[mythtv] [mythtv-commits] Ticket #1805: Backend not responding, with backtrace and log

[f-myth-users at media.mit.edu]

    Date: Fri, 12 May 2006 20:47:25 -0700
    From: Jim Westfall <jwestfall at surrealistic.net>

    MythTV <mythtv at cvs.mythtv.org> wrote [05.13.06]:
    > #1805: Backend not responding, with backtrace and log
    > -------------------------------------+--------------------------------------
    >  Reporter:  tom at redpepperracing.com  |       Owner:  ijr
    >      Type:  defect                   |      Status:  new
    >  Priority:  minor                    |   Milestone:     
    > Component:  mythtv                   |     Version:     
    >  Severity:  medium                   |  
    > -------------------------------------+--------------------------------------
    >  The symptom that I have been experiencing is that the backend will all of
    >  a sudden stop  responding to connection requests. The process is still
    >  running, and it's not eating CPU, but neither a frontend nor mythweb can
    >  connect to the backend. I finally managed to get a backtrace and backend
    >  log when it happened.
    > 
    >  Version:
    >  root at mythtv:/var/log# mythbackend --version
    >  Library API version: 0.19.20060331-1
    >  Source code version: 9918
    >  Options compiled in:
    >   linux debug using_lmsensors using_v4l using_oss using_alsa using_ivtv
    >  using_lirc using_x11 using_xv using_xrandr using_frontend using_backend
    > 
    >  Machine is an AMD Sempron 2200, 512MB RAM, 2xPVR-250.
    > 
    >  See attached backtrace and backend log from around where it happened. I
    >  was experimenting with de-interlace and XvMC settings, so I was going in
    >  and out of live tv a number of times just before it happened. Not sure if
    >  that is related. It also seems to happen around the turn of the hour when
    >  a couple of recordings start. Also of note is that the recordings continue
    >  to actually record until I stop and restart the backend process, and
    >  resume when it comes up.
    > 

    I assume you have a slave backend too?  

    Looking at the backtrace (your master backend?) it appears to have a lock 
    on the socket that is waiting for a slave backend to respond about 
    generating a pixmap.  At the same time the main app thread is trying to 
    process a customEvent, which is blocked trying to get the lock on the 
    same socket.  The main app thread being blocked like this is likely 
    causing all qt event processing to stop.

Interesting.

Is this likely to work the same in 18.1?  At least once a month,
I have a similar lockup, in a setup with one MBE and one combined
FE/SBE.  Communication between the FE and the MBE just hangs.  At
the same time, MythWeb stops being able to serve pages (they
eventually just time out).  There hasn't been much of a pattern
to it, except that I don't think it tends to happen -unless- I'm
doing UI operations pretty much at the same time.  (Obviously,
this is something of a heisenbug, since I can't -tell- that the
lockup has happened unless I -am- trying to use the UI... :)

I'm reasonably sure that the MBE continues to be able to continue
recording in-progress shows, and even starts recording new ones,
in the hung state (though I'm not 100% sure of this recollection).
So I wind up having to wait until there's no activity in the
recordings directory, and then boot the MBE, and -then- I also
have to boot the FE/SBE, since booting the MBE invariably screws
up the FE/SBE no matter why I booted the MBE.  (E.g., once I boot
the MBE, the MBE thinks that the SBE's tuners are unavailable and
won't schedule recordings on them, and sometimes (usually?) the
FE can't even talk to the database, either, although I may be
misremembering that latter part.  Booting the FE/SBE fixes the
problem of unavailable tuners; is this behavior still prevalent
in 19?)

P.S.  Unlike the OP, I'm doing absolutely nothing fancy with video;
my FE is just spitting SD video out the TV-out of a PVR-350.  Also,
my hangs have nothing to do with LiveTV, which I almost never use.