[linux-dvb] [BUG] changeset 9029 (http://linuxtv.org/hg/v4l-dvb/rev/aa3e5cc1d833)

Oliver Endriss o.endriss at gmx.de
Tue Feb 17 01:40:52 CET 2009

Trent Piepho wrote:
> On Sun, 15 Feb 2009, Oliver Endriss wrote:
> > e9hack wrote:
> > > this change set is wrong. The affected functions cannot be called from an interrupt
> > > context, because they may process large buffers. In this case, interrupts are disabled for
> > > a long time. Functions, like dvb_dmx_swfilter_packets(), could be called only from a
> > > tasklet. This change set does hide some strong design bugs in dm1105.c and au0828-dvb.c.
> > >
> > > Please revert this change set and do fix the bugs in dm1105.c and au0828-dvb.c (and other
> > > files).
> >
> > @Mauro:
> >
> > This changeset _must_ be reverted! It breaks all kernels since 2.6.27
> > for applications which use DVB and require a low interrupt latency.
> >
> > It is a very bad idea to call the demuxer to process data buffers with
> > interrupts disabled!
> I agree, this is bad.  The demuxer is far too much work to be done with
> IRQs off.  IMHO, even doing it under a spin-lock is excessive.  It should
> be a mutex.  Drivers should use a work-queue to feed the demuxer.

Agreed, this would be the best solution.

On the other hand, a workqueue handler would be scheduled later, so you
need larger buffers in the driver. Some chipsets have very small

Anway, this would be a major change. All drivers must be carefully
modified and tested for an extended period.

Meanwhile I had a look at the changeset, and I do not understand why
spin_lock_irq... should be required everywhere.

Afaics a driver may safely call dvb_dmx_swfilter_packets,
dvb_dmx_swfilter_204 or dvb_dmx_swfilter from process context, tasklet
or interrupt handler 'as is'.

Could you please explain in more detail what bad things might happen?


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