Issue with DRM and "reimplement IDR and IDA using the radix tree"

[Alexandre Courbot]

On 12/17/2016 01:16 AM, Thierry Reding wrote:
> * PGP Signed by an unknown key
> 
> On Wed, Dec 14, 2016 at 11:08:20PM +0900, Alexandre Courbot wrote:
>> Forgot to add the most relevant list for this issue (linux-next).
>>
>> Stephen, maybe you will want to temporarily revert this patch until this
>> is cleared? This probably affects other users than DRM.
>>
>> On 12/13/2016 04:14 PM, Alexandre Courbot wrote:
>>> Hi Matthew,
>>>
>>> Trying the latest -next on the Jetson TK1 board (with two different DRM
>>> devices and display and render), I noticed that the GPU device probe
>>> always failed with error -ENOSPC. After investigating I figured out that
>>> this was due to the minor device allocation failing when a second DRM
>>> device is added.
>>>
>>> More precisely, when drm_minor_alloc() is called with DRM_MINOR_PRIMARY
>>> (0) as argument for a second time, the call to idr_alloc() (which has a
>>> requested range of 0..64) fails instead of returning 1 as expected. Note
>>> that the first call is successful.
>>>
>>> Reverting "reimplement IDR and IDA using the radix tree" on 20161213's
>>> next fixes the issue for me, suggesting a bug may have slipped in there.
>>>
>>> Not sure how this could be fixed, so reporting the issue for now in case
>>> it is not known yet.
> 
> I can confirm Alex' findings, though the symptoms seem to be slightly
> different, which may be related to me testing on next-20161216 rather
> than next-20161213.
> 
> What I'm seeing is that all drivers get probed correctly, but when an
> application tries to open the DRM device files (/dev/dri/card0 in this
> case), then all devices of a given minor type disappear. So in my case
> upon boot I get this:
> 
> 	# ls -l /dev/dri/
> 	total 0
> 	crw-rw---- 1 root video 226,   0 Dec 16 15:59 card0
> 	crw-rw---- 1 root video 226,   1 Dec 16 15:59 card1
> 	crw-rw---- 1 root video 226, 128 Dec 16 15:59 renderD128
> 
> The modetest program from libdrm is then unable to open any devices:
> 
> 	# modetest
> 	trying to open device 'i915'...failed
> 	trying to open device 'amdgpu'...failed
> 	trying to open device 'radeon'...failed
> 	trying to open device 'nouveau'...failed
> 	trying to open device 'vmwgfx'...failed
> 	trying to open device 'omapdrm'...failed
> 	trying to open device 'exynos'...failed
> 	trying to open device 'tilcdc'...failed
> 	trying to open device 'msm'...failed
> 	trying to open device 'sti'...failed
> 	trying to open device 'tegra'...failed
> 	trying to open device 'imx-drm'...failed
> 	trying to open device 'rockchip'...failed
> 	trying to open device 'atmel-hlcdc'...failed
> 	trying to open device 'fsl-dcu-drm'...failed
> 	trying to open device 'vc4'...failed
> 	trying to open device 'virtio_gpu'...failed
> 	trying to open device 'mediatek'...failed
> 	no device found
> 
> And after that all of the primary minors are gone:
> 
> 	# ls -l /dev/dri/
> 	total 0
> 	crw-rw---- 1 root video 226, 128 Dec 16 15:59 renderD128

That's exactly what I am also getting with 20161216. As it turns out the
patch has changed slightly (my revert did not apply after a rebase), and
the symptoms changed against 20161215, but the fix is the same:
reverting gives me back a working system.

This patch really should be reverted for now. Like Thierry I am
available to test further iterations.