[mythtv] SEGV in DVBRecorder::QualityMonitorHelper

Nick Craig-Wood ncw1 at axis.demon.co.uk
Tue Jun 15 03:09:59 EDT 2004


I've been trying to track down an intermittent crash (only every
couple of days) in 0.15.1.

Since gdb deals so badly with threads I rigged up mythtv to dump core
(ulimit -c 1000000).  This then just dumps the core of the one thread
that SEGVs which is much easier to deal with!

mythtv at crate:~$ gdb -d ../mythtv-0.15.1/libs/libmythtv -s mythbackend-symbols ./mythbackend core.mythbackend.1087248912.26429
GNU gdb 6.1-debian
Copyright 2004 Free Software Foundation, Inc.
[snip]
(gdb) bt
#0  0x4129cb22 in pthread_mutex_lock () from /lib/libpthread.so.0
#1  0x403913e6 in DVBRecorder::QualityMonitorThread (this=0x81284b8)
    at dvbrecorder.cpp:830
#2  0x4039190f in DVBRecorder::QualityMonitorHelper (self=0x390020)
    at dvbrecorder.cpp:865
#3  0x4129be51 in pthread_start_thread () from /lib/libpthread.so.0
#4  0x414a266a in clone () from /lib/libc.so.6
(gdb) up
#1  0x403913e6 in DVBRecorder::QualityMonitorThread (this=0x81284b8)
    at dvbrecorder.cpp:830
830                 pthread_mutex_lock(db_lock);
(gdb) l
825     
826             if (cardid >= 0 &&
827                 db_conn != NULL && db_lock != NULL && dvbchannel != NULL &&
828                 dvbchannel -> FillFrontendStats(fe_stats))
829             {
830                 pthread_mutex_lock(db_lock);
831     
832                 QualityMonitorSample(cardid, fe_stats);
833     
834                 pthread_mutex_unlock(db_lock);
(gdb) print db_lock
$1 = (pthread_mutex_t *) 0x390020
(gdb) print *db_lock
Cannot access memory at address 0x390020

So db_lock appears to have been corrupted.

I wouldn't like to guess exactly why though not without studying the
program a lot more!

I've put the core file, binary and symbols here so anyone can
replicate the above ( 5 MB!)

  http://www.craig-wood.com/nick/mythtv-crash.tar.bz2

This could of course be a memory trample from another thread so I'll
see if I can capture another core...

-- 
Nick Craig-Wood
ncw1 at axis.demon.co.uk


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