linux-kernel - Re: [PATCH v5 11/17] net: sgi: ioc3-eth: no need to stop queue set_multicast

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Date:   Mon, 19 Aug 2019 17:04:53 -0700
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Thomas Bogendoerfer <tbogendoerfer@...e.de>
Cc:     Jonathan Corbet <corbet@....net>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Paul Burton <paul.burton@...s.com>,
        James Hogan <jhogan@...nel.org>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Lee Jones <lee.jones@...aro.org>,
        "David S. Miller" <davem@...emloft.net>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Alessandro Zummo <a.zummo@...ertech.it>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>,
        Evgeniy Polyakov <zbr@...emap.net>, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mips@...r.kernel.org,
        linux-input@...r.kernel.org, netdev@...r.kernel.org,
        linux-rtc@...r.kernel.org, linux-serial@...r.kernel.org
Subject: Re: [PATCH v5 11/17] net: sgi: ioc3-eth: no need to stop queue
 set_multicast_list

On Mon, 19 Aug 2019 18:31:34 +0200, Thomas Bogendoerfer wrote:
> netif_stop_queue()/netif_wake_qeue() aren't needed for changing
> multicast filters. Use spinlocks instead for proper protection
> of private struct.
> 
> Signed-off-by: Thomas Bogendoerfer <tbogendoerfer@...e.de>
> ---
>  drivers/net/ethernet/sgi/ioc3-eth.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/net/ethernet/sgi/ioc3-eth.c b/drivers/net/ethernet/sgi/ioc3-eth.c
> index d862f28887f9..7f85a3bfef14 100644
> --- a/drivers/net/ethernet/sgi/ioc3-eth.c
> +++ b/drivers/net/ethernet/sgi/ioc3-eth.c
> @@ -1542,8 +1542,7 @@ static void ioc3_set_multicast_list(struct net_device *dev)
>  	struct netdev_hw_addr *ha;
>  	u64 ehar = 0;
>  
> -	netif_stop_queue(dev);				/* Lock out others. */
> -
> +	spin_lock_irq(&ip->ioc3_lock);

What does this lock protect? 🤔 No question that stopping TX queues
makes little sense, but this function is only called from
ndo_set_rx_mode(), so with rtnl_lock held. 

I thought it may protect ip->emcr, but that one is accessed with no
locking from the ioc3_timer() -> ioc3_setup_duplex() path..

>  	if (dev->flags & IFF_PROMISC) {			/* Set promiscuous.  */
>  		ip->emcr |= EMCR_PROMISC;
>  		writel(ip->emcr, &regs->emcr);
> @@ -1572,7 +1571,7 @@ static void ioc3_set_multicast_list(struct net_device *dev)
>  		writel(ip->ehar_l, &regs->ehar_l);
>  	}
>  
> -	netif_wake_queue(dev);			/* Let us get going again. */
> +	spin_unlock_irq(&ip->ioc3_lock);
>  }
>  
>  module_pci_driver(ioc3_driver);