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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
Show stats Download patch file Download diff file Expand all files Collapse all files

2
drivers/net/ixgbe/ixgbe_main.c
View file

@ -4001,7 +4001,7 @@ static void ixgbe_set_num_queues(struct ixgbe_adapter *adapter)
done:
/* Notify the stack of the (possibly) reduced Tx Queue count. */
adapter->netdev->real_num_tx_queues = adapter->num_tx_queues;
netif_set_real_num_tx_queues(adapter->netdev, adapter->num_tx_queues);
}
static void ixgbe_acquire_msix_vectors(struct ixgbe_adapter *adapter,

3
include/linux/netdevice.h
View file

@ -1656,6 +1656,9 @@ static inline int netif_is_multiqueue(const struct net_device *dev)
return (dev->num_tx_queues > 1);
}
extern void netif_set_real_num_tx_queues(struct net_device *dev,
unsigned int txq);
/* Use this variant when it is known for sure that it
* is executing from hardware interrupt context or with hardware interrupts
* disabled.

12
include/net/sch_generic.h
View file

@ -313,13 +313,12 @@ extern void qdisc_calculate_pkt_len(struct sk_buff *skb,
extern void tcf_destroy(struct tcf_proto *tp);
extern void tcf_destroy_chain(struct tcf_proto **fl);
/* Reset all TX qdiscs of a device. */
static inline void qdisc_reset_all_tx(struct net_device *dev)
/* Reset all TX qdiscs greater then index of a device. */
static inline void qdisc_reset_all_tx_gt(struct net_device *dev, unsigned int i)
{
unsigned int i;
struct Qdisc *qdisc;
for (i = 0; i < dev->num_tx_queues; i++) {
for (; i < dev->num_tx_queues; i++) {
qdisc = netdev_get_tx_queue(dev, i)->qdisc;
if (qdisc) {
spin_lock_bh(qdisc_lock(qdisc));
@ -329,6 +328,11 @@ static inline void qdisc_reset_all_tx(struct net_device *dev)
}
}
static inline void qdisc_reset_all_tx(struct net_device *dev)
{
qdisc_reset_all_tx_gt(dev, 0);
}
/* Are all TX queues of the device empty? */
static inline bool qdisc_all_tx_empty(const struct net_device *dev)
{

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)
{