netdev - Re: [PATCH v2] ravb: add support for changing MTU

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Message-ID: <b3b37354-f7ee-d2ff-77ae-07bfc4eabe09@gmail.com>
Date:   Fri, 16 Feb 2018 11:45:17 -0800
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Sergei Shtylyov <sergei.shtylyov@...entembedded.com>,
        Niklas Söderlund 
        <niklas.soderlund+renesas@...natech.se>,
        "David S . Miller" <davem@...emloft.net>, netdev@...r.kernel.org
Cc:     linux-renesas-soc@...r.kernel.org
Subject: Re: [PATCH v2] ravb: add support for changing MTU

On 02/16/2018 11:43 AM, Sergei Shtylyov wrote:
> Hello!
> 
> On 02/16/2018 10:42 PM, Florian Fainelli 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@...natech.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?
> 
>    I thought the netif_running() check guards against that. Does it not?

It does, completely missed that, thanks!
-- 
Florian