On Thu, Mar 06, 2025 at 12:25:53AM +0900, Ryosuke Yasuoka wrote: > Some drivers can use vmap in drm_panic, however, vmap is sleepable and > takes locks. Since drm_panic will vmap in panic handler, atomic_vmap > requests pages with GFP_ATOMIC and maps KVA without locks and sleep. In addition to the implicit GFP_KERNEL allocations Vlad mentioned, how is this supposed to work? > + vn = addr_to_node(va->va_start); > + > + insert_vmap_area(va, &vn->busy.root, &vn->busy.head); If someone else is holding the vn->busy.lock because they're modifying the busy tree, you'll corrupt the tree. You can't just say "I can't take a lock here, so I won't bother". You need to figure out how to do something safe without taking the lock. For example, you could preallocate the page tables and reserve a vmap area when the driver loads that would then be usable for the panic situation. I don't know that we have APIs to let you do that today, but it's something that could be added.
