From 6dd80efd75ce7c2dbd9f117cf585ee2b33a42ee1 Mon Sep 17 00:00:00 2001
From: Stanislaw Gruszka <sgruszka@redhat.com>
Date: Tue, 19 Dec 2017 12:33:56 +0100
Subject: [PATCH] rt2x00: do not pause queue unconditionally on error path
Git-commit: 6dd80efd75ce7c2dbd9f117cf585ee2b33a42ee1
Patch-mainline: v4.16-rc1
References: bsc#1051510

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 <sgruszka@redhat.com>
Tested-by: Enrico Mioso <mrkiko.rs@gmail.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 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
@@ -142,22 +142,28 @@ 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;
 
 	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);
 }