linux-kernel - Re: [PATCH] net: dsa: Fix return value check of wait_for_completion

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Date:   Tue, 12 Apr 2022 14:53:26 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Miaoqian Lin <linmq006@...il.com>
Cc:     Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vladimir Oltean <olteanv@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Ansuel Smith <ansuelsmth@...il.com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: dsa: Fix return value check of
 wait_for_completion_timeout

On Tue, Apr 12, 2022 at 02:45:40AM +0000, Miaoqian Lin wrote:
> wait_for_completion_timeout() returns unsigned long not int.
> It returns 0 if timed out, and positive if completed.
> The check for <= 0 is ambiguous and should be == 0 here
> indicating timeout which is the only error case.

Please fix your subject line to indicate which driver you are patching.

Please also read the netdev FAQ which will point out a few other
process issues.

> 
> Fixes: 2cd548566384 ("net: dsa: qca8k: add support for phy read/write with mgmt Ethernet")
> Fixes: 5950c7c0a68c ("net: dsa: qca8k: add support for mgmt read/write in Ethernet packet")
> Signed-off-by: Miaoqian Lin <linmq006@...il.com>
> ---
>  drivers/net/dsa/qca8k.c | 25 +++++++++++++------------
>  1 file changed, 13 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/net/dsa/qca8k.c b/drivers/net/dsa/qca8k.c
> index d3ed0a7f8077..bd8c238955a8 100644
> --- a/drivers/net/dsa/qca8k.c
> +++ b/drivers/net/dsa/qca8k.c
> @@ -300,7 +300,7 @@ static int qca8k_read_eth(struct qca8k_priv *priv, u32 reg, u32 *val, int len)
>  	struct qca8k_mgmt_eth_data *mgmt_eth_data = &priv->mgmt_eth_data;
>  	struct sk_buff *skb;
>  	bool ack;
> -	int ret;
> +	unsigned long ret;

Please sort variables longest to shortest, reverse christmass tree.

>  
>  	skb = qca8k_alloc_mdio_header(MDIO_READ, reg, NULL,
>  				      QCA8K_ETHERNET_MDIO_PRIORITY, len);
> @@ -338,7 +338,7 @@ static int qca8k_read_eth(struct qca8k_priv *priv, u32 reg, u32 *val, int len)
>  
>  	mutex_unlock(&mgmt_eth_data->mutex);
>  
> -	if (ret <= 0)
> +	if (ret == 0)
>  		return -ETIMEDOUT;

Given this change, what happens if -ERESTARTSYS is returned?

Please consider the same question for all cases you change <= to ==.

       Andrew