Just in case the logs were disposed, the root.log error message was:

{{{
DEBUG util.py:453: Executing command: ['/usr/bin/yum', '--installroot', '/var/lib/mock/f23-build-2946317-454290/root/', 'groupinstall', 'build', '--setopt=tsflags=nocontexts'] with env {'LANG': 'en_US.UTF-8', 'TERM': 'vt100', 'SHELL': '/bin/bash', 'LC_MESSAGES': 'C', 'PROMPT_COMMAND': 'printf "\x1b]0;<mock-chroot>\x07<mock-chroot>"', 'PATH': '/usr/bin:/bin:/usr/sbin:/sbin', 'HOME': '/builddir', 'HOSTNAME': 'mock'} and shell False
[...]
Timeout on http://kojipkgs.fedoraproject.org//repos/f23-build/454290/x86_64/toplink/packages/gcc/5.0.0/0.11.fc22/x86_64/gcc-5.0.0-0.11.fc22.x86_64.rpm: (28, 'Operation too slow. Less than 1000 bytes/sec transferred the last 30 seconds')
}}}

The task metadata were:

{{{
Information for task buildArch (yap-6.2.2-13.fc23.src.rpm, x86_64)
ID 8910855
Method buildArch
Parameters SRPM: tasks/772/8910772/yap-6.2.2-13.fc23.src.rpm
Build Tag: f23-build
Arch: x86_64
Keep SRPM? no
Options:
repo_id = 454290
State failed
Created Thu, 12 Feb 2015 17:24:22 UTC
Started Thu, 12 Feb 2015 17:24:23 UTC
Completed Thu, 12 Feb 2015 17:34:57 UTC
Owner ppisar
Channel default
Host buildhw-08.phx2.fedoraproject.org
Arch x86_64
Buildroot /var/lib/mock/f23-build-2946317-454290
Parent build (rawhide, /yap:cbff981ec5af2f6649ef0ceb3d285bce1fe806b7)
}}}

This seemed to be some issue with out squid caching server (kojipkgs). I restarted squid and it went back to normal... not fully sure why it got into this state. ;(

I've just hit the same issue today...

http://koji.fedoraproject.org/koji/taskinfo?taskID=9054152

This seems to be solved now.

At least it has not re-occured.

Please re-open if you see it again.