Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Mon, 19 Aug 2019 17:04:53 -0700
From:   Jakub Kicinski <jakub.kicinski@netronome.com>
To:     Thomas Bogendoerfer <tbogendoerfer@suse.de>
Cc:     Jonathan Corbet <corbet@lwn.net>,
        Ralf Baechle <ralf@linux-mips.org>,
        Paul Burton <paul.burton@mips.com>,
        James Hogan <jhogan@kernel.org>,
        Dmitry Torokhov <dmitry.torokhov@gmail.com>,
        Lee Jones <lee.jones@linaro.org>,
        "David S. Miller" <davem@davemloft.net>,
        Srinivas Kandagatla <srinivas.kandagatla@linaro.org>,
        Alessandro Zummo <a.zummo@towertech.it>,
        Alexandre Belloni <alexandre.belloni@bootlin.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jiri Slaby <jslaby@suse.com>,
        Evgeniy Polyakov <zbr@ioremap.net>, linux-doc@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-mips@vger.kernel.org,
        linux-input@vger.kernel.org, netdev@vger.kernel.org,
        linux-rtc@vger.kernel.org, linux-serial@vger.kernel.org
Subject: Re: [PATCH v5 11/17] net: sgi: ioc3-eth: no need to stop queue
 set_multicast_list
Message-ID: <20190819170440.37ff18d4@cakuba.netronome.com>
In-Reply-To: <20190819163144.3478-12-tbogendoerfer@suse.de>
References: <20190819163144.3478-1-tbogendoerfer@suse.de>
        <20190819163144.3478-12-tbogendoerfer@suse.de>
Organization: Netronome Systems, Ltd.
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: quoted-printable
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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.
>=20
> Signed-off-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
> ---
>  drivers/net/ethernet/sgi/ioc3-eth.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
>=20
> diff --git a/drivers/net/ethernet/sgi/ioc3-eth.c b/drivers/net/ethernet/s=
gi/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_devi=
ce *dev)
>  	struct netdev_hw_addr *ha;
>  	u64 ehar =3D 0;
> =20
> -	netif_stop_queue(dev);				/* Lock out others. */
> -
> +	spin_lock_irq(&ip->ioc3_lock);

What does this lock protect? =F0=9F=A4=94 No question that stopping TX queu=
es
makes little sense, but this function is only called from
ndo_set_rx_mode(), so with rtnl_lock held.=20

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 |=3D EMCR_PROMISC;
>  		writel(ip->emcr, &regs->emcr);
> @@ -1572,7 +1571,7 @@ static void ioc3_set_multicast_list(struct net_devi=
ce *dev)
>  		writel(ip->ehar_l, &regs->ehar_l);
>  	}
> =20
> -	netif_wake_queue(dev);			/* Let us get going again. */
> +	spin_unlock_irq(&ip->ioc3_lock);
>  }
> =20
>  module_pci_driver(ioc3_driver);