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Mykola Kvach
e54a6cd6a1
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>
35 lines
782 B
Bash
35 lines
782 B
Bash
#!/bin/sh
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# The first argument ($1) is:
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# "pre" or "post"
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# The second argument ($2) is:
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# "suspend", "hibernate", "hybrid-sleep", or "suspend-then-hibernate"
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. /etc/xen/scripts/hotplugpath.sh
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SERVICE_NAME="xen-watchdog.service"
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STATE_FILE="${XEN_RUN_DIR}/xen-watchdog-sleep-flag"
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case "$1" in
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pre)
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if systemctl is-active --quiet "${SERVICE_NAME}"; then
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touch "${STATE_FILE}"
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echo "Stopping ${SERVICE_NAME} before $2."
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systemctl stop "${SERVICE_NAME}"
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fi
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;;
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post)
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if [ -f "${STATE_FILE}" ]; then
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echo "Starting ${SERVICE_NAME} after $2."
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systemctl start "${SERVICE_NAME}"
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rm "${STATE_FILE}"
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fi
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;;
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*)
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echo "Script called with unknown action '$1'. Arguments: '$@'"
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exit 1
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;;
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esac
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exit 0
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