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To: Slawomir Mrozowicz <slawomirx.mrozowicz@intel.com>
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From: Olivier Matz <olivier.matz@6wind.com>
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Date: Mon, 16 May 2016 11:22:32 +0200
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Subject: Re: [dpdk-dev] [PATCH] rte mempool: division or modulo by zero
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Hi Slawomir,

On 05/12/2016 02:46 PM, Slawomir Mrozowicz wrote:
> Fix issue reported by Coverity.
> 
> Coverity ID 13243: Division or modulo by zero
> In function call rte_mempool_xmem_size, division by expression total_size
> which may be zero has undefined behavior.
> 
> Fixes: 148f963fb532 ("xen: core library changes")
> 
> Signed-off-by: Slawomir Mrozowicz <slawomirx.mrozowicz@intel.com>
> ---
>  lib/librte_mempool/rte_mempool.c | 18 +++++++++++-------
>  1 file changed, 11 insertions(+), 7 deletions(-)
> 
> diff --git a/lib/librte_mempool/rte_mempool.c b/lib/librte_mempool/rte_mempool.c
> index f8781e1..01668c1 100644
> --- a/lib/librte_mempool/rte_mempool.c
> +++ b/lib/librte_mempool/rte_mempool.c
> @@ -327,15 +327,19 @@ rte_mempool_calc_obj_size(uint32_t elt_size, uint32_t flags,
>  size_t
>  rte_mempool_xmem_size(uint32_t elt_num, size_t elt_sz, uint32_t pg_shift)
>  {
> -	size_t n, pg_num, pg_sz, sz;
> +	size_t n, pg_num, pg_sz;
> +	size_t sz = 0;
>  
> -	pg_sz = (size_t)1 << pg_shift;
> +	if (elt_sz > 0) {
> +		pg_sz = (size_t)1 << pg_shift;
> +		n = pg_sz / elt_sz;
>  
> -	if ((n = pg_sz / elt_sz) > 0) {
> -		pg_num = (elt_num + n - 1) / n;
> -		sz = pg_num << pg_shift;
> -	} else {
> -		sz = RTE_ALIGN_CEIL(elt_sz, pg_sz) * elt_num;
> +		if (n > 0) {
> +			pg_num = (elt_num + n - 1) / n;
> +			sz = pg_num << pg_shift;
> +		} else {
> +			sz = RTE_ALIGN_CEIL(elt_sz, pg_sz) * elt_num;
> +		}
>  	}
>  
>  	return sz;
> 

I think it would be clearer (either for the patch and the code) to avoid
an additional indent, and do something like that:

	size_t
	rte_mempool_xmem_size(uint32_t elt_num, size_t elt_sz,
		uint32_t pg_shift)
	{
		if (elt_sz == 0)
			return 0;

		/* same code as before */

It will also facilitate the merge with
http://patchwork.dpdk.org/dev/patchwork/patch/12057/

Could you please submit a v2 with this logic?

Thanks,
Olivier