linux-kernel - [PATCH 3.19.y-ckt 20/40] net: fec: only clear a queue's work bit if the queue was emptied

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Message-Id: <1464197443-20056-21-git-send-email-kamal@canonical.com>
Date:	Wed, 25 May 2016 10:30:23 -0700
From:	Kamal Mostafa <kamal@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>,
	"David S . Miller" <davem@...emloft.net>,
	Kamal Mostafa <kamal@...onical.com>
Subject: [PATCH 3.19.y-ckt 20/40] net: fec: only clear a queue's work bit if the queue was emptied

3.19.8-ckt22 -stable review patch.  If anyone has any objections, please let me know.

---8<------------------------------------------------------------

From: =?UTF-8?q?Uwe=20Kleine-K=C3=B6nig?= <u.kleine-koenig@...gutronix.de>

commit 1c021bb717a70aaeaa4b25c91f43c2aeddd922de upstream.

In the receive path a queue's work bit was cleared unconditionally even
if fec_enet_rx_queue only read out a part of the available packets from
the hardware. This resulted in not reading any packets in the next napi
turn and so packets were delayed or lost.

The obvious fix is to only clear a queue's bit when the queue was
emptied.

Fixes: 4d494cdc92b3 ("net: fec: change data structure to support multiqueue")
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
Reviewed-by: Lucas Stach <l.stach@...gutronix.de>
Tested-by: Fugang Duan <fugang.duan@....com>
Acked-by: Fugang Duan <fugang.duan@....com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Kamal Mostafa <kamal@...onical.com>
---
 drivers/net/ethernet/freescale/fec_main.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/freescale/fec_main.c b/drivers/net/ethernet/freescale/fec_main.c
index fba3c98..344d7bd 100644
--- a/drivers/net/ethernet/freescale/fec_main.c
+++ b/drivers/net/ethernet/freescale/fec_main.c
@@ -1523,9 +1523,15 @@ fec_enet_rx(struct net_device *ndev, int budget)
 	struct fec_enet_private *fep = netdev_priv(ndev);
 
 	for_each_set_bit(queue_id, &fep->work_rx, FEC_ENET_MAX_RX_QS) {
-		clear_bit(queue_id, &fep->work_rx);
-		pkt_received += fec_enet_rx_queue(ndev,
+		int ret;
+
+		ret = fec_enet_rx_queue(ndev,
 					budget - pkt_received, queue_id);
+
+		if (ret < budget - pkt_received)
+			clear_bit(queue_id, &fep->work_rx);
+
+		pkt_received += ret;
 	}
 	return pkt_received;
 }
-- 
2.7.4