Patch "amd-xgbe: Use wmb before updating current descriptor count" has been added to the 4.2-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    amd-xgbe: Use wmb before updating current descriptor count

to the 4.2-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     amd-xgbe-use-wmb-before-updating-current-descriptor-count.patch
and it can be found in the queue-4.2 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From foo@baz Tue Nov 17 14:34:38 PST 2015
From: "Lendacky, Thomas" <Thomas.Lendacky@amd.com>
Date: Wed, 21 Oct 2015 15:37:05 -0500
Subject: amd-xgbe: Use wmb before updating current descriptor count

From: "Lendacky, Thomas" <Thomas.Lendacky@amd.com>

[ Upstream commit 20a41fba679d665cdae2808e2b9cae97c073351f ]

The code currently uses the lightweight dma_wmb barrier before updating
the current descriptor count. Under heavy load, the Tx cleanup routine
was seeing the updated current descriptor count before the updated
descriptor information. As a result, the Tx descriptor was being cleaned
up before it was used because it was not "owned" by the hardware yet,
resulting in a Tx queue hang.

Using the wmb barrier insures that the descriptor is updated before the
descriptor counter preventing the Tx queue hang. For extra insurance,
the Tx cleanup routine is changed to grab the current decriptor count on
entry and uses that initial value in the processing loop rather than
trying to chase the current value.

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Tested-by: Christoffer Dall <christoffer.dall@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/net/ethernet/amd/xgbe/xgbe-dev.c |    2 +-
 drivers/net/ethernet/amd/xgbe/xgbe-drv.c |    4 +++-
 2 files changed, 4 insertions(+), 2 deletions(-)

--- a/drivers/net/ethernet/amd/xgbe/xgbe-dev.c
+++ b/drivers/net/ethernet/amd/xgbe/xgbe-dev.c
@@ -1595,7 +1595,7 @@ static void xgbe_dev_xmit(struct xgbe_ch
 				  packet->rdesc_count, 1);
 
 	/* Make sure ownership is written to the descriptor */
-	dma_wmb();
+	wmb();
 
 	ring->cur = cur_index + 1;
 	if (!packet->skb->xmit_more ||
--- a/drivers/net/ethernet/amd/xgbe/xgbe-drv.c
+++ b/drivers/net/ethernet/amd/xgbe/xgbe-drv.c
@@ -1807,6 +1807,7 @@ static int xgbe_tx_poll(struct xgbe_chan
 	struct netdev_queue *txq;
 	int processed = 0;
 	unsigned int tx_packets = 0, tx_bytes = 0;
+	unsigned int cur;
 
 	DBGPR("-->xgbe_tx_poll\n");
 
@@ -1814,10 +1815,11 @@ static int xgbe_tx_poll(struct xgbe_chan
 	if (!ring)
 		return 0;
 
+	cur = ring->cur;
 	txq = netdev_get_tx_queue(netdev, channel->queue_index);
 
 	while ((processed < XGBE_TX_DESC_MAX_PROC) &&
-	       (ring->dirty != ring->cur)) {
+	       (ring->dirty != cur)) {
 		rdata = XGBE_GET_DESC_DATA(ring, ring->dirty);
 		rdesc = rdata->rdesc;
 


Patches currently in stable-queue which might be from Thomas.Lendacky@amd.com are

queue-4.2/amd-xgbe-fix-race-between-access-of-desc-and-desc-index.patch
queue-4.2/amd-xgbe-use-wmb-before-updating-current-descriptor-count.patch