Mythbackend crashes frequently

[anonymous]

Running svn revision: 16554. Though this has happened for a while now.

I have a DVB-C set-up (Technotrend card) and currently mythbackend just crashes every few hours. EPG data is updated via EIT.

The logs show following errors just before the crash:

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2008-03-18 10:16:08.893 DB Error (Looking up chanID): Query was:

No error type from QSqlError? Strange... 2008-03-18 10:16:08.907 DB Error (Looking up chanID): Query was:

No error type from QSqlError? Strange... QSqlQuery::exec: empty query 2008-03-18 10:16:08.910 DB Error (Looking up chanID): Query was:

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This is repeated ~hundred times before mythbackend finally crashes with following backtrace:

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* glibc detected * /usr/local/bin/mythbackend: double free or corruption (fasttop): 0x082d5618 * ======= Backtrace: ========= /lib/tls/i686/cmov/libc.so.6[0xb597dd65] /lib/tls/i686/cmov/libc.so.6(cfree+0x90)[0xb5981800] /usr/lib/libstdc++.so.6(_ZdlPv+0x21)[0xb5b46d81] /usr/lib/libstdc++.so.6(_ZdaPv+0x1d)[0xb5b46ddd] /usr/lib/libqt-mt.so.3(_ZN11QStringDataD1Ev+0x34)[0xb642ed30] /usr/lib/libqt-mt.so.3(_ZN11QStringData10deleteSelfEv+0x23)[0xb64264b5] /usr/local/lib/libmyth-0.21.so.0(_ZN12MSqlDatabase12KickDatabaseEv+0x55)[0xb6ae4c67] /usr/local/lib/libmyth-0.21.so.0(_ZN9MSqlQuery7InitConEv+0x56)[0xb6ae96b2]

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This defect looks similar to the one in ticket #4695.

[anonymous]

A crash backtrace

[anonymous]

Attached a gdb.txt file with a backtrace from a segmentation fault that occurred last night. In this case the crash seemed to occur at:

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_ts_writing_listeners[j]->ProcessTSPacket(tspacket);

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#0 0xb7947a6e in MPEGStreamData::ProcessTSPacket (this=0xa930d4a0, tspacket=@0xa7b4e1d0) at mpeg/mpegstreamdata.cpp:986

j = 0 ok = true

#1 0xb79448b7 in MPEGStreamData::ProcessData? (this=0xa930d4a0, buffer=0xa7b4c008 "G\002", len=13724) at mpeg/mpegstreamdata.cpp:944

pkt = (const TSPacket *) 0xa7b4e1d0 pos = 8648

#2 0xb7d5ed38 in DVBStreamHandler::RunTS (this=0x82ce7e0) at dvbstreamhandler.cpp:334

i = 0 len = 13724 remainder = 0 buffer_size = 2820000 buffer = (unsigned char *) 0xa7b4c008 "G\002" dvr_fd = 15 _error = false fd_select_set = {fds_bits = {32768, 0 <repeats 31 times>}}

#3 0xb7d5f44c in DVBStreamHandler::Run (this=0x82ce7e0) at dvbstreamhandler.cpp:221 No locals. #4 0xb7d5f475 in run_dvb_stream_handler_thunk (param=0x82ce7e0) at dvbstreamhandler.cpp:173

mon = (DVBStreamHandler *) 0x82ce7e0

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[anonymous]

Another crash

[anonymous]

Two more crash backtraces

[anonymous]

Some feedback which may be of use to others.

Resolved this type of error message by turning off hyperthreading in the BIOS. Computer is P4 2.8GHz ASUS P4S800D-X running Ubuntu 8.04 desktop with standard Ubuntu MythTV 0.21 packages, ext3 filesystems, UK setup with three Nova T cards, EIT feed only. For info, hyperstreaming was always off in the BIOS.

Other feedback - solved 100% CPU usage by turning off slow deletes - noticed that first auto-expiration after boot made mythbackend go to 100% CPU usage permanently. Turning off slow deletes cured this. Also turned off monit checking of mythtv http socket - suspect this also causes problems in MythTV.

Had one or two seg faults after making these changes (caught by monit), but backend has been stable for 3 days now.

[stuartm]

First backtrace looks like a null or invalid pointer in the _ts_writing_listeners vector. ProcessTSPacket doesn't get a _listener_lock and possibly should to prevent read a value from the vector which has been deleted?

The second backtrace is a QString segfault which is hopefully fixed in trunk.

Third backtrace is useless.

[danielk]

I can't find the bug for the first backtrace, since this ticket is pretty old it is possible it has been fixed, but I can't be sure. In future please open separate tickets for each backtrace.