Building with the attached random configuration file,

mm/mempool.c: In function 'check_element':
mm/mempool.c:65:3: error: implicit declaration of function
'kmap_atomic' [-Werror=implicit-function-declaration]
   void *addr = kmap_atomic((struct page *)element);
   ^
mm/mempool.c:65:16: warning: initialization makes pointer from integer
without a cast
   void *addr = kmap_atomic((struct page *)element);
                ^
mm/mempool.c:68:3: error: implicit declaration of function
'kunmap_atomic' [-Werror=implicit-function-declaration]
   kunmap_atomic(addr);
   ^
mm/mempool.c: In function 'poison_element':
mm/mempool.c:89:16: warning: initialization makes pointer from integer
without a cast
   void *addr = kmap_atomic((struct page *)element);
                ^