netdev - Re: [PATCH v2 net 6/6] net: mvneta: Fix race condition during stopping

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Date:	Wed, 3 Feb 2016 16:01:43 +0800
From:	Jisheng Zhang <jszhang@...vell.com>
To:	Gregory CLEMENT <gregory.clement@...e-electrons.com>
CC:	"David S. Miller" <davem@...emloft.net>,
	<linux-kernel@...r.kernel.org>, <netdev@...r.kernel.org>,
	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
	Lior Amsalem <alior@...vell.com>, Andrew Lunn <andrew@...n.ch>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	Jason Cooper <jason@...edaemon.net>,
	Nadav Haklai <nadavh@...vell.com>,
	Marcin Wojtas <mw@...ihalf.com>, Willy Tarreau <w@....eu>,
	<linux-arm-kernel@...ts.infradead.org>,
	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>
Subject: Re: [PATCH v2 net 6/6] net: mvneta: Fix race condition during
 stopping

On Mon, 1 Feb 2016 14:07:47 +0100 Gregory CLEMENT wrote:

> When stopping the port, the CPU notifier are still there whereas the
> mvneta_stop_dev function calls mvneta_percpu_disable() on each CPUs.
> It was possible to have a new CPU coming at this point which could be
> racy.
> 
> This patch adds a flag preventing executing the code notifier for a new CPU
> when the port is stopping.
> 
> Signed-off-by: Gregory CLEMENT <gregory.clement@...e-electrons.com>
> ---
>  drivers/net/ethernet/marvell/mvneta.c | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
> 
> diff --git a/drivers/net/ethernet/marvell/mvneta.c b/drivers/net/ethernet/marvell/mvneta.c
> index 4d40d2fde7ca..2f53975aa6ec 100644
> --- a/drivers/net/ethernet/marvell/mvneta.c
> +++ b/drivers/net/ethernet/marvell/mvneta.c
> @@ -374,6 +374,7 @@ struct mvneta_port {
>  	 * ensuring that the configuration remains coherent.
>  	 */
>  	spinlock_t lock;
> +	bool is_stopping;
>  
>  	/* Core clock */
>  	struct clk *clk;
> @@ -2916,6 +2917,11 @@ static int mvneta_percpu_notifier(struct notifier_block *nfb,
>  	switch (action) {
>  	case CPU_ONLINE:
>  	case CPU_ONLINE_FROZEN:
> +		/* Configuring the driver for a new CPU while the
> +		 * driver is stopping is racy, so just avoid it.
> +		 */
> +		if (pp->is_stopping)
> +			break;

I still see race. What about another cpu set is_stopping at this point?

Thanks


>  		netif_tx_stop_all_queues(pp->dev);
>  
>  		/* We have to synchronise on tha napi of each CPU
> @@ -3054,9 +3060,17 @@ static int mvneta_stop(struct net_device *dev)
>  {
>  	struct mvneta_port *pp = netdev_priv(dev);
>  
> +	/* Inform that we are stopping so we don't want to setup the
> +	 * driver for new CPUs in the notifiers
> +	 */
> +	pp->is_stopping = true;
>  	mvneta_stop_dev(pp);
>  	mvneta_mdio_remove(pp);
>  	unregister_cpu_notifier(&pp->cpu_notifier);
> +	/* Now that the notifier are unregistered, we can clear the
> +	 * flag
> +	 */
> +	pp->is_stopping = false;
>  	on_each_cpu(mvneta_percpu_disable, pp, true);
>  	free_percpu_irq(dev->irq, pp->ports);
>  	mvneta_cleanup_rxqs(pp);