netdev - Re: [PATCH net-next] net: annotate writes on dev->mtu from ndo_change

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Message-ID: <0bfded05-d4d1-4b60-a3fa-24a2ff6644b5@intel.com>
Date: Mon, 6 May 2024 15:31:10 -0700
From: Jacob Keller <jacob.e.keller@...el.com>
To: Eric Dumazet <edumazet@...gle.com>, "David S . Miller"
	<davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni
	<pabeni@...hat.com>
CC: <netdev@...r.kernel.org>, <eric.dumazet@...il.com>, Simon Horman
	<horms@...nel.org>
Subject: Re: [PATCH net-next] net: annotate writes on dev->mtu from
 ndo_change_mtu()



On 5/6/2024 3:28 AM, Eric Dumazet wrote:
> Simon reported that ndo_change_mtu() methods were never
> updated to use WRITE_ONCE(dev->mtu, new_mtu) as hinted
> in commit 501a90c94510 ("inet: protect against too small
> mtu values.")
> 
> We read dev->mtu without holding RTNL in many places,
> with READ_ONCE() annotations.
> 
> It is time to take care of ndo_change_mtu() methods
> to use corresponding WRITE_ONCE()
> 
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Reported-by: Simon Horman <horms@...nel.org>
> Closes: https://lore.kernel.org/netdev/20240505144608.GB67882@kernel.org/
> ---

Many drivers, but it is fairly mechanical and straight forward. I
noticed one place where you also fixed up the code style, but otherwise
everything looks exactly like a mechanical transformation.

> diff --git a/drivers/net/ethernet/myricom/myri10ge/myri10ge.c b/drivers/net/ethernet/myricom/myri10ge/myri10ge.c
> index 7b7e1c5b00f4728cccfb693e2ab4e32b9613616e..b7d9657a7af3d168ea6fa6acd205d690fc79db06 100644
> --- a/drivers/net/ethernet/myricom/myri10ge/myri10ge.c
> +++ b/drivers/net/ethernet/myricom/myri10ge/myri10ge.c
> @@ -3036,11 +3036,11 @@ static int myri10ge_change_mtu(struct net_device *dev, int new_mtu)
>  		/* if we change the mtu on an active device, we must
>  		 * reset the device so the firmware sees the change */
>  		myri10ge_close(dev);
> -		dev->mtu = new_mtu;
> +		WRITE_ONCE(dev->mtu, new_mtu);
>  		myri10ge_open(dev);
> -	} else
> -		dev->mtu = new_mtu;
> -

Looks like you also fix up the style with { } here. That is fine with me.

> +	} else {
> +		WRITE_ONCE(dev->mtu, new_mtu);
> +	}
>  	return 0;
>  }
>  

The new style is correct, and I see no reason not to commit this now and
fix up the writes.

Reviewed-by: Jacob Keller <jacob.e.keller@...el.com>