netdev - Re: [PATCH net] net: renesas: rswitch: Fix return value in error path of xmit

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Date: Tue, 30 May 2023 13:42:44 +0200
From: Simon Horman <simon.horman@...igine.com>
To: Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>
Cc: s.shtylyov@....ru, davem@...emloft.net, edumazet@...gle.com,
	kuba@...nel.org, pabeni@...hat.com, netdev@...r.kernel.org,
	linux-renesas-soc@...r.kernel.org
Subject: Re: [PATCH net] net: renesas: rswitch: Fix return value in error
 path of xmit

On Mon, May 29, 2023 at 04:38:17PM +0900, Yoshihiro Shimoda wrote:
> Fix return value in the error path of rswitch_start_xmit(). If TX
> queues are full, this function should return NETDEV_TX_BUSY.
> 
> Fixes: 3590918b5d07 ("net: ethernet: renesas: Add support for "Ethernet Switch"")
> Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>

Hi Shimoda-san,

I agree that this is the correct return value for this case.
But I do wonder if, as per the documentation of ndo_start_xmit,
something should be done to avoid getting into such a situation.

 * netdev_tx_t (*ndo_start_xmit)(struct sk_buff *skb,
 *                               struct net_device *dev);
 *      Called when a packet needs to be transmitted.
 *      Returns NETDEV_TX_OK.  Can return NETDEV_TX_BUSY, but you should stop
 *      the queue before that can happen; it's for obsolete devices and weird
 *      corner cases, but the stack really does a non-trivial amount
 *      of useless work if you return NETDEV_TX_BUSY.
 *      Required; cannot be NULL.

以上