Perl application hang in umtxn state

[Václav Haisman]

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Dominique Goncalves wrote:
> Hi,
> 
> I run FreeBSD 7.1-PRERELEASE and with a Perl GTK2 application, Perl
> hang in umtxn state:
> 
>   PID USERNAME    THR PRI NICE   SIZE    RES STATE    TIME   WCPU COMMAND
> 76288 dom           1  53    0 67860K 46080K umtxn    0:02  0.00% perl5.8.8
> 
> And the only way to stop the application is kill -9
> 
> I tried to use ktrace/kdump and ktrace.out show "_umtx_op"
> 
> $ kdump -f ktrace.out
> [...]
>  13199 perl5.8.8 RET   lstat 0
>  13199 perl5.8.8 CALL  gettimeofday(0xbfbfb144,0)
>  13199 perl5.8.8 RET   gettimeofday 0
>  13199 perl5.8.8 CALL  _umtx_op(0xbfbfd18c,0x3,0x1,0,0)
>  13199 perl5.8.8 RET   _umtx_op 0
>  13199 perl5.8.8 CALL  sigprocmask(SIG_BLOCK,0xbfbfd120,0x8121490)
>  13199 perl5.8.8 RET   sigprocmask 0
>  13199 perl5.8.8 CALL  _umtx_op(0x287fb8a0,0x5,0,0,0)
>  13199 perl5.8.8 RET   _umtx_op RESTART
>  13199 perl5.8.8 PSIG  SIGKILL SIG_DFL
> 
> 
> How to debug this hang? (btw I'm not a developer)
You can try rebuilding perl with debugging information. I am not sure
this is the best way but I have used this in my /etc/make.conf:

# Disable binaries stripping.
STRIP=
# Add debugging info to binaries.
CFLAGS?=
CFLAGS+= -g3 -ggdb
CXXFLAGS?=
CXXFLAGS+= -g3 -ggdb

When you have that, try running your test case again. When it blocks
again, attach GDB to the hung process: gdb -p PID `which perl`. And then
obtain the call stack: (gdb) bt.

I suspect there will be some pthreads call on top of the stack. I am not
FreeBSD developer but this seems really similar to situations reported
in thread "umtxn and Apache 2.2" and mine "Process in "uwait" state".

> 
> $ uname -a
> FreeBSD freebsd7 7.1-PRERELEASE FreeBSD 7.1-PRERELEASE #15 r184123:
> Tue Oct 21 16:24:59 CEST 2008
> root at freebsd7:/usr/obj/usr/src/sys/GENERIC  i386
> 
> Thanks for your help,
> Regards.
> 

- --
VH
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