[PATCH] follow_hugetlb_page fix

From: William Lee Irwin III <wli@holomorphy.com>

follow_hugetlb_page() drops out of the loop prematurely and fails to take the
appropriate refcounts if its starting address was not hugepage-aligned.

It looked a bit unclean too, so I rewrote it.  This fixes a bug, and more
importantly, makes the thing readable by something other than a compiler
(e.g.  programmers).

diff --git a/arch/i386/mm/hugetlbpage.c b/arch/i386/mm/hugetlbpage.c
index 6b37833292aa997224af12fced72a79e349e58be..9023cb2a605cf416deea201ad248c0fdbbcb5d91 100644 (file)
--- a/arch/i386/mm/hugetlbpage.c
+++ b/arch/i386/mm/hugetlbpage.c
@@ -129,37 +129,45 @@ nomem:
 int
 follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
                    struct page **pages, struct vm_area_struct **vmas,
-                   unsigned long *st, int *length, int i)
+                   unsigned long *position, int *length, int i)
 {
-       pte_t *ptep, pte;
-       unsigned long start = *st;
-       unsigned long pstart;
-       int len = *length;
-       struct page *page;
+       unsigned long vpfn, vaddr = *position;
+       int remainder = *length;
+
+       WARN_ON(!is_vm_hugetlb_page(vma));
 
-       do {
-               pstart = start;
-               ptep = huge_pte_offset(mm, start);
-               pte = *ptep;
+       vpfn = vaddr/PAGE_SIZE;
+       while (vaddr < vma->vm_end && remainder) {
 
-back1:
-               page = pte_page(pte);
                if (pages) {
-                       page += ((start & ~HPAGE_MASK) >> PAGE_SHIFT);
+                       pte_t *pte;
+                       struct page *page;
+
+                       pte = huge_pte_offset(mm, vaddr);
+
+                       /* hugetlb should be locked, and hence, prefaulted */
+                       WARN_ON(!pte || pte_none(*pte));
+
+                       page = &pte_page(*pte)[vpfn % (HPAGE_SIZE/PAGE_SIZE)];
+
+                       WARN_ON(!PageCompound(page));
+
                        get_page(page);
                        pages[i] = page;
                }
+
                if (vmas)
                        vmas[i] = vma;
-               i++;
-               len--;
-               start += PAGE_SIZE;
-               if (((start & HPAGE_MASK) == pstart) && len &&
-                               (start < vma->vm_end))
-                       goto back1;
-       } while (len && start < vma->vm_end);
-       *length = len;
-       *st = start;
+
+               vaddr += PAGE_SIZE;
+               ++vpfn;
+               --remainder;
+               ++i;
+       }
+
+       *length = remainder;
+       *position = vaddr;
+
        return i;
 }