core: Check unit start rate limiting earlier

Fixes #17433. Currently, if any of the validations we do before we
check start rate limiting fail, we can still enter a busy loop as
no rate limiting gets applied. A common occurence of this scenario
is path units triggering a service that fails a condition check.

To fix the issue, we simply move up start rate limiting checks to
be the first thing we do when starting a unit. To achieve this,
we add a new method to the unit vtable and implement it for the
relevant unit types so that we can do the start rate limit checks
earlier on.

test/TEST-63-ISSUE-17433/Makefile

@@ -0,0 +1 @@
+../TEST-01-BASIC/Makefile

test/TEST-63-ISSUE-17433/test.sh

@@ -0,0 +1,9 @@
+#!/usr/bin/env bash
+set -e
+
+TEST_DESCRIPTION="https://github.com/systemd/systemd/issues/17433"
+
+# shellcheck source=test/test-functions
+. "${TEST_BASE_DIR:?}/test-functions"
+
+do_test "$@"

test/meson.build

@@ -33,6 +33,8 @@ if install_tests
                        install_dir : testdata_dir)
         install_subdir('testsuite-52.units',
                        install_dir : testdata_dir)
+        install_subdir('testsuite-63.units',
+                       install_dir : testdata_dir)
 
         testsuite08_dir = testdata_dir + '/testsuite-08.units'
         install_data('testsuite-08.units/-.mount',

test/testsuite-10.units/test10.service

@@ -1,6 +1,9 @@
 [Unit]
 Requires=test10.socket
 ConditionPathExistsGlob=/tmp/nonexistent
+# Make sure we hit the socket trigger limit in the test and not the service start limit.
+StartLimitInterval=1000
+StartLimitBurst=1000
 
 [Service]
 ExecStart=true

test/testsuite-63.units/test63.path

@@ -0,0 +1,2 @@
+[Path]
+PathExists=/tmp/test63

test/testsuite-63.units/test63.service

@@ -0,0 +1,5 @@
+[Unit]
+ConditionPathExists=!/tmp/nonexistent
+
+[Service]
+ExecStart=true

test/units/testsuite-63.service

@@ -0,0 +1,16 @@
+[Unit]
+Description=TEST-63-ISSUE-17433
+
+[Service]
+ExecStartPre=rm -f /failed /testok
+Type=oneshot
+ExecStart=rm -f /tmp/nonexistent
+ExecStart=systemctl start test63.path
+ExecStart=touch /tmp/test63
+# Make sure systemd has sufficient time to hit the start limit for test63.service.
+ExecStart=sleep 2
+ExecStart=sh -x -c 'test "$(systemctl show test63.service -P ActiveState)" = failed'
+ExecStart=sh -x -c 'test "$(systemctl show test63.service -P Result)" = start-limit-hit'
+ExecStart=sh -x -c 'test "$(systemctl show test63.path -P ActiveState)" = failed'
+ExecStart=sh -x -c 'test "$(systemctl show test63.path -P Result)" = unit-start-limit-hit'
+ExecStart=sh -x -c 'echo OK >/testok'