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

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.

Suggested-by: Alexander Duyck <alexander.duyck@gmail.com>
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Lendacky, Thomas 2015-10-26 17:13:54 -05:00 committed by David S. Miller
parent 8ce675ff39
commit 20986ed826
2 changed files with 5 additions and 1 deletions
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2
drivers/net/ethernet/amd/xgbe/xgbe-dev.c
View File

@ -1595,7 +1595,7 @@ static void xgbe_dev_xmit(struct xgbe_channel *channel)
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 ||

4
drivers/net/ethernet/amd/xgbe/xgbe-drv.c
View File

@ -1816,6 +1816,10 @@ static int xgbe_tx_poll(struct xgbe_channel *channel)
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) &&