[alsa-devel] New snd-hda warning spew

[Takashi Iwai]

On Tue, 15 Mar 2016 18:22:56 +0100,
Takashi Iwai wrote:
> 
> On Tue, 15 Mar 2016 17:02:07 +0100,
> Ville Syrjälä wrote:
> > This other one was seen at least on on SKL:
> > [  124.808525] ------------[ cut here ]------------
> > [  124.808545] WARNING: CPU: 3 PID: 173 at sound/hda/hdac_i915.c:91 snd_hdac_display_power+0xf1/0x110 [snd_hda_core]()
> 
> This is a different one, and it implies that the unbalanced power
> refcount.  Might be related with the recent fix for the recursive
> regmap deadlock.  I'll try later with a SKL machine here, too.
> 
> Didn't you see this before the recent tree, right?  Some good/bad
> commits would be really helpful...

So, we got a full log in bugzilla, and this looks like the on-demand
binding leading to the unbalanced refcount.

Could you try the patch below?  This essentially reverts to the 4.4
state, so a "regression" should be covered, at least.  It's applied on
top of sound.git tree for-linus branch.  (But it should be easily
applicable to older trees, too.)

We need a proper fix later, but now more urgently the CI test
regression has to be papered over.


thanks,

Takashi

-- 8< --
From: Takashi Iwai <tiwai at suse.de>
Subject: [PATCH] ALSA: hda - Workaround for unbalanced i915 power refcount by
 concurrent probe

The recent addition of on-demand i915 audio component binding in the
codec driver seems leading to the unbalanced i915 power refcount,
according to Intel CI tests.  Typically, it gets a kernel WARNING
like:
  WARNING: CPU: 3 PID: 173 at sound/hda/hdac_i915.c:91 snd_hdac_display_power+0xf1/0x110 [snd_hda_core]()
  Call Trace:
   [<ffffffff813fef15>] dump_stack+0x67/0x92
   [<ffffffff81078a21>] warn_slowpath_common+0x81/0xc0
   [<ffffffff81078b15>] warn_slowpath_null+0x15/0x20
   [<ffffffffa00f77e1>] snd_hdac_display_power+0xf1/0x110 [snd_hda_core]
   [<ffffffffa015039d>] azx_intel_link_power+0xd/0x10 [snd_hda_intel]
   [<ffffffffa011e32a>] azx_link_power+0x1a/0x30 [snd_hda_codec]
   [<ffffffffa00f21f9>] snd_hdac_link_power+0x29/0x40 [snd_hda_core]
   [<ffffffffa01192a6>] hda_codec_runtime_suspend+0x76/0xa0 [snd_hda_codec]
   .....

The scenario is like below:
- HD-audio driver and i915 driver are probed concurrently at the
  (almost) same time; HDA bus tries to bind with i915, but it fails
  because i915 initialization is still being processed.
- Later on, HD-audio probes the HDMI codec, where it again tries to
  bind with i915.  At this time, it succeeds.
- At finishing the probe of HDA, it decreases the refcount as if it
  were already bound at the bus probe, since the component is bound
  now.  This triggers a kernel WARNING due to the unbalance.

As a workaround, in this patch, we just disable the on-demand i915
component binding in the codec driver.  This essentially reverts back
to the state of 4.4 kernel.

We know that this is no real solution, but it's a minimalistic simple
change that can be applied to 4.5.x kernel as stable.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=94566
Reported-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
Cc: <stable at vger.kernel.org> # v4.5
Signed-off-by: Takashi Iwai <tiwai at suse.de>
---
 sound/pci/hda/patch_hdmi.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/sound/pci/hda/patch_hdmi.c b/sound/pci/hda/patch_hdmi.c
index 56d3575ee6cc..7ae614d27954 100644
--- a/sound/pci/hda/patch_hdmi.c
+++ b/sound/pci/hda/patch_hdmi.c
@@ -2258,9 +2258,15 @@ static int patch_generic_hdmi(struct hda_codec *codec)
 	/* Try to bind with i915 for Intel HSW+ codecs (if not done yet) */
 	if ((codec->core.vendor_id >> 16) == 0x8086 &&
 	    is_haswell_plus(codec)) {
+#if 0
+		/* on-demand binding leads to an unbalanced refcount when
+		 * both i915 and hda drivers are probed concurrently;
+		 * disabled temporarily for now
+		 */
 		if (!codec->bus->core.audio_component)
 			if (!snd_hdac_i915_init(&codec->bus->core))
 				spec->i915_bound = true;
+#endif
 		/* use i915 audio component notifier for hotplug */
 		if (codec->bus->core.audio_component)
 			spec->use_acomp_notifier = true;
-- 
2.7.4