This is a note to let you know that I've just added the patch titled
net: Add memory barriers to prevent possible race in byte queue limits
to the 3.3-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
net-add-memory-barriers-to-prevent-possible-race-in-byte-queue-limits.patch
and it can be found in the queue-3.3 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <[email protected]> know about it.
>From c58e988584c4664bc1eb8d5efc70ebf007f51ce3 Mon Sep 17 00:00:00 2001
From: Alexander Duyck <[email protected]>
Date: Tue, 7 Feb 2012 02:29:06 +0000
Subject: net: Add memory barriers to prevent possible race in byte queue limits
From: Alexander Duyck <[email protected]>
[ 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 <[email protected]>
Tested-by: Stephen Ko <[email protected]>
Signed-off-by: Jeff Kirsher <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
include/linux/netdevice.h | 49 ++++++++++++++++++++++++++++++----------------
1 file changed, 33 insertions(+), 16 deletions(-)
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -1898,12 +1898,22 @@ static inline void netdev_tx_sent_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_q
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
}
Patches currently in stable-queue which might be from
[email protected] are
queue-3.3/net-add-memory-barriers-to-prevent-possible-race-in-byte-queue-limits.patch
queue-3.3/net-fix-issue-with-netdev_tx_reset_queue-not-resetting-queue-from-xoff-state.patch
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