4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Stanislaw Gruszka <sgrus...@redhat.com>


[ Upstream commit 6dd80efd75ce7c2dbd9f117cf585ee2b33a42ee1 ]

Pausing queue without checking threshold is racy with txdone path.
Moreover we do not need pause queue on any error, but only if queue
is full - in case when we send RTS frame ( other cases of almost full
queue are already handled in rt2x00queue_write_tx_frame() ).

Patch fixes of theoretically possible problem of pausing empty
queue.

Signed-off-by: Stanislaw Gruszka <sgrus...@redhat.com>
Tested-by: Enrico Mioso <mrkiko...@gmail.com>
Signed-off-by: Kalle Valo <kv...@codeaurora.org>
Signed-off-by: Sasha Levin <alexander.le...@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
 drivers/net/wireless/ralink/rt2x00/rt2x00mac.c |   22 ++++++++++++++--------
 1 file changed, 14 insertions(+), 8 deletions(-)

--- a/drivers/net/wireless/ralink/rt2x00/rt2x00mac.c
+++ b/drivers/net/wireless/ralink/rt2x00/rt2x00mac.c
@@ -142,15 +142,25 @@ void rt2x00mac_tx(struct ieee80211_hw *h
        if (!rt2x00dev->ops->hw->set_rts_threshold &&
            (tx_info->control.rates[0].flags & (IEEE80211_TX_RC_USE_RTS_CTS |
                                                
IEEE80211_TX_RC_USE_CTS_PROTECT))) {
-               if (rt2x00queue_available(queue) <= 1)
-                       goto exit_fail;
+               if (rt2x00queue_available(queue) <= 1) {
+                       /*
+                        * Recheck for full queue under lock to avoid race
+                        * conditions with rt2x00lib_txdone().
+                        */
+                       spin_lock(&queue->tx_lock);
+                       if (rt2x00queue_threshold(queue))
+                               rt2x00queue_pause_queue(queue);
+                       spin_unlock(&queue->tx_lock);
+
+                       goto exit_free_skb;
+               }
 
                if (rt2x00mac_tx_rts_cts(rt2x00dev, queue, skb))
-                       goto exit_fail;
+                       goto exit_free_skb;
        }
 
        if (unlikely(rt2x00queue_write_tx_frame(queue, skb, control->sta, 
false)))
-               goto exit_fail;
+               goto exit_free_skb;
 
        /*
         * Pausing queue has to be serialized with rt2x00lib_txdone(). Note
@@ -164,10 +174,6 @@ void rt2x00mac_tx(struct ieee80211_hw *h
 
        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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