Improve sysctl handling on kdump-tools

Also to clarify, manually unloading/reloading kdump doesn't set the params properly:

ubuntu@makedumpfile-e:~$ grep . /proc/sys/kernel/panic_on_warn
0
ubuntu@makedumpfile-e:~$ sudo kdump-config show
DUMP_MODE: kdump
USE_KDUMP: 1
KDUMP_SYSCTL: kernel.panic_on_oops=1 kernel.panic_on_warn=1
KDUMP_COREDIR: /var/crash
crashkernel addr: 0xaa000000
   /var/lib/kdump/vmlinuz: symbolic link to /boot/vmlinuz-5.3.0-10-generic
kdump initrd:
   /var/lib/kdump/initrd.img: symbolic link to /var/lib/kdump/initrd.img-5.3.0-10-generic
current state: ready to kdump

kexec command:
  /sbin/kexec -p --command-line="BOOT_IMAGE=/boot/vmlinuz-5.3.0-10-generic root=PARTUUID=7975ae09-1bd6-4c5f-b460-5f5218cc2327 ro console=tty1 console=ttyS0 systemd.unit=kdump-tools-dump.service nr_cpus=1 irqpoll nousb ata_piix.prefer_ms_hyperv=0" --initrd=/var/lib/kdump/initrd.img /var/lib/kdump/vmlinuz
ubuntu@makedumpfile-e:~$ sudo kdump-config unload
 * unloaded kdump kernel
ubuntu@makedumpfile-e:~$ sudo kdump-config load
 * Creating symlink /var/lib/kdump/vmlinuz
 * Creating symlink /var/lib/kdump/initrd.img
 * loaded kdump kernel
ubuntu@makedumpfile-e:~$ grep . /proc/sys/kernel/panic_on_warn
0

This was somehow removed between kdump-tools 1.5.5 and 1.5.9. I'll see if I can pinpoint the exact version in history and try to find some justification. But this is an old regression.

commit 9a77ef188b24742b595f69891b97d48dc997f5e2
Author: Louis Bouchard <email address hidden>
Date: Thu Jan 29 16:03:04 2015 +0100

    [debian] Fix panic_on_oops faulty handling

    Signed-off-by: Louis Bouchard <email address hidden>

diff --git a/debian/kdump-config b/debian/kdump-config
index 7ea26cab1c95..64489a74757f 100755
--- a/debian/kdump-config
+++ b/debian/kdump-config
@@ -310,9 +310,10 @@ function fadump_register()
        logger -t $NAME "fadump registered successfully"

        # Last step: make sure panic_on_oops is enabled
- if [ -x /sbin/sysctl -a "$KDUMP_SYSCTL" != " " ] ; then
- sysctl -w $KDUMP_SYSCTL >/dev/null
- fi
+ PANIC_ON_OOPS=`/sbin/sysctl kernel.panic_on_oops | cut -d" " -f3`
+ if [ $PANIC_ON_OOPS != "1" ] ; then
+ sysctl -w kernel.panic_on_oops=1 >/dev/null
+ fi
 }

 # Returns: none. prints warnings or exit
@@ -393,9 +394,11 @@ function kdump_load()
        fi

        # Last step: make sure panic_on_oops is enabled
- if [ -x /sbin/sysctl -a "$KDUMP_SYSCTL" != " " ] ; then
- sysctl -w $KDUMP_SYSCTL >/dev/null
- fi
+ PANIC_ON_OOPS=`/sbin/sysctl kernel.panic_on_oops | cut -d" " -f3`
+ if [ $PANIC_ON_OOPS != "1" ] ; then
+ sysctl -w kernel.panic_on_oops=1 >/dev/null
+ fi
+
 }

Thanks Dan for the report and Cascardo for finding the offender commit that introduced this regression!

I think we have room for improvements here, my considerations are:
a) KDUMP_SYSCTL is a misleading name; it seems to be related with sysctls set _when_ dumping, which is also an important thing to control. Despite this, the option meaning was related to the kdump sysctl _triggers_.

b) Even by re-enabling this option we don't have a fine tuning configuration of sysctls during the dump.

So, my idea to fix/improve the situation is: let's have a KDUMP_PANIC_TRIGGERS variable (that defaults to panic_on_oops) and a KDUMP_SYSCTL_ON_DUMP variable that overrides the desired sysctls set on normal kernel when the kdump kernel boots (and which should defaults to have hugepages disabled, since it's a known problem when kdumping to have hugepages "consuming" the system memory).

Cheers,

Guilherme

I've reported a Debian bug with the proposed fixes; the merge report has the information about the approach used to deal with sysctl in kdump: https://salsa.debian.org/debian/makedumpfile/-/merge_requests/2

Cheers,

Guilherme

The Eoan Ermine has reached end of life, so this bug will not be fixed for that release

Guillherme's MR was merged in 1.6.8-1, so marking Fix Released.

Correction: looks like it was 1:1.6.7-4. git-debrebase confused me.