linux-kernel - [PATCH net] net: fec: avoid lock evasion when reading pps

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Date: Mon, 13 May 2024 09:27:23 +0000
From: Hariprasad Kelam <hkelam@...vell.com>
To: Wei Fang <wei.fang@....com>, "davem@...emloft.net" <davem@...emloft.net>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        "kuba@...nel.org"
	<kuba@...nel.org>,
        "pabeni@...hat.com" <pabeni@...hat.com>,
        "shenwei.wang@....com" <shenwei.wang@....com>,
        "xiaoning.wang@....com"
	<xiaoning.wang@....com>,
        "richardcochran@...il.com"
	<richardcochran@...il.com>,
        "andrew@...n.ch" <andrew@...n.ch>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "imx@...ts.linux.dev" <imx@...ts.linux.dev>
Subject: [PATCH net] net: fec: avoid lock evasion when reading pps_enable

See inline,

> The assignment of pps_enable is protected by tmreg_lock, but the read
> operation of pps_enable is not. So the Coverity tool reports a lock evasion
> warning which may cause data race to occur when running in a multithread
> environment. Although this issue is almost impossible to occur, we'd better fix
> it, at least it seems more logically reasonable, and it also prevents Coverity
> from continuing to issue warnings.
> 
> Fixes: 278d24047891 ("net: fec: ptp: Enable PPS output based on ptp clock")
> Signed-off-by: Wei Fang <wei.fang@....com>
> ---
>  drivers/net/ethernet/freescale/fec_ptp.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/net/ethernet/freescale/fec_ptp.c
> b/drivers/net/ethernet/freescale/fec_ptp.c
> index 181d9bfbee22..8d37274a3fb0 100644
> --- a/drivers/net/ethernet/freescale/fec_ptp.c
> +++ b/drivers/net/ethernet/freescale/fec_ptp.c
> @@ -104,14 +104,16 @@ static int fec_ptp_enable_pps(struct
> fec_enet_private *fep, uint enable)
>  	struct timespec64 ts;
>  	u64 ns;
> 
> -	if (fep->pps_enable == enable)
> -		return 0;
> -
>  	fep->pps_channel = DEFAULT_PPS_CHANNEL;
>  	fep->reload_period = PPS_OUPUT_RELOAD_PERIOD;
> 
>  	spin_lock_irqsave(&fep->tmreg_lock, flags);
> 
> +	if (fep->pps_enable == enable) {

Can we atomic_set/get instead of spin_lock here.

Thanks,
Hariprasad k
> +		spin_unlock_irqrestore(&fep->tmreg_lock, flags);
> +		return 0;
> +	}
> +
>  	if (enable) {
>  		/* clear capture or output compare interrupt status if have.
>  		 */
> --
> 2.34.1
>