[Bug 2109303] [NEW] dhclient hang when tons of ip addresses exist

[Dongdong Wang]

Public bug reported:

Ubuntu
==============

No LSB modules are available.
Description:    Ubuntu 24.04.2 LTS
Release:        24.04

Package
==============

isc-dhcp-client:
  Installed: 4.4.3-P1-4ubuntu2
  Candidate: 4.4.3-P1-4ubuntu2
  Version table:
 *** 4.4.3-P1-4ubuntu2 500
        500 http://archive.ubuntu.com/ubuntu noble/universe amd64 Packages
        100 /var/lib/dpkg/status


Steps to Reproduce
==================

# ip l add dev dummy type dummy
# ip l set dev dummy up
# for i in {1..50}; do for j in {1..50}; do ip a a 192.168.$i.$j/24 dev dummy; done; done
# ip -o a show dev dummy | wc -l
2500
# dhclient -v dummy

Result
======

After the operations above, we can see the dhclient hanging. The top command showed the dhclient's memory
was increasing, seemed a memory leak happened.


top - 01:52:58 up 12 days, 23:38,  0 user,  load average: 2.46, 2.44, 2.26
Tasks:   5 total,   1 running,   2 sleeping,   2 stopped,   0 zombie
%Cpu(s):  2.4 us,  1.4 sy,  0.0 ni, 96.1 id,  0.1 wa,  0.0 hi,  0.0 si,  0.0 st
MiB Mem : 772016.8 total, 614728.2 free, 111628.2 used,  50758.8 buff/cache
MiB Swap:      0.0 total,      0.0 free,      0.0 used. 660388.6 avail Mem

    PID USER      PR  NI    VIRT    RES    SHR S  %CPU  %MEM     TIME+ COMMAND
      1 root      20   0    4.5m   3.8m   3.2m S   0.0   0.0   0:00.00 bash
     10 root      20   0    4.6m   4.1m   3.4m S   0.0   0.0   0:00.59 bash
   2869 root      20   0    3.2m   1.3m   1.2m T   0.0   0.0   0:00.00 dhclient
   2870 root      20   0  188.7m 185.9m   2.3m T   0.0   0.0   2:09.55 dhclient
   2879 root      20   0    8.7m   5.0m   2.9m R   0.0   0.0   0:00.00 top

** Affects: isc-dhcp (Ubuntu)
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/2109303

Title:
  dhclient hang when tons of ip addresses exist

Status in isc-dhcp package in Ubuntu:
  New

Bug description:
  Ubuntu
  ==============

  No LSB modules are available.
  Description:    Ubuntu 24.04.2 LTS
  Release:        24.04

  Package
  ==============

  isc-dhcp-client:
    Installed: 4.4.3-P1-4ubuntu2
    Candidate: 4.4.3-P1-4ubuntu2
    Version table:
   *** 4.4.3-P1-4ubuntu2 500
          500 http://archive.ubuntu.com/ubuntu noble/universe amd64 Packages
          100 /var/lib/dpkg/status

  
  Steps to Reproduce
  ==================

  # ip l add dev dummy type dummy
  # ip l set dev dummy up
  # for i in {1..50}; do for j in {1..50}; do ip a a 192.168.$i.$j/24 dev dummy; done; done
  # ip -o a show dev dummy | wc -l
  2500
  # dhclient -v dummy

  Result
  ======

  After the operations above, we can see the dhclient hanging. The top command showed the dhclient's memory
  was increasing, seemed a memory leak happened.

  
  top - 01:52:58 up 12 days, 23:38,  0 user,  load average: 2.46, 2.44, 2.26
  Tasks:   5 total,   1 running,   2 sleeping,   2 stopped,   0 zombie
  %Cpu(s):  2.4 us,  1.4 sy,  0.0 ni, 96.1 id,  0.1 wa,  0.0 hi,  0.0 si,  0.0 st
  MiB Mem : 772016.8 total, 614728.2 free, 111628.2 used,  50758.8 buff/cache
  MiB Swap:      0.0 total,      0.0 free,      0.0 used. 660388.6 avail Mem

      PID USER      PR  NI    VIRT    RES    SHR S  %CPU  %MEM     TIME+ COMMAND
        1 root      20   0    4.5m   3.8m   3.2m S   0.0   0.0   0:00.00 bash
       10 root      20   0    4.6m   4.1m   3.4m S   0.0   0.0   0:00.59 bash
     2869 root      20   0    3.2m   1.3m   1.2m T   0.0   0.0   0:00.00 dhclient
     2870 root      20   0  188.7m 185.9m   2.3m T   0.0   0.0   2:09.55 dhclient
     2879 root      20   0    8.7m   5.0m   2.9m R   0.0   0.0   0:00.00 top

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