Bug 56730 - isc-dhcp-server from bullseye hangs in thread futex while resolving name of ldap server
Summary: isc-dhcp-server from bullseye hangs in thread futex while resolving name of l...
Status: CLOSED FIXED
Alias: None
Product: UCS
Classification: Unclassified
Component: DHCP
Version: UCS 5.1
Hardware: Other Linux
: P5 normal
Target Milestone: UCS 5.1
Assignee: Arvid Requate
QA Contact: Julia Bremer
URL: https://git.knut.univention.de/univen...
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Reported: 2023-10-12 20:04 CEST by Arvid Requate
Modified: 2025-02-05 15:08 CET (History)
2 users (show)

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Description Arvid Requate univentionstaff 2023-10-12 20:04:51 CEST
isc-dhcp-server hangs in UCS 5.1 / Debian bullseye when checking the config:

 /usr/sbin/dhcpd -t -4 -q -cf /etc/dhcp/dhcpd.conf

gdb shows that it seems to hang in a futex wait deadlock between some of its 7 threads when trying getaddrinfo on the name of the ldap server.


In Debian bookworm they embedded bind 9.11.36 as tar ball into isc-dhcp and compile it explicitly without thread support, maybe that is for a reason.

Maybe we should remove the ldap config from the dhcp.conf template during UCS 5.1.
Comment 1 Arvid Requate univentionstaff 2023-10-16 11:59:41 CEST
Adjusted in branch preview/5.1-0:

dacd5ba89d | Deactivate LDAP config in dhcpd.conf during UCS 5.1
b7d03edeef | fixup for the changelogs to match bitflip/changelog-workflow

Build in release-scope ucs_5.1-0:

Package: univention-dhcp
Version: 14.99.0-1A~5.1.0.202310161122
Comment 2 Florian Best univentionstaff 2023-10-17 20:17:25 CEST
That means that during the upgrade to UCS 5.1 no DHCP requests are answered? Or are they answered but with some default config / random IPs?
What happens if another DHCP based server in the domain reboots then?
Maybe we should explicitly mention this in the release notes?
Comment 3 Julia Bremer univentionstaff 2023-10-24 17:09:12 CEST
(In reply to Florian Best from comment #2)
> That means that during the upgrade to UCS 5.1 no DHCP requests are answered?
> Or are they answered but with some default config / random IPs?
> What happens if another DHCP based server in the domain reboots then?
> Maybe we should explicitly mention this in the release notes?

During the upgrade, a number of services won't run, an Administrator is supposed to create a maintainance window during upgrade.
If this is the only DHCP server, DHCP won't work during the upgrade, other systems won't get an IP from this server. I think this ok, and to be expected during an upgrade. 
The upgrade works again, dhcpd doesn't block the upgrade or the listener postrun anymore.

Verified
Comment 4 Florian Best univentionstaff 2024-03-08 11:02:05 CET
univention-dhcp (16.0.1)
f8478a0f716a | fix(dhcp): Reactivate LDAP config in dhcpd.conf after UCS 5.1

univention-dhcp (15.0.3)
5553efab0c4b | Bug #56730: Deactivate LDAP config in dhcpd.conf during UCS 5.1