Un-kill-able process hang at umtxpi state with 100% cpu
BBlister
bblister at gmail.com
Mon Mar 23 11:13:03 UTC 2015
Hi,
On the FreeBSD multiuser student server that I administer, a student managed
to created a program that takes 100% of one of the CPU cores with a process
that cannot be killed.
uname -a
FreeBSD zafora 9.2-STABLE FreeBSD 9.2-STABLE #1 r264312: Thu Apr 10 15:25:33
EEST 2014 root at zafora.icte.uowm.gr:/usr/obj/usr/src/sys/zafora amd64
The process (uses 100% cpu):
[root at zafora ~]# ps axuwww | grep 35662
ictest00301 35662 100.0 0.0 12684 1912 19- R Tue04PM 8343:29.56 ./c1
and
[root at zafora ~]# procstat 35662
PID PPID PGID SID TSID THR LOGIN WCHAN EMUL COMM
35662 35661 35661 20142 20142 4 ictest00301 umtxpi FreeBSD ELF64 c1
which has the parent process of a make command (I killed the parent process,
but nothing happened)
ictest00301 35661 0.0 0.0 6280 320 19- I Tue04PM 0:00.01
make execute
The specific process is blocked (cannot be killed) with the following wait
channels:
[root at zafora ~]# procstat -t 35662
PID TID COMM TDNAME CPU PRI STATE WCHAN
35662 100196 c1 - 2 122 sleep umtxpi
35662 100997 c1 - 0 122 sleep umtxpi
35662 101757 c1 - 1 122 sleep uwait
35662 102464 c1 - 2 120 run umtxpi
Even though I have implemented resource limits in /etc/login.conf as to the
CPU usage, they cannot be enforced, and the server's logfile is filled with
messages:
Mar 23 13:06:46 zafora kernel: pid 35662 (c1), uid 1100301, was killed:
exceeded maximum CPU limit
but nothing happens. Of course
kill -9 35662
has not effect.
How I can kill this process? If one student managed to make an un-killable
process that gets 100% of the CPU with restrictions cannot be enforced, then
soon the server will be filled with such processes, and a
reboot will be mandatory.
Thank you.
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