[linux-dvb] Regression since 2.6.25 kernel: Crash of userspace program leaves DVB device unusable

From: Brendon Higgins <blhiggins@gmail.com>
To: linux-dvb@linuxtv.org
Subject: [linux-dvb] Regression since 2.6.25 kernel: Crash of userspace program leaves DVB device unusable
Date: Sat, 3 Jan 2009 12:00:49 +1000	[thread overview]
Message-ID: <200901031200.56314.blhiggins@gmail.com> (raw)

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Hi,

I've been coming up against a problem that seems to be with the DVB drivers 
that occurs when a program using them, usually VDR in my case, terminates 
uncleanly (segfault, general protection fault). Linux 2.6.25 doesn't have this 
problem, but 2.6.26, 2.6.27, and 2.6.28 do, though 2.6.28 manifests slightly 
differently to the others. I'll focus on what 2.6.28 does. I have a DViCO 
FusionHDTV DVB-T Plus, running on an amd64 Debian Testing (mostly) dual-core 
machine.

After VDR crashes it attemps to restart itself. This was fine on 2.6.25, but on 
later kernels the crash seems to leave the device in some unusable state, 
where no program can subsequently use it - the device files (/dev/dvb) no 
longer exist. (In 2.6.2[67], the files existed, but accessing 
/dev/dvb/adapter0/dvr0 resulted in "No such device".) I had figured out that in 
order to get the device working again it is necessary to "rmmod cx88_dvb 
cx8802; modprobe cx88_dvb". This worked in 2.6.2[67] without trouble, but in 
2.6.28, it's as if the cx88_dvb module gets lost somehow. It doesn't appear in 
lsmod, however:
phi:~# modprobe cx88_dvb
FATAL: Error inserting cx88_dvb 
(/lib/modules/2.6.28/kernel/drivers/media/video/cx88/cx88-dvb.ko): No such 
device
phi:~# rmmod cx88_dvb cx8802
ERROR: Module cx88_dvb does not exist in /proc/modules
phi:~# modprobe cx88_dvb

Note that probing it works only *after* cx8802 was unloaded. As before, now 
the device is accessible.

So it seems something is wrong in the cx8802 module. Something is not being 
cleaned up after a userspace program crashes while using it, leaving the DVB 
system in a broken state.

I'd very much like this to not be the case, since on my system a VDR crash is 
somewhat inevitable, and the automatic restart *was* very handy, back in 
2.6.25.

Peace,
Brendon

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