#!/bin/bash

# This util helps to reduce the workload of kdump service restarting

# on udev event. When hotplugging memory / CPU, multiple udev

# events may be triggered concurrently, and obviously, we don't want

# to restart kdump service for each event.

# This script will be called by udev, and make sure kdump service is

# restart after all events we are watching are settled.

# On each call, this script will update try to aquire the $throttle_lock

# The first instance acquired the file lock will keep waiting for events

# to settle and then reload kdump. Other instances will just exit

# In this way, we can make sure kdump service is restarted immediately

# and for exactly once after udev events are settled.

throttle_lock="/var/lock/kdump-udev-throttle"

exec 9>$throttle_lock

if [ $? -ne 0 ]; then

        echo "Failed to create the lock file! Fallback to non-throttled kdump service restart"

        /bin/kdumpctl reload

        exit 1

fi

flock -n 9

if [ $? -ne 0 ]; then

        echo "Throttling kdump restart for concurrent udev event"

        exit 0

fi

# Wait for at least 1 second, at most 4 seconds for udev to settle

# Idealy we will have a less than 1 second lag between udev events settle

# and kdump reload

sleep 1 && udevadm settle --timeout 3

# Release the lock, /bin/kdumpctl will block and make the process

# holding two locks at the same time and we might miss some events

exec 9>&-

/bin/kdumpctl reload

exit 0