Hi Kairui

On 10/25/18 at 02:21pm, Kairui Song wrote:

Add reload support to kdumpctl, reload will simply unload current loaded kexec crash kernel and initramfs, and load it again.

Changes in /etc/sysconfig/kdump will take effect with kdumpctl reload, but reloading will not check the content of /etc/kdump.conf and won't rebuild anything. reload is fast, the only time-consuming part of kdumpctl reload is loading kernel and initramfs with kexec which is always necessary.

Signed-off-by: Kairui Song kasong@redhat.com

kdump.service | 1 + kdumpctl | 59 +++++++++++++++++++++++++++++++++++++++++++-------- 2 files changed, 51 insertions(+), 9 deletions(-)

diff --git a/kdump.service b/kdump.service index 5144597..f888dd6 100644 --- a/kdump.service +++ b/kdump.service @@ -7,6 +7,7 @@ DefaultDependencies=no Type=oneshot ExecStart=/usr/bin/kdumpctl start ExecStop=/usr/bin/kdumpctl stop +ExecReload=/usr/bin/kdumpctl reload RemainAfterExit=yes StartLimitInterval=0

diff --git a/kdumpctl b/kdumpctl index ece406f..5e139e9 100755 --- a/kdumpctl +++ b/kdumpctl @@ -283,6 +283,16 @@ get_pcs_cluster_modified_files()

setup_initrd() {

• KDUMP_BOOTDIR=$(check_boot_dir "${KDUMP_BOOTDIR}")
• if [ -z "$KDUMP_KERNELVER" ]; then

• kdump_kver=`uname -r`
  

• else

• kdump_kver=$KDUMP_KERNELVER
  

• fi
• kdump_kernel="${KDUMP_BOOTDIR}/${KDUMP_IMG}-${kdump_kver}${KDUMP_IMG_EXT}"
• DEFAULT_INITRD="${KDUMP_BOOTDIR}/initramfs-`uname -r`.img" DEFAULT_INITRD_BAK="${KDUMP_BOOTDIR}/.initramfs-`uname -r`.img.default" if [ $DEFAULT_DUMP_MODE == "fadump" ]; then

@@ -533,16 +543,8 @@ check_rebuild() local _force_no_rebuild force_no_rebuild="0" local ret system_modified="0"

• KDUMP_BOOTDIR=$(check_boot_dir "${KDUMP_BOOTDIR}")
• if [ -z "$KDUMP_KERNELVER" ]; then

• kdump_kver=`uname -r`
  

• else

• kdump_kver=$KDUMP_KERNELVER
  

• fi
• kdump_kernel="${KDUMP_BOOTDIR}/${KDUMP_IMG}-${kdump_kver}${KDUMP_IMG_EXT}" setup_initrd

• if [ $? -ne 0 ]; then return 1 fi

@@ -1004,6 +1006,42 @@ start() echo "Starting kdump: [OK]" }

+reload() +{

• check_current_status
• if [ $? == 1 ]; then

I would be better to use -eq

• echo "Kdump is not running: [WARNING]"
  

• return 0
  

• fi
• if [ $DEFAULT_DUMP_MODE == "fadump" ]; then

• stop_fadump
  

• else

• stop_kdump
  

• fi
• if [ $? != 0 ]; then

better to use -ne, according to below doc, != is used more for pattern matching

• echo "Stopping kdump: [FAILED]"
  

• return 1
  

• fi
• echo "Stopping kdump: [OK]"
• setup_initrd
• if [ $? != 0 ]; then

• echo "Starting kdump: [FAILED]"
  

• return 1
  

• fi
• start_dump
• if [ $? != 0 ]; then

• echo "Starting kdump: [FAILED]"
  

• return 1
  

• fi
• echo "Starting kdump: [OK]"

+}

stop_fadump() { echo 0 > $FADUMP_REGISTER_SYS_NODE @@ -1087,6 +1125,9 @@ main () esac exit $EXIT_CODE ;;

•  reload)
  

• reload
  

• ;;
  

  restart) stop start

-- 2.17.1

Thanks Dave

OK, thanks for the suggestion, will append following commit message in next patch:

We need to make systemd-run execute in non-blocking mode, and do not synchronously wait for the operation to finish, because udev expect the command line in RUN to be finished immediately, however kdumpctl reload may take 0.5-1s for an ordinary reload, or even slower on some machines. So we give systemd-run an explicit --no-block option to run in non-blocking mode. Without --no-blocking, systemd-run will verify, enqueue and wait for the operation to finish. By using the --no-block option, systemd-run will only verify and enqueue the unit then return. In this way we make sure the command is executed asynchronously, and the status will be monitored and logged by systemd, which is reliable and non-blocking. Another thing to mention is that --no-block is only needed after systemd-v220, before v220 systemd-run uses non-blocking mode by default and --no-block option is not available on earlier systemd versions.

On Mon, Oct 29, 2018 at 6:56 PM Dave Young dyoung@redhat.com wrote:

On 10/25/18 at 02:21pm, Kairui Song wrote:

...

According to udev's man page, PROGRAM is either used to determine device's name or whether the device matches the rule. So we should use RUN insteand. Meanwhile, both RUN / PROGRAM only accepts very short-running foreground tasks, but kdump restart may take a long time if there are any device changes that will lead to image rebuild, which may lead to buggy behavior.

On the other hand, memory / CPU hot plug should never trigger a initramfs rebuild.

To solve this problem, we will use new introduced "kdumpctl reload" instead, and use systemd-run to create a transient service unit for the reload and run it in no-block mode, so udev won't be blocked by anything.

Kairui, can you add more words here what is the behavior of "--no-block" and why we have to use it?

...

Also reformat the udev rules to a more maintanceable format.

Signed-off-by: Kairui Song kasong@redhat.com

98-kexec.rules | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/98-kexec.rules b/98-kexec.rules index e32ee13..62ddd69 100644 --- a/98-kexec.rules +++ b/98-kexec.rules @@ -1,4 +1,12 @@ -SUBSYSTEM=="cpu", ACTION=="add", PROGRAM="/bin/systemctl try-restart kdump.service" -SUBSYSTEM=="cpu", ACTION=="remove", PROGRAM="/bin/systemctl try-restart kdump.service" -SUBSYSTEM=="memory", ACTION=="online", PROGRAM="/bin/systemctl try-restart kdump.service" -SUBSYSTEM=="memory", ACTION=="offline", PROGRAM="/bin/systemctl try-restart kdump.service" +SUBSYSTEM=="cpu", ACTION=="add", GOTO="kdump_reload" +SUBSYSTEM=="cpu", ACTION=="remove", GOTO="kdump_reload" +SUBSYSTEM=="memory", ACTION=="online", GOTO="kdump_reload" +SUBSYSTEM=="memory", ACTION=="offline", GOTO="kdump_reload"

+GOTO="kdump_reload_end"

+LABEL="kdump_reload"

+RUN+="/usr/bin/systemctl is-active kdump.service && /usr/bin/systemd-run --no-block /sbin/kdumpctl reload"

+LABEL="kdump_reload_end"

2.17.1

Thanks Dave

-- Best Regards, Kairui Song

On 10/25/18 at 02:21pm, Kairui Song wrote:

Previously, kdump will restart / reload for many times on hotplug event, especially memory hotplug events. Hotplugged memory may generate many udev event as memory are managed and hotplugged in small chunks by the kernel.

This results in unnecessary system workload and an actually longer delay of kdump reload and the hotplug event, as udev will either get blocked or kdumpctl will be waiting for other triggered operation.

To fix this, introduce a kdump-udev-throttler as an agent which will be called by udev and merge concurrent kdump restart requests. Tested with a Hyper-V VM which is failing due to udev timeout previously, no new issues found.

Signed-off-by: Kairui Song kasong@redhat.com

98-kexec.rules | 2 +- kdump-udev-throttler | 54 ++++++++++++++++++++++++++++++++++++++++++++ kexec-tools.spec | 3 +++ 3 files changed, 58 insertions(+), 1 deletion(-) create mode 100755 kdump-udev-throttler

diff --git a/98-kexec.rules b/98-kexec.rules index 62ddd69..2f88c77 100644 --- a/98-kexec.rules +++ b/98-kexec.rules @@ -7,6 +7,6 @@ GOTO="kdump_reload_end"

LABEL="kdump_reload"

-RUN+="/usr/bin/systemctl is-active kdump.service && /usr/bin/systemd-run --no-block /sbin/kdumpctl reload" +RUN+="/usr/bin/systemd-run --no-block /usr/lib/udev/kdump-udev-throttler"

LABEL="kdump_reload_end" diff --git a/kdump-udev-throttler b/kdump-udev-throttler new file mode 100755 index 0000000..9e6bbbf --- /dev/null +++ b/kdump-udev-throttler @@ -0,0 +1,54 @@ +#!/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" +interval=2

+# Don't reload kdump service if kdump service is not started by systemd +systemctl is-active kdump.service &>/dev/null || exit 0

+# Don't restart kdump service if kdump is still starting up in bootup stage +# CPU and memories generates udev event in bootup stage, but they are not hot +# plugged and may result in unneccessary kdump reload +if ! systemctl is-system-running &> /dev/null; then

•    [[ "$(systemctl is-active kdump.service)" == "activating" ]] && exit 0
  

when will the state be activating? Only boot phase?

And when will system state be is-system-running?

Maybe it is not necessary since we do not have this check before and it works well?

+fi

+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 diff --git a/kexec-tools.spec b/kexec-tools.spec index 6330534..91d322f 100644 --- a/kexec-tools.spec +++ b/kexec-tools.spec @@ -29,6 +29,7 @@ Source24: kdump.sysconfig.ppc64le Source25: kdumpctl.8 Source26: live-image-kdump-howto.txt Source27: early-kdump-howto.txt +Source28: kdump-udev-throttler

####################################### # These are sources for mkdumpramfs @@ -171,6 +172,7 @@ install -m 755 %{SOURCE23} $RPM_BUILD_ROOT%{_prefix}/lib/kdump/kdump-lib-initram # For s390x the ELF header is created in the kdump kernel and therefore kexec # udev rules are not required install -m 644 %{SOURCE14} $RPM_BUILD_ROOT%{_udevrulesdir}/98-kexec.rules +install -m 755 %{SOURCE28} $RPM_BUILD_ROOT%{_udevrulesdir}/../kdump-udev-throttler %endif install -m 644 %{SOURCE15} $RPM_BUILD_ROOT%{_mandir}/man5/kdump.conf.5 install -m 644 %{SOURCE16} $RPM_BUILD_ROOT%{_unitdir}/kdump.service @@ -298,6 +300,7 @@ done %config(noreplace,missingok) %{_sysconfdir}/kdump.conf %ifnarch s390x %config %{_udevrulesdir} +%{_udevrulesdir}/../kdump-udev-throttler %endif %{dracutlibdir}/modules.d/* %dir %{_localstatedir}/crash -- 2.17.1

Thanks Dave