Re: 4.10-rc2 oops in DRM connector code

From: Dave Hansen <dave.hansen@intel.com>
To: Daniel Vetter <daniel@ffwll.ch>
Cc: David Airlie <airlied@linux.ie>,
	intel-gfx <intel-gfx@lists.freedesktop.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	dri-devel <dri-devel@lists.freedesktop.org>,
	Daniel Vetter <daniel.vetter@intel.com>
Subject: Re: 4.10-rc2 oops in DRM connector code
Date: Mon, 9 Jan 2017 08:50:22 -0800	[thread overview]
Message-ID: <f56df02a-61ae-e20b-c99a-cfe8ccd45c64@intel.com> (raw)
In-Reply-To: <CAKMK7uEjjmD=Aq5=DC2QmjX2V8PCwwF2hd6N4Ma_oreY_C8iFw@mail.gmail.com>

On 01/09/2017 08:41 AM, Daniel Vetter wrote:
> On Mon, Jan 9, 2017 at 2:40 PM, Dave Hansen <dave.hansen@intel.com> wrote:
>> Well, now I found where the -2 comes from.
>> intel_dp_register_mst_connector() calls drm_connector_register(), which
>> fails to add the kobject (warning below).  But, it does zero error
>> checking on the drm_connector_register() call and leaves the
>> partially-constructed connector in place.
>>
>> The next time some poor, hapless code goes and tries to do anything with
>> that kdev, they oops.  I'm perplexed by this, though.  The
>> drm_dp_mst_topology_cbs->register_connector just returns void.  It seems
>> a bit goofy that it can't even _return_ failure.
>>
>> Is there some stable code to go back to here?  Or, is there something
>> about my configuration that's unique?  I really wonder why nobody else
>> is running into this.
>>
>> There's probably some other race going on here.  This warning doesn't
>> happen on every boot.
> This smells more like the root-cause: Something goes wrong on boot
> that prevents connectors from properly registering, then we fall over
> later on. And the register callback is intentionally void, assuming
> that any prep work has been done earlier and that therefore the
> register step can't fail. Can you pls check whether the oops later on
> only happens together with this warning at boot, or whether they're
> not correlated?

Looking through my logs, I can't find any instance of the oops without
the warning at boot.  So I do think the later oops is entirely caused by
the issue warned about in early boot.

My distro kernel (4.4.0-57-generic) is also unstable, but I haven't
managed to capture a good oops there.  It's hitting this, which I assume
is unrelated:

	WARNING: CPU: 0 PID: 41 at /build/linux-lts-xenial-FdAdUy/linux-
	lts-xenial-4.4.0/ubuntu/i915/intel_pm.c:3675
	skl_update_other_pipe_wm+0x191/0x1a0 [i915_bpo]()

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