kdump-emergency: fix "Transaction is destructive" emergency failure

We met a problem that the kdump emergency service failed to
start when the target dump timeout(we passed "rd.timeout=30"
to kdump), it reported "Transaction is destructive" messages:

  [ TIME ] Timed out waiting for device dev-mapper-fedora\x2droot.device.
  [DEPEND] Dependency failed for Initrd Root Device.
  [ SKIP ] Ordering cycle found, skipping System Initialization
  [DEPEND] Dependency failed for /sysroot.
  [DEPEND] Dependency failed for Initrd Root File System.
  [DEPEND] Dependency failed for Reload Configuration from the Real Root.
  [ SKIP ] Ordering cycle found, skipping System Initialization
  [ SKIP ] Ordering cycle found, skipping Initrd Default Target
  [DEPEND] Dependency failed for File System Check on /dev/mapper/fedora-root.
  [  OK  ] Reached target Initrd File Systems.
  [  OK  ] Stopped dracut pre-udev hook.
  [  OK  ] Stopped dracut cmdline hook.
           Starting Setup Virtual Console...
           Starting Kdump Emergency...
  [  OK  ] Reached target Initrd Default Target.
  [  OK  ] Stopped dracut initqueue hook.
  Failed to start kdump-error-handler.service: Transaction is destructive.
  See system logs and 'systemctl status kdump-error-handler.service' for details.
  [FAILED] Failed to start Kdump Emergency.
  See 'systemctl status emergency.service' for details.
  [DEPEND] Dependency failed for Emergency Mode.

This is because in case of root failure, initrd-root-fs.target
will trigger systemd emergency target which requires the systemd
emergency service actually is kdump-emergency.service, then our
kdump-emergency.service starts kdump-error-handler.service with
"systemctl isolate"(see 99kdumpbase/kdump-emergency.service, we
replace systemd's with this one under kdump).

This will lead to systemd two contradictable jobs queued as an
atomic transaction:
job 1) the emergency service gets started by initrd-root-fs.target
job 2) the emergency service gets stopped due to "systemctl isolate"
thereby throwing "Transaction is destructive".

In order to solve it, we can utilize "IgnoreOnIsolate=yes" for both
kdump-emergency.service and kdump-emergency.target. Unit with attribute
"IgnoreOnIsolate=yes" won't be stopped when isolating another unit,
they can keep going as expected in case be triggered by any failure.

We add kdump-emergency.target dedicated to kdump the similar way
as did for kdump-emergency.service(i.e. will replace systemd's
emergency.target with kdump-emergency.target under kdump), and
adds "IgnoreOnIsolate=yes" into both of them.

Signed-off-by: Xunlei Pang <xlpang@redhat.com>
Acked-by: Dave Young <dyoung@redhat.com>
Acked-by: Pratyush Anand <panand@redhat.com>
[bhe: improve the patch log about IgnoreOnIsolate="]

dracut-kdump-emergency.service

@@ -12,6 +12,7 @@
 [Unit]
 Description=Kdump Emergency
 DefaultDependencies=no
+IgnoreOnIsolate=yes
 
 [Service]
 ExecStart=/usr/bin/systemctl --no-block isolate kdump-error-handler.service

dracut-kdump-emergency.target

@@ -0,0 +1,14 @@
+#  This file is part of systemd.
+#
+#  systemd is free software; you can redistribute it and/or modify it
+#  under the terms of the GNU Lesser General Public License as published by
+#  the Free Software Foundation; either version 2.1 of the License, or
+#  (at your option) any later version.
+
+[Unit]
+Description=Emergency Mode
+Documentation=man:systemd.special(7)
+Requires=emergency.service
+After=emergency.service
+AllowIsolate=yes
+IgnoreOnIsolate=yes

dracut-module-setup.sh

@@ -734,8 +734,9 @@ install() {
     ln_r "$systemdsystemunitdir/kdump-capture.service" "$systemdsystemunitdir/initrd.target.wants/kdump-capture.service"
     inst "$moddir/kdump-error-handler.sh" "/usr/bin/kdump-error-handler.sh"
     inst "$moddir/kdump-error-handler.service" "$systemdsystemunitdir/kdump-error-handler.service"
-    # Replace existing emergency service
+    # Replace existing emergency service and emergency target
     cp "$moddir/kdump-emergency.service" "$initdir/$systemdsystemunitdir/emergency.service"
+    cp "$moddir/kdump-emergency.target" "$initdir/$systemdsystemunitdir/emergency.target"
     # Also redirect dracut-emergency to kdump error handler
     ln_r "$systemdsystemunitdir/emergency.service" "$systemdsystemunitdir/dracut-emergency.service"
 

kexec-tools.spec

@@ -41,6 +41,7 @@ Source103: dracut-kdump-error-handler.sh
 Source104: dracut-kdump-emergency.service
 Source105: dracut-kdump-error-handler.service
 Source106: dracut-kdump-capture.service
+Source107: dracut-kdump-emergency.target
 
 Requires(post): systemd-units
 Requires(preun): systemd-units
@@ -216,6 +217,7 @@ cp %{SOURCE103} $RPM_BUILD_ROOT/etc/kdump-adv-conf/kdump_dracut_modules/99kdumpb
 cp %{SOURCE104} $RPM_BUILD_ROOT/etc/kdump-adv-conf/kdump_dracut_modules/99kdumpbase/%{remove_dracut_prefix %{SOURCE104}}
 cp %{SOURCE105} $RPM_BUILD_ROOT/etc/kdump-adv-conf/kdump_dracut_modules/99kdumpbase/%{remove_dracut_prefix %{SOURCE105}}
 cp %{SOURCE106} $RPM_BUILD_ROOT/etc/kdump-adv-conf/kdump_dracut_modules/99kdumpbase/%{remove_dracut_prefix %{SOURCE106}}
+cp %{SOURCE107} $RPM_BUILD_ROOT/etc/kdump-adv-conf/kdump_dracut_modules/99kdumpbase/%{remove_dracut_prefix %{SOURCE107}}
 chmod 755 $RPM_BUILD_ROOT/etc/kdump-adv-conf/kdump_dracut_modules/99kdumpbase/%{remove_dracut_prefix %{SOURCE100}}
 chmod 755 $RPM_BUILD_ROOT/etc/kdump-adv-conf/kdump_dracut_modules/99kdumpbase/%{remove_dracut_prefix %{SOURCE101}}