Hello Paolo,
        See below.

On Oct 20, Paolo Pisati wrote:
> from my dmesg:
> [snip]
> exclusive sleep mutex pcm0:mixer (pcm mixer) r = 0 (0xc2d34540) locked @ 
> /usr/src/sys/dev/sound/pcm/mixer.c:322

        Could you try deleting the snd_mtxlock and snd_mtxunlock in
mixer_hwvol_init() in mixer.c?  I think it's uneeded as the function
is only called in particular device instance creation and no-one
should be able touch it yet.

> 
> acquiring duplicate lock of same type: "pcm channel"
>  1st pcm0:record:0 @ /usr/src/sys/dev/sound/pcm/sound.c:195
>  2nd pcm0:play:0 @ /usr/src/sys/dev/sound/pcm/sound.c:195
> Stack backtrace:

        Please try my "wild guess" patch that is attached.  I tried to
re-arrange the routine to only hold one locked channel at a time.  I
suppose another option would be flag the lock type as having
duplicates ok.

        --Mat

-- 
        If you optimize everything, you will always be unhappy.
                        - Don Knuth
--- dspold.c    Sun Sep 14 17:49:38 2003
+++ dsp.c       Tue Oct 21 14:38:44 2003
@@ -174,6 +174,8 @@
        intrmask_t s;
        u_int32_t fmt;
        int devtype;
+       int rdref;
+       int error;
 
        s = spltty();
        d = dsp_get_info(i_dev);
@@ -209,6 +211,8 @@
                panic("impossible devtype %d", devtype);
        }
 
+       rdref = 0;
+
        /* lock snddev so nobody else can monkey with it */
        pcm_lock(d);
 
@@ -251,67 +255,66 @@
                        return EBUSY;
                }
                /* got a channel, already locked for us */
-       }
-
-       if (flags & FWRITE) {
-               /* open for write */
-               wrch = pcm_chnalloc(d, PCMDIR_PLAY, td->td_proc->p_pid, -1);
-               if (!wrch) {
-                       /* no channel available */
-                       if (flags & FREAD) {
-                               /* just opened a read channel, release it */
-                               pcm_chnrelease(rdch);
-                       }
-                       /* exit */
-                       pcm_unlock(d);
-                       splx(s);
-                       return EBUSY;
-               }
-               /* got a channel, already locked for us */
-       }
-
-       i_dev->si_drv1 = rdch;
-       i_dev->si_drv2 = wrch;
-
-       /* Bump refcounts, reset and unlock any channels that we just opened,
-        * and then release device lock.
-        */
-       if (flags & FREAD) {
                if (chn_reset(rdch, fmt)) {
                        pcm_chnrelease(rdch);
                        i_dev->si_drv1 = NULL;
-                       if (wrch && (flags & FWRITE)) {
-                               pcm_chnrelease(wrch);
-                               i_dev->si_drv2 = NULL;
-                       }
                        pcm_unlock(d);
                        splx(s);
                        return ENODEV;
                }
+
                if (flags & O_NONBLOCK)
                        rdch->flags |= CHN_F_NBIO;
                pcm_chnref(rdch, 1);
                CHN_UNLOCK(rdch);
+               rdref = 1;
+               /*
+                * Record channel created, ref'ed and unlocked
+                */
        }
+
        if (flags & FWRITE) {
-               if (chn_reset(wrch, fmt)) {
-                       pcm_chnrelease(wrch);
-                       i_dev->si_drv2 = NULL;
-                       if (flags & FREAD) {
-                               CHN_LOCK(rdch);
-                               pcm_chnref(rdch, -1);
-                               pcm_chnrelease(rdch);
-                               i_dev->si_drv1 = NULL;
-                       }
-                       pcm_unlock(d);
-                       splx(s);
-                       return ENODEV;
+           /* open for write */
+           wrch = pcm_chnalloc(d, PCMDIR_PLAY, td->td_proc->p_pid, -1);
+           error = 0;
+
+           if (!wrch)
+               error = EBUSY; /* XXX Right return code? */
+           else if (chn_reset(wrch, fmt))
+               error = ENODEV;
+
+           if (error != 0) {
+               if (wrch) {
+                   /*
+                    * Free play channel
+                    */
+                   pcm_chnrelease(wrch);
+                   i_dev->si_drv2 = NULL;
                }
-               if (flags & O_NONBLOCK)
-                       wrch->flags |= CHN_F_NBIO;
-               pcm_chnref(wrch, 1);
-               CHN_UNLOCK(wrch);
+               if (rdref) {
+                   /*
+                    * Lock, deref and release previously created record channel
+                    */
+                   CHN_LOCK(rdch);
+                   pcm_chnref(rdch, -1);
+                   pcm_chnrelease(rdch);
+                   i_dev->si_drv1 = NULL;
+               }
+
+               pcm_unlock(d);
+               splx(s);
+               return error;
+           }
+
+           if (flags & O_NONBLOCK)
+               wrch->flags |= CHN_F_NBIO;
+           pcm_chnref(wrch, 1);
+           CHN_UNLOCK(wrch);
        }
+
+       i_dev->si_drv1 = rdch;
+       i_dev->si_drv2 = wrch;
+
        pcm_unlock(d);
        splx(s);
        return 0;
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