Patch "amd-xgbe: Fix race between access of desc and desc index" has been added to the 4.2-stable tree

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

amd-xgbe: Fix race between access of desc and desc index

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-fix-race-between-access-of-desc-and-desc-index.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 <[email protected]> know about it.

From: "Lendacky, Thomas" <[email protected]>
Date: Mon, 26 Oct 2015 17:13:54 -0500
Subject: amd-xgbe: Fix race between access of desc and desc index

From: "Lendacky, Thomas" <[email protected]>

[ Upstream commit 20986ed826cbb36bb8f2d77f872e3c52d8d30647 ]

During Tx cleanup it's still possible for the descriptor data to be read ahead of the descriptor index. A memory barrier is required between the read of the descriptor index and the start of the Tx cleanup loop. This allows a change to a lighter-weight barrier in the Tx transmit routine just before updating the current descriptor index.

Since the memory barrier does result in extra overhead on arm64, keep the previous change to not chase the current descriptor value. This prevents the execution of the barrier for each loop performed.

---
 drivers/net/ethernet/amd/xgbe/xgbe-dev.c |    2 +-
 drivers/net/ethernet/amd/xgbe/xgbe-drv.c |    4 ++++
 2 files changed, 5 insertions(+), 1 deletion(-)

@@ -1595,7 +1595,7 @@ static void xgbe_dev_xmit(struct xgbe_ch
 				  packet->rdesc_count, 1);
 
 	/* Make sure ownership is written to the descriptor */
-	wmb();
+	smp_wmb();
 
 	ring->cur = cur_index + 1;
 	if (!packet->skb->xmit_more ||

@@ -1816,6 +1816,10 @@ static int xgbe_tx_poll(struct xgbe_chan
 		return 0;
 
 	cur = ring->cur;
+
+	/* Be sure we get ring->cur before accessing descriptor data */
+	smp_rmb();
+
 	txq = netdev_get_tx_queue(netdev, channel->queue_index);
 
 	while ((processed < XGBE_TX_DESC_MAX_PROC) &&

Patches currently in stable-queue which might be from [email protected] 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