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rt2x00: fix random stalls
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Is possible that we stop queue and then do not wake up it again,
especially when packets are transmitted fast. That can be easily
reproduced with modified tx queue entry_num to some small value e.g. 16.

If mac80211 already hold local->queue_stop_reason_lock, then we can wait
on that lock in both rt2x00queue_pause_queue() and
rt2x00queue_unpause_queue(). After drooping ->queue_stop_reason_lock
is possible that __ieee80211_wake_queue() will be performed before
__ieee80211_stop_queue(), hence we stop queue and newer wake up it
again.

Another race condition is possible when between rt2x00queue_threshold()
check and rt2x00queue_pause_queue() we will process all pending tx
buffers on different cpu. This might happen if for example interrupt
will be triggered on cpu performing rt2x00mac_tx().

To prevent race conditions serialize pause/unpause by queue->tx_lock.

Cc: stable@vger.kernel.org
Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
Acked-by: Gertjan van Wingerde <gwingerde@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
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Stanislaw Gruszka authored and linvjw committed Mar 12, 2012
1 parent 210787e commit 3780d03
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Showing 3 changed files with 17 additions and 1 deletion.
6 changes: 5 additions & 1 deletion drivers/net/wireless/rt2x00/rt2x00dev.c
Expand Up @@ -426,10 +426,14 @@ void rt2x00lib_txdone(struct queue_entry *entry,
/*
* If the data queue was below the threshold before the txdone
* handler we must make sure the packet queue in the mac80211 stack
* is reenabled when the txdone handler has finished.
* is reenabled when the txdone handler has finished. This has to be
* serialized with rt2x00mac_tx(), otherwise we can wake up queue
* before it was stopped.
*/
spin_lock_bh(&entry->queue->tx_lock);
if (!rt2x00queue_threshold(entry->queue))
rt2x00queue_unpause_queue(entry->queue);
spin_unlock_bh(&entry->queue->tx_lock);
}
EXPORT_SYMBOL_GPL(rt2x00lib_txdone);

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9 changes: 9 additions & 0 deletions drivers/net/wireless/rt2x00/rt2x00mac.c
Expand Up @@ -152,13 +152,22 @@ void rt2x00mac_tx(struct ieee80211_hw *hw, struct sk_buff *skb)
if (unlikely(rt2x00queue_write_tx_frame(queue, skb, false)))
goto exit_fail;

/*
* Pausing queue has to be serialized with rt2x00lib_txdone(). Note
* we should not use spin_lock_bh variant as bottom halve was already
* disabled before ieee80211_xmit() call.
*/
spin_lock(&queue->tx_lock);
if (rt2x00queue_threshold(queue))
rt2x00queue_pause_queue(queue);
spin_unlock(&queue->tx_lock);

return;

exit_fail:
spin_lock(&queue->tx_lock);
rt2x00queue_pause_queue(queue);
spin_unlock(&queue->tx_lock);
exit_free_skb:
ieee80211_free_txskb(hw, skb);
}
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3 changes: 3 additions & 0 deletions drivers/net/wireless/rt2x00/rt2x00queue.c
Expand Up @@ -619,6 +619,9 @@ int rt2x00queue_write_tx_frame(struct data_queue *queue, struct sk_buff *skb,
else if (test_bit(REQUIRE_DMA, &queue->rt2x00dev->cap_flags))
rt2x00queue_align_frame(skb);

/*
* That function must be called with bh disabled.
*/
spin_lock(&queue->tx_lock);

if (unlikely(rt2x00queue_full(queue))) {
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