test: race condition on DRI2 buffers allocation when going fullscreen

This test program exposes a problem related to window resizing
(or going fullscreen), which is may happen exactly between "back"
and "front" DRI2 buffers allocation.

The xtrace log with some annotations:

000:<:004c:  8: DRI2-Request(151,3): CreateDrawable drawable=0x02200001
000:<:004d: 16: DRI2-Request(151,5): GetBuffers drawable=0x02200001 attachments={attachment=BackLeft(0x00000001)};
000:>:004d:52: Reply to GetBuffers: width=480 height=480 buffers={attachment=BackLeft(0x00000001)
                                    name=0x00000157 pitch=1920 cpp=4 flags=0x00000000};

Get the BackLeft buffer.

000:<:004e:  4: Request(43): GetInputFocus
000:>:004e:32: Reply to GetInputFocus: revert-to=PointerRoot(0x01) focus=0x02200001
000:<:004f: 24: Request(16): InternAtom only-if-exists=false(0x00) name='_NET_WM_STATE'
000:>:004f:32: Reply to InternAtom: atom=0xff("_NET_WM_STATE")
000:<:0050: 32: Request(16): InternAtom only-if-exists=false(0x00) name='_NET_WM_STATE_FULLSCREEN'
000:>:0050:32: Reply to InternAtom: atom=0x102("_NET_WM_STATE_FULLSCREEN")
000:<:0051: 44: Request(25): SendEvent propagate=false(0x00) destination=0x00000170 event-mask=SubstructureNotify,SubstructureRedirect
                             ClientMessage(33) format=0x20 window=0x02200001 type=0xff("_NET_WM_STATE")
                             data=0x01,0x00,0x00,0x00,0x02,0x01,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00;
000:<:0052:  4: Request(43): GetInputFocus
000:>:0052: Event DRI2-InvalidateBuffers(102) drawable=0x02200001

Here the X server attempts to notify the client side DRI2 code in the Mali blob
that the DRI2 buffer must be requested again. But this event gets happily ignored.

000:>:0052: Event Expose(12) window=0x02200001 x=0 y=0 width=1920 height=1080 count=0x0000
000:>:0052:32: Reply to GetInputFocus: revert-to=PointerRoot(0x01) focus=0x02200001
000:<:0053:  8: Request(3): GetWindowAttributes window=0x02200001
000:<:0054:  8: Request(14): GetGeometry drawable=0x02200001
000:>:0053:44: Reply to GetWindowAttributes: backing-store=NotUseful(0x00) visual=0x00000021 class=InputOutput(0x0001)
                                             bit-gravity=Forget(0x00) win-gravity=NorthWest(0x01) backing-planes=0xffffffff
                                             backing-pixel=0x00000000 save-under=false(0x00) map-is-installed=true(0x01)
                                             map-state=Viewable(0x02) override-redirect=false(0x00) colormap=0x00000020
                                             all-event-masks=PointerMotion,Exposure,StructureNotify,FocusChange,PropertyChange
                                             your-event-mask=PointerMotion,Exposure do-not-propagate-mask=0 unused=0x0000
000:>:0054:32: Reply to GetGeometry: depth=0x18 root=0x00000170 x=0 y=0 width=1920 height=1080 border-width=0
001:<:000c: 12: Request(98): QueryExtension name='DRI2'
001:>:000c:32: Reply to QueryExtension: present=true(0x01) major-opcode=151 first-event=101 first-error=0
001:<:000d: 32: DRI2-Request(151,8): SwapBuffers drawable=0x02200001 target_msc_hi=0 target_msc_lo=0
                                     divisor_hi=0 divisor_lo=0 remainder_hi=0 remainder_lo=0
001:>:000d: Event DRI2-BufferSwapComplete(101) drawable=0x00000002 ust_hi=35651585 ust_lo=0 msc_hi=0 msc_lo=0 sbc_hi=0 sbc_lo=1

Here the DRI2 code from the Mali blob tries to swap buffers (with the
hope that the allocated BackLeft would go to front)

001:>:000d:32: Reply to SwapBuffers: swap_hi=0 swap_lo=4096
000:<:0055:  8: DRI2-Request(151,3): CreateDrawable drawable=0x02200001
000:<:0056: 16: DRI2-Request(151,5): GetBuffers drawable=0x02200001 attachments={attachment=BackLeft(0x00000001)};
000:>:0056:52: Reply to GetBuffers: width=1920 height=1080 buffers={attachment=BackLeft(0x00000001)
                                    name=0x00000159 pitch=7680 cpp=4 flags=0x00000000};

And requests for the new BackLeft DRI2 buffer.

000:<:0057:  4: Request(43): GetInputFocus
000:>:0057:32: Reply to GetInputFocus: revert-to=PointerRoot(0x01) focus=0x02200001
000:<:0058:  8: Request(3): GetWindowAttributes window=0x02200001
000:<:0059:  8: Request(14): GetGeometry drawable=0x02200001
000:>:0058:44: Reply to GetWindowAttributes: backing-store=NotUseful(0x00) visual=0x00000021 class=InputOutput(0x0001)
                                             bit-gravity=Forget(0x00) win-gravity=NorthWest(0x01) backing-planes=0xffffffff
                                             backing-pixel=0x00000000 save-under=false(0x00) map-is-installed=true(0x01)
                                             map-state=Viewable(0x02) override-redirect=false(0x00) colormap=0x00000020
                                             all-event-masks=PointerMotion,Exposure,StructureNotify,FocusChange,PropertyChange
                                             your-event-mask=PointerMotion,Exposure do-not-propagate-mask=0 unused=0x0000
000:>:0059:32: Reply to GetGeometry: depth=0x18 root=0x00000170 x=0 y=0 width=1920 height=1080 border-width=0
000:<:005a:  8: Request(3): GetWindowAttributes window=0x02200001
000:<:005b:  8: Request(14): GetGeometry drawable=0x02200001
000:>:005a:44: Reply to GetWindowAttributes: backing-store=NotUseful(0x00) visual=0x00000021 class=InputOutput(0x0001)
                                             bit-gravity=Forget(0x00) win-gravity=NorthWest(0x01) backing-planes=0xffffffff
                                             backing-pixel=0x00000000 save-under=false(0x00) map-is-installed=true(0x01)
                                             map-state=Viewable(0x02) override-redirect=false(0x00) colormap=0x00000020
                                             all-event-masks=PointerMotion,Exposure,StructureNotify,FocusChange,PropertyChange
                                             your-event-mask=PointerMotion,Exposure do-not-propagate-mask=0 unused=0x0000
000:>:005b:32: Reply to GetGeometry: depth=0x18 root=0x00000170 x=0 y=0 width=1920 height=1080 border-width=0
001:<:000e: 32: DRI2-Request(151,8): SwapBuffers drawable=0x02200001 target_msc_hi=0 target_msc_lo=0
                                     divisor_hi=0 divisor_lo=0 remainder_hi=0 remainder_lo=0
001:>:000e: Event DRI2-BufferSwapComplete(101) drawable=0x00000002 ust_hi=35651585 ust_lo=0 msc_hi=0 msc_lo=0 sbc_hi=0 sbc_lo=2

And here it is simply swapping the buffers.

001:>:000e:32: Reply to SwapBuffers: swap_hi=0 swap_lo=4096
000:<:005c:  8: Request(3): GetWindowAttributes window=0x02200001
000:<:005d:  8: Request(14): GetGeometry drawable=0x02200001
000:>:005c:44: Reply to GetWindowAttributes: backing-store=NotUseful(0x00) visual=0x00000021 class=InputOutput(0x0001)
                                             bit-gravity=Forget(0x00) win-gravity=NorthWest(0x01) backing-planes=0xffffffff
                                             backing-pixel=0x00000000 save-under=false(0x00) map-is-installed=true(0x01)
                                             map-state=Viewable(0x02) override-redirect=false(0x00) colormap=0x00000020
                                             all-event-masks=PointerMotion,Exposure,StructureNotify,FocusChange,PropertyChange
                                             your-event-mask=PointerMotion,Exposure do-not-propagate-mask=0 unused=0x0000
000:>:005d:32: Reply to GetGeometry: depth=0x18 root=0x00000170 x=0 y=0 width=1920 height=1080 border-width=0

And now it is polling for the change of window geometry. The same
"SwapBuffers -> GetGeometry -> SwapBuffers" pattern keeps repeating.

Signed-off-by: Siarhei Siamashka <siarhei.siamashka@gmail.com>