core: path: Re-enter waiting if target is deactivating

Previously, path units would remain in the running state while their
target unit is deactivating. This left a window of time where the target
unit is no longer operational (i.e. it is busy deactivating/cleaning
up/etc) but the path unit would continue to ignore inotify events. In
short: any inotify event that occurs while the target unit deactivates
would be completely lost.

With this commit, the path will go back into a waiting state when the
target unit starts deactivating. This means that any inotify event that
occurs while the target unit deactivates will queue a start job.

src/core/path.c

@@ -582,7 +582,7 @@ static void path_enter_waiting(Path *p, bool initial, bool from_trigger_notify)
 
         /* If the triggered unit is already running, so are we */
         trigger = UNIT_TRIGGER(UNIT(p));
-        if (trigger && !UNIT_IS_INACTIVE_OR_FAILED(unit_active_state(trigger))) {
+        if (trigger && !UNIT_IS_INACTIVE_OR_DEACTIVATING(unit_active_state(trigger))) {
                 path_set_state(p, PATH_RUNNING);
                 path_unwatch(p);
                 return;
@@ -853,11 +853,11 @@ static void path_trigger_notify_impl(Unit *u, Unit *other, bool on_defer) {
                 return;
 
         if (p->state == PATH_RUNNING &&
-            UNIT_IS_INACTIVE_OR_FAILED(unit_active_state(other))) {
+            UNIT_IS_INACTIVE_OR_DEACTIVATING(unit_active_state(other))) {
                 if (!on_defer)
                         log_unit_debug(u, "Got notified about unit deactivation.");
         } else if (p->state == PATH_WAITING &&
-                   !UNIT_IS_INACTIVE_OR_FAILED(unit_active_state(other))) {
+                   !UNIT_IS_INACTIVE_OR_DEACTIVATING(unit_active_state(other))) {
                 if (!on_defer)
                         log_unit_debug(u, "Got notified about unit activation.");
         } else

test/testsuite-63.units/test63-pr-30768.path

@@ -0,0 +1,3 @@
+# SPDX-License-Identifier: LGPL-2.1-or-later
+[Path]
+PathChanged=/tmp/copyme

test/testsuite-63.units/test63-pr-30768.service

@@ -0,0 +1,5 @@
+# SPDX-License-Identifier: LGPL-2.1-or-later
+[Service]
+ExecStart=cp -v /tmp/copyme /tmp/copied
+# once cp exits, service goes into deactivating state and then runs ExecStop
+ExecStop=flock -e /tmp/noexit true

test/units/testsuite-63.sh

@@ -80,6 +80,46 @@ output=$(systemctl list-jobs --no-legend)
 assert_not_in "test63-issue-24577.service" "$output"
 assert_in "test63-issue-24577-dep.service" "$output"
 
+# Test for race condition fixed by https://github.com/systemd/systemd/pull/30768
+# Here's the schedule of events that we to happen during this test:
+#       (This test)                     (The service)
+#                                       .path unit monitors /tmp/copyme for changes
+#       Take lock on /tmp/noexeit       ↓
+#       Write to /tmp/copyme            ↓
+#       Wait for deactivating           Started
+#       ↓                               Copies /tmp/copyme to /tmp/copied
+#       ↓                               Tells manager it's shutting down
+#       Ensure service did the copy     Tries to lock /tmp/noexit and blocks
+#       Write to /tmp/copyme            ↓
+#
+# Now at this point the test can diverge. If we regress, this second write is
+# missed and we'll see:
+#       ... (second write)              ... (blocked)
+#       Drop lock on /tmp/noexit        ↓
+#       Wait for service to do copy     Unblocks and exits
+#       ↓                               (dead)
+#       ↓
+#       (timeout)
+#       Test fails
+#
+# Otherwise, we'll see:
+#       ... (second write)              ... (blocked)
+#       Drop lock on /tmp/noexit        ↓ and .path unit queues a new start job
+#       Wait for service to do copy     Unblocks and exits
+#       ↓                               Starts again b/c of queued job
+#       ↓                               Copies again
+#       Test Passes
+systemctl start test63-pr-30768.path
+exec {lock}<>/tmp/noexit
+flock -e $lock
+echo test1 > /tmp/copyme
+# shellcheck disable=SC2016
+timeout 30 bash -c 'until test "$(systemctl show test63-pr-30768.service -P ActiveState)" = deactivating; do sleep .2; done'
+diff /tmp/copyme /tmp/copied
+echo test2 > /tmp/copyme
+exec {lock}<&-
+timeout 30 bash -c 'until diff /tmp/copyme /tmp/copied; do sleep .2; done'
+
 systemctl log-level info
 
 touch /testok