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@xxxxxxxxxxxxxxx> know about it. >From foo@baz Tue Nov 17 14:34:38 PST 2015 From: "Lendacky, Thomas" <Thomas.Lendacky@xxxxxxx> Date: Wed, 21 Oct 2015 15:37:05 -0500 Subject: amd-xgbe: Use wmb before updating current descriptor count From: "Lendacky, Thomas" <Thomas.Lendacky@xxxxxxx> [ 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@xxxxxxx> Tested-by: Christoffer Dall <christoffer.dall@xxxxxxxxxx> Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- 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@xxxxxxx 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 -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html