LinuxKPI interval 'tree' is an O(N) circular list — sole live consumer (radeon_vm.c GEM_VA path) turns it into unprivileged per-ioctl O(N) kernel scans (O(N^2) mapping churn), a kernel-CPU amplification DoS on radeon-equipped systems

Summary

The shim implements the API as a circular list where every ported driver assumes an O(log N) rbtree: the ONLY live consumer is radeon_vm's GEM_VA ioctl path - each map/unmap/removal walks the full list under vm->mutex. Unpriv render user with N~1e5 mapped nodes drives O(N^2) kernel pointer-chase churn, again en masse at teardown. Hardware-gated (radeon GPU); mechanism certain. INTERVAL_TREE_DEFINE fix (the template already ships in drm_mm.c).