linux-kernel - Re: [PATCH 1/2] IB/hfi1: Fix a parameter of find_first

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Date:   Fri, 26 Aug 2016 09:35:11 -0400
From:   Doug Ledford <dledford@...hat.com>
To:     Christophe JAILLET <christophe.jaillet@...adoo.fr>,
        mike.marciniszyn@...el.com, dennis.dalessandro@...el.com,
        sean.hefty@...el.com, hal.rosenstock@...il.com
Cc:     linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-janitors@...r.kernel.org
Subject: Re: [PATCH 1/2] IB/hfi1: Fix a parameter of find_first_bit.

On 8/26/2016 12:49 AM, Christophe JAILLET wrote:
> The 2nd parameter of 'find_first_bit' is the number of bits to search.
> In this case, we are passing 'sizeof(unsigned long)' which is likely to
> be 4 or 8.

If the size can be 4 or 8, then using 64 universally is not correct.
Why not use sizeof() * 8 (or << 3)?

> It is likely that the number of bits of 'port_mask' was expected here. This
> variable is a 'u64', so use 64 instead.
> 
> It has been spotted by the following coccinelle script:
> @@
> expression ret, x;
> 
> @@
> *  ret = \(find_first_bit \| find_first_zero_bit\) (x, sizeof(...));
> 
> Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>
> ---
> Not sure that using 64 directly is the best option.
> Maybe '8 * sizeof(port_mask)' as used in the same file for
> 'for_each_set_bit' would be better
> ---
>  drivers/infiniband/hw/hfi1/mad.c | 12 ++++--------
>  1 file changed, 4 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/infiniband/hw/hfi1/mad.c b/drivers/infiniband/hw/hfi1/mad.c
> index 1263abe01999..2c6c138c41b2 100644
> --- a/drivers/infiniband/hw/hfi1/mad.c
> +++ b/drivers/infiniband/hw/hfi1/mad.c
> @@ -2632,8 +2632,7 @@ static int pma_get_opa_datacounters(struct opa_pma_mad *pmp,
>  	 * port the request came in on.
>  	 */
>  	port_mask = be64_to_cpu(req->port_select_mask[3]);
> -	port_num = find_first_bit((unsigned long *)&port_mask,
> -				  sizeof(port_mask));
> +	port_num = find_first_bit((unsigned long *)&port_mask, 64);
>  
>  	if ((u8)port_num != port) {
>  		pmp->mad_hdr.status |= IB_SMP_INVALID_FIELD;
> @@ -2836,8 +2835,7 @@ static int pma_get_opa_porterrors(struct opa_pma_mad *pmp,
>  	 * port the request came in on.
>  	 */
>  	port_mask = be64_to_cpu(req->port_select_mask[3]);
> -	port_num = find_first_bit((unsigned long *)&port_mask,
> -				  sizeof(port_mask));
> +	port_num = find_first_bit((unsigned long *)&port_mask, 64);
>  
>  	if (port_num != port) {
>  		pmp->mad_hdr.status |= IB_SMP_INVALID_FIELD;
> @@ -3009,8 +3007,7 @@ static int pma_get_opa_errorinfo(struct opa_pma_mad *pmp,
>  	 * the request came in on.
>  	 */
>  	port_mask = be64_to_cpu(req->port_select_mask[3]);
> -	port_num = find_first_bit((unsigned long *)&port_mask,
> -				  sizeof(port_mask));
> +	port_num = find_first_bit((unsigned long *)&port_mask, 64);
>  
>  	if (port_num != port) {
>  		pmp->mad_hdr.status |= IB_SMP_INVALID_FIELD;
> @@ -3246,8 +3243,7 @@ static int pma_set_opa_errorinfo(struct opa_pma_mad *pmp,
>  	 * the request came in on.
>  	 */
>  	port_mask = be64_to_cpu(req->port_select_mask[3]);
> -	port_num = find_first_bit((unsigned long *)&port_mask,
> -				  sizeof(port_mask));
> +	port_num = find_first_bit((unsigned long *)&port_mask, 64);
>  
>  	if (port_num != port) {
>  		pmp->mad_hdr.status |= IB_SMP_INVALID_FIELD;
> 


-- 
Doug Ledford <dledford@...hat.com>
    GPG Key ID: 0E572FDD



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