Summary

vmap_lock acquired ONLY around SLIST_INSERT_HEAD in vmap() (64-66) and around SLIST_REMOVE in vunmap() (88-90). List-traversal reads -- search loop in vunmap() (77-85) and entire is_vmalloc_addr() (99-102) -- walk global vmap_list with NO lock. Process-wide singly-linked list shared by every DRM buffer operation. Concurrent vmap()/vunmap()/is_vmalloc_addr() pair corrupts list reads freed memory or causes vunmap search to follow stale ->sle_next into freed vmap struct (UAF). SLIST_FOREACH_MUTABLE tmp_vmp prefetch does not protect against concurrently freed head. Two threads vunmap() same addr (i915 dmabuf vunmap path racing GEM-object-destroy vunmap) both find entry unlocked both kmem_free and kfree: double-free of kernel_map VA and M_DRM slab object exploitable for arbitrary kernel code execution via slab grooming. Reachable: local user DRM device access N threads GEM create+mmap+close/destroy loop i915 routes pin/unpin through vmap/vunmap/is_vmalloc_addr on global list no per-list serialization. Impact panic through heap UAF/double-free potential LPE.