From owner-p4-projects@FreeBSD.ORG  Fri Jan 19 17:14:30 2007
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From: Hans Petter Selasky <hselasky@c2i.net>
To: "Attilio Rao" <attilio@freebsd.org>
Date: Fri, 19 Jan 2007 18:14:03 +0100
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Cc: perforce@freebsd.org
Subject: Re: PERFORCE change 113164 for review
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On Friday 19 January 2007 17:58, Attilio Rao wrote:
> 2007/1/19, Hans Petter Selasky <hselasky@freebsd.org>:
> > http://perforce.freebsd.org/chv.cgi?CH=113164
> >
> > Change 113164 by hselasky@hselasky_mini_itx on 2007/01/19 16:56:15
> >
> >         The sound mutex needs to allow recursion, else the
> >         new "uaudio" will not work.
> >
> > Affected files ...
> >
> > .. //depot/projects/usb/src/sys/dev/sound/pcm/sound.c#3 edit
> >
> > Differences ...
> >
> > ==== //depot/projects/usb/src/sys/dev/sound/pcm/sound.c#3 (text+ko) ====
> >
> > @@ -78,7 +78,7 @@
> >         m = malloc(sizeof(*m), M_DEVBUF, M_WAITOK | M_ZERO);
> >         if (m == NULL)
> >                 return NULL;
> > -       mtx_init(m, desc, type, MTX_DEF);
> > +       mtx_init(m, desc, type, MTX_DEF|MTX_RECURSE);
> >         return m;
> >  #else
> >         return (void *)0xcafebabe;
>
> Recursed mutexes very often are symptomatic of some some bug...
> it is the case? why the mutex is recursed?
>

Because my system shares the lock with the "pcm channel" of the sound system. 
That means it uses "c->lock" (see below) to protect the isochronous USB 
transfers. The problem is that my USB callback calls "chn_intr()" which also 
locks the same lock.

Maybe this should be addressed by Ariff A. ?

void
chn_intr(struct pcm_channel *c)
{
        CHN_LOCK(c);
        c->interrupts++;
        if (c->direction == PCMDIR_PLAY)
                chn_wrintr(c);
        else
                chn_rdintr(c);
        CHN_UNLOCK(c);
}

--HPS