core/automount: tear down autofs when the unit vanished across reload
When an automount unit ceases to exist across daemon-reload (observed: because a generator no longer emits it), its deserialized state still makes `automount_coldplug()` pick up the autofs pipe and resume the unit as waiting/running. But nothing can serve that mount point anymore. The kernel keeps blocking every process that touches the mount point until PID 1 answers (which it won't), forever. To fix this, fail pending requests and unmount the autofs when coldplugging an automount unit that is not loaded anymore. Fixes #43700 Signed-off-by: Martin Pitt <martin@amutable.com>
This commit is contained in:
Martin Pitt
Executable
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#!/usr/bin/env bash
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# SPDX-License-Identifier: LGPL-2.1-or-later
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set -eux
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set -o pipefail
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# An automount unit that vanishes across daemon-reload must not leave its autofs mount point armed,
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# there's nothing left to answer it.
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# See https://github.com/systemd/systemd/issues/43700
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# PID 1 declares automount units unsupported without this device, e.g. in the nspawn containers CI runs in
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if [[ ! -e /dev/autofs ]]; then
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echo "autofs is not available, skipping automount tests"
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exit 77
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fi
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# The errno text asserted below is strerror()'s
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export LC_ALL=C
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MOUNT_POINT=/tmp/TEST-07-PID1-issue-43700
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UNIT=$(systemd-escape --path "$MOUNT_POINT")
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STAT_ERR=/tmp/TEST-07-PID1-issue-43700.stderr
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CURSOR=/tmp/TEST-07-PID1-issue-43700.cursor
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at_exit() {
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set +e
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[[ -n "${WAITER_PID:-}" ]] && kill "$WAITER_PID"
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systemctl stop "$UNIT".automount "$UNIT".mount
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# A file system may sit on top of an armed autofs; detach both without stepping into either
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while [[ -n "$(fstype "$MOUNT_POINT")" ]]; do
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umount -l "$MOUNT_POINT" || break
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done
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rm -f /run/systemd/system/"$UNIT".{auto,}mount "$STAT_ERR" "$CURSOR"
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systemctl unmask "$UNIT".automount
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systemctl daemon-reload
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systemctl reset-failed "$UNIT".automount "$UNIT".mount
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rmdir "$MOUNT_POINT"
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}
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trap at_exit EXIT
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# The file system type of the topmost mount at a path, read from mountinfo so that the check itself does not
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# trigger the automount: statfs() would, as its path lookup asks for automounting.
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fstype() {
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awk -v where="$1" '$5 == where { for (i = 7; $i != "-"; i++) {}; type = $(i + 1) } END { print type }' /proc/self/mountinfo
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}
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write_automount() {
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cat >/run/systemd/system/"$UNIT".automount <<EOF
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[Automount]
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Where=$MOUNT_POINT
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EOF
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}
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# A mount unit that never completes: the mount job waits for the nonexisting device
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write_hanging_mount() {
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cat >/run/systemd/system/"$UNIT".mount <<EOF
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[Mount]
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What=/dev/disk/by-label/does-not-exist
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Where=$MOUNT_POINT
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Type=ext4
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EOF
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}
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mkdir -p /run/systemd/system "$MOUNT_POINT"
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# An automount unit that still exists after daemon-reload stays armed and serves its mount point
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write_automount
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cat >/run/systemd/system/"$UNIT".mount <<EOF
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[Mount]
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What=tmpfs
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Where=$MOUNT_POINT
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Type=tmpfs
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EOF
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systemctl daemon-reload
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systemctl start "$UNIT".automount
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systemctl daemon-reload
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systemctl is-active "$UNIT".automount
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[[ "$(fstype "$MOUNT_POINT")" == autofs ]]
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# Only PID 1 can answer this, and a regression that leaves the autofs unserved would block it forever,
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# taking the exit trap and the rest of TEST-07-PID1 with it
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timeout -k 5 -s KILL 60 ls "$MOUNT_POINT"
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systemctl is-active "$UNIT".mount
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[[ "$(fstype "$MOUNT_POINT")" == tmpfs ]]
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# PID 1's log lines are matched without _PID=1: right after a daemon-reexec it still logs to kmsg, and the
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# journal's kernel transport carries no trusted PID. Every match below is bounded by a cursor, which each
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# journalctl advances past the line it found, as the cases log the same message more than once.
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journalctl -n 0 --cursor-file="$CURSOR"
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# Vanishing underneath a file system already mounted on top leaves that file system alone
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rm /run/systemd/system/"$UNIT".{auto,}mount
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systemctl daemon-reload
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journalctl --sync
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journalctl --cursor-file="$CURSOR" --grep "abandoning automount point '$MOUNT_POINT'"
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# The unit went away with its file rather than sticking around as a failed one
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(! systemctl is-active "$UNIT".automount)
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(! systemctl is-failed "$UNIT".automount)
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systemctl is-active "$UNIT".mount
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[[ "$(fstype "$MOUNT_POINT")" == tmpfs ]]
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ls "$MOUNT_POINT"
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# The autofs underneath was given up: once exposed again, accessing it must not hang
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umount "$MOUNT_POINT"
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[[ "$(fstype "$MOUNT_POINT")" == autofs ]]
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rc=0
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timeout -k 5 -s KILL 60 ls "$MOUNT_POINT" || rc=$?
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[[ $rc -ne 137 ]]
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umount -l "$MOUNT_POINT"
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# Both mounts went away behind PID 1's back, and it processes mount table changes rate-limited. Wait for
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# it to catch up, or the next case's mount unit starts out as already mounted and never gets a job.
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timeout 30 bash -c "until [[ \$(systemctl show -p ActiveState --value '$UNIT.mount') == inactive ]]; do sleep .5; done"
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# Vanishing while a request waits for the mount fails the request and disarms the mount point
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for reload in daemon-reload daemon-reexec; do
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write_automount
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write_hanging_mount
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systemctl daemon-reload
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systemctl start "$UNIT".automount
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# Trigger the automount, which blocks in the kernel until PID 1 answers. Only SIGKILL gets it out of
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# that wait before then, so a regression must fail the test here rather than hang it.
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timeout -k 5 -s KILL 60 stat "$MOUNT_POINT"/x 2>"$STAT_ERR" &
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WAITER_PID=$!
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timeout 10 bash -c "until systemctl list-jobs | grep -F '$UNIT.mount' >/dev/null; do sleep .5; done"
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# Both units vanish while the mount job is still waiting for its device
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rm /run/systemd/system/"$UNIT".{auto,}mount
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systemctl "$reload"
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# The waiter must fail promptly with the error the teardown sends, rather than hang until its timeout
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# kills it (rc=137) or fail for some other reason
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rc=0
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wait "$WAITER_PID" || rc=$?
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unset WAITER_PID
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[[ $rc -ne 0 && $rc -ne 137 ]]
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grep -F 'Host is down' "$STAT_ERR"
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journalctl --sync
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journalctl --cursor-file="$CURSOR" --grep "tearing down automount point '$MOUNT_POINT'"
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(! systemctl is-active "$UNIT".automount)
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(! systemctl is-failed "$UNIT".automount)
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# The autofs mount point is gone as well
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[[ -z "$(fstype "$MOUNT_POINT")" ]]
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done
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# Masking counts as vanishing too: the unit stops being loaded, so nothing serves the mount point anymore
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write_automount
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write_hanging_mount
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systemctl daemon-reload
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systemctl start "$UNIT".automount
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[[ "$(fstype "$MOUNT_POINT")" == autofs ]]
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systemctl mask "$UNIT".automount
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systemctl daemon-reload
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journalctl --sync
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journalctl --cursor-file="$CURSOR" --grep "tearing down automount point '$MOUNT_POINT'"
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(! systemctl is-active "$UNIT".automount)
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[[ -z "$(fstype "$MOUNT_POINT")" ]]
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systemctl unmask "$UNIT".automount
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rm /run/systemd/system/"$UNIT".{auto,}mount
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systemctl daemon-reload
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