confusions and panic provided that the following conditions are met:
1) WITNESS is enabled (watch/trace).
2) Using modules, instead of statically linked (Not a strict
requirement, but easier to reproduce this way).
3) 2 or more modules share the same mtx type ("sound softc").
- They might share the same name (strcmp() == 0), but it always
point to different address.
4) Repetitive kldunload/load on any module that shares the same mtx
type (Not a strict requirement, but easier to reproduce this way).
Consider module A and module B:
- From enroll() - subr_witness.c:
* Load module A. Everything seems fine right now.
wA-w_refcount == 1 ; wA-w_name = "sound softc"
* Load module B.
* w->w_name == description will always fail.
("sound softc" from A and B point to different address).
* wA->w_refcount > 0 && strcmp(description, wA->w_name) == 0
* enroll() will return wA instead of returning (possibly unique)
wB.
wA->w_refcount++ , == 2.
* Unload module A, mtx_destroy(), wA->w_name become invalid,
but wA->w_refcount-- become 1 instead of 0. wA will not be
removed from witness list.
* Some other places call mtx_init(), iterating witness list,
found wA, failed on wA->w_name == description
* wA->w_refcount > 0 && strcmp(description, wA->w_name)
* Panic on strcmp() since wA->w_name no longer point to valid
address.
Note that this could happened in other places as well, not just sound
(eg. consider lots of drivers that share simmilar MTX_NETWORK_LOCK).
Solutions (for sound case):
1) Provide unique mtx type string for each mutex creation (chosen)
or
2) Put "sound softc" global variable somewhere and use it.
Use bus_get_dma_tag() to obtain the parent DMA tag to make the drivers
a little bit more non-ia32/amd64 friendly.
There is no man page for bus_get_dma_tag, so this is modelled after
rev. 1.62 of src/sys/dev/sound/pci/es137x.c by marius.
Inspired by: commit by marius
- fix "No sound in KDE":
The problem is related to the implementation of Envy24(1712) hardware
mixer support in the driver. Envy24(1712) has very precise 36bit wide
hardware mixer, which is superior that vchans (software sound mixer in
the kernel). The driver supports Envy24(1712) hardware mixer, so up to
10 channels (5 stereo pairs) can be playback simultaneously.
However, there are problems with the implementation of Envy24(1712)
hardware mixer support in the driver, one of them is the problem with
"no sound in KDE":
When playing back several channels simultaneously and
stoping one of the channels, sound starts to stutter and
plays at very low speed.
Another problem is:
Playing back simultaneously more than one 24bit/32bit
sound file or 16bit sound file and 24bit/32bit sound
file doesn't work as expected.
Submitted by: "Konstantin Dimitrov" <kosio.dimitrov@gmail.com>
yet. More commits to follow.
I got no response from the author, but since the driver is BSD licensed
I don't think he will complain. :-)
I got it from http://people.freebsd.org/~lofi/envy24.tar.gz
Written by: Katsurajima Naoto <raven@katsurajima.seya.yokohama.jp>
