Re: [git pull] drm for 3.19-rc1

[Daniel Vetter <daniel@ffwll.ch>]

On Mon, Dec 15, 2014 at 04:35:29PM -0800, Linus Torvalds wrote:
> On Sun, Dec 14, 2014 at 11:17 PM, Dave Airlie <airlied@linux.ie> wrote:
> >
> > i915:
> >         Initial Skylake (SKL) support
> >         gen3/4 reset work
> >         start of dri1/ums removal
> >         infoframe tracking
> >         fixes for lots of things.
> 
> So I'm not sure how happy I am about this. It seems to work, but on
> the very first boot I get this:
> 
>   ------------[ cut here ]------------
>   WARNING: CPU: 1 PID: 1292 at
> drivers/gpu/drm/i915/i915_gem_execbuffer.c:125
> eb_lookup_vmas.isra.18+0x333/0x3d0 [i915]()
>   GPU use of dumb buffer is illegal.
>   Modules linked in: ip6t_rpfilter bnep ip6t_REJECT nf_reject_ipv6
> bluetooth nf_conntrack_ipv6 ...
>    video
>   CPU: 1 PID: 1292 Comm: Xorg Not tainted 3.18.0-09423-g988adfdffdd4 #1
>   Hardware name:                  /DH87RL, BIOS
> RLH8710H.86A.0327.2014.0924.1645 09/24/2014
>   Call Trace:
>     dump_stack+0x45/0x57
>     warn_slowpath_common+0x80/0xc0
>     warn_slowpath_fmt+0x41/0x50
>     ? sg_kfree+0x30/0x30
>     eb_lookup_vmas.isra.18+0x333/0x3d0 [i915]
>     i915_gem_do_execbuffer.isra.25+0x50d/0xd80 [i915]
>     ? unlock_page+0x6d/0x80
>     i915_gem_execbuffer2+0xb1/0x2c0 [i915]
>     drm_ioctl+0x19c/0x630 [drm]
>     do_vfs_ioctl+0x2e0/0x4e0
>     ? file_has_perm+0x87/0xa0
>     ? __audit_syscall_entry+0xac/0x100
>     SyS_ioctl+0x81/0xa0
>     ? do_page_fault+0xc/0x10
>     system_call_fastpath+0x12/0x17
>   ---[ end trace cb3c78163212ca1d ]---
> 
> apparently Introduced by commit 355a70183848 ("drm/gem: Warn on
> illegal use of the dumb buffer interface v2")
> 
> The commit says "the next step is to fail".
> 
> And I want to make it painfully clear that if somebody breaks existing
> working setups, they don't get to work on the kernel.
> 
> So get rid of the warning. And get rid of the notion that you can just
> fail. You can try to fix Xorg, and then come back to this - in a
> couple of years - when it no longer happens.

Yeah this patch should have been merged ever, I guess Chris reply' in the
original was lost. Anyway the real fail here is that we didn't spot this
in time. Well QA reported a bug, but 2 weeks after the patch landed, not
marked as a regression, not handled by the bug team and no one else seems
to have noticed either. Like I've mentioned at KS we have a bit a problem
with this stuff in i915 land, I'll chase people some more. Maybe it helps.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch