netdev - Re: [PATCH][next] net: stmmac: replace redundant comparison with true

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Message-ID: <20210415143409.GC6021@kadam>
Date:   Thu, 15 Apr 2021 17:34:09 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Colin King <colin.king@...onical.com>
Cc:     Giuseppe Cavallaro <peppe.cavallaro@...com>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        Jose Abreu <joabreu@...opsys.com>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        netdev@...r.kernel.org, linux-stm32@...md-mailman.stormreply.com,
        linux-arm-kernel@...ts.infradead.org,
        kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH][next] net: stmmac: replace redundant comparison with true

On Thu, Apr 15, 2021 at 09:37:57AM +0100, Colin King wrote:
> From: Colin Ian King <colin.king@...onical.com>
> 
> The comparison of the u32 variable queue with <= zero is always true
> since an unsigned can never be negative. Replace the conditional
> check with the boolean true to simplify the code.  The while loop
> will terminate because of the zero check on queue before queue is
> decremented.
> 
> Addresses-Coverity: ("Unsigned compared against 0")
> Signed-off-by: Colin Ian King <colin.king@...onical.com>
> ---
>  drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> index e3e22200a4fd..6e5b4c4b375c 100644
> --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> @@ -1673,7 +1673,7 @@ static void stmmac_reinit_rx_buffers(struct stmmac_priv *priv)
>  	return;
>  
>  err_reinit_rx_buffers:
> -	while (queue >= 0) {

This is an off by one from what the original developer was intending
because we're freeing the most recent queue that wasn't allocated.
In other words, we're freeing everything that we need to plus *one
more thing that we don't need to*.  But it's harmless in this case:

The better fix would be to make queue an int type and do:

	while (--queue >= 0)
		dma_free_rx_skbufs(priv, queue);