[net-next 05/14] net: Add memory barriers to prevent possible race in byte queue limits
flat view
STALE5298d
REVIEWED: 1 (0M)
From: Jeff Kirsher <hidden>
Date: 2012-03-13 04:03:59
Subsystem:
networking drivers, networking [general], the rest · Maintainers:
Andrew Lunn, "David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds
1 review trailer.
From: Alexander Duyck <redacted> 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 <redacted> Tested-by: Stephen Ko <redacted> Signed-off-by: Jeff Kirsher <redacted> --- include/linux/netdevice.h | 49 ++++++++++++++++++++++++++++++-------------- 1 files changed, 33 insertions(+), 16 deletions(-)
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 4bf314f..4535a4e 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h@@ -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 }
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1.7.7.6