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SubjectRe: [PATCH 5/5] mempolicy: fix a memory corruption by refcount imbalance in alloc_pages_vma()
On Mon, 20 Aug 2012, Mel Gorman wrote:

> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index 45f9825..82e872f 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -1545,15 +1545,28 @@ struct mempolicy *get_vma_policy(struct task_struct *task,
> struct vm_area_struct *vma, unsigned long addr)
> {
> struct mempolicy *pol = task->mempolicy;
> + int got_ref;

New variable. Need to set it to zero?

>
> if (vma) {
> if (vma->vm_ops && vma->vm_ops->get_policy) {
> struct mempolicy *vpol = vma->vm_ops->get_policy(vma,
> addr);
> - if (vpol)
> + if (vpol) {
> pol = vpol;
> - } else if (vma->vm_policy)
> + got_ref = 1;

Set the new variable. But it was not initialzed before. So now its 1 or
undefined?

> + }
> + } else if (vma->vm_policy) {
> pol = vma->vm_policy;
> +
> + /*
> + * shmem_alloc_page() passes MPOL_F_SHARED policy with
> + * a pseudo vma whose vma->vm_ops=NULL. Take a reference
> + * count on these policies which will be dropped by
> + * mpol_cond_put() later
> + */
> + if (mpol_needs_cond_ref(pol))
> + mpol_get(pol);
> + }
> }
> if (!pol)
> pol = &default_policy;
>

I do not see any use of got_ref. Can we get rid of the variable?




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