netdev - Re: [PATCH net] net: ethernet: mtk_eth_soc: fix uninitialized variable

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Date: Thu, 7 Sep 2023 18:21:31 +0200
From: Simon Horman <horms@...nel.org>
To: Daniel Golle <daniel@...rotopia.org>
Cc: Dan Carpenter <dan.carpenter@...aro.org>, Felix Fietkau <nbd@....name>,
	John Crispin <john@...ozen.org>, Sean Wang <sean.wang@...iatek.com>,
	Mark Lee <Mark-MC.Lee@...iatek.com>,
	Lorenzo Bianconi <lorenzo@...nel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Matthias Brugger <matthias.bgg@...il.com>,
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH net] net: ethernet: mtk_eth_soc: fix uninitialized
 variable

On Thu, Sep 07, 2023 at 04:14:20PM +0100, Daniel Golle wrote:
> Variable dma_addr in function mtk_poll_rx can be uninitialized on
> some of the error paths. In practise this doesn't matter, even random
> data present in uninitialized stack memory can safely be used in the
> way it happens in the error path.
> 
> However, in order to make Smatch happy make sure the variable is
> always initialized.
> 
> Signed-off-by: Daniel Golle <daniel@...rotopia.org>
> ---
>  drivers/net/ethernet/mediatek/mtk_eth_soc.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/mediatek/mtk_eth_soc.c b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
> index 31090490d47ce..6342eac90793e 100644
> --- a/drivers/net/ethernet/mediatek/mtk_eth_soc.c
> +++ b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
> @@ -2119,11 +2119,11 @@ static int mtk_poll_rx(struct napi_struct *napi, int budget,
>  	u8 *data, *new_data;
>  	struct mtk_rx_dma_v2 *rxd, trxd;
>  	int done = 0, bytes = 0;
> +	dma_addr_t dma_addr = NULL;

Hi Daniel,

I'm not sure that NULL is a valid value for a variable of type dma_addr_t.
Is DMA_MAPPING_ERROR more appropriate here?

Flagged by Sparse and, W=1 builds with gcc-13 and clang-16.

>  
>  	while (done < budget) {
>  		unsigned int pktlen, *rxdcsum;
>  		struct net_device *netdev;
> -		dma_addr_t dma_addr;
>  		u32 hash, reason;
>  		int mac = 0;
>  
> -- 
> 2.42.0
>