netdev - [PATCH v2] davinci_emac: Do not free all rx dma descriptors during init

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Date:	Thu, 23 Feb 2012 12:14:17 +0100
From:	Christian Riesch <christian.riesch@...cron.at>
To:	<netdev@...r.kernel.org>
CC:	<davinci-linux-open-source@...ux.davincidsp.com>,
	<linux-arm-kernel@...ts.infradead.org>,
	Christian Riesch <christian.riesch@...cron.at>,
	<stable@...r.kernel.org>, "Hegde, Vinay" <vinay.hegde@...com>,
	Cyril Chemparathy <cyril@...com>,
	Sascha Hauer <s.hauer@...gutronix.de>
Subject: [PATCH v2] davinci_emac: Do not free all rx dma descriptors during init

This patch fixes a regression that was introduced by

commit 0a5f38467765ee15478db90d81e40c269c8dda20
davinci_emac: Add Carrier Link OK check in Davinci RX Handler

Said commit adds a check whether the carrier link is ok. If the link is
not ok, the skb is freed and no new dma descriptor added to the rx dma
channel. This causes trouble during initialization when the carrier
status has not yet been updated. If a lot of packets are received while
netif_carrier_ok returns false, all dma descriptors are freed and the
rx dma transfer is stopped.

The bug occurs when the board is connected to a network with lots of
traffic and the ifconfig down/up is done, e.g., when reconfiguring
the interface with DHCP.

The bug can be reproduced by flood pinging the davinci board while doing
ifconfig eth0 down
ifconfig eth0 up
on the board.

After that, the rx path stops working and the overrun value reported
by ifconfig is counting up.

This patch reverts commit 0a5f38467765ee15478db90d81e40c269c8dda20
and instead issues warnings only if cpdma_chan_submit returns -ENOMEM.

Signed-off-by: Christian Riesch <christian.riesch@...cron.at>
Cc: <stable@...r.kernel.org>
Cc: Hegde, Vinay <vinay.hegde@...com>
Cc: Cyril Chemparathy <cyril@...com>
Cc: Sascha Hauer <s.hauer@...gutronix.de>
---

Hi,
Since my first submission of this patch yesterday I did additional tests
with suspend/rtcwake. My tests confirmed that the solution in this
patch solves the problem that was addressed by commit
0a5f38467765ee15478db90d81e40c269c8dda20 while not destroying the
rx communication channel. 

Changes since v1:
- Removed the 'RFC' from subject line
- Added more information to the commit message
- Added stable tag, I think this patch meets the rules in
  Documentation/stable_kernel_rules.txt

Regards, Christian

 drivers/net/ethernet/ti/davinci_emac.c |    6 ++++--
 1 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/ti/davinci_emac.c b/drivers/net/ethernet/ti/davinci_emac.c
index 4fa0bcb..4b2f545 100644
--- a/drivers/net/ethernet/ti/davinci_emac.c
+++ b/drivers/net/ethernet/ti/davinci_emac.c
@@ -1009,7 +1009,7 @@ static void emac_rx_handler(void *token, int len, int status)
 	int			ret;

 	/* free and bail if we are shutting down */
-	if (unlikely(!netif_running(ndev) || !netif_carrier_ok(ndev))) {
+	if (unlikely(!netif_running(ndev))) {
 		dev_kfree_skb_any(skb);
 		return;
 	}
@@ -1038,7 +1038,9 @@ static void emac_rx_handler(void *token, int len, int status)
 recycle:
 	ret = cpdma_chan_submit(priv->rxchan, skb, skb->data,
 			skb_tailroom(skb), GFP_KERNEL);
-	if (WARN_ON(ret < 0))
+
+	WARN_ON(ret == -ENOMEM);
+	if (unlikely(ret < 0))
 		dev_kfree_skb_any(skb);
 }

-- 
1.7.0.4

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