netdev - RE: [PATCH linux-next] net:stmmac: Fix the unsigned expression compared with zero

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Date:   Thu, 15 Jul 2021 10:12:04 +0000
From:   Joakim Zhang <qiangqing.zhang@....com>
To:     "menglong8.dong@...il.com" <menglong8.dong@...il.com>,
        "davem@...emloft.net" <davem@...emloft.net>
CC:     "peppe.cavallaro@...com" <peppe.cavallaro@...com>,
        "alexandre.torgue@...s.st.com" <alexandre.torgue@...s.st.com>,
        "joabreu@...opsys.com" <joabreu@...opsys.com>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "mcoquelin.stm32@...il.com" <mcoquelin.stm32@...il.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-stm32@...md-mailman.stormreply.com" 
        <linux-stm32@...md-mailman.stormreply.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Zhang Yunkai <zhang.yunkai@....com.cn>,
        Zeal Robot <zealci@....com.cn>
Subject: RE: [PATCH linux-next] net:stmmac: Fix the unsigned expression
 compared with zero


> -----Original Message-----
> From: menglong8.dong@...il.com <menglong8.dong@...il.com>
> Sent: 2021年7月15日 15:46
> To: davem@...emloft.net
> Cc: peppe.cavallaro@...com; alexandre.torgue@...s.st.com;
> joabreu@...opsys.com; kuba@...nel.org; mcoquelin.stm32@...il.com;
> netdev@...r.kernel.org; linux-stm32@...md-mailman.stormreply.com;
> linux-arm-kernel@...ts.infradead.org; linux-kernel@...r.kernel.org; Zhang
> Yunkai <zhang.yunkai@....com.cn>; Zeal Robot <zealci@....com.cn>
> Subject: [PATCH linux-next] net:stmmac: Fix the unsigned expression compared
> with zero
> 
> From: Zhang Yunkai <zhang.yunkai@....com.cn>
> 
> WARNING:  Unsigned expression "queue" compared with zero.
> Reported-by: Zeal Robot <zealci@....com.cn>
> Signed-off-by: Zhang Yunkai <zhang.yunkai@....com.cn>
> ---
>  drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 8 ++------
>  1 file changed, 2 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> index 7b8404a21544..a4cf2c640531 100644
> --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> @@ -1699,7 +1699,7 @@ static int init_dma_rx_desc_rings(struct net_device
> *dev, gfp_t flags)
>  	return 0;
> 
>  err_init_rx_buffers:
> -	while (queue >= 0) {
> +	do {
>  		struct stmmac_rx_queue *rx_q = &priv->rx_queue[queue];
> 
>  		if (rx_q->xsk_pool)
> @@ -1710,11 +1710,7 @@ static int init_dma_rx_desc_rings(struct
> net_device *dev, gfp_t flags)
>  		rx_q->buf_alloc_num = 0;
>  		rx_q->xsk_pool = NULL;
> 
> -		if (queue == 0)
> -			break;
> -
> -		queue--;
> -	}
> +	} while (queue--);
> 
>  	return ret;
>  }


This is a real Coverity issue since queue variable is defined as u32, but there is no breakage from logic, it will break while loop when queue equal 0, and queue[0] actually need be handled.
After your code change, queue[0] will not be handled, right? It will break the logic. If you want to fix the this issue, I think the easiest way is to define queue variable to int.

Best Regards,
Joakim Zhang
> --
> 2.25.1