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net: decreasing real_num_tx_queues needs to flush qdisc

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Reducing real_num_queues needs to flush the qdisc otherwise
skbs with queue_mappings greater then real_num_tx_queues can
be sent to the underlying driver.

The flow for this is,

dev_queue_xmit()
	dev_pick_tx()
		skb_tx_hash()  => hash using real_num_tx_queues
		skb_set_queue_mapping()
	...
	qdisc_enqueue_root() => enqueue skb on txq from hash
...
dev->real_num_tx_queues -= n
...
sch_direct_xmit()
	dev_hard_start_xmit()
		ndo_start_xmit(skb,dev) => skb queue set with old hash

skbs are enqueued on the qdisc with skb->queue_mapping set
0 < queue_mappings < real_num_tx_queues.  When the driver
decreases real_num_tx_queues skb's may be dequeued from the
qdisc with a queue_mapping greater then real_num_tx_queues.

This fixes a case in ixgbe where this was occurring with DCB
and FCoE. Because the driver is using queue_mapping to map
skbs to tx descriptor rings we can potentially map skbs to
rings that no longer exist.

Signed-off-by: John Fastabend <john.r.fastabend@intel.com>
Tested-by: Ross Brattain <ross.b.brattain@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
John Fastabend 2010-07-01 13:21:57 +00:00 • committed by David S. Miller
parent 4ef6acff83
commit f0796d5c73
4 changed files with 30 additions and 5 deletions
Download patch file Download diff file Expand all files Collapse all files

18
net/core/dev.c
View file

@ -1553,6 +1553,24 @@ static void dev_queue_xmit_nit(struct sk_buff *skb, struct net_device *dev)
rcu_read_unlock();
}
/*
* Routine to help set real_num_tx_queues. To avoid skbs mapped to queues
* greater then real_num_tx_queues stale skbs on the qdisc must be flushed.
*/
void netif_set_real_num_tx_queues(struct net_device *dev, unsigned int txq)
{
unsigned int real_num = dev->real_num_tx_queues;
if (unlikely(txq > dev->num_tx_queues))
;
else if (txq > real_num)
dev->real_num_tx_queues = txq;
else if (txq < real_num) {
dev->real_num_tx_queues = txq;
qdisc_reset_all_tx_gt(dev, txq);
}
}
EXPORT_SYMBOL(netif_set_real_num_tx_queues);
static inline void __netif_reschedule(struct Qdisc *q)
{