drm/i915: Add object locking to vm_fault_cpu

Take a simple lock so we hold ww around (un)pin_pages as needed.
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20210323155059.628690-24-maarten.lankhorst@linux.intel.com

drivers/gpu/drm/i915/gem/i915_gem_mman.c

@@ -246,6 +246,9 @@ static vm_fault_t vm_fault_cpu(struct vm_fault *vmf)
 		     area->vm_flags & VM_WRITE))
 		return VM_FAULT_SIGBUS;
 
+	if (i915_gem_object_lock_interruptible(obj, NULL))
+		return VM_FAULT_NOPAGE;
+
 	err = i915_gem_object_pin_pages(obj);
 	if (err)
 		goto out;
@@ -269,6 +272,7 @@ static vm_fault_t vm_fault_cpu(struct vm_fault *vmf)
 	i915_gem_object_unpin_pages(obj);
 
 out:
+	i915_gem_object_unlock(obj);
 	return i915_error_to_vmf_fault(err);
 }