[mythtv-users] Could realtime commercial flagging cause hard lockup/freeze/hang?

[finlay]

Brian Foddy wrote:
> On Tuesday 03 June 2008, finlay wrote:
>   
>> Greg Grotsky wrote:
>>     
>>> Hello all,
>>>
>>>   I've been a mythtv user for a few years.  My configuration is a
>>> single system frontend/backend.  Since it's inception I have been
>>> using realtime commercial flagging and it has worked very well.
>>> However, I recently updated my mythtv svn tree (to 17392 from an
>>> update 5/3/08) and every once in a while the system completely hangs.
>>> It hangs to the point where the magic Alt-SysRq-REISUB does not reboot
>>> it, no SSH, no three-fingered-salute, no nothing.
>>>
>>>   I get nothing in my logs (FE, BE, syslog, messages, etc) and it
>>> appears to happen when recording and doing commercial detection.  It
>>> froze three times over three days and I started to worry.  I
>>> completely disabled commercial detection and it worked for two days
>>> straight so I decided to turn comflagging back on because the queue
>>> was huge.  It detected all the commercials in the recorded shows and
>>> the next day while recording and comflagging it died again!  So I
>>> turned off the realtime comflag option and it has been working for two
>>> days now without a hang.
>>>
>>>   I thought maybe it was a memory issue so I sacrificed a few shows
>>> and ran memtest86 overnight; it completed 12 cycles and didn't report
>>> any errors.  None of the information I have proves anything but so far
>>> it's looking like some update done in may to the comflagger is the
>>> culprit.  Anyone have information that supports or debunks this
>>> theory?  It's not a big loss to not have realtime comflagging but it
>>> was a cool geek thing to tout. :)
>>>       
>> I had something similar happen to my system recently while using
>> realtime commflag. After much futzing around with hardware I finally
>> realized that the OS seemed to be the problem. I had upgraded the system
>> from Ubuntu 710 to 804 a few weeks before and everything seemed OK but
>> then the problems started - system lockup when recording and
>> commflagging but working fine otherwise. I finally installed a clean
>> version of Mythbuntu 804 and everything has been working great for the
>> last 2 weeks.
>> John
>>     
>
> I'd guess its some kernel deadlock with a device driver.  What tuner card
> is (are) running during the process.  If the machine is really busy, and
> you have some of the kernel preempt settings on, and there is a bug
> in the driver, it could cause a hard crash.
>
> What type of computer?  Multi-core, dual CPU?  Using SMP kernel?
> These can cause driver bugs more readily.  If its an SMP instance,
> try your test with SMP disabled (there is a kernel param that will do this).
>
> The commercial scan itself is probably (haven't looked at code, but
> I can't imagine) doing anything other than standard file I/O using
> normal calls, so root or not, I don't see it the problem.  But if it
> keeps the system busy, it could cause other faults to show up.
>
> In general, hard lock ups / crashes are due to faulty / buggy device drivers
> or hardware failures.  
>   
My point is that lockups aren't always hardware related. My situation is 
somewhat reminicent of having to do a fresh install of Windows 
periodically to clear out the cruft that has accumulated. In this case 
the cruft may have been from an OS upgrade.

John