On Wed, Mar 07, 2012 at 06:08:52PM +0000, Mel Gorman wrote:
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index 06b145f..013d981 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -1843,18 +1843,24 @@ struct page *
> alloc_pages_vma(gfp_t gfp, int order, struct vm_area_struct *vma,
> unsigned long addr, int node)
> {
> - struct mempolicy *pol = get_vma_policy(current, vma, addr);
> + struct mempolicy *pol;
> struct zonelist *zl;
> struct page *page;
> + unsigned int cpuset_mems_cookie;
> +
> +retry_cpuset:
> + pol = get_vma_policy(current, vma, addr);
> + cpuset_mems_cookie = get_mems_allowed();
>
> - get_mems_allowed();
> if (unlikely(pol->mode == MPOL_INTERLEAVE)) {
> unsigned nid;
>
> nid = interleave_nid(pol, vma, addr, PAGE_SHIFT + order);
> mpol_cond_put(pol);
> page = alloc_page_interleave(gfp, order, nid);
> - put_mems_allowed();
> + if (unlikely(!put_mems_allowed(cpuset_mems_cookie) && !page))
> + goto retry_cpuset;
> +
> return page;
> }
> zl = policy_zonelist(gfp, pol, node);
So I think this patch is broken (still). Suppose we have an
INTERLEAVE mempol like 0x3 and change it to 0xc.
Original: 0x3
Rebind Step 1: 0xf /* set bits */
Rebind Step 2: 0xc /* clear bits */
Now look at what can happen with offset_il_node() when its ran
concurrently with step 2:
nnodes = nodes_weight(pol->v.nodes); /* observes 0xf and returns 4 */
/* now we clear the actual bits */
target = (unsigned int)off % nnodes; /* assume target >= 2 */
c = 0;
do {
nid = next_node(nid, pol->v.nodes);
c++;
} while (c <= target);
/* here nid := MAX_NUMNODES */
This nid is then blindly inserted into node_zonelist() which does an
NODE_DATA() array access out of bounds and off we go.
This would suggest we put the whole seqcount thing inside
offset_il_node().
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