Patch "net/mlx4_en: fixup xdp tx irq to match rx" has been added to the 4.8-stable tree

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

net/mlx4_en: fixup xdp tx irq to match rx

to the 4.8-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:
net-mlx4_en-fixup-xdp-tx-irq-to-match-rx.patch
and it can be found in the queue-4.8 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Brenden Blanco <[email protected]>
Date: Thu, 13 Oct 2016 13:13:11 -0700
Subject: net/mlx4_en: fixup xdp tx irq to match rx

From: Brenden Blanco <[email protected]>

[ Upstream commit 958b3d396d7f80755e2c2e6a8f873a669f38de10 ]

In cases where the number of tx rings is not a multiple of the number of rx rings, the tx completion event will be handled on a different core from the transmit and population of the ring. Races on the ring will lead to a double-free of the page, and possibly other corruption.

The rings are initialized by default with a valid multiple of rings, based on the number of cpus, therefore an invalid configuration requires ethtool to change the ring layout. For instance 'ethtool -L eth0 rx 9 tx 8' will cause packets received on rx0, and XDP_TX'd to tx48, to be completed on cpu3 (48 % 9 == 3).

Resolve this discrepancy by shifting the irq for the xdp tx queues to start again from 0, modulo rx_ring_num.

---
 drivers/net/ethernet/mellanox/mlx4/en_cq.c |    8 ++++++++
 1 file changed, 8 insertions(+)

@@ -127,7 +127,15 @@ int mlx4_en_activate_cq(struct mlx4_en_p
 		/* For TX we use the same irq per
 		ring we assigned for the RX    */
 		struct mlx4_en_cq *rx_cq;
+		int xdp_index;
 
+		/* The xdp tx irq must align with the rx ring that forwards to
+		 * it, so reindex these from 0. This should only happen when
+		 * tx_ring_num is not a multiple of rx_ring_num.
+		 */
+		xdp_index = (priv->xdp_ring_num - priv->tx_ring_num) + cq_idx;
+		if (xdp_index >= 0)
+			cq_idx = xdp_index;
 		cq_idx = cq_idx % priv->rx_ring_num;
 		rx_cq = priv->rx_cq[cq_idx];
 		cq->vector = rx_cq->vector;

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

queue-4.8/net-mlx4_en-fixup-xdp-tx-irq-to-match-rx.patch