[PATCH 0/3] ALSA: hda - Avoid potential deadlock

[Thierry Reding]

From: Thierry Reding <treding@xxxxxxxxxx>

The Tegra HDA controller driver committed in v3.16 causes deadlocks when
loaded as a module. The reason is that the driver core will lock the HDA
controller device upon calling its probe callback and the probe callback
then goes on to create child devices for detected codecs and loads their
modules via a request_module() call. This is problematic because the new
driver will immediately be bound to the device, which will in turn cause
the parent of the codec device (the HDA controller device) to be locked
again, causing a deadlock.

This problem seems to have been present since the modularization of the
HD-audio driver in commit 1289e9e8b42f ("ALSA: hda - Modularize HD-audio
driver"). On Intel platforms this has been worked around by splitting up
the probe sequence into a synchronous and an asynchronous part where the
request_module() calls are asynchronous and hence avoid the deadlock.

An alternative proposal is provided in this series of patches. Rather
than relying on explicit request_module() calls to load kernel modules
for HDA codec drivers, this implements a uevent callback for the HDA bus
to advertises the MODALIAS information to the userspace helper.

Effectively this results in the same modules being loaded, but it uses
the more canonical infrastructure to perform this. Deferring the module
loading to userspace removes the need for the explicit request_module()
calls and works around the recursive locking issue because both drivers
will be bound from separate contexts.

Thierry

Thierry Reding (3):
  ALSA: hda/hdmi - Add missing MODALIAS information
  ALSA: hda - Advertise MODALIAS in uevent
  ALSA: hda: Do not rely on explicit module loading

 sound/hda/hda_bus_type.c   | 12 +++++++
 sound/pci/hda/hda_bind.c   | 80 ----------------------------------------------
 sound/pci/hda/patch_hdmi.c |  3 ++
 3 files changed, 15 insertions(+), 80 deletions(-)

-- 
2.5.0

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