Comment 1 for bug 1545401

3133 static int do_numa_page(struct mm_struct *mm, struct vm_area_struct *vma,
3134 unsigned long addr, pte_t pte, pte_t *ptep, pmd_t *pmd)
3135 {
/* ... */
3144
3145 /* A PROT_NONE fault should not end up here */
3146 BUG_ON(!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE)));
3147

3235 static int handle_pte_fault(struct mm_struct *mm,
3236 struct vm_area_struct *vma, unsigned long address,
3237 pte_t *pte, pmd_t *pmd, unsigned int flags)
3238 {
/* ... */
3265 if (pte_protnone(entry))
3266 return do_numa_page(mm, vma, address, entry, pte, pmd);
3267

handle_pte_fault() appears to ensure that it calls do_numa_page() only on the exact condition do_numa_page() considers a bug.

http://lxr.free-electrons.com/source/mm/memory.c?v=4.2#L3146
http://lxr.free-electrons.com/source/mm/memory.c?v=4.2#L3266