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Date:   Mon, 4 Mar 2019 06:00:23 +0000
From:   Naoya Horiguchi <n-horiguchi@...jp.nec.com>
To:     Mike Kravetz <mike.kravetz@...cle.com>
CC:     David Rientjes <rientjes@...gle.com>,
        Jing Xiangfeng <jingxiangfeng@...wei.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "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" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4] mm/hugetlb: Fix unsigned overflow in
 __nr_hugepages_store_common()

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@...cle.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@...wei.com>
> > Tested-by: Jing Xiangfeng <jingxiangfeng@...wei.com>
> > Acked-by: David Rientjes <rientjes@...gle.com>
> 
> Thanks Jing and David!
> 
> Here is the patch with an updated commit message and above tags:
> 
> From: Mike Kravetz <mike.kravetz@...cle.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@...wei.com>
> Signed-off-by: Mike Kravetz <mike.kravetz@...cle.com>
> Tested-by: Jing Xiangfeng <jingxiangfeng@...wei.com>
> Acked-by: David Rientjes <rientjes@...gle.com>

Looks good to me with improved comments.
Thanks everyone.

Reviewed-by: Naoya Horiguchi <n-horiguchi@...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
> 
> 

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