dnsmasq is consuming ~100% of one CPU

[Colin Ian King]

I did a clean install of trusty and upgraded to utopic on a desktop and on the next reboot I observed one CPU was being totally pegged by dnsmasq

top:

top - 17:15:32 up 16 min, 4 users, load average: 1.02, 1.02, 0.69
Tasks: 197 total, 2 running, 193 sleeping, 2 stopped, 0 zombie
%Cpu(s): 15.8 us, 9.5 sy, 1.1 ni, 73.6 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
KiB Mem: 7930260 total, 1369624 used, 6560636 free, 34480 buffers
KiB Swap: 8139772 total, 0 used, 8139772 free. 767456 cached Mem

  PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
 1433 nobody 20 0 42248 1664 1376 R 100.0 0.0 15:55.66 dnsmasq
    1 root 20 0 34152 3316 1460 S 0.0 0.0 0:00.92 init
    2 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kthreadd
    3 root 20 0 0 0 0 S 0.0 0.0 0:00.00 ksoftirqd/0

strace show it spinning on:

select(8, [0 3 6 7], [], [6], NULL) = 1 (in [0])
recvmsg(0, 0x7fffdb2aa6d0, 0) = -1 ENOTSOCK (Socket operation on non-socket)
accept(0, 0, NULL) = -1 ENOTSOCK (Socket operation on non-socket)
select(8, [0 3 6 7], [], [6], NULL) = 1 (in [0])
recvmsg(0, 0x7fffdb2aa6d0, 0) = -1 ENOTSOCK (Socket operation on non-socket)
accept(0, 0, NULL) = -1 ENOTSOCK (Socket operation on non-socket)

So we're getting ENOTSOCK on fd 0, which is /dev/null :

total 0
dr-x------ 2 root root 0 Apr 30 17:21 .
dr-xr-xr-x 9 nobody dip 0 Apr 30 17:21 ..
lrwx------ 1 root root 64 Apr 30 17:21 0 -> /dev/null
lrwx------ 1 root root 64 Apr 30 17:21 1 -> /dev/null
lrwx------ 1 root root 64 Apr 30 17:21 2 -> /dev/null
lrwx------ 1 root root 64 Apr 30 17:21 3 -> socket:[12881]
lrwx------ 1 root root 64 Apr 30 17:21 4 -> socket:[12883]
lrwx------ 1 root root 64 Apr 30 17:21 5 -> socket:[12884]
lrwx------ 1 root root 64 Apr 30 17:21 6 -> socket:[12885]
lr-x------ 1 root root 64 Apr 30 17:21 7 -> pipe:[13568]
l-wx------ 1 root root 64 Apr 30 17:21 8 -> pipe:[13568]
lrwx------ 1 root root 64 Apr 30 17:21 9 -> socket:[13570]

ProblemType: Bug
DistroRelease: Ubuntu 14.10
Package: dnsmasq (not installed)
ProcVersionSignature: Ubuntu 3.13.0-24.46-generic 3.13.9
Uname: Linux 3.13.0-24-generic x86_64
ApportVersion: 2.14.2-0ubuntu1
Architecture: amd64
Date: Wed Apr 30 17:17:00 2014
InstallationDate: Installed on 2014-04-30 (0 days ago)
InstallationMedia: Ubuntu 14.04 LTS "Trusty Tahr" - Release amd64 (20140417)
SourcePackage: dnsmasq
UpgradeStatus: No upgrade log present (probably fresh install)

[Colin Ian King (colin-king)]

Sending a bug report by ubuntu-bug is impossible since I can't resolve any hostnames with dnsmasq borked like this. This happens on every reboot too.