netdev - [PATCH] net/fec: call netif_carrier

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Message-Id: <1374758875-7926-1-git-send-email-u.kleine-koenig@pengutronix.de>
Date:	Thu, 25 Jul 2013 15:27:55 +0200
From:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
To:	netdev@...r.kernel.org
Cc:	"David S. Miller" <davem@...emloft.net>,
	Fabio Estevam <fabio.estevam@...escale.com>,
	Frank Li <Frank.Li@...escale.com>,
	Shawn Guo <shawn.guo@...aro.org>, kernel@...gutronix.de,
	Hector Palacios <hector.palacios@...i.com>,
	Tim Sander <tim.sander@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: [PATCH] net/fec: call netif_carrier_off when not having link

Without this patch I see a machine running an -rt patched Linux being
stuck in sch_direct_xmit when it looses link while there is still a
packet to be send. In this case the fec_enet_start_xmit routine returns
NETDEV_TX_BUSY which makes the network stack reschedule the packet and
so sch_direct_xmit calls fec_enet_start_xmit again.

The right fix is to tell the network stack that the link was lost (using
netif_carrier_off) so that it doesn't even try to get rid of the pending
packets.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
---
Hello,

this resembles a problem described on the linux-rt mailing list some
time ago:

	http://thread.gmane.org/gmane.linux.rt.user/7815

So I Cc:d the people that participated in that thread.

IMHO this is 3.11 material (assuming I did it right) and is even worth
backporting as I think the problem exists in mainline, too, just harder
to trigger.

Best regards
Uwe

 drivers/net/ethernet/freescale/fec_main.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/drivers/net/ethernet/freescale/fec_main.c b/drivers/net/ethernet/freescale/fec_main.c
index 0642006..631bd5a 100644
--- a/drivers/net/ethernet/freescale/fec_main.c
+++ b/drivers/net/ethernet/freescale/fec_main.c
@@ -280,11 +280,6 @@ fec_enet_start_xmit(struct sk_buff *skb, struct net_device *ndev)
 	unsigned short	status;
 	unsigned int index;
 
-	if (!fep->link) {
-		/* Link is down or auto-negotiation is in progress. */
-		return NETDEV_TX_BUSY;
-	}
-
 	/* Fill in a Tx ring entry */
 	bdp = fep->cur_tx;
 
@@ -459,6 +454,11 @@ fec_restart(struct net_device *ndev, int duplex)
 		netif_tx_lock_bh(ndev);
 	}
 
+	if (!fep->link)
+		netif_carrier_off(ndev);
+	else
+		netif_carrier_on(ndev);
+
 	/* Whack a reset.  We should wait for this. */
 	writel(1, fep->hwp + FEC_ECNTRL);
 	udelay(10);
-- 
1.8.3.2

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