On Fri, 14 Feb 2014 10:09:58 -0500 Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx> wrote: > Fengguang reported smatch error about potential NULL pointer access. > > In updated page table walker, we never run ->hugetlb_entry() callback > on the address without vma. This is because __walk_page_range() checks > it in advance. So we can assume non-NULL vma in pagemap_hugetlb(). > > ... > > --- a/fs/proc/task_mmu.c > +++ b/fs/proc/task_mmu.c > @@ -1032,9 +1032,9 @@ static int pagemap_hugetlb(pte_t *pte, unsigned long addr, unsigned long end, > pagemap_entry_t pme; > unsigned long hmask; > > - WARN_ON_ONCE(!vma); > + BUG_ON(!vma); Let's just remove it altogether. > - if (vma && (vma->vm_flags & VM_SOFTDIRTY)) > + if (vma->vm_flags & VM_SOFTDIRTY) The null deref oops will provide us the same info as the BUG_ON. It will require a *little* more thinking to work out that `vma' was NULL, but it will be pretty obvious. This requires knowing offsetof(vm_area_struct, vm_flags). I use a gdb macro: define offsetof set $off = &(((struct $arg0 *)0)->$arg1) printf "%d 0x%x\n", $off, $off end akpm3:/usr/src/25> gdb fs/proc/task_mmu.o ... (gdb) offsetof vm_area_struct vm_flags 80 0x50 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>