Bug 109956

https://intel-gfx-ci.01.org/tree/drm-tip/drmtip_216/fi-bsw-n3050/igt@kms_plane@plane-panning-bottom-right-suspend-pipe-c-planes.html

<4> [61.382525] ======================================================
<4> [61.382528] WARNING: possible circular locking dependency detected
<4> [61.382532] 5.0.0-rc5-g041ba1d6aa0f-drmtip_216+ #1 Tainted: G     U           
<4> [61.382535] ------------------------------------------------------
<4> [61.382538] kms_plane/1072 is trying to acquire lock:
<4> [61.382542] 00000000e7bea55b (&dev->struct_mutex){+.+.}, at: i915_gem_fault+0x1f8/0x850 [i915]
<4> [61.382656] 
but task is already holding lock:
<4> [61.382658] 00000000c73dd26a (&mm->mmap_sem){++++}, at: __do_page_fault+0x133/0x500
<4> [61.382668] 
which lock already depends on the new lock.