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

[Dave Airlie]

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?

Dave.