systemd: Add hooks to stop/start xen-watchdog on suspend/resume

This patch adds a systemd sleep hook script to stop the xen-watchdog
service before system suspend and start it again after resume.

Stopping the watchdog before a system suspend operation may look unsafe.
Let's imagine the following situation: 'systemctl suspend' does not
interact with the running service at all. In such a case, the Xen
watchdog daemon freezes just before suspend. If this happens, for
example, right before sending a ping, and Xen has not yet marked the
domain as suspended (is_shutting_down), the Xen watchdog timer may
trigger a false alert.

This is an almost impossible situation, because typically:
    ping time = watchdog timeout / 2

and the watchdog timeout is usually set to a relatively large value
(dozens of seconds).

Still, this is more likely with very short watchdog timeouts. It may
happen in the following scenarios:
    * Significant delays occur between freezing Linux tasks and
      triggering the ACPI or PSCI sleep request or handler.
    * Long delays happen inside Xen between the entrance to the sleep
      trigger and the actual forwarding of the sleep request further.

A similar situation may occur on resume with short timeouts. During the
resume operation, Xen restores timers and the domain context. The Xen
watchdog timer also resumes. If it schedules the domain right before the
watchdog timeout expires, and the daemon responsible for pinging is not
yet running, a timeout might occur.

Both scenarios are rare and typically require very small watchdog
timeouts combined with significant delays in Xen or the Linux kernel
during suspend/resume flows.

Conceptually, however, if activating and pinging the Xen watchdog is the
responsibility of the domain and its services, then the domain should
also manage the watchdog service/daemon lifecycle. This is similar to
what is already done by the Xen watchdog driver inside the Linux kernel.

Signed-off-by: Mykola Kvach <mykola_kvach@epam.com>
Reviewed-by: Denis Mukhin <dmukhin@ford.com>
Reviewed-by: Anthony PERARD <anthony.perard@vates.tech>

config/Tools.mk.in

@@ -53,6 +53,7 @@ CONFIG_LIBFSIMAGE   := @libfsimage@
 CONFIG_SYSTEMD      := @systemd@
 XEN_SYSTEMD_DIR     := @SYSTEMD_DIR@
 XEN_SYSTEMD_MODULES_LOAD := @SYSTEMD_MODULES_LOAD@
+XEN_SYSTEMD_SLEEP_DIR := @SYSTEMD_SLEEP_DIR@
 CONFIG_9PFS         := @ninepfs@
 
 LINUX_BACKEND_MODULES := @LINUX_BACKEND_MODULES@

m4/systemd.m4

@@ -28,6 +28,12 @@ AC_DEFUN([AX_SYSTEMD_OPTIONS], [
 		[set directory for systemd modules load files [PREFIX/lib/modules-load.d/]]),
 		[SYSTEMD_MODULES_LOAD="$withval"], [SYSTEMD_MODULES_LOAD=""])
 	AC_SUBST(SYSTEMD_MODULES_LOAD)
+
+	AC_ARG_WITH(systemd-sleep,
+		AS_HELP_STRING([--with-systemd-sleep=DIR],
+		[set directory for systemd sleep script files [PREFIX/lib/systemd/system-sleep/]]),
+		[SYSTEMD_SLEEP_DIR="$withval"], [SYSTEMD_SLEEP_DIR=""])
+	AC_SUBST(SYSTEMD_SLEEP_DIR)
 ])
 
 AC_DEFUN([AX_ENABLE_SYSTEMD_OPTS], [
@@ -69,6 +75,14 @@ AC_DEFUN([AX_CHECK_SYSTEMD_LIBS], [
 	AS_IF([test "x$SYSTEMD_MODULES_LOAD" = x], [
 	    AC_MSG_ERROR([SYSTEMD_MODULES_LOAD is unset])
 	], [])
+
+	AS_IF([test "x$SYSTEMD_SLEEP_DIR" = x], [
+	    PKG_CHECK_VAR([SYSTEMD_SLEEP_DIR], [systemd], [systemdsleepdir])
+	], [])
+
+	AS_IF([test "x$SYSTEMD_SLEEP_DIR" = x], [
+	    AC_MSG_ERROR([SYSTEMD_SLEEP_DIR is unset])
+	], [])
 ])
 
 AC_DEFUN([AX_CHECK_SYSTEMD], [

tools/configure

@@ -652,6 +652,7 @@ ac_subst_vars='LTLIBOBJS
 LIBOBJS
 pvshim
 ninepfs
+SYSTEMD_SLEEP_DIR
 SYSTEMD_MODULES_LOAD
 SYSTEMD_DIR
 systemd
@@ -847,6 +848,7 @@ with_xenstored
 enable_systemd
 with_systemd
 with_systemd_modules_load
+with_systemd_sleep
 enable_9pfs
 enable_pvshim
 '
@@ -881,7 +883,8 @@ pixman_LIBS
 libzstd_CFLAGS
 libzstd_LIBS
 LIBNL3_CFLAGS
-LIBNL3_LIBS'
+LIBNL3_LIBS
+SYSTEMD_SLEEP_DIR'
 
 
 # Initialize some variables set by options.
@@ -1589,6 +1592,9 @@ Optional Packages:
   --with-systemd-modules-load=DIR
                           set directory for systemd modules load files
                           [PREFIX/lib/modules-load.d/]
+  --with-systemd-sleep=DIR
+                          set directory for systemd sleep script files
+                          [PREFIX/lib/systemd/system-sleep/]
 
 Some influential environment variables:
   CC          C compiler command
@@ -1630,6 +1636,8 @@ Some influential environment variables:
   LIBNL3_CFLAGS
               C compiler flags for LIBNL3, overriding pkg-config
   LIBNL3_LIBS linker flags for LIBNL3, overriding pkg-config
+  SYSTEMD_SLEEP_DIR
+              value of systemdsleepdir for systemd, overriding pkg-config
 
 Use these variables to override the choices made by `configure' or to help
 it to find libraries and programs with nonstandard names/locations.
@@ -10138,6 +10146,17 @@ fi
 
 
 
+# Check whether --with-systemd-sleep was given.
+if test ${with_systemd_sleep+y}
+then :
+  withval=$with_systemd_sleep; SYSTEMD_SLEEP_DIR="$withval"
+else $as_nop
+  SYSTEMD_SLEEP_DIR=""
+fi
+
+
+
+
 
 		if test "x$enable_systemd" != "xno"
 then :
@@ -10176,6 +10195,43 @@ then :
 
 	    as_fn_error $? "SYSTEMD_MODULES_LOAD is unset" "$LINENO" 5
 
+fi
+
+	if test "x$SYSTEMD_SLEEP_DIR" = x
+then :
+
+
+if test -n "$SYSTEMD_SLEEP_DIR"; then
+    pkg_cv_SYSTEMD_SLEEP_DIR="$SYSTEMD_SLEEP_DIR"
+ elif test -n "$PKG_CONFIG"; then
+    if test -n "$PKG_CONFIG" && \
+    { { printf "%s\n" "$as_me:${as_lineno-$LINENO}: \$PKG_CONFIG --exists --print-errors \"systemd\""; } >&5
+  ($PKG_CONFIG --exists --print-errors "systemd") 2>&5
+  ac_status=$?
+  printf "%s\n" "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
+  test $ac_status = 0; }; then
+  pkg_cv_SYSTEMD_SLEEP_DIR=`$PKG_CONFIG --variable="systemdsleepdir" "systemd" 2>/dev/null`
+		      test "x$?" != "x0" && pkg_failed=yes
+else
+  pkg_failed=yes
+fi
+ else
+    pkg_failed=untried
+fi
+SYSTEMD_SLEEP_DIR=$pkg_cv_SYSTEMD_SLEEP_DIR
+
+if test "x$SYSTEMD_SLEEP_DIR" = x""
+then :
+
+fi
+
+fi
+
+	if test "x$SYSTEMD_SLEEP_DIR" = x
+then :
+
+	    as_fn_error $? "SYSTEMD_SLEEP_DIR is unset" "$LINENO" 5
+
 fi
 
 

tools/hotplug/Linux/systemd/Makefile

@@ -5,6 +5,8 @@ XEN_SYSTEMD_MODULES := xen.conf
 
 XEN_SYSTEMD_MOUNT := proc-xen.mount
 
+XEN_SYSTEMD_SLEEP_SCRIPT := xen-watchdog-sleep.sh
+
 XEN_SYSTEMD_SERVICE := xenstored.service
 XEN_SYSTEMD_SERVICE += xenconsoled.service
 XEN_SYSTEMD_SERVICE += xen-qemu-dom0-disk-backend.service
@@ -15,7 +17,8 @@ XEN_SYSTEMD_SERVICE += xendriverdomain.service
 
 ALL_XEN_SYSTEMD :=	$(XEN_SYSTEMD_MODULES)  \
 			$(XEN_SYSTEMD_MOUNT)	\
-			$(XEN_SYSTEMD_SERVICE)
+			$(XEN_SYSTEMD_SERVICE)	\
+			$(XEN_SYSTEMD_SLEEP_SCRIPT)
 
 .PHONY: all
 all:	$(ALL_XEN_SYSTEMD)
@@ -31,15 +34,18 @@ distclean: clean
 install: $(ALL_XEN_SYSTEMD)
 	$(INSTALL_DIR) $(DESTDIR)$(XEN_SYSTEMD_DIR)
 	$(INSTALL_DIR) $(DESTDIR)$(XEN_SYSTEMD_MODULES_LOAD)
+	$(INSTALL_DIR) $(DESTDIR)$(XEN_SYSTEMD_SLEEP_DIR)
 	$(INSTALL_DATA) *.service $(DESTDIR)$(XEN_SYSTEMD_DIR)
 	$(INSTALL_DATA) *.mount $(DESTDIR)$(XEN_SYSTEMD_DIR)
 	$(INSTALL_DATA) *.conf $(DESTDIR)$(XEN_SYSTEMD_MODULES_LOAD)
+	$(INSTALL_PROG) $(XEN_SYSTEMD_SLEEP_SCRIPT) $(DESTDIR)$(XEN_SYSTEMD_SLEEP_DIR)
 
 .PHONY: uninstall
 uninstall:
 	rm -f $(DESTDIR)$(XEN_SYSTEMD_MODULES_LOAD)/*.conf
 	rm -f $(DESTDIR)$(XEN_SYSTEMD_DIR)/*.mount
 	rm -f $(DESTDIR)$(XEN_SYSTEMD_DIR)/*.service
+	rm -f $(DESTDIR)$(XEN_SYSTEMD_SLEEP_DIR)/$(XEN_SYSTEMD_SLEEP_SCRIPT)
 
 $(XEN_SYSTEMD_MODULES):
 	rm -f $@.tmp

tools/hotplug/Linux/systemd/xen-watchdog-sleep.sh

@@ -0,0 +1,34 @@
+#!/bin/sh
+
+# The first argument ($1) is:
+#     "pre" or "post"
+# The second argument ($2) is:
+#     "suspend", "hibernate", "hybrid-sleep", or "suspend-then-hibernate"
+
+. /etc/xen/scripts/hotplugpath.sh
+
+SERVICE_NAME="xen-watchdog.service"
+STATE_FILE="${XEN_RUN_DIR}/xen-watchdog-sleep-flag"
+
+case "$1" in
+pre)
+    if systemctl is-active --quiet "${SERVICE_NAME}"; then
+        touch "${STATE_FILE}"
+        echo "Stopping ${SERVICE_NAME} before $2."
+        systemctl stop "${SERVICE_NAME}"
+    fi
+    ;;
+post)
+    if [ -f "${STATE_FILE}" ]; then
+        echo "Starting ${SERVICE_NAME} after $2."
+        systemctl start "${SERVICE_NAME}"
+        rm "${STATE_FILE}"
+    fi
+    ;;
+*)
+    echo "Script called with unknown action '$1'. Arguments: '$@'"
+    exit 1
+    ;;
+esac
+
+exit 0