Re: [PATCH v4] mm/hugetlb: Fix unsigned overflow in __nr_hugepages_store_common()

Oscar Salvador
2019-03-06T09:41:38Z

On Mon, Mar 04, 2019 at 08:15:40PM -0800, Mike Kravetz wrote:
> In addition, the code in __nr_hugepages_store_common() which tries to
> handle the case of not being able to allocate a node mask would likely
> result in incorrect behavior. Luckily, it is very unlikely we will
> ever take this path. If we do, simply return ENOMEM.

Hi Mike,

I still thnk that we could just get rid of the NODEMASK_ALLOC machinery
here, it adds a needlessly complexity IMHO.
Note that before "(5df66d306ec9: mm: fix comment for NODEMASK_ALLOC)",
the comment about the size was wrong, showing a much bigger size that it
actually was, and I would not be surprised if people started to add
NODEMASK_ALLOC here and there because of that.

Actually, there was a little talk about removing NODEMASK_ALLOC altogether,
but some further checks must be done before.

> Reported-by: Jing Xiangfeng <jingxiangfeng@huawei.com>
> Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>

But the overall change looks good to me:

Reviewed-by: Oscar Salvador <osalvador@suse.de>

> ---
> mm/hugetlb.c | 42 +++++++++++++++++++++++++++++++++---------
> 1 file changed, 33 insertions(+), 9 deletions(-)
>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index c5c4558e4a79..5a190a652cac 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -2274,7 +2274,7 @@ static int adjust_pool_surplus(struct hstate *h, nodemask_t *nodes_allowed,
> }
>
> #define persistent_huge_pages(h) (h->nr_huge_pages - h->surplus_huge_pages)
> -static int set_max_huge_pages(struct hstate *h, unsigned long count,
> +static int set_max_huge_pages(struct hstate *h, unsigned long count, int nid,
> nodemask_t *nodes_allowed)
> {
> unsigned long min_count, ret;
> @@ -2289,6 +2289,28 @@ static int set_max_huge_pages(struct hstate *h, unsigned long count,
> goto decrease_pool;
> }
>
> + spin_lock(&hugetlb_lock);
> +
> + /*
> + * Check for a node specific request.
> + * Changing node specific huge page count may require a corresponding
> + * change to the global count. In any case, the passed node mask
> + * (nodes_allowed) will restrict alloc/free to the specified node.
> + */
> + if (nid != NUMA_NO_NODE) {
> + unsigned long old_count = count;
> +
> + count += h->nr_huge_pages - h->nr_huge_pages_node[nid];
> + /*
> + * User may have specified a large count value which caused the
> + * above calculation to overflow. In this case, they wanted
> + * to allocate as many huge pages as possible. Set count to
> + * largest possible value to align with their intention.
> + */
> + if (count < old_count)
> + count = ULONG_MAX;
> + }
> +
> /*
> * Increase the pool size
> * First take pages out of surplus state. Then make up the
> @@ -2300,7 +2322,6 @@ static int set_max_huge_pages(struct hstate *h, unsigned long count,
> * pool might be one hugepage larger than it needs to be, but
> * within all the constraints specified by the sysctls.
> */
> - spin_lock(&hugetlb_lock);
> while (h->surplus_huge_pages && count > persistent_huge_pages(h)) {
> if (!adjust_pool_surplus(h, nodes_allowed, -1))
> break;
> @@ -2421,16 +2442,19 @@ static ssize_t __nr_hugepages_store_common(bool obey_mempolicy,
> nodes_allowed = &node_states[N_MEMORY];
> }
> } else if (nodes_allowed) {
> + /* Node specific request */
> + init_nodemask_of_node(nodes_allowed, nid);
> + } else {
> /*
> - * per node hstate attribute: adjust count to global,
> - * but restrict alloc/free to the specified node.
> + * Node specific request, but we could not allocate the few
> + * words required for a node mask. We are unlikely to hit
> + * this condition. Since we can not pass down the appropriate
> + * node mask, just return ENOMEM.
> */
> - count += h->nr_huge_pages - h->nr_huge_pages_node[nid];
> - init_nodemask_of_node(nodes_allowed, nid);
> - } else
> - nodes_allowed = &node_states[N_MEMORY];
> + return -ENOMEM;
> + }
>
> - err = set_max_huge_pages(h, count, nodes_allowed);
> + err = set_max_huge_pages(h, count, nid, nodes_allowed);
> if (err)
> goto out;
>
> --
> 2.17.2
>

--
Oscar Salvador
SUSE L3