linux-kernel - Re: [PATCH] ASoC: dapm: Do not traverse widget hooks to snd-soc-dummy

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Message-ID: <1458219853.24844.10.camel@intel.com>
Date:	Thu, 17 Mar 2016 13:04:15 +0000
From:	"Pan, Harry" <harry.pan@...el.com>
To:	"lars@...afoo.de" <lars@...afoo.de>,
	"broonie@...nel.org" <broonie@...nel.org>
CC:	"lgirdwood@...il.com" <lgirdwood@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"gs0622@...il.com" <gs0622@...il.com>,
	"alsa-devel@...a-project.org" <alsa-devel@...a-project.org>,
	"tiwai@...e.com" <tiwai@...e.com>,
	"perex@...ex.cz" <perex@...ex.cz>
Subject: Re: [PATCH] ASoC: dapm: Do not traverse widget hooks to
 snd-soc-dummy

> I'd say as a quick fix for stable check that card is not NULL in
> dapm_widget_show_component(). And as a longterm fix get rid of
> dapm_widget
> file. Nobody should hopefully use it anymore with debugfs being
> available as
> the far better alternative.
> 
> - Lars

Well, that was my original approach while I realized problem
is caused by de-referencing a null pointer to its member of
'widget' list.

i.e.
https://chromium-review.googlesource.com/#/c/331285/3/sound/soc/soc-dap
m.c

+   if (WARN_ON(!codec->component.card))
+       return 0;
+

Additional remark is that I was working on chromium-os v3.18 kernel,
so that the interface and argument are sort of different than what
I then cherry-pick'ed then sent, which was based on latest 4.5.

Then I was stuck at here couple days keeping hunting root cause,
Turned out I found that commit skipped probing dummy component.

Long story short.

-Harry