[Bug 1314708] [NEW] dnsmasq is consuming ~100% of one CPU

[Colin King]

Public bug reported:

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)

** Affects: dnsmasq (Ubuntu)
     Importance: High
         Status: New


** Tags: amd64 apport-bug utopic

** Changed in: dnsmasq (Ubuntu)
   Importance: Undecided => High

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Title:
  dnsmasq is consuming ~100% of one CPU

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