ALSA: hda/cs_dsp_ctl: Fix mutex inversion when creating controls

Redesign the creation of ALSA controls so that the cs_dsp
pwr_lock is not held when calling snd_ctl_add(). Instead of
creating the ALSA control from the cs_dsp control_add callback,
do it after cs_dsp_power_up() has completed. The existing
functions are changed to return void instead of passing errors
back - this duplicates the original behaviour, as cs_dsp does
not abort firmware load if creation of a control fails.

It is safe to walk the control list without taking any mutex
provided that the caller is not trying to load a new firmware
or remove the driver in parallel. There is no other situation
that the list can change. So the caller can trigger creation
of ALSA controls after cs_dsp_power_up() has returned. A cs_dsp
control will have a non-NULL priv pointer if we have created
an ALSA control.

With the previous code the ALSA controls were created from
the cs_dsp control_add callback. But this is called with
pwr_lock held (as it is part of the DSP power-up sequence).
The kernel lock checking will show a mutex inversion between
this and the control creation path:

control_add
  pwr_lock held, takes controls_rwsem (in snd_ctl_add)

get/put
  controls_rwsem held, takes pwr_lock to call cs_dsp.

This is not completely theoretical. Although the time window
is very small, it is possible for these to run in parallel
and deadlock the old implementation.

Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com>
Signed-off-by: Stefan Binding <sbinding@opensource.cirrus.com>
Link: https://lore.kernel.org/r/20221011143552.621792-4-sbinding@opensource.cirrus.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>

1 files changed, 1 insertions, 1 deletions

diff --git a/sound/pci/hda/hda_cs_dsp_ctl.h b/sound/pci/hda/hda_cs_dsp_ctl.h
index 4babc69cf2f0..2cf93359c4f2 100644
--- a/sound/pci/hda/hda_cs_dsp_ctl.h
+++ b/sound/pci/hda/hda_cs_dsp_ctl.h
@@ -29,7 +29,7 @@ struct hda_cs_dsp_ctl_info {
 
 extern const char * const hda_cs_dsp_fw_ids[HDA_CS_DSP_NUM_FW];
 
-int hda_cs_dsp_control_add(struct cs_dsp_coeff_ctl *cs_ctl, struct hda_cs_dsp_ctl_info *info);
+void hda_cs_dsp_add_controls(struct cs_dsp *dsp, const struct hda_cs_dsp_ctl_info *info);
 void hda_cs_dsp_control_remove(struct cs_dsp_coeff_ctl *cs_ctl);
 int hda_cs_dsp_write_ctl(struct cs_dsp *dsp, const char *name, int type,
 			 unsigned int alg, const void *buf, size_t len);