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

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Message-ID: <20241107121307.GN5006@unreal>
Date: Thu, 7 Nov 2024 14:13:07 +0200
From: Leon Romanovsky <leon@...nel.org>
To: Halil Pasic <pasic@...ux.ibm.com>
Cc: Wenjia Zhang <wenjia@...ux.ibm.com>, 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>,
	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>,
	linux-cifs@...r.kernel.org
Subject: Re: [PATCH net] net/smc: Fix lookup of netdev by using
 ib_device_get_netdev()

On Thu, Nov 07, 2024 at 12:56:43PM +0100, Halil Pasic wrote:
> On Wed, 6 Nov 2024 15:59:10 +0200
> Leon Romanovsky <leon@...nel.org> wrote:
> 
> > > Does  fs/smb/server/transport_rdma.c qualify as inside of RDMA core code?  
> > 
> > RDMA core code is drivers/infiniband/core/*.
> 
> Understood. So this is a violation of the no direct access to the
> callbacks rule.

It is not rule, but more common sense. Callbacks don't provide any
module reference counting, module autoload e.t.c

It is very rare situation where you call device callbacks from one subsystem
in another. I'm not familiar with such situations.

> 
> > 
> > > I would guess it is not, and I would not actually mind sending a patch
> > > but I have trouble figuring out the logic behind  commit ecce70cf17d9
> > > ("ksmbd: fix missing RDMA-capable flag for IPoIB device in
> > > ksmbd_rdma_capable_netdev()").  
> > 
> > It is strange version of RDMA-CM. All other ULPs use RDMA-CM to avoid
> > GID, netdev and fabric complexity.
> 
> I'm not familiar enough with either of the subsystems. Based on your
> answer my guess is that it ain't outright bugous but still a layering 
> violation. Copying linux-cifs@...r.kernel.org so that 
> the smb are aware.
> 
> Thank you very much for all the explanations!
> 
> Regards,
> Halil