Commit 3f1baa91 authored by Sankararaman Jayaraman's avatar Sankararaman Jayaraman Committed by Jakub Kicinski
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vmxnet3: Fix tx queue race condition with XDP 



If XDP traffic runs on a CPU which is greater than or equal to
the number of the Tx queues of the NIC, then vmxnet3_xdp_get_tq()
always picks up queue 0 for transmission as it uses reciprocal scale
instead of simple modulo operation.

vmxnet3_xdp_xmit() and vmxnet3_xdp_xmit_frame() use the above
returned queue without any locking which can lead to race conditions
when multiple XDP xmits run in parallel on different CPU's.

This patch uses a simple module scheme when the current CPU equals or
exceeds the number of Tx queues on the NIC. It also adds locking in
vmxnet3_xdp_xmit() and vmxnet3_xdp_xmit_frame() functions.

Fixes: 54f00cce ("vmxnet3: Add XDP support.")
Signed-off-by: default avatarSankararaman Jayaraman <sankararaman.jayaraman@broadcom.com>
Signed-off-by: default avatarRonak Doshi <ronak.doshi@broadcom.com>
Reviewed-by: default avatarSimon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20250131042340.156547-1-sankararaman.jayaraman@broadcom.com
Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parent a8aa6a6d

drivers/net/vmxnet3/vmxnet3_xdp.c

+12 −2
Original line number Diff line number Diff line
@@ -28,7 +28,7 @@ vmxnet3_xdp_get_tq(struct vmxnet3_adapter *adapter) 
	if (likely(cpu < tq_number))

		tq = &adapter->tx_queue[cpu];

	else

		tq = &adapter->tx_queue[reciprocal_scale(cpu, tq_number)];

		tq = &adapter->tx_queue[cpu % tq_number];



	return tq;

}
@@ -124,6 +124,7 @@ vmxnet3_xdp_xmit_frame(struct vmxnet3_adapter *adapter, 
	u32 buf_size;

	u32 dw2;



	spin_lock_irq(&tq->tx_lock);

	dw2 = (tq->tx_ring.gen ^ 0x1) << VMXNET3_TXD_GEN_SHIFT;

	dw2 |= xdpf->len;

	ctx.sop_txd = tq->tx_ring.base + tq->tx_ring.next2fill;
@@ -134,6 +135,7 @@ vmxnet3_xdp_xmit_frame(struct vmxnet3_adapter *adapter, 


	if (vmxnet3_cmd_ring_desc_avail(&tq->tx_ring) == 0) {

		tq->stats.tx_ring_full++;

		spin_unlock_irq(&tq->tx_lock);

		return -ENOSPC;

	}
@@ -142,8 +144,10 @@ vmxnet3_xdp_xmit_frame(struct vmxnet3_adapter *adapter, 
		tbi->dma_addr = dma_map_single(&adapter->pdev->dev,

					       xdpf->data, buf_size,

					       DMA_TO_DEVICE);

		if (dma_mapping_error(&adapter->pdev->dev, tbi->dma_addr))

		if (dma_mapping_error(&adapter->pdev->dev, tbi->dma_addr)) {

			spin_unlock_irq(&tq->tx_lock);

			return -EFAULT;

		}

		tbi->map_type |= VMXNET3_MAP_SINGLE;

	} else { /* XDP buffer from page pool */

		page = virt_to_page(xdpf->data);
@@ -182,6 +186,7 @@ vmxnet3_xdp_xmit_frame(struct vmxnet3_adapter *adapter, 
	dma_wmb();

	gdesc->dword[2] = cpu_to_le32(le32_to_cpu(gdesc->dword[2]) ^

						  VMXNET3_TXD_GEN);

	spin_unlock_irq(&tq->tx_lock);



	/* No need to handle the case when tx_num_deferred doesn't reach

	 * threshold. Backend driver at hypervisor side will poll and reset
@@ -225,6 +230,7 @@ vmxnet3_xdp_xmit(struct net_device *dev, 
{

	struct vmxnet3_adapter *adapter = netdev_priv(dev);

	struct vmxnet3_tx_queue *tq;

	struct netdev_queue *nq;

	int i;



	if (unlikely(test_bit(VMXNET3_STATE_BIT_QUIESCED, &adapter->state)))
@@ -236,6 +242,9 @@ vmxnet3_xdp_xmit(struct net_device *dev, 
	if (tq->stopped)

		return -ENETDOWN;



	nq = netdev_get_tx_queue(adapter->netdev, tq->qid);



	__netif_tx_lock(nq, smp_processor_id());

	for (i = 0; i < n; i++) {

		if (vmxnet3_xdp_xmit_frame(adapter, frames[i], tq, true)) {

			tq->stats.xdp_xmit_err++;
@@ -243,6 +252,7 @@ vmxnet3_xdp_xmit(struct net_device *dev, 
		}

	}

	tq->stats.xdp_xmit += i;

	__netif_tx_unlock(nq);



	return i;

}