[PATCH] mm: pte_offset_map_lock loops

Convert those common loops using page_table_lock on the outside and
pte_offset_map within to use just pte_offset_map_lock within instead.

These all hold mmap_sem (some exclusively, some not), so at no level can a
page table be whipped away from beneath them.  But whereas pte_alloc loops
tested with the "atomic" pmd_present, these loops are testing with pmd_none,
which on i386 PAE tests both lower and upper halves.

That's now unsafe, so add a cast into pmd_none to test only the vital lower
half: we lose a little sensitivity to a corrupt middle directory, but not
enough to worry about.  It appears that i386 and UML were the only
architectures vulnerable in this way, and pgd and pud no problem.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 3 insertions, 4 deletions

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 11d824f282f1..902d4c9eccdc 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -228,9 +228,9 @@ static int check_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
 {
         pte_t *orig_pte;
         pte_t *pte;
+        spinlock_t *ptl;
 
-        spin_lock(&vma->vm_mm->page_table_lock);
-        orig_pte = pte = pte_offset_map(pmd, addr);
+        orig_pte = pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
         do {
                 unsigned long pfn;
                 unsigned int nid;
@@ -246,8 +246,7 @@ static int check_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
                 if (!node_isset(nid, *nodes))
                         break;
         } while (pte++, addr += PAGE_SIZE, addr != end);
-        pte_unmap(orig_pte);
-        spin_unlock(&vma->vm_mm->page_table_lock);
+        pte_unmap_unlock(orig_pte, ptl);
         return addr != end;
 }