rmap: fix walk during fork
Andrea Arcangeli [Wed, 22 Sep 2010 20:05:12 +0000 (13:05 -0700)]
The below bug in fork led to the rmap walk finding the parent huge-pmd
twice instead of just once, because the anon_vma_chain objects of the
child vma still point to the vma->vm_mm of the parent.

The patch fixes it by making the rmap walk accurate during fork.  It's not
a big deal normally but it worth being accurate considering the cost is
the same.

Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Acked-by: Johannes Weiner <jweiner@redhat.com>
Acked-by: Rik van Riel <riel@redhat.com>
Acked-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/fork.c

index b7e9d60..c445f8c 100644 (file)
@@ -356,10 +356,10 @@ static int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm)
                if (IS_ERR(pol))
                        goto fail_nomem_policy;
                vma_set_policy(tmp, pol);
+               tmp->vm_mm = mm;
                if (anon_vma_fork(tmp, mpnt))
                        goto fail_nomem_anon_vma_fork;
                tmp->vm_flags &= ~VM_LOCKED;
-               tmp->vm_mm = mm;
                tmp->vm_next = tmp->vm_prev = NULL;
                file = tmp->vm_file;
                if (file) {