Hi All,<br><br>I just experienced a backend SIGSEGV and I thought before I get too involved in debugging it I should check with the list to see if any experts can identify the problem. I am running SVN Rev 14309 in what is effectively an optimised build with debug symbols (I'm using the
release-dbg profile from <a href="http://svn.mythtv.org/trac/ticket/3589">http://svn.mythtv.org/trac/ticket/3589</a>). Also I have a master backend running also the frontend and a remote machine also running both BE/FE - the dump is of the master BE. Here is what I see in GDB:
<br><br>myth_master ~ # gdb /usr/local/bin/mythbackend /core.4224<br>GNU gdb 6.6<br><...><br>Core was generated by `/usr/local/bin/mythbackend --verbose general,important --logfile /var/log/mytht'.<br>Program terminated with signal 11, Segmentation fault.
<br>#0 0x00002aea07167170 in QMutex::lock () from /usr/qt/3/lib/libqt-mt.so.3<br>(gdb) bt<br>#0 0x00002aea07167170 in QMutex::lock () from /usr/qt/3/lib/libqt-mt.so.3<br>#1 0x00002aea05e36b97 in MythSocket::UpRef (this=0x69006e006f004d) at
mythsocket.cpp:61<br>#2 0x000000000047d2ce in PlaybackSock::SendReceiveStringList (this=0x1be0750, strlist=@0x4d018540) at playbacksock.cpp:63<br>#3 0x000000000047f8d0 in PlaybackSock::GetDiskSpace (this=0x1be0750, o_strlist=@0x4d018a40) at
playbacksock.cpp:99<br>#4 0x00000000004b96f2 in BackendQueryDiskSpace (strlist=@0x4d018a40, encoderList=0x607460, consolidated=false, allHosts=true) at backendutil.cpp:137<br>#5 0x00000000004ba2e8 in GetFilesystemInfos (tvList=0x607460, fsInfos=@0x4d018c40) at
backendutil.cpp:227<br>#6 0x0000000000414f73 in AutoExpire::CalcParams (this=0x751b00) at autoexpire.cpp:115<br>#7 0x0000000000417faa in SpawnUpdateThread (autoExpireInstance=0x751b00) at autoexpire.cpp:933<br>#8 0x00002aea07c2b257 in ?? () from /lib/libpthread.so.0
<br>#9 0x00002aea0828bafd in clone () from /lib/libc.so.6<br>#10 0x0000000000000000 in ?? ()<br>(gdb) frame 2<br>#2 0x000000000047d2ce in PlaybackSock::SendReceiveStringList (this=0x1be0750, strlist=@0x4d018540) at playbacksock.cpp
:63<br>63 sock->UpRef();<br>(gdb) print this<br>$18 = (PlaybackSock * const) 0x1be0750<br>(gdb) print *this<br>$19 = {_vptr.PlaybackSock = 0x20004e004e0041, sock = 0x69006e006f004d, hostname = {static null = {
<br> static null = <same as static member of an already seen type>, d = 0x60bda0, static shared_null = 0x60bda0}, d = 0x200072006f0074,<br> static shared_null = 0x60bda0}, ip = {static null = {static null = <same as static member of an already seen type>, d = 0x60bda0,
<br> static shared_null = 0x60bda0}, d = 0x6800740079006d, static shared_null = 0x60bda0}, local = 95, events = false, blockshutdown = 102,<br> backend = false, sockLock = <incomplete type>, expectingreply = false, disconnected = true, refCount = -1, m_parent = 0x7601e0}
<br>(gdb) print *this->sock<br>Cannot access memory at address 0x69006e006f004d<br>(gdb) list<br>58 }<br>59<br>60 bool PlaybackSock::SendReceiveStringList(QStringList &strlist)<br>61 {<br>62 sock->Lock();
<br>63 sock->UpRef();<br>64<br>65 sockLock.lock();<br>66 expectingreply = true;<br>67<br>(gdb)<br><br><br>Note that the sock member is invalid and that the refCount of the PlaybackSock is -1. Interestingly enough there is another thread that is also using the exact same PlaybackSock, and is pretty much in the same code:
<br><br><br>(gdb) thread 21<br>[Switching to thread 21 (process 4347)]#0 0x00002aea07c31a98 in ?? () from /lib/libpthread.so.0<br>(gdb) bt<br>#0 0x00002aea07c31a98 in ?? () from /lib/libpthread.so.0<br>#1 0x00002aea07c2dbdb in ?? () from /lib/libpthread.so.0
<br>#2 0x00002aea07c2d533 in pthread_mutex_lock () from /lib/libpthread.so.0<br>#3 0x00002aea071672bd in QRealMutexPrivate::lock () from /usr/qt/3/lib/libqt-mt.so.3<br>#4 0x00002aea05e28510 in MythSocket::Lock (this=<value optimized out>) at
mythsocket.cpp:564<br>#5 0x000000000047d2c1 in PlaybackSock::SendReceiveStringList (this=0x1be0750, strlist=@0x0) at playbacksock.cpp:62<br>#6 0x000000000047f8d0 in PlaybackSock::GetDiskSpace (this=0x1be0750, o_strlist=@0x448076a0) at
playbacksock.cpp:99<br>#7 0x00000000004b96f2 in BackendQueryDiskSpace (strlist=@0x448076a0, encoderList=0x607460, consolidated=false, allHosts=true) at backendutil.cpp:137<br>#8 0x00000000004ba2e8 in GetFilesystemInfos (tvList=0x607460, fsInfos=@0x44807920) at
backendutil.cpp:227<br>#9 0x000000000041d560 in AutoExpire::ExpireRecordings (this=0x751b00) at autoexpire.cpp:325<br>#10 0x0000000000425a44 in AutoExpire::RunExpirer (this=0x751b00) at autoexpire.cpp:275<br>#11 0x0000000000425a59 in AutoExpire::ExpirerThread (param=0x2aaab13a4f38) at
autoexpire.cpp:547<br>#12 0x00002aea07c2b257 in ?? () from /lib/libpthread.so.0<br>#13 0x00002aea0828bafd in clone () from /lib/libc.so.6<br>#14 0x0000000000000000 in ?? ()<br>(gdb) frame 5<br>#5 0x000000000047d2c1 in PlaybackSock::SendReceiveStringList (this=0x1be0750, strlist=@0x0) at
playbacksock.cpp:62<br>62 sock->Lock();<br>(gdb) print this<br>$20 = (PlaybackSock * const) 0x1be0750<br>(gdb) print *this<br>$21 = {_vptr.PlaybackSock = 0x20004e004e0041, sock = 0x69006e006f004d, hostname = {static null = {
<br> static null = <same as static member of an already seen type>, d = 0x60bda0, static shared_null = 0x60bda0}, d = 0x200072006f0074,<br> static shared_null = 0x60bda0}, ip = {static null = {static null = <same as static member of an already seen type>, d = 0x60bda0,
<br> static shared_null = 0x60bda0}, d = 0x6800740079006d, static shared_null = 0x60bda0}, local = 95, events = false, blockshutdown = 102,<br> backend = false, sockLock = <incomplete type>, expectingreply = false, disconnected = true, refCount = -1, m_parent = 0x7601e0}
<br>(gdb) list<br>57 return false;<br>58 }<br>59<br>60 bool PlaybackSock::SendReceiveStringList(QStringList &strlist)<br>61 {<br>62 sock->Lock();<br>63 sock->UpRef();<br>
64<br>65 sockLock.lock();<br>66 expectingreply = true;<br>(gdb)<br><br><br>I didn't notice any other interesting threads - the only thing in the backend log at the time of the dump is:<br><br>2007-09-30 23:57:
20.264 Event socket closed. No connection to the backend.<br>2007-09-30 23:57:20.264 Event socket closed. No connection to the backend.<br><br><br>I'll continue to investigate and open a ticket when I isolate the problem, but if anyone wants to short-circuit the effort I won't complain :-)
<br><br>Cheers,<br>Russell.<br><br><br><br>