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net: Add memory barriers to prevent possible race in byte queue limits 

This change adds a memory barrier to the byte queue limit code to address a
possible race as has been seen in the past with the
netif_stop_queue/netif_wake_queue logic.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Tested-by: Stephen Ko <stephen.s.ko@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
This commit is contained in:
Alexander Duyck 2012-02-07 02:29:06 +00:00 committed by Jeff Kirsher
parent 5c4903549c
commit b37c0fbe3f
1 changed files with 33 additions and 16 deletions
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49
include/linux/netdevice.h
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@ -1899,12 +1899,22 @@ static inline void netdev_tx_sent_queue(struct netdev_queue *dev_queue,
{
#ifdef CONFIG_BQL
dql_queued(&dev_queue->dql, bytes);
if (unlikely(dql_avail(&dev_queue->dql) < 0)) {
set_bit(__QUEUE_STATE_STACK_XOFF, &dev_queue->state);
if (unlikely(dql_avail(&dev_queue->dql) >= 0))
clear_bit(__QUEUE_STATE_STACK_XOFF,
&dev_queue->state);
}
if (likely(dql_avail(&dev_queue->dql) >= 0))
return;
set_bit(__QUEUE_STATE_STACK_XOFF, &dev_queue->state);
/*
* The XOFF flag must be set before checking the dql_avail below,
* because in netdev_tx_completed_queue we update the dql_completed
* before checking the XOFF flag.
*/
smp_mb();
/* check again in case another CPU has just made room avail */
if (unlikely(dql_avail(&dev_queue->dql) >= 0))
clear_bit(__QUEUE_STATE_STACK_XOFF, &dev_queue->state);
#endif
}
@ -1917,16 +1927,23 @@ static inline void netdev_tx_completed_queue(struct netdev_queue *dev_queue,
unsigned pkts, unsigned bytes)
{
#ifdef CONFIG_BQL
if (likely(bytes)) {
dql_completed(&dev_queue->dql, bytes);
if (unlikely(test_bit(__QUEUE_STATE_STACK_XOFF,
&dev_queue->state) &&
dql_avail(&dev_queue->dql) >= 0)) {
if (test_and_clear_bit(__QUEUE_STATE_STACK_XOFF,
&dev_queue->state))
netif_schedule_queue(dev_queue);
}
}
if (unlikely(!bytes))
return;
dql_completed(&dev_queue->dql, bytes);
/*
* Without the memory barrier there is a small possiblity that
* netdev_tx_sent_queue will miss the update and cause the queue to
* be stopped forever
*/
smp_mb();
if (dql_avail(&dev_queue->dql) < 0)
return;
if (test_and_clear_bit(__QUEUE_STATE_STACK_XOFF, &dev_queue->state))
netif_schedule_queue(dev_queue);
#endif
}