linux-kernel - Re: [PATCH v4] mm/hugetlb: Fix unsigned overflow in __nr_hugepages_store

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Date:   Wed, 6 Mar 2019 10:41:34 +0100
From:   Oscar Salvador <osalvador@...e.de>
To:     Mike Kravetz <mike.kravetz@...cle.com>
Cc:     Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Rientjes <rientjes@...gle.com>,
        Jing Xiangfeng <jingxiangfeng@...wei.com>,
        "mhocko@...nel.org" <mhocko@...nel.org>,
        "hughd@...gle.com" <hughd@...gle.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
        linux-kernel@...r.kernel.org, Alexandre Ghiti <alex@...ti.fr>
Subject: Re: [PATCH v4] mm/hugetlb: Fix unsigned overflow in
 __nr_hugepages_store_common()

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@...wei.com>
> Signed-off-by: Mike Kravetz <mike.kravetz@...cle.com>

But the overall change looks good to me:

Reviewed-by: Oscar Salvador <osalvador@...e.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