[mythtv-users] Could realtime commercial flagging cause hard lockup/freeze/hang?
finlay at moeraki.com
Wed Jun 4 07:47:59 UTC 2008
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.
> 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.
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