Comment 7 for bug 1212160

On Tue, Nov 12, 2013 at 01:33:11PM +0100, David Henningsson wrote:
> Hi,
>
> This is a real oldie, but better late than never.
>
> A while back, I discovered that this patch would help against a kernel
> panic when "cat /proc/asound/card0/codec0" was executed on this machine,
> which was running an fglrx driver.
>
> I asked for a stable backport, but Takashi wanted testing to make sure
> this was actually fixed by the patch [1]. And now, several months later,
> I have this confirmation [2].
>
> The test was conducted on an 3.5 Ubuntu kernel, based on the 3.5
> extended stable tree, but would apply equally well to 3.4.
>
> I'm attaching the backported patch - it applied cleanly, I've just added
> an extra section with an explanation.
>

Thank you David, I'll queue it for the 3.5 kernel.

Cheers,
--
Luis

> -- David Henningsson, Canonical Ltd. https://launchpad.net/~diwic
>
> [1]
> http://mailman.alsa-project.org/pipermail/alsa-devel/2013-March/060132.html
>
> [2] https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1212160/comments/4

> From 76aabf83ca9c8cff2dd9e3bb5300e3778e0baf7d Mon Sep 17 00:00:00 2001
> From: Takashi Iwai <email address hidden>
> Date: Wed, 20 Jun 2012 16:32:22 +0200
> Subject: [PATCH] ALSA: hda - Move one-time init codes from
> generic_hdmi_init()
>
> The codes to initialize work struct or create a proc interface should
> be called only once and never although it's called many times through
> the init callback. Move that stuff into patch_generic_hdmi() so that
> it's called only once.
>
> Signed-off-by: Takashi Iwai <email address hidden>
>
> (cherry picked from commit 8b8d654b55648561287bd8baca0f75f964a17038)
>
> This is being backported to 3.4 and 3.5 due to prevention of kernel
> panic. The kernel panic was observed by executing
> 'cat /proc/asound/card0/codec0' on a particular machine, which was
> - running in battery mode
> - having an external HDMI monitor connected
> - running the fglrx driver.
>
> In short, the one-time init code initializes a delayed_work struct.
> Then, I believe the following happened:
> 1) the delayed_work was activated
> 2) the delayed_work struct was reinitialized by the init code
> 3) when the delayed_work timed out (ready to run the callback function),
> the kernel panic happened because the delayed_work struct had
> been corrupted in step 2.
>
> BugLink: https://bugs.launchpad.net/bugs/1212160
> Signed-off-by: David Henningsson <email address hidden>
> ---
> sound/pci/hda/patch_hdmi.c | 22 +++++++++++++++++-----
> 1 file changed, 17 insertions(+), 5 deletions(-)
>
> diff --git a/sound/pci/hda/patch_hdmi.c b/sound/pci/hda/patch_hdmi.c
> index 02a6e3f..ef917bf 100644
> --- a/sound/pci/hda/patch_hdmi.c
> +++ b/sound/pci/hda/patch_hdmi.c
> @@ -1282,23 +1282,34 @@ static int generic_hdmi_build_controls(struct hda_codec *codec)
> return 0;
> }
>
> -static int generic_hdmi_init(struct hda_codec *codec)
> +static int generic_hdmi_init_per_pins(struct hda_codec *codec)
> {
> struct hdmi_spec *spec = codec->spec;
> int pin_idx;
>
> for (pin_idx = 0; pin_idx < spec->num_pins; pin_idx++) {
> struct hdmi_spec_per_pin *per_pin = &spec->pins[pin_idx];
> - hda_nid_t pin_nid = per_pin->pin_nid;
> struct hdmi_eld *eld = &per_pin->sink_eld;
>
> - hdmi_init_pin(codec, pin_nid);
> - snd_hda_jack_detect_enable(codec, pin_nid, pin_nid);
> -
> per_pin->codec = codec;
> INIT_DELAYED_WORK(&per_pin->work, hdmi_repoll_eld);
> snd_hda_eld_proc_new(codec, eld, pin_idx);
> }
> + return 0;
> +}
> +
> +static int generic_hdmi_init(struct hda_codec *codec)
> +{
> + struct hdmi_spec *spec = codec->spec;
> + int pin_idx;
> +
> + for (pin_idx = 0; pin_idx < spec->num_pins; pin_idx++) {
> + struct hdmi_spec_per_pin *per_pin = &spec->pins[pin_idx];
> + hda_nid_t pin_nid = per_pin->pin_nid;
> +
> + hdmi_init_pin(codec, pin_nid);
> + snd_hda_jack_detect_enable(codec, pin_nid, pin_nid);
> + }
> snd_hda_jack_report_sync(codec);
> return 0;
> }
> @@ -1343,6 +1354,7 @@ static int patch_generic_hdmi(struct hda_codec *codec)
> return -EINVAL;
> }
> codec->patch_ops = generic_hdmi_patch_ops;
> + generic_hdmi_init_per_pins(codec);
>
> init_channel_allocations();
>
> --
> 1.7.9.5
>