From mboxrd@z Thu Jan  1 00:00:00 1970
From: Florian Fainelli <f.fainelli@gmail.com>
Subject: Re: [PATCH v2] ravb: add support for changing MTU
Date: Fri, 16 Feb 2018 11:42:09 -0800
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References: <20180216161008.12882-1-niklas.soderlund+renesas@ragnatech.se>
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Cc: linux-renesas-soc@vger.kernel.org
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        <niklas.soderlund+renesas@ragnatech.se>,
        Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>,
        "David S . Miller" <davem@davemloft.net>, netdev@vger.kernel.org
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On 02/16/2018 08:10 AM, Niklas Söderlund wrote:
> Allow for changing the MTU within the limit of the maximum size of a
> descriptor (2048 bytes). Add the callback to change MTU from user-space
> and take the configurable MTU into account when configuring the
> hardware.
> 
> Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
> ---

>  
> +static int ravb_change_mtu(struct net_device *ndev, int new_mtu)
> +{
> +	if (netif_running(ndev))
> +		return -EBUSY;
> +
> +	ndev->mtu = new_mtu;
> +	netdev_update_features(ndev);

Don't you somehow need to quiesce the RX DMA and make sure you that you
re-allocate all RX buffers within priv->rx_skb[q][entry] such that they
will be able to accept a larger buffer size?

If we put the ravb interface under high RX load and we change the MTU on
the fly, can we crash the kernel?
-- 
Florian