sound/pcm/* bugs (was: Re: page fault panic tracked down (selwakeuppri()) - really sound/pcm/*)

Stefan Ehmann shoesoft at
Wed Jan 7 22:48:51 PST 2004

On Wed, 2004-01-07 at 21:15, Don Lewis wrote:
> Try the following patch.  I won't guarantee that you still won't see
> panics, but at least it should panic cleanly instead of stomping on some
> innocent block of memory that corrupts data or some critical structure
> that will trigger a mysterious and hard to debug panic at some later
> time.
> The reason for changing the KASSERT to a test and an explicit call to
> panic() is to make sure that the error is always caught because the
> sound code is typically not compiled with INVARIANTS, so the KASSERT
> will typically be ignored.  The vchan stuff really needs a proper fix,
> but I don't understand the sound code well enough.

Nice patch - unfortunately sound doesn't work any longer with vchans
enabled (which is set to 4 at boot time here).

I get "pcm0:virtual:0: play interrupt timeout, channel dead" whenever I
try to play anything.

However, if I do "hw.snd.pcm0.vchans: 4 -> 0" it works nice again.

I'll probably try later if I'm able to get a panic with vchans disabled
(Especially those that had - at least not in an obvious way - any sound
stuff in backtrace)
If not, maybe the panic gets triggered if for some reason the dsp device
isn't ready again after a song played and a new virtual dsp device is
opened and vchan code gets in action (combined with other bad things).

It can't be vchans alone because I just had three mpg123s open and they
just played fine.

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