netdev - Re: [PATCH 2/2] net/mlx4: avoid overloading user/kernel pointers

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Message-Id: <b1d02aee-17cb-4461-8f02-b5bd513790ae@app.fastmail.com>
Date:   Thu, 20 Apr 2023 10:51:58 +0200
From:   "Arnd Bergmann" <arnd@...db.de>
To:     "Tariq Toukan" <ttoukan.linux@...il.com>,
        "Arnd Bergmann" <arnd@...nel.org>,
        "Yishai Hadas" <yishaih@...dia.com>,
        "Jason Gunthorpe" <jgg@...pe.ca>,
        "Leon Romanovsky" <leon@...nel.org>
Cc:     "David S . Miller" <davem@...emloft.net>,
        "Eric Dumazet" <edumazet@...gle.com>,
        "Jakub Kicinski" <kuba@...nel.org>,
        "Paolo Abeni" <pabeni@...hat.com>, linux-rdma@...r.kernel.org,
        linux-kernel@...r.kernel.org, Netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH 2/2] net/mlx4: avoid overloading user/kernel pointers

On Wed, Apr 19, 2023, at 09:09, Tariq Toukan wrote:
> On 18/04/2023 14:47, Arnd Bergmann wrote:
>
> Now we should maintain the values of the two pointers before any call. 
> I'm not sure this is less error-prune. One can mistakenly update 
> kbuf_addr for example without nullifying ubuf_addr.

That would cause a compiler warning about the uninitialized variable.

> Also, I'm not a big fan of passing two pointers when exactly one of them 
> is effectively used.
> We can think maybe of passing a union of both types, and a boolean 
> indicating which pointer type is to be used.

This is basically what you have today. I've dropped this patch from
my randconfig tree and will ignore the problem.

    Arnd