i915 hang and large allocation (~3.7-rc4)

i915 hang and large allocation (~3.7-rc4)

[Dave Hansen]

I've been seeing a little goofiness with i915 video under the 3.7-rc's.
It looks like I'm seeing two separate issues.  One, that the video
hardware hangs, spits some errors in dmesg, and then video acceleration
seems to stop working.  Two, when it does this, apport goes digging in
debugfs for information about the hang.  When it does this, something
does an order-9 (2MB) kmalloc() which fails.

While debugfs is expected to be a _bit_ rickety, I do think order-9
is a bit excessive for an in-kernel allocation, even a temporary
one.  I'm not quite sure if it has done this for a long time, and I'm
only hitting it now since I'm seeing a _separate_ i915 hang.

Relevant parts of dmesg, lspci, and kernel config are here:

	http://sr71.net/~dave/linux/i915-wonky/

Re: i915 hang and large allocation (~3.7-rc4)

[Daniel Vetter]

On Mon, Nov 12, 2012 at 02:44:46PM -0800, Dave Hansen wrote:
> I've been seeing a little goofiness with i915 video under the 3.7-rc's.
> It looks like I'm seeing two separate issues.  One, that the video
> hardware hangs, spits some errors in dmesg, and then video acceleration
> seems to stop working.  Two, when it does this, apport goes digging in
> debugfs for information about the hang.  When it does this, something
> does an order-9 (2MB) kmalloc() which fails.
> 
> While debugfs is expected to be a _bit_ rickety, I do think order-9
> is a bit excessive for an in-kernel allocation, even a temporary
> one.  I'm not quite sure if it has done this for a long time, and I'm
> only hitting it now since I'm seeing a _separate_ i915 hang.
> 
> Relevant parts of dmesg, lspci, and kernel config are here:
> 
> 	http://sr71.net/~dave/linux/i915-wonky/

Ironlake gpu, so if this is a regression introduced in 3.7 and things work
normally in 3.6, it's likely that you're hitting a variant of

https://bugs.freedesktop.org/show_bug.cgi?id=55984

It'd be best if you can subscribe yourselfes there, so that all potential
testers are at the same place.

For the 2MB allocation, this is a known problem, unfortunately reworking
the dump code will be major work. Which is why it hasn't been done yet.
But fixing that is somewhere on our giant todo list.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch