RE: [PATCH net-next 01/10] net/smc: add missing dev_put

[Parav Pandit <parav@mellanox.com>]

Hi Ursula, Dave, Hans,

> -----Original Message-----
> From: linux-rdma-owner@vger.kernel.org [mailto:linux-rdma-
> owner@vger.kernel.org] On Behalf Of Ursula Braun
> Sent: Wednesday, September 20, 2017 6:58 AM
> To: davem@davemloft.net
> Cc: netdev@vger.kernel.org; linux-rdma@vger.kernel.org; linux-
> s390@vger.kernel.org; jwi@linux.vnet.ibm.com; schwidefsky@de.ibm.com;
> heiko.carstens@de.ibm.com; raspl@linux.vnet.ibm.com;
> ubraun@linux.vnet.ibm.com
> Subject: [PATCH net-next 01/10] net/smc: add missing dev_put
> 
> From: Hans Wippel <hwippel@linux.vnet.ibm.com>
> 
> In the infiniband part, SMC currently uses get_netdev which calls dev_hold on
> the returned net device. However, the SMC code never calls dev_put on that net
> device resulting in a wrong reference count.
> 
> This patch adds a dev_put after the usage of the net device to fix the issue.
> 
> Signed-off-by: Hans Wippel <hwippel@linux.vnet.ibm.com>
> Signed-off-by: Ursula Braun <ubraun@linux.vnet.ibm.com>
> ---
>  net/smc/smc_ib.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/net/smc/smc_ib.c b/net/smc/smc_ib.c index
> 547e0e113b17..0b5852299158 100644
> --- a/net/smc/smc_ib.c
> +++ b/net/smc/smc_ib.c
> @@ -380,6 +380,7 @@ static int smc_ib_fill_gid_and_mac(struct smc_ib_device
> *smcibdev, u8 ibport)
>  	ndev = smcibdev->ibdev->get_netdev(smcibdev->ibdev, ibport);
>  	if (ndev) {
>  		memcpy(&smcibdev->mac, ndev->dev_addr, ETH_ALEN);
> +		dev_put(ndev);

I am sorry for providing late comments. smc_ib_fill_gid_and_mac() is not coded correctly.
Few fixes are needed.
1. ULP such as SMC should not open code/deference any function pointer like get_netdev() of the IB device.
2. Replace ib_query_gid(..., NULL)
With
ib_query_gid(..., gid_attr);

Use gid_attr.ndev to get the MAC address.
Do dev_put(gid_attr.ndev);

Code should look like below,

struct ib_gid_attr gid_attr;

rc = ib_query_gid(..., &gid_attr);
if (rc || !gid_addr.ndev)
	return -ENODEV;
else
	memcpy(smcibdev->mac, ndev->dev_addr, ETH_ALEN);
dev_put(gid_addr.ndev);