[PATCH] xfree86: detach scanout pixmaps when detaching output GPUs

[Aaron Plattner]

On 05/06/2013 03:43 PM, Dave Airlie wrote:
> On Tue, May 7, 2013 at 6:17 AM, Aaron Plattner <aplattner at nvidia.com> wrote:
>> On 05/05/2013 04:23 PM, Dave Airlie wrote:
>>>
>>> On Thu, May 2, 2013 at 5:55 AM, Aaron Plattner <aplattner at nvidia.com>
>>> wrote:
>>>>
>>>> On 04/30/2013 11:30 PM, Dave Airlie wrote:
>>>>>
>>>>> On Wed, May 1, 2013 at 7:14 AM, Aaron Plattner <aplattner at nvidia.com>
>>>>> wrote:
>>>>>>
>>>>>> Commit 8f4640bdb9d3988148e09a08d2c7e3bab1d538d6 fixed a bit of a
>>>>>> chicken-and-egg problem by detaching GPU screens when their providers
>>>>>> are destroyed, which happens before CloseScreen is called.  However,
>>>>>> this created a new problem: the GPU screen tears down its RandR crtc
>>>>>> objects during CloseScreen and if one of them is active, it tries to
>>>>>> detach the scanout pixmap then.  This crashes because
>>>>>> RRCrtcDetachScanoutPixmap tries to get the master screen's screen
>>>>>> pixmap, but crtc->pScreen->current_master is already NULL at that
>>>>>> point.
>>>>>>
>>>>>> It doesn't make sense for an unbound GPU screen to still be scanning
>>>>>> out its former master screen's pixmap, so detach them first when the
>>>>>> provider is destroyed.
>>>>>
>>>>>
>>>>> Any instructions on how to reproduce this? I've been trying to get it
>>>>> to happen here.
>>>>
>>>>
>>>> 1. Start X on an Intel system with a DisplayLink device attached.
>>>> 2. xrandr --setprovideroutputsource 1 0
>>>> 3. xrandr --output DVI-0 --off (unless you apply "xfree86: don't enable
>>>> anything in xf86InitialConfiguration for GPU screens")
>>>> 4. xrandr --auto
>>>> 5. Terminate the X server.
>>>>
>>>> Program received signal SIGSEGV, Segmentation fault.
>>>> 0x8010be62 in RRCrtcDetachScanoutPixmap (crtc=crtc at entry=0x80259740) at
>>>> ../../randr/rrcrtc.c:370
>>>> 370     ../../randr/rrcrtc.c: No such file or directory.
>>>> (gdb) bt
>>>> #0  0x8010be62 in RRCrtcDetachScanoutPixmap (crtc=crtc at entry=0x80259740)
>>>> at ../../randr/rrcrtc.c:370
>>>> #1  0x8010bfab in RRCrtcDestroyResource (value=0x80259740, pid=63) at
>>>> ../../randr/rrcrtc.c:678
>>>> #2  0x80062fbe in doFreeResource (res=0x8025bc58, skip=skip at entry=0) at
>>>> ../../dix/resource.c:873
>>>> #3  0x8006415b in FreeClientResources (client=0x8023f350) at
>>>> ../../dix/resource.c:1139
>>>> #4  0x800641fc in FreeAllResources () at ../../dix/resource.c:1154
>>>> #5  0x8002b556 in main (argc=3, argv=0xbffff704, envp=0xbffff714) at
>>>> ../../dix/main.c:321
>>>> (gdb) p crtc->pScreen->current_master
>>>> $1 = (ScreenPtr) 0x0
>>>> (gdb) p crtc->pScreen->myNum
>>>> $2 = 256
>>>>
>>>>> I did notice that xrandr is now broken for detach? how are you detaching
>>>>> btw?
>>>>> xrandr --setoutputprovidersource 0x67 0x0 should detach I would think,
>>>>> but it fails now.
>>>>
>>>>
>>>> Yeah, I noticed that too, and hacked it up to allow me to test it.  I'll
>>>> try to clean up the change for review.
>>>>
>>>> The crash doesn't occur at detach time or if I pull the USB cable.
>>>
>>>
>>> I'm having absolutely no luck reproducing this with the X server
>>> master + my for-keithp tree pulled in.
>>>
>>> I'm not sure what I could be doing different than you are, I've even
>>> valgrinded it.
>>
>>
>> That's really weird.  I wonder if stuff is initializing in a different order
>> on your system for some reason.  I just rebuilt at commit
>> 2746c681639f9512e6e45fb8d0151b996b6aff7f and verified that the problem still
>> occurs.
>
> Can you attach a full Xorg log where it happens?

Attached.  I built the server from commit 
6993f8b459e25b1a7a0a03e209688a28ce6c2c56 this time.

-- 
Aaron
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