On Thu, Mar 28, 2019 at 03:05:33PM -0700, Mike Kravetz wrote:
> 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 within the routine
> set_max_huge_pages() where the lock is held.
>
> 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.
>
> Reported-by: Jing Xiangfeng <jingxiangfeng@xxxxxxxxxx>
> Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Looks good to me.
Reviewed-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
> ---
> This was sent upstream during 5.1 merge window, but dropped as it was
> based on an earlier version of Alex Ghiti's patch which was dropped.
> Now rebased on top of Alex Ghiti's "[PATCH v8 0/4] Fix free/allocation
> of runtime gigantic pages" series which was just added to mmotm.
>
> mm/hugetlb.c | 41 ++++++++++++++++++++++++++++++++++-------
> 1 file changed, 34 insertions(+), 7 deletions(-)
>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index f3e84c1bef11..f79ae4e42159 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -2287,13 +2287,33 @@ 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;
>
> 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;
> + }
> +
> /*
> * Gigantic pages runtime allocation depend on the capability for large
> * page range allocation.
> @@ -2445,15 +2465,22 @@ static ssize_t __nr_hugepages_store_common(bool obey_mempolicy,
> }
> } else if (nodes_allowed) {
> /*
> - * per node hstate attribute: adjust count to global,
> - * but restrict alloc/free to the specified node.
> + * Node specific request. count adjustment happens in
> + * set_max_huge_pages() after acquiring hugetlb_lock.
> */
> - 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];
> + } else {
> + /*
> + * 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.
> + */
> + err = -ENOMEM;
> + goto out;
> + }
>
> - err = set_max_huge_pages(h, count, nodes_allowed);
> + err = set_max_huge_pages(h, count, nid, nodes_allowed);
>
> out:
> if (nodes_allowed != &node_states[N_MEMORY])
> --
> 2.20.1
>
>
