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authorAlexander Duyck <alexander.h.duyck@intel.com>2012-02-07 02:29:06 +0000
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2012-05-12 09:32:19 -0700
commit4680d7ad59b1aeab6bd04d326523cf8e6b305f02 (patch)
tree33a9373494cfcf2c761e658f2a6329a0ae578d86
parent4f3f1e28d64084bae113cf9d3ca516bdc43046ad (diff)
net: Add memory barriers to prevent possible race in byte queue limits
[ Upstream commit b37c0fbe3f6dfba1f8ad2aed47fb40578a254635 ] 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> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--include/linux/netdevice.h49
1 files changed, 33 insertions, 16 deletions
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 4f3b01a3d696..ebf598097890 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -1898,12 +1898,22 @@ 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
}
@@ -1916,16 +1926,23 @@ 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
}