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

Naoya Horiguchi
2019-03-04T06:10:03Z

On Tue, Feb 26, 2019 at 11:32:24AM -0800, Mike Kravetz wrote:
> On 2/25/19 10:21 PM, David Rientjes wrote:
> > On Tue, 26 Feb 2019, Jing Xiangfeng wrote:
> >> On 2019/2/26 3:17, David Rientjes wrote:
> >>> On Mon, 25 Feb 2019, Mike Kravetz wrote:
> >>>
> >>>> Ok, what about just moving the calculation/check inside the lock as in the
> >>>> untested patch below?
> >>>>
> >>>> Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
>
> <snip>
>
> >>>
> >>> Looks good; Jing, could you test that this fixes your case?
> >>
> >> Yes, I have tested this patch, it can also fix my case.
> >
> > Great!
> >
> > Reported-by: Jing Xiangfeng <jingxiangfeng@huawei.com>
> > Tested-by: Jing Xiangfeng <jingxiangfeng@huawei.com>
> > Acked-by: David Rientjes <rientjes@google.com>
>
> Thanks Jing and David!
>
> Here is the patch with an updated commit message and above tags:
>
> From: Mike Kravetz <mike.kravetz@oracle.com>
> Date: Tue, 26 Feb 2019 10:43:24 -0800
> Subject: [PATCH] hugetlbfs: fix potential over/underflow setting node specific
> nr_hugepages
>
> The number of node specific huge pages can be set via a file such as:
> /sys/devices/system/node/node1/hugepages/hugepages-2048kB/nr_hugepages
> When a node specific value is specified, the global number of huge
> pages must also be adjusted. This adjustment is calculated as the
> specified node specific value + (global value - current node value).
> If the node specific value provided by the user is large enough, this
> calculation could overflow an unsigned long leading to a smaller
> than expected number of huge pages.
>
> To fix, check the calculation for overflow. If overflow is detected,
> use ULONG_MAX as the requested value. This is inline with the user
> request to allocate as many huge pages as possible.
>
> It was also noticed that the above calculation was done outside the
> hugetlb_lock. Therefore, the values could be inconsistent and result
> in underflow. To fix, the calculation is moved to within the routine
> set_max_huge_pages() where the lock is held.
>
> Reported-by: Jing Xiangfeng <jingxiangfeng@huawei.com>
> Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
> Tested-by: Jing Xiangfeng <jingxiangfeng@huawei.com>
> Acked-by: David Rientjes <rientjes@google.com>

Looks good to me with improved comments.
Thanks everyone.

Reviewed-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>

> ---
> mm/hugetlb.c | 34 ++++++++++++++++++++++++++--------
> 1 file changed, 26 insertions(+), 8 deletions(-)
>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index b37e3100b7cc..a7e4223d2df5 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 +2289,23 @@ 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. Adjust global count, but
> + * 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];
> + /*
> + * If user specified count causes overflow, set to
> + * largest possible value.
> + */
> + if (count < old_count)
> + count = ULONG_MAX;
> + }
> +
> /*
> * Increase the pool size
> * First take pages out of surplus state. Then make up the
> @@ -2300,7 +2317,6 @@ 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 +2437,18 @@ 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
> + * node mask. Pass in ALL nodes, and clear nid.
> */
> - count += h->nr_huge_pages - h->nr_huge_pages_node[nid];
> - init_nodemask_of_node(nodes_allowed, nid);
> - } else
> + nid = NUMA_NO_NODE;
> nodes_allowed = &node_states[N_MEMORY];
> + }
>
> - 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
>
>