linux-kernel - Re: [PATCH net 2/4] net: ravb: Allow RX loop to move past DMA mapping errors

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Date: Thu, 11 Apr 2024 19:37:50 +0300
From: Sergey Shtylyov <s.shtylyov@....ru>
To: Paul Barker <paul.barker.ct@...renesas.com>, "David S. Miller"
	<davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski
	<kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Niklas Söderlund <niklas.soderlund+renesas@...natech.se>,
	Geert Uytterhoeven <geert+renesas@...der.be>
CC: <netdev@...r.kernel.org>, <linux-renesas-soc@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net 2/4] net: ravb: Allow RX loop to move past DMA mapping
 errors

On 4/11/24 2:44 PM, Paul Barker wrote:

> The RX loops in ravb_rx_gbeth() and ravb_rx_rcar() skip to the next loop
> interation if a zero-length descriptor is seen (indicating a DMA mapping

   Iteration. :-)

> error). However, the current rx descriptor index `priv->cur_rx[q]` was

   RX?

> incremented at the end of the loop and so would not be incremented when
> we skip to the next loop iteration. This would cause the loop to keep
> seeing the same zero-length descriptor instead of moving on to the next
> descriptor.
> 
> As the loop counter `i` still increments, the loop would eventually
> terminate so there is no risk of being stuck here forever - but we
> should still fix this to avoid wasting cycles.
> 
> To fix this, the rx descriptor index is incremented at the top of the

   RX?

> loop, in the for statement itself. The assignments of `entry` and `desc`
> are brought into the loop to avoid the need for duplication.
> 
> Fixes: d8b48911fd24 ("ravb: fix ring memory allocation")
> Signed-off-by: Paul Barker <paul.barker.ct@...renesas.com>

Reviewed-by: Sergey Shtylyov <s.shtylyov@....ru>

[...]

MBR, Sergey