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

On 10/02/2017 10:36 PM, Parav Pandit wrote:

Hi Ursula, Dave, Hans,

quoted

-----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 <redacted>

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 <redacted>
Signed-off-by: Ursula Braun <redacted>
---
 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);

Thanks, Parav!
Following your fix ideas I plan to change the function into this one:

static int smc_ib_fill_gid_and_mac(struct smc_ib_device *smcibdev, u8 ibport)
{
        struct ib_gid_attr gattr;
        int rc;

        rc = ib_query_gid(smcibdev->ibdev, ibport, 0,
                          &smcibdev->gid[ibport - 1], &gattr);
        /* the SMC protocol requires specification of the roce MAC address;
         * if net_device cannot be determined, it can be derived from gid 0
         */
        if (rc)
                return rc;

        if (gattr.ndev) {
                memcpy(&smcibdev->mac, gattr.ndev->dev_addr, ETH_ALEN);
                dev_put(gattr.ndev);
        } else {
                memcpy(&smcibdev->mac[ibport - 1][0],
                       &smcibdev->gid[ibport - 1].raw[8], 3);
                memcpy(&smcibdev->mac[ibport - 1][3],
                       &smcibdev->gid[ibport - 1].raw[13], 3);
                smcibdev->mac[ibport - 1][0] &= ~0x02;
        }
        return 0;
}

If you agree, I will submit the corresponding patch including a
	Suggested-by: Parav Pandit [off-list ref]

Regards, Ursula