ath9k: fix rx descriptor related race condition

Similar to a race condition that exists in the tx path, the hardware
might re-read the 'next' pointer of a descriptor of the last completed
frame. This only affects non-EDMA (pre-AR93xx) devices.

To deal with this race, defer clearing and re-linking a completed rx
descriptor until the next one has been processed.

Cc: stable@vger.kernel.org
Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/ath/ath9k/ath9k.h b/drivers/net/wireless/ath/ath9k/ath9k.h
index 505c615..0d69b13 100644
--- a/drivers/net/wireless/ath/ath9k/ath9k.h
+++ b/drivers/net/wireless/ath/ath9k/ath9k.h
@@ -79,10 +79,6 @@
 		       sizeof(struct ath_buf_state));		\
 	} while (0)
 
-#define ATH_RXBUF_RESET(_bf) do {		\
-		(_bf)->bf_stale = false;	\
-	} while (0)
-
 /**
  * enum buffer_type - Buffer type flags
  *
@@ -315,6 +311,7 @@
 	struct ath_descdma rxdma;
 	struct ath_rx_edma rx_edma[ATH9K_RX_QUEUE_MAX];
 
+	struct ath_buf *buf_hold;
 	struct sk_buff *frag;
 
 	u32 ampdu_ref;