generator: order cryptsetup/verity/integrity after systemd-udevd

During soft-reboot teardown, systemd-cryptsetup@.service's ExecStop runs
libcryptsetup's crypt_deactivate(), which issues DM_REMOVE with a udev
cookie and blocks in dm_udev_wait() until 95-dm-notify.rules decrements
the cookie semaphore via "dmsetup udevcomplete $env{DM_COOKIE}".

The generated cryptsetup unit had only After=systemd-udevd-kernel.socket,
not After=systemd-udevd.service. The .socket has IgnoreOnIsolate=yes and
is not stopped during soft-reboot, so it provides no ordering at all for
the service teardown. Meanwhile systemd-udevd.service has
Conflicts=soft-reboot.target (added in 0d1819e791) and stops as soon as
soft-reboot.target starts, with no ordering relative to cryptsetup's
ExecStop.

Once udevd's device monitor event source is disabled in manager_exit(),
pending DM_REMOVE uevents are no longer processed and the cookie
semaphore stays at 1 forever, blocking soft-reboot at "Stopping
Cryptography Setup..." until JobTimeoutSec=30min on soft-reboot.target
fires.

Add systemd-udevd.service to the After= ordering of the generated
cryptsetup, veritysetup and integritysetup units. By systemd's job
ordering rules (job_compare() in src/core/job.c), when two units are
both being stopped and one has After= the other, the After= unit is
stopped first. So with cryptsetup@*.service After=systemd-udevd.service,
cryptsetup stops first (cookie acknowledged by the still-live udevd),
then udevd stops.

Putting After=umount.target on systemd-udevd.service does not work: at
soft-reboot, udevd's stop job runs concurrently with umount.target's
start job, and JOB_STOP unconditionally precedes JOB_START in the
transaction (see src/core/job.c:1742). The ordering has to be expressed
between two stop jobs, which is what putting After=systemd-udevd.service
on the dm consumers achieves.

Fixes: #40298

src/integritysetup/integritysetup-generator.c

@@ -80,7 +80,11 @@ static int create_disk(
                 "SourcePath=%s\n"
                 "DefaultDependencies=no\n"
                 "IgnoreOnIsolate=true\n"
-                "After=integritysetup-pre.target systemd-udevd-kernel.socket\n"
+                /* The systemd-udevd.service ordering is mostly about shutdown, not startup: on stop the dm
+                 * device is detached via an ioctl carrying a udev cookie that blocks in dm_udev_wait() until
+                 * udev releases it (95-dm-notify.rules). Stopping before udevd keeps it around to service the
+                 * cookie; otherwise during soft-reboot/shutdown udevd may exit first and the detach hangs. */
+                "After=integritysetup-pre.target systemd-udevd-kernel.socket systemd-udevd.service\n"
                 "Before=blockdev@dev-mapper-%%i.target\n"
                 "Wants=blockdev@dev-mapper-%%i.target\n"
                 "Conflicts=umount.target\n"

src/shared/generator.c

@@ -921,7 +921,12 @@ int generator_write_cryptsetup_unit_section(FILE *f, const char *source) {
         fprintf(f,
                 "\n"
                 "DefaultDependencies=no\n"
-                "After=cryptsetup-pre.target systemd-udevd-kernel.socket systemd-tpm2-setup-early.service\n"
+                /* The ordering against systemd-udevd.service is mostly about shutdown, not startup: on stop
+                 * the device is detached via a device-mapper ioctl that carries a udev cookie, and we block in
+                 * dm_udev_wait() until udev releases it (see 95-dm-notify.rules). Ordering After= it means we
+                 * are stopped first, while udevd is still around to service that cookie; otherwise during
+                 * soft-reboot/shutdown udevd may exit first and the detach hangs until the job timeout. */
+                "After=cryptsetup-pre.target systemd-udevd-kernel.socket systemd-udevd.service systemd-tpm2-setup-early.service\n"
                 "Before=blockdev@dev-mapper-%%i.target\n"
                 "Wants=blockdev@dev-mapper-%%i.target\n"
                 "IgnoreOnIsolate=true\n");
@@ -993,7 +998,11 @@ int generator_write_veritysetup_unit_section(FILE *f, const char *source) {
         fprintf(f,
                 "DefaultDependencies=no\n"
                 "IgnoreOnIsolate=true\n"
-                "After=veritysetup-pre.target systemd-udevd-kernel.socket\n"
+                /* The systemd-udevd.service ordering is mostly about shutdown, not startup: on stop the dm
+                 * device is detached via an ioctl carrying a udev cookie that blocks in dm_udev_wait() until
+                 * udev releases it (95-dm-notify.rules). Stopping before udevd keeps it around to service the
+                 * cookie; otherwise during soft-reboot/shutdown udevd may exit first and the detach hangs. */
+                "After=veritysetup-pre.target systemd-udevd-kernel.socket systemd-udevd.service\n"
                 "Before=blockdev@dev-mapper-%%i.target\n"
                 "Wants=blockdev@dev-mapper-%%i.target\n");