netdev - Re: [PATCH 2/2] net: ll_temac: improve reset of buffer on dma mapping

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Message-ID: <20230130124215.1a06c5af@kernel.org>
Date:   Mon, 30 Jan 2023 12:42:15 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     esben@...nix.com
Cc:     Jonas Suhr Christensen <jsc@...raculum.org>,
        netdev@...r.kernel.org, davem@...emloft.net, edumazet@...gle.com,
        pabeni@...hat.com, michal.simek@...inx.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] net: ll_temac: improve reset of buffer on dma
 mapping

On Mon, 30 Jan 2023 13:40:56 +0100 esben@...nix.com wrote:
> > On Thu, 26 Jan 2023 11:16:07 +0100 Jonas Suhr Christensen wrote:  
> >> Free buffer and set pointer to null on dma mapping error.  
> >
> > Why? I don't see a leak. You should provide motivation in the commit
> > message.  
> 
> I don't think there is a leak.  But if one of the dma_map_single() calls
> in temac_dma_bd_init() fails, the error handling calls into
> temac_dma_bd_release(), which will then call dma_unmap_single() on the
> address that failed to be mapped.

I see, seems worth fixing. Please explain that in the commit message,
it's not immediately clear what the concern is, otherwise.
On top of that please add a Fixes tag here as well and repost.

> Can we be sure that doing so is always safe?  If not, this change
> ensures that we only unmap buffers that were succesfully mapped.