netdev - Re: [PATCH net] net/smc: Fix lookup of netdev by using ib_device_get

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Message-ID: <20241027201857.GA1615717@unreal>
Date: Sun, 27 Oct 2024 22:18:57 +0200
From: Leon Romanovsky <leon@...nel.org>
To: Wenjia Zhang <wenjia@...ux.ibm.com>
Cc: Wen Gu <guwen@...ux.alibaba.com>,
	"D. Wythe" <alibuda@...ux.alibaba.com>,
	Tony Lu <tonylu@...ux.alibaba.com>,
	David Miller <davem@...emloft.net>,
	Jakub Kicinski <kuba@...nel.org>,
	Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>,
	netdev@...r.kernel.org, linux-rdma@...r.kernel.org,
	linux-s390@...r.kernel.org, Heiko Carstens <hca@...ux.ibm.com>,
	Jan Karcher <jaka@...ux.ibm.com>, Gerd Bayer <gbayer@...ux.ibm.com>,
	Alexandra Winter <wintera@...ux.ibm.com>,
	Halil Pasic <pasic@...ux.ibm.com>,
	Nils Hoppmann <niho@...ux.ibm.com>,
	Niklas Schnell <schnelle@...ux.ibm.com>,
	Thorsten Winkler <twinkler@...ux.ibm.com>,
	Karsten Graul <kgraul@...ux.ibm.com>,
	Stefan Raspl <raspl@...ux.ibm.com>, Aswin K <aswin@...ux.ibm.com>
Subject: Re: [PATCH net] net/smc: Fix lookup of netdev by using
 ib_device_get_netdev()

On Fri, Oct 25, 2024 at 09:23:55AM +0200, Wenjia Zhang wrote:
> Commit c2261dd76b54 ("RDMA/device: Add ib_device_set_netdev() as an
> alternative to get_netdev") introduced an API ib_device_get_netdev.
> The SMC-R variant of the SMC protocol continued to use the old API
> ib_device_ops.get_netdev() to lookup netdev. 

I would say that calls to ibdev ops from ULPs was never been right
thing to do. The ib_device_set_netdev() was introduced for the drivers.

So the whole commit message is not accurate and better to be rewritten.

> As this commit 8d159eb2117b
> ("RDMA/mlx5: Use IB set_netdev and get_netdev functions") removed the
> get_netdev callback from mlx5_ib_dev_common_roce_ops, calling
> ib_device_ops.get_netdev didn't work any more at least by using a mlx5
> device driver.

It is not a correct statement too. All modern drivers (for last 5 years)
don't have that .get_netdev() ops, so it is not mlx5 specific, but another
justification to say that SMC-R was doing it wrong.

> Thus, using ib_device_set_netdev() now became mandatory.

ib_device_set_netdev() is mandatory for the drivers, it is nothing to do
with ULPs.

> 
> Replace ib_device_ops.get_netdev() with ib_device_get_netdev().

It is too late for me to do proper review for today, but I would say
that it is worth to pay attention to multiple dev_put() calls in the
functions around the ib_device_get_netdev().

> 
> Fixes: 54903572c23c ("net/smc: allow pnetid-less configuration")
> Fixes: 8d159eb2117b ("RDMA/mlx5: Use IB set_netdev and get_netdev functions")

It is not related to this change Fixes line.

> Reported-by: Aswin K <aswin@...ux.ibm.com>
> Reviewed-by: Gerd Bayer <gbayer@...ux.ibm.com>
> Signed-off-by: Wenjia Zhang <wenjia@...ux.ibm.com>
> ---
>  net/smc/smc_ib.c   | 8 ++------
>  net/smc/smc_pnet.c | 4 +---
>  2 files changed, 3 insertions(+), 9 deletions(-)
> 
> diff --git a/net/smc/smc_ib.c b/net/smc/smc_ib.c
> index 9297dc20bfe2..9c563cdbea90 100644
> --- a/net/smc/smc_ib.c
> +++ b/net/smc/smc_ib.c
> @@ -899,9 +899,7 @@ static void smc_copy_netdev_ifindex(struct smc_ib_device *smcibdev, int port)
>  	struct ib_device *ibdev = smcibdev->ibdev;
>  	struct net_device *ndev;
>  
> -	if (!ibdev->ops.get_netdev)
> -		return;
> -	ndev = ibdev->ops.get_netdev(ibdev, port + 1);
> +	ndev = ib_device_get_netdev(ibdev, port + 1);
>  	if (ndev) {
>  		smcibdev->ndev_ifidx[port] = ndev->ifindex;
>  		dev_put(ndev);
> @@ -921,9 +919,7 @@ void smc_ib_ndev_change(struct net_device *ndev, unsigned long event)
>  		port_cnt = smcibdev->ibdev->phys_port_cnt;
>  		for (i = 0; i < min_t(size_t, port_cnt, SMC_MAX_PORTS); i++) {
>  			libdev = smcibdev->ibdev;
> -			if (!libdev->ops.get_netdev)
> -				continue;
> -			lndev = libdev->ops.get_netdev(libdev, i + 1);
> +			lndev = ib_device_get_netdev(libdev, i + 1);
>  			dev_put(lndev);
>  			if (lndev != ndev)
>  				continue;
> diff --git a/net/smc/smc_pnet.c b/net/smc/smc_pnet.c
> index 1dd362326c0a..8566937c8903 100644
> --- a/net/smc/smc_pnet.c
> +++ b/net/smc/smc_pnet.c
> @@ -1054,9 +1054,7 @@ static void smc_pnet_find_rdma_dev(struct net_device *netdev,
>  		for (i = 1; i <= SMC_MAX_PORTS; i++) {
>  			if (!rdma_is_port_valid(ibdev->ibdev, i))
>  				continue;
> -			if (!ibdev->ibdev->ops.get_netdev)
> -				continue;
> -			ndev = ibdev->ibdev->ops.get_netdev(ibdev->ibdev, i);
> +			ndev = ib_device_get_netdev(ibdev->ibdev, i);
>  			if (!ndev)
>  				continue;
>  			dev_put(ndev);
> -- 
> 2.43.0
> 
>