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Replace inotifywait with polling in cgroup cleanup #37

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Replace inotifywait with polling in cgroup cleanup #37

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34 changes: 16 additions & 18 deletions usr/libexec/tb-updater/sandbox-update-torbrowser
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Original file line number Diff line number Diff line change
Expand Up @@ -67,35 +67,33 @@ cleanup_dir_as_tb_updater() {
}

cleanup() {
local xhost_output cgroup_empty_str inotifywait_subshell_pid \
inotifywait_fd
local xhost_output cgroup_empty_str cgroup_drained poll_count

if [ -n "${tb_updater_cgroup}" ] && validate_uuid "${tb_updater_cgroup_name}"; then
cgroup_empty_str="populated 0
frozen 0"
(
true "exec {inotifywait_fd}<"
exec {inotifywait_fd}< <(inotifywait --quiet --monitor --event modify "${tb_updater_cgroup}/cgroup.events")
# shellcheck disable=SC2064
trap "kill -s KILL $!" EXIT INT TERM
while IFS=$'\n' read -r _; do
if printf '%s\n' '1' > "${tb_updater_cgroup}/cgroup.kill"; then
## Poll cgroup.events until the cgroup is empty, rather than using
## inotifywait which consumes an inotify watch from the kernel's
## limited pool and can cause ENOSPC on watch-constrained systems.
## cgroup.kill sends SIGKILL, so draining should be near-instant.
cgroup_drained='false'
poll_count=0
while [ "${poll_count}" -lt 50 ]; do
if [ "$(cat "${tb_updater_cgroup}/cgroup.events")" = "${cgroup_empty_str}" ]; then
rmdir "${tb_updater_cgroup}" \
|| log warn "Cannot remove tb-updater cgroup at '${tb_updater_cgroup}'!"
cgroup_drained='true'
break
fi
done <&"${inotifywait_fd}"
) &
inotifywait_subshell_pid="$!"
## inotifywait itself requires some time to initialize. 1/20th of a second
## seems to be enough on rather slow hardware. so use 1/10th of a second
## for good measure.
light_sleep 0.1
if printf '%s\n' '1' > "${tb_updater_cgroup}/cgroup.kill"; then
wait "${inotifywait_subshell_pid}"
light_sleep 0.1
poll_count=$((poll_count + 1))
done
if [ "${cgroup_drained}" != 'true' ]; then
log warn "Timed out waiting for tb-updater cgroup at '${tb_updater_cgroup}' to drain!"
fi
else
log warn "Cannot kill tb-updater cgroup at '${tb_updater_cgroup}'!"
kill "${inotifywait_subshell_pid}"
fi
fi

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