From mboxrd@z Thu Jan 1 00:00:00 1970 From: Kevin Hilman Subject: Re: [PATCH 0/3] ALSA: hda - Avoid potential deadlock Date: Wed, 23 Sep 2015 11:01:34 -0700 Message-ID: <7ha8sddngh.fsf@deeprootsystems.com> References: <1442484006-9614-1-git-send-email-thierry.reding@gmail.com> Mime-Version: 1.0 Content-Type: text/plain Return-path: In-Reply-To: <1442484006-9614-1-git-send-email-thierry.reding@gmail.com> (Thierry Reding's message of "Thu, 17 Sep 2015 12:00:03 +0200") Sender: linux-kernel-owner@vger.kernel.org To: Thierry Reding Cc: Takashi Iwai , alsa-devel@alsa-project.org, Tyler Baker , Jon Hunter , linux-tegra@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org List-Id: alsa-devel@alsa-project.org Thierry Reding writes: > From: Thierry Reding > > 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 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