Comment 2 for bug 1496172

StacktraceTop:
 __kgem_retire_rq (kgem=kgem@entry=0x7facfc48c000, rq=rq@entry=0x7facfc48c4c0) at ../../../src/sna/kgem.c:3063
 __kgem_retire_requests_upto (kgem=0x7facfc48c000, bo=0x5609c855d610) at ../../../src/sna/kgem.c:3254
 kgem_bo_retire (bo=0x5609c855d610, kgem=0x7facfc48c000) at ../../../src/sna/kgem.c:781
 kgem_bo_sync__cpu (kgem=kgem@entry=0x7facfc48c000, bo=bo@entry=0x5609c855d610) at ../../../src/sna/kgem.c:6918
 write_boxes_inplace__tiled (kgem=0x7facfc48c000, src=src@entry=0x7face9893000 "", stride=stride@entry=128, bpp=bpp@entry=32, src_dx=src_dx@entry=0, src_dy=src_dy@entry=0, bo=0x5609c855d610, dst_dx=0, dst_dy=0, box=0x7ffef3fc96a0, n=1) at ../../../src/sna/sna_io.c:687