[uml-devel] umls unresponsive & consuming 100% cpu time

["Bram Matthys (Syzop)" <syzop@vulnscan.org>]

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Hi,

I'm experiencing the following problem:
I upgraded from 2.6.20.1 to 2.6.25 on both the host and the uml's.
Now, after some time (unsure how soon), the uml's appear to hang.
It seems though, that they are not completely freezed, but just very very
very slow (or rather.. 99% unresponsive).

top:
~  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
~ 5434 virt      20   0  128m  89m  89m R   99  4.5 269:40.81 linux
..so consuming nearly 100% cpu.

When typing a letter at the console (I run the umls in a screen), it goes
slow, sometimes it takes up to a minute or so... so I can hardly login
(actually it does process/buffer my line, but by the time the username is
entered and it prompts for the password the login time of 60s is exceeded).
Also, there are no errors (like kernel warnings) displayed on the console.

When pinging I get:
PING slave (192.168.22.11) 56(84) bytes of data.
~From slave (192.168.22.1) icmp_seq=2 Destination Host Unreachable
~From slave (192.168.22.1) icmp_seq=3 Destination Host Unreachable
- -more more-
64 bytes from slave (192.168.22.11): icmp_seq=26 ttl=64 time=111 ms
- -yes, just one.. then delay... and then..-
ping: sendmsg: No buffer space available
ping: sendmsg: No buffer space available
- -more-

When doing a version request using uml_mconsole I get a respond after delay
of like 25 seconds, then quick subsequent requests work too, then they no
longer do for like 34 seconds, then a reply, etc etc etc.

I'm not sure if this is actually correct (I know the 'linux' image
corresponds to the running slave kernel but I'm unsure about the backtrace
it shows), but here's some gdb stuff:
- -gdb-
srv1:/home/virt# gdb linux 5434
GNU gdb 6.4.90-debian
Copyright (C) 2006 Free Software Foundation, Inc.
GDB is free software, covered by the GNU General Public License, and you are
welcome to change it and/or distribute copies of it under certain conditions.
Type "show copying" to see the conditions.
There is absolutely no warranty for GDB.  Type "show warranty" for details.
This GDB was configured as "i486-linux-gnu"...Using host libthread_db
library "/lib/tls/i686/cmov/libthread_db.so.1".

Attaching to program: /home/virt/linux, process 5434
0x0809647a in update_xtime_cache ()
(gdb) bt
#0  0x0809647a in update_xtime_cache ()
(gdb) c
Continuing.
^C
Program received signal SIGINT, Interrupt.
0x08096477 in update_xtime_cache ()
(gdb) bt
#0  0x08096477 in update_xtime_cache ()
(gdb) c
Continuing.
^C
Program received signal SIGINT, Interrupt.
0x0809645a in update_xtime_cache ()
(gdb) bt
#0  0x0809645a in update_xtime_cache ()
(gdb) c
Continuing.
^C
Program received signal SIGINT, Interrupt.
0x0809645d in update_xtime_cache ()
(gdb) bt
#0  0x0809645d in update_xtime_cache ()
(gdb)
..so each time I ctrl+c after a few secs to see where it's at, it's in there..

Any ideas what this could be?

Or any help on how to get additional / useful info?

TIA,

	Bram.

- --
Bram Matthys
Software developer/IT consultant        syzop@vulnscan.org
PGP key:                       www.vulnscan.org/pubkey.asc
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