linux-kernel - Re: [Intel-gfx] [Regression] BUG: unable to handle kernel NULL pointer dereference

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Message-ID: <20150301093001.GA1696@nest>
Date:	Sun, 1 Mar 2015 12:30:01 +0300
From:	Andrey Skvortsov <andrej.skvortzov@...il.com>
To:	Chris Wilson <chris@...is-wilson.co.uk>,
	Daniel Vetter <daniel.vetter@...el.com>,
	Jani Nikula <jani.nikula@...ux.intel.com>,
	David Airlie <airlied@...ux.ie>,
	intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org, Sitsofe Wheeler <sitsofe@...il.com>
Subject: Re: [Intel-gfx] [Regression] BUG: unable to handle kernel NULL
 pointer dereference

On 01 Mar, Chris Wilson wrote:
> On Sun, Mar 01, 2015 at 12:57:01AM +0300, Andrey Skvortsov wrote:
> > On 28 Feb, Chris Wilson wrote:
> > > On Sat, Feb 28, 2015 at 03:20:37PM +0300, Andrey Skvortsov wrote:
> > > > Unfortunately this is not the last bug, that breaks i915/drm working
> > > > on my laptop. Sometimes system successfully loads with couple warnings mentioned in
> > > > previous mail:
> > > > 
> > > > [   26.922953] WARNING: CPU: 1 PID: 767 at drivers/gpu/drm/i915/i915_gem.c:4525 i915_gem_free_object+0x13f/0x288 [i915]()
> > > > [   26.922954] WARN_ON(obj->frontbuffer_bits)
> > > 
> > > That's inocuous, but for the serious hang, you may want to try
> > > video=SVIDEO-1:d on the kernel commandline to workaround the hang. (Check
> > > /sys/class/drm/card/ for the actual name of the connector for TV). I
> > > think Ville mentioned he was looking/looked at the atomic-vs-load_detect
> > > changes that is at the heart of the issue here. (Admittedly he did say
> > > it was worthy of a drink or two.)
> > > -Chris
> > 
> > Thank you for the help. I've tried to add to the kernel command line
> > 'video=card0-SVIDEO-1:d video=card0-VGA-1:d'. But despite of that
> > kernel crashes with 'BUG: unable to handle kernel NULL pointer
> > dereference at' occasionally.
> 
> Remove the card0- and combine both into a single video= stanza:
> video=SVIDEO-1:d,VGA-1:d

I've just tried that, but the crash with NULL pointer dereference still happens.

-- 
Best regards,
Andrey Skvortsov

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