linux-kernel - Re: sound: -EPERM on first mplayer invocation

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Date:	Tue, 04 Aug 2009 11:16:16 +0200
From:	Takashi Iwai <tiwai@...e.de>
To:	Denys Vlasenko <vda.linux@...glemail.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: sound: -EPERM on first mplayer invocation

At Tue, 4 Aug 2009 11:01:43 +0200,
Denys Vlasenko wrote:
> 
> On Monday 03 August 2009 08:55, Takashi Iwai wrote:
> > Denys Vlasenko wrote:
> > > Hi,
> > > 
> > > For a long time I observe the following nuisance:
> > > when I run mplayer for the very first time after boot,
> > > I can't adjust the volume. mplayer spews this to stderr:
> > > 
> > > alsa-control: error setting left channel, Operation not permitted
> > > 
> > > This happens even if I login as root and run mplayer as root.
> > > 
> > > I tracked it down to snd_ctl_elem_write in sound/core/control.c
> > > 
> ...
> > > 
> > > Thus, vd->owner != file.
> > > 
> > > As I said, it only happens on very first run of mplayer,
> > > and it isn't a recent change, I think I saw it at least
> > > for one year with different kernels.
> > > 
> > > Takashi, any idea what might be happening here?
> > > How can I help you more with tracking it down?
> > 
> > This implies that another process (e.g. a sound daemon like PA)
> > already opened the device and locked this specific control element.
> > If so, this is no bug but the right behavior.
> > Check "fuser /dev/snd/controlC*".
> 
> Nothing uses them:
> 
> shadow:~# lsof -nP | grep '/dev/.*control'
> shadow:~# fuser /dev/snd/controlC*
> shadow:~#
> 
> I tried running bare X with only xterm and mplayer,

Hm, but according to your debug session, the vd->owner is set
to a different value, right?  Check vd->owner_pid in the error path.
It'll show the pid blocking that control element.


Takashi
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