemd-mount -o nodev "$what" "$where"
    random_sleep

    verify "$i"

    systemd-mount --umount "$what" "$where"
}

variant_3() {
    local i
    i="$1"
    what="$PREFIX/disk-$i.img"
    where="$PREFIX/mount/$i"

    mount -o nodev "$what" "$where"
    #random_sleep 1
    sleep 1

    verify "$i"

    umount "$where"
}

variant_4() {
    local i
    i="$1"
    unit_name="$(systemd_mp "$i").mount"

    if [[ "$i" == 1 ]]; then
        cp "$PREFIX/$unit_name" "/etc/systemd/system/$unit_name"
    fi

    random_sleep
    systemctl daemon-reload

    if [[ "$i" == 1 ]]; then
        systemctl start "$unit_name"
        random_sleep

        verify "$i"

        systemctl stop "$unit_name"

        rm -f "/etc/systemd/system/$unit_name"
    fi
}

# variant_5 is same as variant_0

some_failed=0
[[ "$variant" == "5" ]] && losetup -l
for r in $(seq $LOOPS); do
    echo "--- run $r $(date)"
    [[ "$variant" == "3" ]] && losetup -l

    for idx in $(seq $COUNT); do
        (
            set -eu
            case "$variant" in
                0)
                    variant_0 "$idx"
                    ;;
                1)
                    variant_1 "$idx"
                    ;;
                2)
                    variant_2 "$idx"
                    ;;
                3)
                    variant_3 "$idx"
                    ;;
                4)
                    variant_4 "$idx"
                    ;;
                5)
                    variant_0 "$idx"
                    ;;
            esac
        ) &
    done

    for _ in $(seq $COUNT); do
        if ! wait -n ; then
            some_failed=1
        fi
    done
    if [[ "$some_failed" != "0" ]]; then
        break
    fi
    if [[ "$variant" == "3" ]]; then
        losetup -D || true
        losetup -l
    fi
done