From mboxrd@z Thu Jan 1 00:00:00 1970 From: Takashi Iwai Subject: Re: [PATCH 0/3] ALSA: hda - Avoid potential deadlock Date: Sat, 19 Sep 2015 18:42:25 +0200 Message-ID: References: <1442484006-9614-1-git-send-email-thierry.reding@gmail.com> Mime-Version: 1.0 (generated by SEMI 1.14.6 - "Maruoka") Content-Type: text/plain; charset=US-ASCII Return-path: In-Reply-To: <1442484006-9614-1-git-send-email-thierry.reding-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> Sender: linux-tegra-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Thierry Reding Cc: alsa-devel-K7yf7f+aM1XWsZ/bQMPhNw@public.gmane.org, Kevin Hilman , Tyler Baker , linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, Jon Hunter , linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-tegra-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-tegra@vger.kernel.org On Thu, 17 Sep 2015 12:00:03 +0200, Thierry Reding wrote: > > 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. This looks like a sane cleanup at a glance, but I can't review in details now because I'm traveling on vacation. I'll take a closer look in the next week. thanks, Takashi > > 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 > >