drm/imagination: Break an object reference loop

Summary

In the Linux kernel, the following vulnerability has been resolved: drm/imagination: Break an object reference loop When remaining resources are being cleaned up on driver close, outstanding VM mappings may result in resources being leaked, due to an object reference loop, as shown below, with each object (or set of objects) referencing the object below it: PVR GEM Object GPU scheduler "finished" fence GPU scheduler “scheduled” fence PVR driver “done” fence PVR Context PVR VM Context PVR VM Mappings PVR GEM Object The reference that the PVR VM Context has on the VM mappings is a soft one, in the sense that the freeing of outstanding VM mappings is done as part of VM context destruction; no reference counts are involved, as is the case for all the other references in the loop. To break the reference loop during cleanup, free the outstanding VM mappings before destroying the PVR Context associated with the VM context.