[mythtv-commits] Ticket #581: SBE termination cases MBE mutex crash

[MythTV]

#581: SBE termination cases MBE mutex crash
------------------------------+---------------------------------------------
 Reporter:  enorm1 at gmail.com  |       Owner:  GoToDev
     Type:  defect            |      Status:  new    
 Priority:  critical          |   Milestone:         
Component:  mythtv            |     Version:  0.18.1 
 Severity:  medium            |  
------------------------------+---------------------------------------------
My master backend is crashing when the slave backend is terminated.
 This does not always occur but rougly every other restart
 of the slave backend will cause this segfault.

 I don't know if this has anything to do with anything but the
 capture-cards of the slave has higher priority than the
 card of the mbe.

 I'm using:

 * http://svn.mythtv.org/svn/branches/release-0-18-fixes/mythtv

 * gentoo x11-libs/qt-3.3.4-r8

 * gentoo dev-db/mysql-4.1.14

 on both servers.

 The problem occurs in 0.18.1 as well (that's why i switched to 0.18.fixes)

 I've been trying to look into the code, but the
 PlaybackSock.sockLock attribute seems 100% legit.
 It's a private attribute only used by one class method.

 Browsing the code it looks like the PlaybackSock instance
 is deleted by MainServer::endConnection() when the slave backend
 terminates.
 This while the schedules thread is still using the instance.
 A simple mutex would probably solve the problem.

 To me this problem is critical since i intend to run the slave backend
 on a "on-demand" basis, and there is no point in developing
 a scheduler addon (that starts the sbe when needed), if the
 mbe crashes like this.

 {{{
 (gdb) run
 Starting program: /usr/bin/mythbackend --verbose quiet --logfile
 /var/log/mythtv/mythbackend.log
 [Thread debugging using libthread_db enabled]
 [New Thread 16384 (LWP 26094)]
 Qt: gdb: -nograb added to command-line options.
          Use the -dograb option to enforce grabbing.
 [New Thread 32769 (LWP 26100)]
 [New Thread 16386 (LWP 26101)]
 [New Thread 32771 (LWP 26103)]
 [New Thread 49156 (LWP 26104)]
 [New Thread 65541 (LWP 26105)]
 [New Thread 81926 (LWP 26106)]
 [New Thread 98311 (LWP 26107)]
 [New Thread 114696 (LWP 26110)]
 [New Thread 131081 (LWP 26111)]
 [New Thread 147466 (LWP 26112)]
 [New Thread 163851 (LWP 26113)]

 Program received signal SIGSEGV, Segmentation fault.
 [Switching to Thread 32771 (LWP 26103)]
 0x45525f59 in ?? ()


 (gdb) thread apply all bt full
 Thread 12 (Thread 163851 (LWP 26113)):
 #0  0xb66f2094 in __pthread_sigsuspend () from /lib/libpthread.so.0
 No symbol table info available.
 #1  0xb66f1ed9 in __pthread_wait_for_restart_signal () from
 /lib/libpthread.so.0
 No symbol table info available.
 #2  0xb66edfdb in pthread_cond_wait at GLIBC_2.0 () from /lib/libpthread.so.0
 No symbol table info available.
 #3  0xb2fd1e08 in ?? ()
 No symbol table info available.
 #4  0x00000000 in ?? ()
 No symbol table info available.
 #5  0x080fdea8 in ?? ()
 No symbol table info available.
 #6  0xb66ede80 in pthread_cond_destroy at GLIBC_2.0 () from
 /lib/libpthread.so.0
 No symbol table info available.
 Previous frame inner to this frame (corrupt stack?)
 #0  0x45525f59 in ?? ()
 (gdb) st
 start     step      stepi     stepping  stop


 (gdb) backtrace
 #0  0x45525f59 in ?? ()
 #1  0xb6e548c8 in QMutex::unlock () from /usr/qt/3/lib/libqt-mt.so.3
 #2  0x08095023 in PlaybackSock::SendReceiveStringList (this=0x80e1218,
 strlist=@0xb57d1ba0) at playbacksock.cpp:60
 #3  0x08095725 in PlaybackSock::IsBusy (this=0x80e1218, capturecardnum=1)
 at playbacksock.cpp:145
 #4  0x0805d9ee in EncoderLink::IsBusy (this=0x80f3460) at
 encoderlink.cpp:65
 #5  0x0809d5ed in Scheduler::RunScheduler (this=0x80f3db0) at
 scheduler.cpp:1127
 #6  0x0809e553 in Scheduler::SchedulerThread (param=0x80f3db0) at
 scheduler.cpp:1293
 #7  0xb66ef18e in pthread_start_thread () from /lib/libpthread.so.0
 #8  0xb66ef334 in pthread_start_thread_event () from /lib/libpthread.so.0
 #9  0xb659eaaa in clone () from /lib/libc.so.6
 (gdb)
 }}}

-- 
Ticket URL: <http://cvs.mythtv.org/trac/ticket/581>
MythTV <http://www.mythtv.org/>
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