netdev - Re: [PATCH v2] net: fec: Use a spinlock to guard `fep->ptp_clk

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Date:   Mon, 5 Sep 2022 09:38:04 +0200
From:   Marc Kleine-Budde <mkl@...gutronix.de>
To:     Csókás Bence <csokas.bence@...lan.hu>,
        netdev@...r.kernel.org
Cc:     Andrew Lunn <andrew@...n.ch>,
        Richard Cochran <richardcochran@...il.com>,
        kernel@...gutronix.de,
        Francesco Dolcini <francesco.dolcini@...adex.com>,
        Jakub Kicinski <kuba@...nel.org>,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH v2] net: fec: Use a spinlock to guard `fep->ptp_clk_on`

On 9/1/22 4:04 PM, Csókás Bence wrote:
> Mutexes cannot be taken in a non-preemptible context,
> causing a panic in `fec_ptp_save_state()`. Replacing
> `ptp_clk_mutex` by `tmreg_lock` fixes this.

I was on holidays, but this doesn't look good.

> Fixes: 6a4d7234ae9a ("net: fec: ptp: avoid register access when ipg clock is disabled")
> Fixes: f79959220fa5 ("fec: Restart PPS after link state change")
> Reported-by: Marc Kleine-Budde <mkl@...gutronix.de>
> Link: https://lore.kernel.org/all/20220827160922.642zlcd5foopozru@pengutronix.de/
> Signed-off-by: Csókás Bence <csokas.bence@...lan.hu>
> ---
>  drivers/net/ethernet/freescale/fec.h      |  1 -
>  drivers/net/ethernet/freescale/fec_main.c | 17 +++++++-------
>  drivers/net/ethernet/freescale/fec_ptp.c  | 28 ++++++++---------------
>  3 files changed, 19 insertions(+), 27 deletions(-)
> 
> diff --git a/drivers/net/ethernet/freescale/fec.h b/drivers/net/ethernet/freescale/fec.h
> index 0cebe4b63adb..38f095260e1f 100644
> --- a/drivers/net/ethernet/freescale/fec.h
> +++ b/drivers/net/ethernet/freescale/fec.h
> @@ -557,7 +557,6 @@ struct fec_enet_private {
>  	struct clk *clk_2x_txclk;
>  
>  	bool ptp_clk_on;
> -	struct mutex ptp_clk_mutex;
>  	unsigned int num_tx_queues;
>  	unsigned int num_rx_queues;
>  
> diff --git a/drivers/net/ethernet/freescale/fec_main.c b/drivers/net/ethernet/freescale/fec_main.c
> index b0d60f898249..ab1ee9508f76 100644
> --- a/drivers/net/ethernet/freescale/fec_main.c
> +++ b/drivers/net/ethernet/freescale/fec_main.c
> @@ -2028,6 +2028,7 @@ static void fec_enet_phy_reset_after_clk_enable(struct net_device *ndev)
>  static int fec_enet_clk_enable(struct net_device *ndev, bool enable)
>  {
>  	struct fec_enet_private *fep = netdev_priv(ndev);
> +	unsigned long flags;
>  	int ret;
>  
>  	if (enable) {
> @@ -2036,15 +2037,15 @@ static int fec_enet_clk_enable(struct net_device *ndev, bool enable)
>  			return ret;
>  
>  		if (fep->clk_ptp) {
> -			mutex_lock(&fep->ptp_clk_mutex);
> +			spin_lock_irqsave(&fep->tmreg_lock, flags);
>  			ret = clk_prepare_enable(fep->clk_ptp);

clock_prepare() (and thus clk_prepare_enable()) must not be called from atomic
context.

Marc

-- 
Pengutronix e.K.                 | Marc Kleine-Budde           |
Embedded Linux                   | https://www.pengutronix.de  |
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