Messages in this thread | | | From | Kevin Hilman <> | Subject | Re: [PATCH 0/3] ALSA: hda - Avoid potential deadlock | Date | Wed, 23 Sep 2015 11:01:34 -0700 |
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Thierry Reding <thierry.reding@gmail.com> writes:
> From: Thierry Reding <treding@nvidia.com> > > 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.
Tested-by: Kevin Hilman <khilman@linaro.org>
FWIW, I tested this on top of next-20150923, and it solves the boot problem I'm seeing on tegra124-jetson-tk1 with module loading.
Kevin
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